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Effect of prelay calcium and molting on egg production in white leghorn hens Sanky Nagarajan, Hephzibah 1997

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EFFECT OF PRELAY CALCIUM AND MOLTING ON EGG PRODUCTION IN WHITE LEGHORN HENS by HEPHZIBAH SANKY NAGARAJAN B.V.Sc, Madras Veterinary College, 1993 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Animal Science) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1997 © Hephzibah Sanky Nagarajan, 1997 In presenting this thesis in partial fulfilment, of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives! It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.. / Department of AVm^U Sc\£,OCe The University of British Columbia Vancouver, Canada Date \<Z^ DE-6 (2/88) Abstract Two prelay and one molt studies were conducted to study the effect of dietary calcium supplementation and molting on subsequent egg production in White Leghorn hens. In prelay study I, the effect of 1, 2, 3.5% dietary calcium at 16, 17 and 18 weeks was studied with 1,248 pullets. There was no significant difference in egg production, egg weight or specific gravity. However there was a difference in the distribution of egg size. Revenue, total feed consumption and profit were calculated. There was higher profit from feeding a commercial prelay diet (2% calcium) at 16 weeks of age. In prelay study II, 625 chicks from two strains (H & N and Hyline ) were used to study the effect of prelay calcium on egg production. They were subjected to four treatments containing three levels of calcium (1, 2, and 3.5% ) at 16 and 17 weeks of age. There was no significant difference in egg production, egg weight or egg specific gravity . However, there was a difference in egg size. Revenue, total feed consumption and profit were calculated. Treatment 3 which involved feeding a grower diet between 16-17 weeks and a prelay diet from 17 weeks to first egg was beneficial as it had a higher profit in the Hyline strain but treatment 2 which involved feeding a prelay diet from 16 weeks to first egg was found to be beneficial in terms of profit in H&N strain. In the molt study, the same birds as in prelay study I were subjected to molting at 57 weeks of age for a period of 20 days. During the molting the birds were fed cracked corn. Five ii layers were sacrificed at random and their tibias and femurs were removed for measurement of calcium in the medullary bone before and after molting them. Calcium was higher in the medullary bones before molting which was due to the effect of the layer diet fed earlier. In the post molt period the hens were fed eight diets containing two levels of protein (17 and 15%), calcium (2 and 3.25%) and available phosphorus (0.32 and 0.25%). Three birds per treatment were sacrificed and the right tibia and femur analyzed for medullary bone calcium content to determine the effect of postmolt diets on medullary bone calcium. There was no significant difference in the calcium contents of medullary bone between the tibia and femur for all the treatments. However treatment 4 which supplied 17% protein, 3.25% calcium, and 0.25% phosphorus gave a higher percentage of calcium in the tibia and femur and produced more extra large eggs. There was no significant difference in egg production, egg weight or specific gravity among all treatments. iii Table of Contents Abstract ii List of Tables viii List of Figures x Acknowledgments xii Chapter 1 Introduction 1 1.1 Introduction to Thesis 1 1.1.1 Overview 1 1.1.2 Outline of Chapter 2 1.2 Importance of Calcium and Phosphorus on Egg Production 2 1.2.1 Calcium Homeostasis 6 1.2.2 Sources of Calcium and Phosphorus 8 1.2.3 Requirement of Calcium and Phosphorus 10 1.2.4 Dietary Calcium during the Prelay stage 12 1.3 Molting 14 iv 1.3.1 Advantages of Molting 14 1.3.2 Disadvantages of Molting 15 1.3.3 Methods of Molting 15 1.3.4 Factors Essential for a Successful Induced Molt 18 1.3.5 Postmolt Diet 21 1.4 Medullary Bone 23 1.4.1 Structure and Formation of Medullary Bone 24 1.4.2 Medullary Bone and Egg Laying Cycle 24 1.4.3 Medullary Bone and Calcium 25 Chapter 2 Effect of Dietary Prelay Calcium Level on Subsequent Egg Production 27 2.1 Abstract 27 2.2 Introduction 29 2.3 Material and Methods , 31 2.3.1 Management of Pullets Prior to the Experiments 31 2.3.2 Design and Treatments in Prelay Study 1 33 2.3.3 Design and Treatments in Prelay Study II 33 2.3.4 Chemical Analyses of Feed 35 2.3.5 Statistical Analysis 37 2.3.6 Economic Analysis 37 v 2.4 Results 38 2.5 Discussion 63 2.6 Conclusions 67 Chapter 3 Effect of PostMolt Diet on Medullary Bone Reserves and Subsequent Egg Production in White Leghorn Hens 69 3.1 Abstract 69 3.2 Introduction 70 3.3 Material and Methods 73 3.3.1 Design and Treatment 73 3.3.2 Management 74 3.3.3 Laboratory Analyses 77 3.3.4 Chemical Analyses of Feed 78 3.3.5 Statistical Analysis 79 3.4 Results 79 3.5 Discussion 92 3.6 Conclusions 95 Chapter 4 Discussion 96 Chapter 5 Conclusions 104 vi Bibliography 108 Appendix A Egg Prices and Feed Cost Used in Economic Analysis 118 Appendix B Graphs For Prelay Studies 119 Appendix C Graphs For Molt Study 125 vii List of Tables Table 2.1 Analysis of prelay feed samples (Prelay Study I) 35 Table 2.2 Composition of prelay diets (Prelay Study II) 36 Table 2.3 Calculated analysis of prelay diets (Prelay Study II) 37 Table 2.4 Effect of prelay diet on subsequent egg size (%) (Prelay Study I) 40 Table 2.5 Effect of prelay treatments on revenue, feed cost and profit (Prelay Study I) 43 Table 2.6 The effect of dietary treatments on hen performance (16 to 28 weeks of age) 48 Table 2.7 The effect of dietary treatments on hen performance (29 to 35 weeks of age) 49 Table 2.8 Effect of prelay diet on egg size in H&N and Hyline strains 52 Table 2.9 Effect of prelay diet on revenue, feedcost and profit in H&N and Hyline strains... 55 Table 2.10 The effect of dietary treatments on H&N and Hyline strains (16 to 28 weeks of age) 61 Table 2.11 The effect of dietary treatments on H&N and Hyline strains (29 to 36 weeks of age) 62 viii Table 3.1 Composition of the postmolt diets 73 Table 3.2 Calculated analysis of postmolt diets 74 Table 3.3 Determined values for postmolt diets 79 Table 3.4 Effect of postmolt diets on percentage egg grade 83 Table 3.5 Calcium content of the medullary bone before molt 85 Table 3.6 Calcium content of the medullary bone after molt 85 Table 3.7 Effect of postmolt diets on medullary bone calcium content of tibia 86 Table 3.8 Effect of postmolt diets on medullary bone calcium content of femur 87 Table 3.9 The effect of postmolt diets on hen performance (60 to 69 weeks of age) 90 Table 3.10 The effect of postmolt diets on hen performance (70 to 77 weeks of age) 91 Table A. l Egg price per dozen of eggs 118 Table A.2 Cost of feed per thousand kg 118 ix List of Figures Fig. 2.1: Effect of prelay diet on total egg production 39 Fig. 2.2: Effect of prelay diet on subsequent egg size 42 Fig. 2.3: Effect of prelay diet on revenue generated due to egg production 44 Fig. 2.4: Effect of prelay diet on cost of feed 45 Fig. 2.5: Effect of prelay diet on profit 46 Fig. 2.6: Effect of prelay diet on total egg production in H&N and Hyline 51 Fig. 2.7: Effect of prelay diet on percentage egg size in H&N and Hyline 54 Fig. 2.8: Effect of prelay diet on revenue in H&N and Hyline 57 Fig. 2.9: Effect of prelay diet on feed cost in H&N and Hyline 58 Fig. 2.10: Effect of prelay diet on profit in H&N and Hyline 59 Fig. 3.1: Effect of molt diet on total egg production 82 Fig. 3.2: Effect of molt diet on average egg size 84 Fig. 3.3: Effect of molt diet on percentage calcium in the medullary bones 88 x Fig. B.l: Effect of prelay diet on gradable egg production 119 Fig. B.2: Effect of prelay diet on average egg weight 120 Fig. B.3: Effect of prelay diet on average specific gravity 121 Fig.B.4: Effect of prelay diet on gradable egg production in H&N and Hyline 122 Fig. B.5: Effect of prelay diet on average egg weight in H&N and Hyline 123 Fig. B.6: Effect of prelay diet on average egg specific gravity in H&N and Hyline 124 Fig. C.l: Effect of molt diet on gradable egg production 125 Fig. C.2: Effect of molt diet on average egg weight 126 Fig. C.3: Effect of molt diet on average egg specific gravity 127 xi Acknowledgments First of all, I would like to thank my graduate supervisor, Dr. R. Blair, for his patient and knowledgeable supervision. I would like to thank the University of British Columbia, for granting me the University Graduate Fellowship for the first year of my program and also for the bursaries awarded in the second year. I would like to thank Mr. Dan Worsley in the awards and financial aid for his time and patient hearing and awarding me a bursary to help me pursue my program of study. I would also like to thank the B.C. Egg Producer's Association for awarding me a bursary. I would like to especially thank Dr. Jacqueline Jacob for her constant guidance and other members of the graduate committee Dr. Tom Scott and Dr. K. Cheng. I would like to also thank the farm staff at the South Campus (Avian Research Center) Clara, Cathleen, and Chris specially during my period of research at the farm and also the department lab technicians Siva and Tara and my co-workers Sami, Suleiman and Mahesh for their contribution of time and labour. I would also like to extend my sincere thanks to my dear husband Saurin for his constant encouragement, help and support throughout my master's program. I would also like to thank my family in India for their constant prayer and financial support. But most of all I would like to thank my Lord Jesus Christ for providing all the help and support to enable me to complete this thesis successfully. xii 1 Chapter 1 Introduction 1.1 Introduction to Thesis 1.1.1 Overview This thesis describes the effect of prelay calcium content and molting on egg production in White Leghorn hens. Calcium is an essential element for egg production and has to be supplemented to layers at the appropriate time of lay to enhance egg production and shell quality. Three experiments were conducted in this study. The first experiment describes the effect of various feeding programs currently used in the layer industry during the prelay period in the prelay study I and to determine if there is any difference among two strains of White Leghorns in terms of egg performance in prelay study II. The second experiment deals with the influence of postmolt prelay diet on medullary bone calcium reserves and its subsequent effect on egg production. 2 1.1.2 Outline of Chapter The purpose of Chapter 1 is to provide background information, introduce the topics to be discussed later in the remainder of the thesis and outline the rest of the thesis. Section 1.2 describes the importance of calcium and phosphorus on egg production including sources of calcium and phosphorus, requirements for calcium and phosphorus. Section 1.3 describes methods and factors affecting a successful molt, advantages and disadvantages of molting, postmolt diet and postmolt performance. Section 1.4 describes the structure of medullary bone and the importance of medullary bone and calcium in the egg laying cycle. 1.2 Importance of Calcium and Phosphorus on Egg Production Shell quality continues to be a major problem with commercial laying hens. Roland (1977) estimated that 4.8% of eggs were lost due to problems in the egg shell. Proper egg shell formation is therefore necessary to prevent breakage during handling and to protect the inner contents of the egg from contamination. There are several ways to assess egg shell strength. One method is to determine the specific gravity by Archimedes' principle in which the eggs are weighed in air and then submerged in tap water and then re-weighed . Measures of shell strength can be obtained by using the egg shell tester described by Voisey and MacDonald (1978). Another method of assessing the shell strength is shell is separated from the inner contents of the egg, are washed, dried and weighed together with the shell 3 membranes (Hamilton 1978a). The type of diet fed during this prelay period can affect the level of egg production, egg shell quality and egg size during the laying period. Hurwitz and Bar, (1971) and Meyer et al., (1971) have studied the influence of prelay calcium and phosphorus on layer performance. The level of dietary calcium during this prelay period is of considerable importance. Normal eggs contain about 2 g of calcium in their shell (Mahmoud et al., 1994). During egg shell formation the bird obtains some of the required calcium from its medullary bone reserves (Clunies et al., 1992). It is important therefore that the pullet build up these bone reserves prior to the start of lay. A large amount of research has been done to study the effect of various levels of calcium on laying hens (NRC, 1994). Various levels of calcium are fed due to the variation in the demand for calcium during the period between shell forming and non shell forming days (Morris and Taylor, 1967). Taylor and Kirkley (1967) found that there was increased retention of dietary calcium and phosphorus during shell forming days. The fact that calcium is an important mineral for egg shell formation makes it necessary for calcium to be added in the layer diet. Also, restricting calcium in the diet will cause laying to cease in sexually mature hens during the normal laying period (Gilbert and Blair, 1975). However they resume laying once they are fed a calcium adequate diet within a short time. Also the restriction of dietary calcium affects the reproductive performance of the laying hens. Taylor et al., (1962) found that hens fed a calcium deficient diet normally stopped laying after 10-14 days. This 4 cessation is mainly due to the failure of gonadotropin secretion by the anterior pituitary which prevents the bird from ovulating. It is thought that the fall in diffusible calcium level in the blood of calcium deficient hens reduces the hypothalamic stimulation by the pituitary gland (Taylor, 1965). The egg shell calcium content decreases from about 2 g per egg shell to about 1 g during the first 7 days during which the hens are fed calcium deficient diets, but returns to normal levels within 6-8 days on feeding a laying diet (Hurwitz and Bar, 1966). The level of calcium to be added in the layer diet is around 3.5g/kg (NRC, 1994). Scott et al., (1971) reported that egg production and feed consumption were reduced when the level of calcium was increased to 5% of the diet. Damron and Harms (1980) reported that egg production was significantly higher with 3.5% calcium than with either 2.5% or 6% calcium in the diet. The relationship of calcium to feed consumption is complex. In certain conditions, when dietary calcium is above the level required, feed intake can either increase or decrease. These opposite responses can occur because dietary calcium reduces energy density of the diet and makes it difficult for hens to meet their energy requirements. However, excess calcium in the diet can also reduce its palatability and thus reduce feed consumption by the chicken (Maclntyre et al., 1964). On the other hand, when the level of calcium is marginal (less than that required for shell quality but not enough to reduce production), hens over consume feed to obtain more calcium and energy and may become affected with fatty liver syndrome within a few weeks (Nesheim et al., 1979, Lennards and Roland, 1981). 5 Little research has been done to examine the differences in calcium metabolism of hens laying eggs with thick or thin shells. Holocombe et al., (1977) studied the effect of feeding 3% and 5% calcium to hens laying eggs with thick and thin shells and found that both groups responded similarly to the changes in calcium level of the diet. Abdou et al., (1993) compared the effect of feeding diets with different calcium and phosphorus levels to hens producing heavy or light shelled eggs. They found that feeding a calcium deficient diet resulted in a significant reduction in shell weight for both heavy and light shell weight hens. Also shell thickness was adversely affected when the low calcium diet was fed. They also found that calcium utilization was significantly better for high shell weight hens than low shell weight hens. Clunies et al., (1992 a) found that hens laying eggs with thick shells retained more calcium than hens laying eggs with thin shells. Phosphorus is also an important nutrient in the diet of laying hens. Phosphate source, particle size and dietary levels are particularly important. In the case of layers, dicalcium phosphate is the primary source of phosphorus. Numerous studies on the dietary phosphorus requirement have been carried out. Hamilton and Sibbald (1977), Edwards and Suso (1981) suggested that 0.4 or 0.45% total dietary phosphorus was adequate for egg production and shell quality. Said et al., (1984) suggested that total phosphorus at 0.5% with dicalcium phosphate used as an inorganic source, results in better egg shell quality and egg production. 6 Egg shell quality is an important factor when considering the phosphorus need of the laying hen. Miles et al., (1983) showed that egg shell quality as measured by specific gravity was inversely related to dietary phosphorus levels above 0.5%. Roland et al., (1990) found that egg specific gravity was greatly influenced by phosphorus source during 4 and 6 weeks of an 8 week experimental period. Particle size and source of phosphorus also influence phosphorus utilization. Vandepopuliere and Lyons (1992) investigated the effects of feeding various levels of dietary phosphorus from two sources (dicalcium or defluorinated phosphates) and particle size on laying hen performance as measured by egg shell quality, egg production, feed consumption and body weight. They observed a difference in feed consumption for hens fed dicalcium phosphate and the coarser form of defluorinated phosphate. They also investigated feeding phosphorus at 0.5% and 0.4% levels and observed a significant difference, the hens fed the 0.4% dietary phosphorus lost more weight during the experiment, feed consumption, egg weight, body weight were depressed and there was a reduction in egg production and egg mass. These results showed the significance of phosphorus in relation to egg production in the diet of layers. 1.2.1 Calcium Homeostasis The laying hen possesses a remarkable calcium homeostatic mechanism. Calcium homeostasis is achieved by balancing the efficiency of intestinal calcium absorption, renal calcium excretion and bone mineral metabolism to the bird's calcium requirements. The 7 hormones controlling this mechanism are parathyroid hormone, calcitonin and 1,25 dihydroxycholecalciferol. In birds the increased calcium demands during the laying cycle are accommodated by an appropriate increase in intestinal calcium absorption (Bar et al., 1978) and a decrease in renal excretion (Deluca et al., 1990). During the reproductive activity in the female chicken, endogenous estrogen mediates changes in the function of the kidney that involves two major calcium regulating hormones parathyroid hormone and 1,25 dihydroxycholecalciferol (Elaroussi et al., 1993). The number of parathyroid hormone receptor sites and the activity of parathyroid hormone dependent adenylate cyclase are elevated in the kidney of mature egg laying females, when compared to either the mature male or immature chicken of either sex (Forte et al., 1983). Singh et al., (1986) suggested that the major endocrine change during calcium deficiency is an increase in parathyroid hormone activity. They showed a reciprocal relationship between the concentration of parathyroid hormone and calcium. Mean concentration of parathyroid hormone in birds fed low calcium diets was more than twice that of control birds during shell formation when there was a need for more calcium . Calcium appetite is the ability of an animal to selectively consume calcium rich substrates to meets its calcium requirement. This was thought to exist in the domestic fowl and was confirmed by Hughes and WoodGush (1971). Chickens deprived of calcium in the diet were able to discriminate in favor of a calcium mash to a diet that was not supplemented with 8 calcium. They also suggested that the calcium intake was regulated on an hour to hour basis depending on the need for egg-shell formation. 1.2.2 Sources of Calcium and Phosphorus Calcium for the layer diet can be obtained from various sources. Some of the sources are oyster shells, shell grit, limestone, and dicalcium phosphate. Numerous reports have shown the usefulness of feeding various calcium sources either in the pulverized or granulated form on egg shell quality. Scott et al., (1971) and Roland (1986) have shown a positive effect of calcium with a coarse particle size on egg shell quality. Tortuero and Centero (1973) showed that large particle calcium sources increased nitrogen retention and metabolizable energy. The increased intake of large particles of calcium just prior to the onset of shell formation may also result in better egg shell quality (Mongin and Sauveur, 1979). Roland and Harms (1973) also postulated that the retention of calcium particles in the gizzard and slow solubility may also make calcium available during the shell forming period especially during the night when there is no feed intake by the bird. Reid and Weber (1976) reported that there was some difference between calcium carbonate from minerals and from animal deposits like oyster shell and concluded that the difference in the calcium sources was due to their physical and chemical composition. Oyster shell is the most commonly used marine particle size source of calcium but it is also an expensive source of calcium. Guinotte and Nus (1990) conducted an experiment to study the effect of sea shells (calcium source) treated with 9 phosphoric acid on egg shell quality, compared with oyster shell and limestone both in the pulverized and granulated forms. They found that particulate or ground sea shell and ground oyster shells were equal to particulate limestone as calcium supplements for egg shell quality. The calcium solubility rate was maximum when the calcium sources were finely ground irrespective of their origin. This may be due to the higher particulate area of ground calcium sources. Rabon and Roland (1985) and Cheng and Coon (1987) reported that despite the differences in physical characteristics of calcium sources (i.e.) size, solubility and particulate area there was little effect due to origin or particle size of calcium on egg shell quality and egg production. However, Roland (1986) reported that changes in particle size increase egg shell quality when level of calcium in the diet is marginal or under higher environmental temperatures. Feed consumption was higher in hens fed particulate oyster shells (Roland and Harms, 1973). So it can be seen that limestone, oyster shell, and sea shell can be used as good sources of calcium for efficient egg production Particle size and source of phosphorus also determine the effect on phosphorus utilization. Scongberg et al., (1988) reported that the phosphorus in reagent grade dicalcium phosphate was 93% available and in feed grade dicalcium phosphate it was 72% available. However in defluorinated phosphorus it was only 45% available. Vandepopuliere and Lyons (1992) conducted an experiment to study the effect of dicalcium phosphate and defluorinated phosphorus as inorganic phosphorus sources on egg shell 10 quality. They found that for both sources a significant linear increase in feed consumption, egg weight and body weight gain occurred as total phosphorus level in the diet increased. Potter (1988) also found that the bioavailablity of phosphorus from defluorinated phosphate was nearly identical with that of dicalcium phosphate. These findings suggests that phosphorus is an essential element for egg shell quality and egg weight and is independent of source of phosphorus. Having studied the sources of calcium and phosphorus it is important to know the requirements of these minerals for optimum egg production in layers. Subsection 1.2.3 deals with calcium and phosphorus requirements and subsection 1.2.4 with prelay calcium. 1.2.3 Requirement of Calcium and Phosphorus Although the calcium and phosphorus requirements of laying hens has been a subject of numerous investigations in the past, the requirements for these minerals is still not quite established. The NRC (1994) recommended 3.75 g per hen per day and the available phosphorus at around 350 mg per hen per day throughout the production cycle. Some reports suggested that improved shell quality may be achieved by feeding calcium above the NRC requirements (Gleaves et al., 1977, Keshavarz 1987 and Clunies et al., 1992 b). Thus the layer industry uses a step-up calcium phase feeding regimen with increasing age (Ousterhout, 1980). The reason that such an approach has been adopted by the layer 11 industry is that the calcium need for shell formation is increased with increased shell weight resulting from increased egg weight. Also the hen's ability to absorb calcium from the digestive system and to mobilize calcium from the medullary bone is reduced with age (Peterson, 1965). A condition called "Cage layer fatigue" due to insufficient calcium occurs in layers that are frequently moved from the pullet to the layer barns causing additional stress to layers. Cage layer fatigue is a type of osteoporosis characterized by withdrawal of calcium phosphate not only from the medullary bone but also from the cortical bone, particularly of the long bones of the legs. This disease also occurs in hens that are confined to cages and in many cases the hens suffering from this condition have recovered when removed from cages and placed on litter floors. The bone becomes very thin and fragile and fractures easily as the minerals especially calcium gets depleted so much that the legs are not able to support the weight of the hens. Researchers have reported that dietary phosphorus can be reduced with age without affecting the egg performance (Sell et al., 1987). Hamilton and Sibbald (1977) also found that shell quality may be improved by reducing the dietary phosphorus level. Keshavarz and Nakajima (1993) conducted an experiment to re-evaluate the effect of dietary calcium and phosphorus levels on egg shell quality and performance. They found that the estimated calcium requirement by NRC (1994) was adequate for egg shell formation and that hens can tolerate up to 6 g per hen per day without any adverse effects and a step down available 12 phosphorus phase feeding regimen can be used without any adverse effect on performance. They also found that 350 mg per hen per day of available phosphorus was sufficient for egg production. 1.2.4 Dietary Calcium during the Prelay stage Shell quality is a problem on many farms, resulting in increased losses from egg breakage. There is still considerable variation in the type of feed given to replacement pullets just prior to the start of lay. The onset of egg production requires a major change in the bird's calcium metabolism related to shell formation. Bell and Siller (1962) reported that calcium equilibrium involves some seven separate mechanisms which cause a sudden change in the birds' calcium status. In general there are three basic feeding programs currently used in the industry. The first involves feeding a grower/ developer diet containing 1% calcium until the first egg is laid and then switching to a layer feed containing 3.5% calcium. There is some research indicating that pullets on such a feeding program use dietary calcium more efficiently. Other reports, however, suggest that feeding a low calcium diet during this prelay period results in inadequate ovary and oviduct development (Nevalainen 1969) and insufficient build up of medullary bone reserves (Miller and Sunde 1975 and Scott et al., 1977). The second feeding program involves the introduction of a layer diet containing (3.5%) as early as 16 weeks of age. This helps in building up medullary bones but since excess calcium is excreted it may cause undue stress on the kidney (Niznik et al., 1985). The 13 third feeding program involves feeding a prelay diet containing (2% calcium) from 16 weeks of age until first egg. Since the actual egg production starts around 18-20 weeks this diet is called "prelay calcium" or "prelay diet" because it is fed just prior to the laying period (around 16 weeks). Advantages of Prelay Calcium: The use of a 2% calcium, prelay diet represents a compromise between the first two feeding systems because it provides the pullet with more calcium than is provided in most grower diets without providing the excess calcium contained in the layer diets. A prelay diet also allows for the build up of the medullary bone reserves of calcium without adversely affecting kidney function. Disadvantages of an Early Layer Diet: When fed a diet containing 3.5% calcium during 16 weeks of age, early maturing pullets showed cage layer fatigue, smaller egg size, flat egg production peaks, decreased egg shell quality, and increased mortality. Increased water intake and manure moisture content persisted throughout the laying cycle of the bird. Excess calcium in the layer diet imposes undue stress on the pullets' kidneys since this calcium is in excess of the immediate requirement and therefore must be excreted. This is thought to cause urolithiasis in the pullets (Shane and Young, 1969 and Niznik et al., 1985). But research has shown that urolithiasis is not only due to excess calcium but also due to water deprivation, metabolic alkalosis due to elevated sodium and potassium over chloride ratios, and also exposure of pullets to nephrotrophic strains of infectious bronchitis (Julian 1982). 14 1.3 Molting Molting is a physiological response that results in body weight loss (Mrosovsky and Sherry 1980), feather loss (Herremans 1986, 1988) a pause in oviposition concomitant with regression of the hen's reproductive tract (Brake and Thaxton 1979) and a decrease in feed intake and activity. It is commonly practiced with egg type layers and turkey breeders and also practiced with broiler breeders in some areas. The induction of molting in commercial laying hens has been done to extend the economic productivity of layer flocks along with recuperation of the reproductive tract for better egg shell quality and egg production (Russzler 1986). Because of increasing economic pressures the commercial egg industry must make maximum use of its resources. For the egg marketer, induced molting offers a means of matching the egg supply with market conditions. Molted flocks produce a higher proportion of larger eggs than do first cycle flocks. 1.3.1 Advantages of Molting During periods when high prices or premiums are paid for larger eggs, which occurs usually during the summer, using the molted flock is favorable. Periods when the price spread between medium and large eggs is small, which usually occurs during the winter and spring months, using pullet flocks is beneficial (Carey et al., 1987). Regardless of the time of the year, if flock placements and molting schedules can be adjusted to take advantages of 15 anticipated market conditions, molted flocks can produce greater returns per hen than single cycle flocks. Induced molting also reduces the hen cost per dozen eggs because it lengthens the productive life of the hens. 1.3.2 Disadvantages of Molting The major disadvantage of molting is that it leads to poorer feed efficiency. The birds have to be out of production for 14-17 days (Carey et al., 1987). The extent to which the feed efficiency will drop depends on the strain, season, equipment, housing type, nutrition and whether the molting technique is applied properly. Increased concern over animal welfare restricts the methods available to induce molting in commercial layer flocks. Also concern for the welfare of hens exposed to long periods of feed withdrawal and research accidents due to feeding mis-formulated diets have created considerable interest in alternate molting methods that are less stressful but capable of yielding comparable economic results (Buhr and Cunningham 1994). Subsection 1.3.3 and 1.3.4 deals with different methods of molting and factors essential for a successful molt. 1.3.3 Methods of Molting A successful molting program requires close co-operation between the production and marketing segments of the farm. A variety of induced molting methods are used today. 16 Methods of inducing molt in laying flocks has been a subject of controversy. Feed deprivation is one of the most widely utilized methods of molt induction (Brake, 1992). Studies have shown that wild birds exhibit anorexia during the annual molt (Mrosovsky and Sherry 1980) and lose about 40% of their body weight. So it is thought that molting and feed deprivation are compatible characters of the normal physiology of the avian species. Swanson and Bell (1974 a) classified various molting techniques into different groups such as withdrawal of feed and water, use of a low nutrient density diet and feeding of anti-ovulatory drugs. Low nutrient density diets have been used to avoid the necessity of feed and water removal. Gilbert and Blair (1975) used low calcium diets, while Whitehead and Shannon, (1974) used low sodium diets. Anti-ovulatory drugs and feed additives including progesterone and high iodine levels have been used (Wilson et al., 1969). High levels of dietary aluminium have also been used to bring about molting (Hussein et al., 1989). Feeding naturally occurring plant or plant by-products such as grape pomace (McKeen, 1984) or Guar meal (Zimmermann and Andrews, 1987) also induce molting. Stevenson and Jackson (1984) showed that alteration of the dietary mineral balance by inclusion of copper sulphate induced molting. Feeding zinc at 1% to 2% of the diet brought about molting (Berry and Brake, 1985, Cunningham and McCormick, 1985). Aggrey et al., (1990) found that feed deprivation increases pecking. Hembree et al., (1978) observed increased agnostic acts during feed removal period. Mrosovsky and Sherry 17 (1980) reported that molting may have a survival value but Russzler (1986) observed increased mortality with long versus short periods of feed withdrawal. Feed restriction programs generally involve 5 days of feed removal. Low sodium and high zinc diets have been tried to induce a short 'pause' in lay rather than a distinct molt. But these 'pause' methods using minerals are not as reliable as the classical feed and water withdrawal methods. It is not possible to quantitate the economic advantages of a molting program as this depends on local economic conditions, egg prices and prices for the various egg weight classes. When egg prices are high, a short molt program is beneficial whereas with low egg prices especially for large and extra large eggs there is an advantage with rapid return to production. Two main criteria to be considered in a molting program are body weight and mortality. The most important criterion is body weight. Ideally it is best for birds to have about the same weight in the second laying cycle as when they started their first cycle. This means that the degree of feed restriction must be sufficient to cause weight loss equivalent to that gained by the bird during the first cycle. In practice this is often difficult to achieve. Brake and Thaxton (1979) found that one fourth of the mass lost during a fast reduced the body weight by 25% and was directly attributed to a loss in liver, ovary and oviduct weights and showed that both regression and subsequent development of organs must be related to feeding 18 postmolt diets rich in protein. Baker et al., (1983) concluded that a loss in body weight of about 27 to 31% produced optimum postmolt performance. Brake and Carey (1983) showed better postmolt performance when there was a loss of 35% body weight. Carter and Ward (1981) reported better postmolt production in birds deprived of feed to lose 30% body weight. Brake and Thaxton (1979) suggested that for most strains an approximate 30% body weight loss is necessary for a proper force molt and post molt performance. Cracked grain without supplementation has been fed during the period of molt (Swanson and Bell 1971, Harms 1983, Brake and Thaxton, 1979) as a more humane method than to completely deprive the hen of it's feed. The next criterion is mortality. Mortality should not increase substantially during a molt. The mortality should not exceed 1.3-1.5% over the entire molting period. If mortality is higher than this the degree of feed restriction should be reevaluated. Other criteria for an optimum force molting method are that it must rapidly get the entire flock out of production, it must keep the flock out until it has had an adequate rest, it must bring the flock back into production rapidly, it must be simple and foolproof, and it should rapidly lead to high subsequent performance. 1.3.4 Factors Essential for a Successful Induced Molt Age of Flock: The age of the flock has a profound influence on the success of an induced molt. If molting is done in flocks less than 57 weeks of age, the molting will be hampered by 19 the hens' resistance to cease production. On the other hand, if the flock is more than 67 weeks old, the potential for restoring shell quality is greatly diminished and the overall economic advantage of an induced molt is considerably reduced. The second laying cycle of the flock should end at 100-105 weeks of age as this would enable to match egg production with demand and reduce bird cost per dozen eggs. (Carey et al., 1987). Nutrition and Lighting: To cause the birds to stop laying abruptly, they should be " conditioned' by exposing them to constant light (24 hours per day) for 7 days before withdrawing feed (Carey et al., 1987). These hens will then experience the maximum decrease in day length at the time of feed withdrawal. Appropriate management of the lighting program for the flock is critical during the fasting and weight loss phase. The fundamental requirement is to provide constant or decreasing light for 21 days after feed withdrawal. Maximum day length does not need to exceed 16 hours for adequate stimulation. The addition of supplemental calcium during the final 2 days before the feed is removed improves the shell quality of the final eggs laid before production ceases (Carey et al., 1987). About 90 kg of oyster shell per tonne can be added in addition to the normal ingredients for best results. Alternately, oyster shell can be top dressed in the house at the rate of 2.27 kg per hundred hens. 20 Season of the Year: A cool environment causes birds to lose weight more rapidly. If weight loss occurs too rapidly, regression of the reproductive tract will not be complete. If the flock achieves the targeted weight loss before the twelfth day after feed withdrawal, the temperature within the house may have been too low. For the flock that has lost weight too rapidly one should begin limited feeding as soon as the target weight loss has been achieved. A higher house temperature may retard weight loss. If the target weight loss has not occurred by the eighteenth day after feed withdrawal, limited feeding should begin and weight loss should be monitored (Carey et al., 1987) Flock History and Mortality: If the flock has experienced some sort of challenge such as disease, exposure to mycotoxin or environmental stress that has significantly affected egg production or livability in the first cycle, livability during the fasting period may decrease below 98%. The extent of the effect of the disease depends on the nature and severity of challenge, and how long the flock has had to recover from the challenge. Before initiating a molt the production records of the flock should be examined. If there has been a notable disease challenge during the last 8-10 weeks of the first cycle of the flock, the livability during the molt may be lower than normal. If this challenge was severe and occurred recently it is not advisable to molt the flock. 21 1 . 3 . 5 Postmolt Diet Once molting is accomplished the period following the molting is termed the "postmolt period" and the diet given to the flocks to return to production is known as the "postmolt diet". Hens that have been fasted must never be returned immediately to full feed. For the first 2 days only 4.5 kg of feed per hundred hens must be offered to prevent severe crop impaction. After this adjustment period, the hens should be given full feed. Before the onset of production the hens must be fed diets that promote rejuvenation of the reproductive tract and maximization of feather growth. Two factors to be considered in the postmolt diets are protein and calcium. Harms (1983) indicated that recovery diets with higher levels of nutrients than recommended resulted in a quicker return to production. The diet utilized during this prelay (postmolt) period varied from ground corn to high protein molt diets (Brake and Thaxton, 1979). The level of calcium in these molt diets generally approximated 1.0%. This level of calcium is recommended during the non laying periods to prevent kidney damage (Shane and Young, 1969). One of the main objectives of a molting program is rapid return to egg production and a low level of dietary calcium is known to inhibit reproduction (Nevalainen 1969). These findings suggest that an adequate amount of calcium should be incorporated into the postmolt prelay diet. Protein is also important nutrient which has to be in sufficient amounts in the postmolt diet. Brake and Thaxton (1979) postulated that weight loss of liver, oviduct and ovary and 22 their subsequent rejuvenation were related to postmolt performance. Hence during the recovery period, adequate nutrients must be provided for the rehabilitation of body components. Brake and Thaxton (1979) reported that hens must be fed at least 16% protein during the recovery period as this helped in earlier regeneration of the regressed reproductive tract and earlier return to egg production than hens fed an 8.9% protein corn diet. Harms (1983) also found that hens receiving a 16.2% protein diet returned to production early than those receiving an 8.6% protein diet. He further postulated that if adequate amounts of methionine, tryptophan and lysine were given, the protein requirement would be less than 16% before the egg production period begins. These findings show the importance of protein in a postmolt prelay diet. The amount of protein used in postmolt diets not only helps in feather replacement (Andrews et al., 1987a), but also in various postmolt performance factors like rejuvenation of the ovary and oviduct (Harms, 1983). Harms (1983) and Andrews et al., (1987) found that hens that received a 16% crude protein postmolt diet regained body weight more quickly following the fast, also came into production faster and peaked sooner than those fed 9% crude protein postmolt diets. Koelkebeck et al., (1991) conducted an experiment to study the effect of protein and methionine levels in postmolt diets on postmolt performance. They found that hens regained body weight more quickly, returned to egg production faster and had higher egg weight when fed 16 or 13% crude protein postmolt diets than when fed 10% protein postmolt diets, and that supplementation of methionine resulted only in increased egg weight. These studies show that the protein 23 content of the postmolt diet influences the postmolt performance and that it should be around 16% for good hen performance. The postmolt prelay diet is mainly given to build up adequate reserves of calcium in the medullary bone so that it can be used up in egg shell formation during the second cycle. It is therefore necessary to consider dietary calcium in relation to the medullary bone. Section 1.4 and its subsections describe the structure and the role of medullary bone in the egg laying cycle. 1.4 Medullary Bone In the case of birds and reptiles which have an ability to lay eggs with calcified egg shells, there is massive development of the endosteal areas of the long bones which act as a reservoir of minerals, such as calcium, which are required for shell calcification. This endosteal bone is known as "medullary bone" (Dacke, 1979) which is a non-structural type of woven bone and is normally found in the long bones of female egg laying birds (Bonnucci and Gherardi, 1975). It consists of a system of bone spicules that grow out from endosteal surfaces which fill the marrow spaces (Dacke, 1979). Medullary bone is usually formed in female birds shortly before the onset of egg production and lasts throughout the egg laying period. 24 1.4.1 Structure and Formation of Medullary Bone In female birds, medullary bone formation is stimulated by the synergistic actions of androgens and estrogens together with the maturation of the ovarian follicles (Dacke, 1979). The mineral phase of the medullary bone is similar to that of the cortical bone and consists of a hydroxyapatite lattice. In the cortical bone the hydroxyapatite crystals are found around the organic matrix while in the medullary bone these crystals are randomly distributed throughout the matrix. Medullary bone is more calcified than cortical bone and its collagen fibril content is lower but the apatite to collagen ratio is higher (Taylor et al., 1971). Non-collagen protein, proteoglycans and carbohydrates are also more abundant in medullary bone than in cortical bone. 1.4.2 Medullary Bone and Egg Laying Cycle Van de Velde et al., (1984 b) reported that in chicks there was a direct relationship between bone formation and bone resorption. In both phases the number of nuclei per osteoclast and number of osteoclasts were more or less similar. They also showed that during the active period the resorbing surface (i.e.) the ruffled border per active osteoclast, increased and although the number of osteoclasts remained constant, the percentage of active osteoclasts increased. They also found that only the degree of calcification was increased during the laying period and that there was no change in the volume of osteoclasts. 25 1.4.3 Medullary Bone and Calcium It has been proposed for a long time that medullary bone acts as a labile calcium store for egg shell formation. Medullary bone is highly vascularised and mineralized and can be metabolized faster than cortical bone (Hurwitz 1965, Simkiss, 1967). Van de Velde et al., (1984 a) and Bell and Freeman (1971) reported that medullary bone is known to function as a calcium store for egg shell production and undergoes alternate periods of intense formation and severe depletion during the laying cycle. Bloom et al., (1958) showed that there was no correlation between medullary bone volume and size of egg in the reproductive tract. They also found that during shell calcification there was an increase in osteoblast and osteoclast numbers and a further increase in osteoclast numbers as shell calcification became complete. They also found that when hens were fed a diet deficient in calcium, the medullary bone matrix was composed only of osteoid. Normally, dietary calcium directly supplies part of the calcium for egg shell formation and the rest is taken from the skeleton. This requires the need for adequate calcium in the diet and the building up of medullary bone calcium for adequate egg shell calcification The mechanism by which medullary bone metabolism is affected by different dietary levels of calcium still remains controversial. Taylor and Moore (1954) reported that there was only a small change in medullary bone density compared to a greater reduction in cortical bone when birds were fed a diet low in calcium. However, Hurwitz and Bar (1966) showed a 26 significant depletion in medullary bone calcium of laying hens as the level of calcium in the diet was decreased. Studies conducted by Clunies et al., (1992 b) showed that dietary calcium level had a significant effect upon total medullary bone calcium reserves but that the relationship was not linear. Since these studies were mainly concerned with medullary bone and calcium reserves and did not take into account the effect of dietary phosphorus and molting on egg production, the study described in Chapter 3 deals with different levels of dietary phosphorus and calcium on egg shell formation. Since calcium and phosphorus are both important for bone and egg shell formation this study was undertaken to study their effects on the medullary bone content of chickens and to study the subsequent effect on egg shell formation. Also, since the medullary bone calcium content was not evaluated in the previous studies this trial addressed the state of the medullary bone during the molting and post molting periods. 27 Chapter 2 Effect of Dietary Prelay Calcium Level on Subsequent Egg Production 2.1 Abstract Two prelay studies were conducted using three levels of dietary calcium at 1%, 2% and 3.5% fed at 16, 17 and 18 weeks to determine the effect of dietary calcium on egg production in White Leghorn hens. In prelay study I, a total of 1,248 pullets of H&N strain were subjected to six treatments. The pullets in treatment 1 were fed a commercial pullet grower diet (1% calcium) from 16 weeks to first egg, the pullets in treatments 2 and 3 were fed a commercial prelay diet (2.6% calcium) from 16 and 17 weeks, respectively until first egg. Pullets in treatments 4, 5, and 6 were fed a commercial layer diet (4.4% calcium) at 16, 17, 18 weeks to first egg, respectively. In prelay study n, 624 pullets of H&N and Hyline strains were reared in battery cages and subjected to four treatments. The pullets in treatment 1 were fed a commercial pullet grower diet (1.1% calcium) from 16 weeks to first egg, the pullets in treatment 2 were fed a commercial prelay diet (1.8% calcium) from 16 weeks until first egg. Pullets in treatment 3 were fed a commercial pullet grower diet (1.1% calcium) from 16-17 weeks of age and then a commercial prelay diet (1.8% calcium) from 17 weeks of age until first egg. The pullets in treatment 4 were fed a commercial layer diet (3.3% calcium) from 16 weeks of age. Individual egg weights, specific gravity and feed 28 consumptions were recorded every two weeks. Egg production and mortality were also recorded daily. In prelay study I, there was no significant difference in the level of egg production, average egg weight or egg specific gravity for the different groups of pullets. However, there was a difference in distribution of egg size. The dollar value of eggs produced and the total feed consumed were determined for each treatment and the net revenue per hen calculated. Although the means were not statistically different, there was a trend for a higher net revenue from the pullets receiving the prelay diet from 16 weeks of age until first egg. When the prelay diet was introduced one week later (at 17 weeks) the net revenue per hen was similar to that of the pullets receiving the grower diet until first egg. For the pullets switched from the grower diet directly to the layer diet, the trend was for the net revenue to be reduced the later the layer diet was introduced. In prelay study II, there was no significant difference in the level of egg production, average egg weight or egg specific gravity for the different groups of pullet but there was a difference in distribution of egg size. Economic analysis was calculated using the profit, revenue and feed cost. Treatment 1 and 2 resulted in a higher revenue in H&N strain and treatment 4 for Hyline. Treatment 4 had a higher feed cost for H&N strain and treatment 1 for Hyline. However in both strains the feed cost was less for treatment 3. Although the means were not statistically different, there was a trend for a higher profit from the pullets 29 receiving the prelay diet from 17 weeks to first egg in the Hyline strain and feeding the prelay diet at 16 weeks in the case of H&N strain of pullets. Based on these results, there appears to be a benefit in feeding a higher calcium diet (> 1%) prior to egg production, i.e. either at 16 or 17 weeks depending on the strain and that the use of the prelay diet appeared to be more economical with regards to profit and feed cost than the grower or layer diets. 2.2 Introduction Laying hens require sufficient calcium to produce the strong shells needed for current marketing conditions. Shell quality is a problem on many farms, resulting in increased losses from egg breakage during handling. Dietary calcium levels fed during the prelay period may have an effect on shell quality in the subsequent laying cycle. There is a still considerable variation in the levels of calcium given to pullets prior to egg production. Prolonged feeding of a grower diet has been reported to improve the pullet's efficiency of calcium utilization, so that when a layer diet with higher calcium is introduced a greater proportion of calcium is absorbed and retained. Other reports have suggested that prolonged feeding of a low calcium diet is detrimental to bone mineralization (Miller and Sunde 1975, Scott et al., 1977) and that low calcium is inadequate for development of the ovary and oviduct (Nevalainen 1969), and egg production (Gilbert et al., 1981). It has been suggested by some researchers that high levels of calcium should be fed during the prelay period (16 weeks) to allow to build the bone reserves of calcium prior to first egg (Scott et al., 1977, Meyer et al., 1971). Scott et al., 30 (1977) in his study found that feeding 1% dietary calcium was inadequate for maximum bone mineralization prior to lay and suggested that higher levels should be fed during the time of medullary bone development. Classen and Scott (1982) have confirmed the bird's requirements for calcium during the prelay stage based on the bird's ability to self-select calcium diets. They studied the ability of pullets to selectively consume calcium during the growing and early laying periods. They found that the birds consumed more calcium on days when oviposition occurred than when no eggs were laid. They also found that calcium consumption by calcium self-selection pullets increased to over 2% 19 days prior to first egg and remained relatively constant until first ovulation. They concluded that feed intake (calcium and total feed), percent hen day egg production, egg weight, and egg specific gravity were all significantly higher for birds on the calcium self-selection treatment. The early introduction of a layer diet has been shown to be beneficial in terms of optimizing calcium balance of the bird. However, it has been argued that feeding excess calcium prior to lay imposes undue stress on the pullets' kidneys since this calcium is in excess of the immediate requirement and must be excreted (Niznik et al., 1985). In addition, early introduction of the layer diet appears to result in increased water intake and manure moisture which persists throughout the laying cycle of the bird (Wideman 1985). There are reports suggesting that early introduction of layer diets may also result in reduced egg size, feed efficiency and egg production (Hurwitz and Bar 1966). 31 The use of a 2% calcium prelay diet represents a compromise between the grower and layer diet because it provides pullets with more calcium than is provided in most grower diets without providing excess calcium as in layer diets. Such diets allow for the build up of the medullary bone reserves of calcium without adversely affecting kidney function. The objective of the current studies were to evaluate the effect of the various feeding programs currently being used by local producers during the period just prior to start of lay on subsequent egg production and egg shell quality in H&N and Hyline strain of White Leghorn pullets. 2.3 Material and Methods 2.3.1 Management of Pullets Prior to the Experiments Housing: The chicks were housed in pullet room. There were three rows with 24 cages per row with a total of 72 cages. Each cage was 0.61m x 1.04 m (0.63 sq m) . There was a total of 1,248 pullets. The floor space recommended for pullets was 0.031 sq m per chick. Therefore, 17-18 chicks were housed in one cage. The recommended feeder space was 2.5 cm per chick and the recommended water space was one cup per eight chicks. Diets: During the period between 0-6 weeks the pullets were fed a starter diet containing 20% crude protein, and 2915-3025 kcal/kg energy and during the period between 6-16 weeks 32 they were given a developer diet containing 16% crude protein and 3025-3135 kcal/kg of energy. Lighting: The pullets were exposed to 12 hours of light from 16-18 weeks of age and from 19 weeks to end of the production period they were exposed to 16 hours of light per day. Temperature: The initial temperature was 31°C , it was then reduced by 2°C per week until 21°C was reached. Body weight: In the first prelay trial a sample of pullets from three cages per row were individually weighed at 3, 6, 9 and 12 weeks. Three cages per row for each strain of pullets, so a total of 162 chicks per strain was individually weighed at 3, 6, 9 and 12 weeks of age. Once the pullets were moved to the layer cages six birds per row from previously labeled cages were weighed at 16 and 20 weeks of age in both trials. Beak trimming: The beaks were trimmed for the chicks at 7 days of age. 33 2.3.2 Design and Treatments in Prelay Study I A feeding trial was conducted with 1,248, 16 week old pullets. During the prelay periods the pullets were subjected to one of the six treatments shown below: 1. A commercial pullet grower diet (1% calcium) from 16 weeks until first egg 2. A commercial prelay diet (2% calcium) from 16 weeks until first egg 3. A commercial prelay diet (2% calcium) from 17 weeks until first egg 4. A commercial layer diet (3.5% calcium) from 16 weeks 5. A commercial layer diet (3.5% calcium) from 17 weeks 6. A commercial layer diet (3.5% calcium) from 18 weeks There were four replications for each of the six treatments. A replicate (row) was composed of 26 cages at 2 pullets per cage, i.e. a total of 52 pullets per replicate. For each of the six treatments four rows were randomly chosen. 2.3.3 Design and Treatments in Prelay Study II A feeding trial was conducted with 1,248, 16 weeks old pullets. During the prelay periods the pullets were subjected to one of the four treatments as shown below: 34 1. A commercial pullet grower diet ( 1% calcium) from 16 weeks until first egg 2. A commercial prelay diet (2% calcium) from 16 weeks until first egg 3. A commercial pullet grower diet (1% calcium) to 17 weeks of age and then a commercial prelay diet (2% calcium) from 17 weeks of age until first egg 4. A commercial layer diet (3.5% calcium) from 16 weeks There were six replications for each of the four treatments. A replicate was composed of 26 cages at 2 pullets per cage, total of 52 pullets per replicate. During the experimental periods, the pullets were housed in battery cages with two pullets per cage. The pullets were given water and feed ad libitum. Feed intake and feed consumption for each diet fed was measured until the birds were switched to the next treatment and age at first egg recorded. Also individual egg weights and specific gravity of all eggs until the birds reached 20% of production were measured. Thereafter, individual egg weights and specific gravity of all eggs laid during a 2 day period were measured every week until peak production was achieved. These data were used as a representative sample of all eggs that were produced during the experimental period. Specific gravity was determined using sodium chloride solutions ranging in specific gravity from 1.065 to 1.100 in increments of 0.005 units (floatation method). Egg production in terms of total eggs per hen day, cracked eggs, soft-shelled eggs and the incidence of mortality was monitored daily. 35 2.3.4 Chemical Analyses of Feed After ashing, calcium in the feed was determined by atomic absorption spectrophotometry (Heckman 1967) and phosphorus using the Shimadzu colorimeter method (Cavell 1955). Percentage of crude fat in the feed sample was determined as ether extract by the Goldfisch method as per the procedures outlined in (A.O.A.C. 1990). Percentage crude protein in the feed was determined by first determining the amount of nitrogen in the feed sample by the autoanalyser method (A.O.A.C. 1980) and the percentage crude protein was calculated by multiplying the percentage nitrogen by 6.25. Specific gravity was determined using sodium chloride solutions ranging in specific gravity from 1.065 to 1.100 in increments of 0.005 units (floatation method). The diets were analyzed for moisture, crude protein, ether extract (fat content), calcium and phosphorus. The results are given in Tables 2.1 and 2.3 for both the prelay trials. Table 2.1 Analysis of prelay feed samples (Prelay Study I) Type of Ether Crude Ash Available Calcium Feed Extract Protein % Phosphorus % % % % Developer 2.38 18.95 2.00 0.34 1.00 Prelay 2.54 19.25 4.72 0.23 2.56 Layer 2.64 19.5 8.39 0.28 4.44 Table 2.2 Composition of prelay diets (Prelay Study II) Ingredients Developer Prelay Layer Corn 64.4 61.1 54.0 Soyabean meal 19.7 19.7 19.0 Barley 10.0 10.0 10.0 Meat meal 2.0 2.5 4.3 Limestone 1.7 4.3 7.8 Available fat - 0.6 3.2 Trace mineral 0.5 0.5 0.5 Vitamin premix 0.5 0.5 0.5 Salt 0.4 0.3 0.3 Dicalcium phosphate 0.40 - -DL- methionine 0.2 0.2 0.2 Total 100 100 100 37 Table 2.3 Calculated analysis of prelay diets (Prelay Study II) Developer Prelay Layer Crude Protein % 17.0 17.0 17.0 Ether Extract % 3.10 3.66 6.16 Ash% 4.83 7.38 11.06 Calcium % 1.00 2.00 3.50 Available Phosphorus % 0.32 0.25 0.32 Lysine % 0.80 0.80 0.80 Methionine+Cysteine % 0.72 0.72 0.72 2.3.5 Statistical Analysis Data was analyzed under the General Linear Models procedure of SAS software, and the differences in mean was detected by Tukey's Studentized Range test (P < 0.05). 2.3.6 Economic Analysis The dollar value of eggs produced and total feed consumed were determined for each treatment and the net revenue per hen housed was calculated. The egg price for each egg type and feed costs for both trials are given in Appendix A. 38 2.4 Results Prelay Study I Fig. 2.1 shows the percentage hen day egg production starting from 19 weeks to 35 weeks. Eggs were collected daily and hen days were calculated to determine the weekly egg production. Hen days are days in which a hen is potentially able to produce one egg. This takes into account the daily mortality. The lines in the graph are for the different treatments the pullets were subjected to. In Appendix B, Fig. B.l shows the percentage gradable hen day production starting at 19 weeks to 35 weeks. The eggs that were collected were separated into cracked eggs and soft shelled eggs apart from the eggs that had proper shell formation. Those eggs that had a well developed egg shell could be marketed and hence were termed gradable eggs. 39 100 19 21 23 25 27 29 Age in weeks 31 33 35 —e—Treat 1 - - a- - - Treat 2 - -A - Treat 3 - -x - Treat 4 - -x- - Treat 5 --o-- Treat 6 Fig. 2.1: Effect of prelay diet on total egg production Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 40 In Appendix B, Fig. B.2 represents the effect of prelay diet on subsequent average egg weight. The lines on this graph show the average egg weights for the different treatments. There was no significant difference in egg weight among the treatments. Fig. 2.2 shows the effect of prelay diet on subsequent egg size. After weighing, the eggs were sorted into peewee, small, medium, large, extra large and jumbo based on their egg weight. All the eggs that weighed less than 42 g were grouped as peewee eggs, between 42 to 49 g as small, from 49 to 56 g as medium, between 56 to 64 g as large, from 64 to 72 g as extra large and eggs weighing over 72 g were classified as jumbo eggs. The stacked bar graphs shows the percentage of different sizes of eggs produced for each of the six treatments. Table 2.4 Effect of prelay diet on subsequent egg size (%) (Prelay Study I) Treatment PeeWee Small Medium Large Extra Large Jumbo 1 0.9 7.8 31.2 48.2 9.4 2.6 2 1.1 9.1 29.5 45.7 12.1 2.6 3 1.3 7.9 31.1 47.0 10.1 2.6 4 1.4 8.1 29.5 47.0 11.4 2.7 5 1.1 8.8 32.6 44.4 10.1 3.1 6 1.2 8.9 34.7 43.3 9.7 2.3 41 Among all treatments, hens on treatment 2 produced more extra large eggs which is clear from Fig. 2.2 and Table 2.4. The stacked bars for each of the treatment are a representation of all the eggs produced during the experimental period. Thus, one can use Fig. 2.2 to determine egg production by egg types for any given treatment. For example, in order to estimate the number of small eggs produced with treatment 1, one can use the percentage value of small eggs from Fig. 2.2 and multiply by the total eggs produced for that treatment. In Appendix B, Fig. B.3 shows the effect of treatments on egg specific gravity. The data were available only upto 24 weeks. There was no significant difference in specific gravity for all the six treatments. Total revenue relating to production on a given treatment can be obtained by using the respective egg production data and the value of the different types of eggs. Fig. 2.3 shows the effect of prelay diet on egg revenue in relation to eggs produced. The bars on the graph represent different treatments. Although the means were not significantly different, there was a trend for higher revenue from the pullets receiving the prelay diet from 16 weeks of age until first egg i.e. for treatment 2. When the prelay diet was introduced one week later (at 17 weeks) the revenue per hen housed was similar to that of the pullets receiving the grower diet until first egg. For those pullets switched from the grower diet to the layer diet the trend was for reduced revenue the later the layer diet was introduced. 42 Treat 1 Treat 2 Treat 3 Treat 4 Treat 5 Treat 6 Fig. 2.2: Effect of prelay diet on subsequent egg size Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 43 Fig. 2.4 represents the effect of prelay diet on subsequent feed costs. Feed consumption of the hens were recorded daily and the feed cost was calculated. The feeds were purchased at a certain price from the feed company and the feed costs for different feeds were determined. Fig. 2.5 shows the effect of prelay diet on gross profit, i.e. egg value less the feed cost. The bars on the graph show the results obtained with different treatments. From this graph we can conclude that the use of a commercial prelay diet with approximately 2.6% calcium at 16 weeks of age appeared to be more economical than the use of a commercial layer diet with approximately 4.4% calcium. The data summarizing Figs. 2.3 - 2.5 are given in Table 2.5. Table 2.5 Effect of prelay treatments on revenue, feed cost and profit (Prelay Study I) Treatment Revenue ($/bird) Feed ($/bird) Profit ($/bird) 1 6.5 3.1 3.4 2 6.7 3.2 3.6 3 6.5 3.1 3.4 4 6.6 3.2 3.4 5 6.6 3.1 3.5 6 6.5 3.1 3.4 44 1500 1400 f 1300 3 C S 1200 cc 1100 1000 T—1 m 1^- vn -1—> -i—» > •4—> -t—> a a a cd o <D CD (D (D 5-1 J-H l - i H H H H H H Fig. 2.3: Effect of prelay diet on revenue generated due to egg production Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 45 (0 o o T3 0) CU 700 650 600 550 500 450 400 1 — 1 <N m « o MO •4—> -*-> +-> •«-> •t-j cd cd cd cd cd cd CD cu CD CD CD (D J - I U i 5-1 J - H H H H H H H Fig. 2.4: Effect of prelay diet on cost of feed Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 46 800 700 I 600 0L 500 400 co 1^- in •»-» •t—> ••—> -»—> +-> c d t^—> a c d c d c d c d CD CD 0) CD CD * - i * H S-H U i H H H H H H Fig. 2.5: Effect of prelay diet on profit Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 47 Tables 2.6 and 2.7 shows the effect of dietary treatments on hen performance for two periods from 16-28 weeks and 29-35 weeks respectively. For each period, weekly percentage total egg production, gradable production, egg weight, egg mass and egg specific gravity were averaged and were subjected to statistical analysis for standard error of mean (SEM) and level of significance. Total egg production and gradable egg production were calculated from 20 to 28 weeks unlike other parameters which were calculated from 16 to 28 weeks. The standard error of mean given in the table is the maximum value among all the treatments. Since feed weight back were performed monthly, feed per day and feed conversion were determined weekly by taking average of the monthly feed consumption data. The egg mass was calculated using average egg weight and percentage total egg production on a weekly basis. There was no significant difference among the means for different treatments. 48 Table 2.6 The effect of dietary treatments on hen performance (16 to 28 weeks of age) Total egg production (%) Gradable egg production (%) Egg weight Egg mass (g) (g per hen per day) Feed/day (g per hen per day) Feed conversion (g:g) Egg specific gravity Treat 1 49.5 49.1 49.4 30.1 106.8 3.55 1.099 Treat 2 51.7 51.4 50.6 30.9 107.6 3.48 1.099 Treat 3 50.2 49.9 49.7 29.9 106.4 3.56 1.098 Treat 4 51.4 51.1 49.7 30.6 109.5 3.57 1.098 Treat 5 51.1 50.6 51.7 31.0 107.7 3.47 1.099 Treat 6 49.0 48.6 50.1 29.4 107.2 3.64 1.099 SEM 15.5 15.5 2.7 8.20 6.3 0.13 0.001 Notes: SEM-Standard error of Overall mean, Treat-Treatment Differences among means in each column are not significant (P > 0.05) Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 49 Table 2.7 The effect of dietary treatments on hen performance (29 to 35 weeks of age) Total egg Gradable Egg weight Egg mass Feed /day Feed production egg (g) (g per hen per (g per hen conversion (%) production day) per day) (g:g) (%) Treat 1 90.6 89.7 60.9 55.6 141.4 2.54 Treat 2 90.3 89.8 60.9 55.6 139.8 2.52 Treat 3 89.3 88.7 60.8 55.1 137.8 2.50 Treat 4 90.3 90.0 61.0 55.7 139.1 2.50 Treat 5 89.0 88.5 60.3 53.8 139.4 2.59 Treat 6 89.7 89.2 60.3 54.7 138.9 2.54 SEM 1.7 1.7 0.8 1.0 1.1 0.002 Notes: SEM-Standard error of Overall mean, Treat-Treatment Differences among means in each column are not significant (P > 0.05) Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 50 Prelay study II The pullets were fed a starter diet, developer diet and then fed the prelay diet followed by the layer diet during the experimental period. Fig. 2.6 shows the percentage hen day egg production starting from 20 weeks to 36 weeks. Eggs were collected daily and hen days were calculated to determine the weekly egg production. Hen days are days in which the hen is assumed to produce one egg per day. This is calculated using the daily mortality data. The lines in the graph are for the different treatments the pullets were subjected to. There was no significant difference in the level of egg production for different treatments for both the strains. The egg production was around 70% in week 29 for all treatments in both the strains which may be due to environment or management. The egg production reached about 80% for both the H&N and Hyline. In Appendix B Fig. B.4 shows the percentage hen day production (gradable eggs) starting at 20 weeks to 36 weeks. The eggs that were collected were separated into cracked eggs and soft shelled eggs apart from the eggs that had proper shell formation. Those eggs that have a well developed egg shell can be marketed and hence called gradable eggs. For calculating the percentage gradable eggs the daily mortality and hen days are to be determined. 20 24 28 32 36 Age in weeks —e— H &N Treat 1 —&— H &N Treat 2 — t r — H &N Treat 3 — * — H &N Treat 4 - - x- - • HylineTreat 1 - - o - • HylineTreat 2 - - + - • HylineTreat 3 HylineTreat 4 Fig. 2.6: Effect of prelay diet on total egg production in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 52 In Appendix B Fig. B.5 represents the effect of prelay diet on subsequent average egg weight. Every alternate week on two consecutive days eggs were collected for determining egg weight. These data were used as a representative sample of all the eggs that were produced during the experimental period. The lines on this graph show the average egg weights for the different treatments. There was no significant difference in egg weight among the treatments. Table 2.8 Effect of prelay diet on egg size in H&N and Hyline strains H&N Treat 1 Hyline Treat 1 H&N Treat 2 Hyline Treat 2 H&N Treat 3 Hyline Treat 3 H&N Treat 4 Hyline Treat 4 PW 4.61 4.42 3.99 4.95 3.44 4.74 3.27 4.41 s 20.80 27.30 19.33 26.10 20.59 26.49 18.75 23.69 M 38.42 39.91 37.97 39.08 36.79 40.03 37.55 40.23 L 28.84 21.40 29.94 22.04 30.49 22.68 31.76 24.35 EL 4.10 4.32 5.88 5.39 5.61 4.25 4.98 5.18 J 3.23 2.36 2.89 2.45 3.07 1.81 3.70 2.13 Note: PW-Peewee, S- Small, M-Medium, L-Large, EL-Extra large, J-Jumbo. Treat-Treatment 53 Fig. 2.7 shows the effect of prelay diet on subsequent egg size. The eggs that were weighed alternate weeks on two consecutive days were then sorted into peewee, small, medium, large, extra large and jumbo based on their egg weight as in first prelay trial. The stacked bar graphs shows the percentage of different sizes of eggs produced for each of the four treatments. Among all treatments, treatment 2, 3 and 4 resulted in more of large and medium eggs which is clear from Fig. 2.7 in the case of H&N strain and treatment 4 resulted in more large and medium eggs in the case of Hyline birds. On the whole, H&N strain of pullets produced more large eggs when compared with the Hyline strain. The stacked bars for each of the treatment are representative of all the eggs produced during experimental period. In Appendix B Fig. B.6 shows the effect of average specific gravity for both strains. There was no significant difference in egg specific gravity among the treatments for both the strains. Fig. 2.8 shows the effect of prelay diet on the revenue of eggs produced. Total revenue of a given treatment can be obtained by using egg production data and value of eggs for different type of eggs. The bars on the graph represent different treatments. Although the means were not significantly different, there was a trend for higher revenue from the pullets under treatment 1 and 2 in the case of H&N and under treatment 4 for the Hyline strain. 54 Fig. 2.7: Effect of prelay diet on percentage egg size in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 55 Fig. 2.9 represents the effect of prelay diet on subsequent feed costs. Feed consumption of the hens were recorded daily and the feed cost was calculated. The feeds were purchased at a certain price from the feed company and the feed costs for different feeds were determined. Treatment 4 which is a commercial layer diet was expensive for H&N and treatment 1 which is a commercial grower diet was expensive for the Hyline strains. Treatment 3 which is a combination of the grower diet and a commercial prelay diet was found to be least expensive for both the strains. Table 2.9 Effect of prelay diet on revenue, feedcost and profit in H&N and Hyline strains Treatment Treat 1 Treat 1 Treat 2 Treat 2 Treat3 Treat3 Treat 4 Treat 4 Strain H&N Hyline H&N Hyline H&N Hyline H&N Hyline Revenue 7.55 7.42 7.55 7.47 7.41 7.44 7.46 7.48 Feed cost 3.46 3.51 3.44 3.48 3.32 3.32 3.56 3.46 Profit 4.09 3.91 4.10 4.00 4.09 4.13 3.90 4.02 Fig. 2.10 shows the effect of prelay diet on profit. Profit is egg value less the feed cost. The bars on the graph show the different treatments. From this graph we can conclude that the use of a commercial prelay diet with approximately 1.8% calcium at 16 weeks of age (treatment 3) appeared to be more economical than the use of a commercial layer diet with approximately 3.3% calcium in the case of H&N strain although there was not much of a 56 difference in terms of profit for both treatment 1 and 3 for H&N. In the case of Hyline birds there was a higher profit from pullets subjected to treatment 3 which is feeding a grower diet upto 17 weeks and thereafter feeding a commercial prelay diet till first egg. Another advantage in feeding the prelay diet is that the cost of the prelay diet is comparatively less than that of the commercial layer diet and it results in a better profit than the layer diet. This was especially true in the case of Hyline, also in the case of H&N strain this was true because there was not a significant difference in terms of profit when comparing treatment 1, 2 and 3. In either case, feeding the prelay diet is beneficial as it supplies the hen with the required amount of calcium to build up its calcium reserves when compared to the excess provided by the layer diet as both treatment 3 and treatment 2 was supplemented with the prelay diet. The profit was less for treatment 4 which is the commercial layer diet for both the strains. When comparing treatment 1 which is the commercial grower diet H&N had a higher profit when compared with Hyline. The data summarizing Figs. 2.8 - 2.10 are given in Table 2.9 57 1200 1100 f 1000 3 IS g 900 800 700 i • • • • H&N Treat 1 T T 1 * Hyline Treat 1 H&N Treat 2 Hyline Treat 2 H&N Treat 3 Hyline Treat 3 H&N Treat 4 Hyline Treat 4 Fig. 2.8: Effect of prelay diet on revenue in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 600 • 550 I—| —— = 1—I — g 500 - 1 I 1 I -§ 450 - — — -2 400 - -350 -- -300 " - J — I ' l l ' I ' ' I I ' I I ' 1 I • I I • ' -^ S ^ S t S ^ S ^ S ^ S ^ g Fig. 2.9: Effect of prelay diet on feed cost in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 650 600 a 550 > en wo " 500 450 X £ 5 ta <*) g X H z 2 Fig. 2.10: Effect of prelay diet on profit in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 60 Tables 2.10 and 2.11 show the effect of dietary treatments on hen performance for two periods from 16-28 weeks and 29-35 weeks respectively. For each period, weekly percentage total egg production, gradable production, egg weight, egg mass and egg specific gravity were averaged and were subjected to statistical analysis for standard error of mean (SEM) and level of significance. Total egg production and gradable egg production were calculated from 20 to 28 weeks unlike other parameters which were calculated from 16 to 28 weeks. The standard error of mean given in the table is the maximum value among all the treatments. Since feed weight back were performed monthly, feed per day and feed conversion were determined weekly by taking average of the monthly feed consumption data. The egg mass was calculated using average egg weight and percentage total egg production on a weekly basis. There was no significant difference among the means for different treatments. 61 Table 2.10 The effect of dietary treatments on H&N and Hyline strains (16 to 28 weeks of age) H&N Total egg production (%) Gradable egg production (%) Egg Feed/day Egg mass weight (g) (g/hen/day) (g/hen/day) Feed conversion ratio (g:g) Egg specific gravity Treat 1 61.61 61.19 48.99 93.5 32.1 2.91 1.098 Treat 2 59.80 59.23 49.41 93.2 31.5 2.96 1.098 Treat 3 62.42 62.01 49.16 97.3 33.0 2.95 1.099 Treat 4 59.17 58.61 50.06 97.0 31.6 3.07 1.098 SEM 8.7 8.7 2 4.8 5.2 0.05 0.001 Hyline Total egg production (%) Gradable egg production (%) Egg Feed/day Egg mass weight (g) (g/hen/day) (g/hen/day) Feed conversion ratio (g:g) Egg specific gravity Treat 1 63.65 62.84 48.95 94.8 33.1 2.87 1.098 Treat 2 63.94 63.11 49.39 94.2 33.2 2.84 1.098 Treat 3 64.04 63.46 49.23 94.7 33.4 2.84 1.098 Treat 4 62.22 61.60 49.35 93.4 32.5 2.88 1.098 SEM 6.9 6.9 1.2 4.1 3.4 0.03 0.001 Notes: Differences among means in each column are not significant (P > 0.05). SEM-Standard Error of Overall mean. Treat- Treatment 62 Table 2.11 The effect of dietary treatments on H&N and Hyline strains (29 to 36 weeks of age) H&N Total egg production (%) Gradable egg production (%) Egg weight (g) Feed/day Egg mass (g/hen/day) (g/hen/day) Feed conversion ratio (g:g) Egg specific gravity Treat 1 79.35 79.10 58.01 119.2 46.9 2.54 1.094 Treat 2 80.21 79.83 58.25 118.8 47.5 2.50 1.094 Treat 3 81.21 80.81 58.35 124.4 48.1 2.59 1.094 Treat 4 77.44 77.05 58.78 118.8 46.7 2.54 1.094 SEM 1.1 1.1 0.9 1.7 1.5 0.005 0.001 Hyline Total egg production (%) Gradable egg production (%) Egg weight (g) Feed/day Egg mass (g/hen/day) (g/hen/day) Feed conversion ratio (g:g) Egg specific gravity Treat 1 76.26 76.06 56.33 116.9 43.5 2.68 1.094 Treat 2 74.66 74.13 56.72 113.1 43.2 2.62 1.094 Treat 3 75.49 75.29 56.19 115.6 43.0 2.69 1.094 Treat 4 75.07 74.74 57.04 114.3 43.5 2.63 1.094 SEM 1.0 1.0 1.2 1.5 1.4 0.006 0.001 Notes: Differences among means in each column are not significant (P > 0.05). SEM-Standard Error of Overall mean. Treat- Treatment 63 2.5 Discussion The diets were analyzed for calcium content using atomic absorption spectrophotometry. In prelay study I, the determined calcium levels in the developer, prelay and layer diets are 1.0%, 2.6% and 4.4 % respectively and in prelay study II, the determined calcium levels in the developer, prelay and layer diets are 1.1%, 1.8% and 3.3% compared to the expected values of 2.0%, 1.0% and 3.5%. This difference in the calculated versus the expected values could be due to many reasons like inaccuracies in dilution rates while making up the solutions for calcium determination, strength of the sample solutions and concentration of lanthanum used in the atomic absorption spectrophotometer, absorption of moisture during storage of feed. In prelay study II, there was a benefit in feeding the prelay diet at 1.8% calcium starting from 17 weeks of age until first egg and it was also economical in terms of feed cost for both the strains which can be seen from (Fig. 2.9) than the layer diet which contains approximately 3.3% calcium. Weekly egg production or egg weight was not influenced by dietary levels of calcium irrespective of the time when these diets were introduced i.e. at 16, 17 or 18 weeks (Appendix B Figs. B.l , B.2). Brake et al., (1984) also found that diets containing 1%, 2.5% and 3.5% calcium did not affect the hen's performance in terms of egg production and egg 64 weight which agrees well with the current trial. However, in a study done by Roland et al., (1985), a significant decrease in egg production as the dietary calcium level decreased was noted. In another study by Keshavarz (1986), there was a tendency for decreased egg production with increasing dietary levels of calcium. In the present study however no such differences in egg production were noticed whether the dietary calcium levels increased or decreased. Furthermore, there was no difference in egg specific gravity for the weeks it was measured (Fig. B.3), suggesting no difference in shell quality among the different treatments, although this is not in accordance with the study conducted by Roland et al., (1985) in which the egg specific gravity was significantly decreased in hens fed a 1% calcium diet compared to hens fed 4.4% calcium diet suggesting that egg specific gravity and shell weight are directly related to dietary calcium level. Feed consumption, feed conversion ratio, egg mass along with egg production and egg weight were calculated for two periods during the experiment (Tables 2.6-2.7). There was no significant difference among the means for different treatments (P > 0.05). This result, however, did not agree with the conclusions made by Roland et al., (1985) who found that the average feed intake of the laying pullets that were fed 1% calcium was significantly greater than hens fed a diet containing 3.75% calcium. In the present prelay trial no such differences in feed intake were noticed. 65 Considering egg size, there was a difference in the distribution of egg size, which does not support the findings of Hamilton and Cipera (1981) who stated that prelay calcium diet did not have any effect on egg size. Miller and Sunde ( 1975) found that hens fed a low calcium diet (0.5-0.6%) produced more larger eggs than hens fed a higher calcium diet (3%). In the current prelay study no such differences in egg size due to low dietary calcium level was noticeable, although hens fed a prelay diet containing 2-2.6% calcium produced more extra large eggs. Also after the introduction of the layer diet, shell formation was normal regardless of the prelay calcium treatment, which agrees with the work of Leeson et al., (1986). Nevalainen (1969) also reported that dietary prelay calcium concentration could influence maturity because inadequate levels of calcium would adversely affect the development of ovary and oviduct. In this trial there was no significant effect of diet on age at first egg which agrees with the findings of Leeson et al., (1986). Miller and Sunde (1975) and Gilbert et al., (1978) indicated that the dietary prelay calcium level had no effect on maturity and Lennards et al., (1981) indicated that 0.58% calcium was adequate for ovulation but not for shell quality. In this study the prelay diet contained 2.6% calcium, which appeared to be sufficient to meet the calcium requirement of the bird for egg production, since there was no evidence of an adverse effect on subsequent egg production. Miller and Sunde (1975) indicated that low calcium level of 0.5-0.6% calcium versus high calcium 3% diets resulted in large egg size. No such effect was seen in actual egg size but in prelay study I, there was a difference in distribution of eggs in that feeding a prelay diet with 2.6% calcium 66 resulted in pullets producing more extra large eggs and the net revenue was higher from the pullets that were fed a prelay diet with 2.6% calcium from 16 weeks. On the other hand when the prelay diet was introduced one week later i.e. at 17 weeks rather than at 16 weeks of age the net revenue per hen housed was similar to that of pullets receiving the grower diet until first egg. Feeding pullets a prelay diet with 2-2.6% calcium therefore appears to be beneficial. There was a reduced net revenue from those pullets which received the layer diet at 18 weeks rather than at 16 weeks. This suggests that the net revenue was reduced the later the layer diet was introduced. Another advantage in feeding the prelay diet containing 2.6% calcium starting from 16 weeks of age is that the cost of the prelay diet is comparatively less than that of the commercial layer diet and appeared to be more economical than the layer diet that contained approximately 3.5% calcium. Feeding a prelay diet is also beneficial as it supplies the hen with the required amount of calcium to build up its calcium reserves when compared to the excess provided by the layer diet thus reducing kidney damage caused by excess calcium. In prelay study II, feeding prelay diet with approximately 1.8% calcium was found to be beneficial in both the strains and that in the Hyline it should be introduced at 17 weeks and in the H&N at week 16. Also when comparing the feed cost the prelay diet had a lesser feed cost than the commercial grower or the layer diets. Considering the profit from both strains it appeared that feeding the prelay diet at 16 weeks was found to be beneficial in the H&N 67 strain and feeding prelay diet at 17 weeks of age for the Hyline strain. (Fig. 2.10). All the same, irrespective of the time of introduction, whether it be 16 or 17 weeks the prelay diet was found to be beneficial in both the strains than the grower or the layer diets. 2.6 Conclusions Based on the results of prelay study I, we can conclude that there is a benefit in feeding a higher calcium (i.e.>l%) diet prior to egg production and that this diet should be introduced as early as 16 weeks of age. The use of a commercial prelay diet with approximately 2.6% calcium appeared to be more economical than the use of a commercial layer diet with approximately 4.4% calcium. From prelay study II, we can conclude that there is a benefit in feeding a higher calcium (i.e.>l%) diet prior to egg production and that this diet should be introduced as early as 16 weeks of age in the case of the H&N strain and 17 weeks in Hyline strain. Based on these results we can conclude that supplementing a prelay with approximately 1.8% calcium was beneficial whether it was supplemented at 16 or 17 weeks of age. In addition, prelay diet represents a compromise between the grower and layer diet because it provides the pullet with more calcium than is provided in most grower diets without providing the large excess provided by the layer diets. Such diets should also allow for build up of medullary bone reserves without adversely affecting kidney function. It must not be forgotten that each 68 strain has its own characteristics in terms of growth rate, feed conversion ratio, body weight, livability and egg production so there tends to be a variation in terms of the time of supplementation of the prelay diet which is either 16 or 17 weeks. 69 Chapter 3 Effect of PostMoIt Diet on Medullary Bone Reserves and Subsequent Egg Production in White Leghorn Hens. 3.1 Abstract An experiment was conducted to determine the effect of postmolt diets on percentage calcium in bone reserves and on subsequent egg production in White Leghorn hens. A total of 1080 birds was used in the experiment. Fourteen days before the molting period, daily egg production, weekly average egg weight and specific gravity data were recorded. Five layers were sacrificed at random and their long bones were removed for measurement of calcium in the medullary bone and their reproductive tracts were removed for assessment of size and development before molting them. During the molting period the birds were fed cracked corn. The molting period lasted for 20 days, at the end of which five layers were sacrificed and their long bones removed to determine the percentage calcium. During the period after the molt the hens were subjected to eight treatments consisting of 8 postmolt diets. The eight diets were formulated to contain two levels of calcium, (3.25%, 2%) phosphorus (0.32%, 0.25%) and protein (17%, 15%) arranged in a 2x2x2 factorial layout. When the layers of a particular treatment attained 5% production all layers were switched to a commercial layer diet. Individual egg weights, specific gravity and feed consumption were recorded every 2 weeks. Egg production and mortality were also recorded daily. There was no significant 70 difference in egg production among the eight treatments. The percentage egg production declined as the age of the hens advanced, reaching 90% at 65 weeks and 80% at week 75. There was no significant difference in average egg weight and specific gravity. However, there was a difference in egg size. The hens produced more large and extra large eggs than prelay trial. Hens under treatment 4 which is a combination of 3.6% calcium, 0.42% phosphorus and 16.3% protein produced more extra large eggs. Peewee, small and medium eggs contributed to less than 5% of the total egg production. There was no significant difference in percentage of calcium among the long bones. However, hens subjected to treatment 4 had higher percentage of calcium in the medullary bones of both tibia and femur compared to the other treatments. Based on these results we can conclude that treatment 4 which is a combination of 3.6% calcium, 0.42% phosphorus and 16.3% protein resulted in larger egg size and higher retention of calcium in the medullary bones. 3.2 Introduction A large amount of research has been done to study the effect of feeding various amounts of calcium and phosphorus on egg shell formation (Gilbert et al., 1981; Ousterhout 1980). Calcium metabolism in birds, especially in egg laying domestic fowl, is characterized by a large turnover of calcium which is due to the fact that the egg shell contains about 2 g of calcium (Gilbert 1983). The medullary bone acts as a calcium reservoir for egg shell 71 formation in birds and is often found to undergo alternate periods of intense formation and depletion in the ovulatory period (Van de Velde et al., 1984 a ,b.). The bone mineral used for shell formation will be replenished when there is no egg shell calcification. This makes it necessary for the prelay diet to contain adequate calcium and phosphorus in the appropriate ratio for the hen to have sufficient reserves in the bone to enable good egg production with excellent shell quality. After a period of egg production, the birds have to be subjected to a process called 'molting', which is a natural process which results in shedding of feathers and renewing them after a period of time. Molting in laying hens is carried out as the medullary calcium reserves get depleted due to continuous egg production. Egg shell weight and shell quality are found to improve significantly following the molt (Garlich et al., 1984). In the layers, this molting program helps the birds to not only rejuvenate its reproductive system, but also to replenish the medullary bone calcium reserves thus enhancing subsequent egg production. Molting can be achieved by many means such as feed and water withdrawal, use of high zinc and low calcium diets, which ultimately causes stress to the birds promoting shedding of feathers and in reducing body weight (Mc Cormick et al., 1983 and Swanson et al., 1974). However, some of the methods of molting only induces a pause in oviposition and not a complete molt. The molting period lasts for about 4 weeks. The postmolt prelay period follows the molting period during which time the diet should contain adequate amounts of calcium and phosphorus to promote medullary bone reserves 72 and bring the birds back into lay with good egg shell quality. Egg shell quality is an important parameter from an economic point of view since eggs with poor shells tend to break easily while handling during marketing resulting in economic loss to the poultry industry. The reason by which this medullary bone metabolism is effected by differences in dietary calcium and phosphorus level is controversial. Also calcium and phosphorus are important to prevent the occurrence of osteoporosis and therefore have to be supplemented in the proper ratio in the postmolt prelay diet. This postmolt prelay period also lasts for about 4 weeks. The main objective of this study was to determine the effect of different levels of protein, calcium and phosphorus in helping build up the reserves of these minerals in the hens and to determine their effect on further egg production. It was carried out by feeding diets containing different levels of calcium and phosphorus and determining the effect of each diet on medullary bone reserves of calcium phosphorus and protein and on subsequent egg production and egg quality. Also, during molting there is a reduction in body weight, which necessitates the supplementation of adequate protein which is the main body builder. 73 3.3 Material and Methods 3.3.1 Design and Treatment A total of 1080, 57-week- old H&N strain hens were used in this trial. During the post-molt period the hens were subjected to eight different treatments. Table 3.1 Composition of the postmolt diets Ingredients Dietl Diet2 Diet3 Diet4 Diet5 Diet6 Diet7 Diet8 Corn 61.9 61.1 55.3 54.5 67.0 66.8 61.3 60.6 Soyabean 17.8 19.7 18.8 20.7 13.5 14.5 13.2 15.1 Barley 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Meat meal 4.2 2.5 4.2 2.6 3.2 2.4 4.5 2.8 Limestone 3.9 4.3 7.1 7.5 4.1 4.3 7.1 7.5 Available fat 0.5 0.6 2.8 2.9 2.1 2.0 2.0 2.1 Vitamin premix 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Trace mineral 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Salt 0.3 0.3 0.3 0.3 0.4 0.4 0.3 0.3 D-L methionine 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Total 100 100 100 100 100 100 100 100 74 Table 3.2 Calculated analysis of postmolt diets Dietl Diet2 Diet3 Diet4 Diet5 Diet6 Diet7 Diet8 Crude Protein % 17.00 17.00 17.00 17.0 15.00 15.00 15.00 15.00 Ether Extract % 3.71 3.66 5.76 5.70 3.26 3.18 5.21 5.16 Ash% 7.36 7.38 10.44 10.47 7.16 7.25 10.25 10.27 Calcium % 2.00 2.00 3.25 3.25 2.00 2.00 3.25 3.25 Available 0.32 0.25 0.32 0.25 0.32 0.25 0.32 0.25 Phosphorus % Lysine % 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 Methionine 0.72 0.72 0.72 0.72 0.72 0.72 0.72 0.72 -(-Cysteine % The experimental diets were formulated to contain two levels of calcium (3.25%,2%), two levels of phosphorus (0.32%,0.25%) and two levels of protein (17%,15%) arranged in a 2x2x2 factorial layout. There were three replications of each of the eight treatments. There was a total of 45 hens per replicate and a total of 135 layers per treatment. 3.3.2 Management Prior to Molting:. Eighteen days before the molting period the hens were redistributed so that there was on equal number of hens per row. The hens were fed the layer diet until molting began and were subjected to 16 hours of light per day with an intensity of 10 lux units. Just 1 day before molt, the sample birds from the previously labeled cages were 75 weighed to ascertain the weight of the birds before molting. Data such as daily egg production, weekly average egg weight by row from two consecutive days production and weekly average specific gravity by row were collected prior to molt. The addition of supplemental calcium to the feed during the final 2 days before molting is induced improves the shell quality of the final eggs laid before production ceases. Therefore 2 days before the molt, oyster shell was top dressed at the rate of 2.27kg /100 hens. (Since there were 45 hens per row the top dressing was given at the rate of 1.02 kg per row. Molting Period: On day 0, five layers were sacrificed and the tibia and femur were removed for measurement of percentage calcium in the medullary bone and the reproductive tracts were removed for assessment of size and development before molting process. Molting was initiated by decreasing day length to 1 hour for 10 days. The hens were then exposed to 8 hours of light from day 11 to 19. Starting on day 1 of the molt the hens were fed only cracked corn until an appropriate weight loss of about 30% was achieved. On day 20, day length was increased to 14 hours. The success of a molt depends on accurate body weight monitoring. The premolt weight of the hens is one of the most important pieces of information in the entire program. One day prior to the molt (day 0), all the hens in 144 cages (3 pairs of cages per row) were weighed. The cages were marked so that the layers could be weighed for subsequent sampling. Body weights were determined again on day 7 and day 9 of the molt and the average weight loss 76 per day calculated. From this estimated weight loss it was possible to predict when the hens would reach target weight loss of around 30%. When the target weight loss was achieved, the molting period was terminated the hens were fed one of the eight postmolt diets. The molting period lasted for 20 days. The postmolt diets were fed till the hens reached 5% egg production and this period lasted for 15 days, after which the hens were switched to the layer diet. Postmolt Prelay Period: The eight postmolt diets were fed till 5% production was achieved. Prior to feeding the postmolt diets, five layers at random were sacrificed and the tibia and femur were removed for analysis of percentage of calcium in the medullary bones of femur and tibia. The data that were collected during this period included day of first egg, egg production, feed consumption per row, mortality, egg weight and egg specific gravity from two consecutive days' production. Also one layer per row was sacrificed at random and the tibia and femur were removed to determine the percentage of calcium retained in the medullary bone in relation to treatment. Laying Period: When the layers of a particular treatment attained 5% production, all layers on that postmolt diet were switched to a commercial layer diet. Egg production was then monitored for 4 months. The other data that were collected during the period were mortality, barn temperature, daily egg production such as total eggs, cracked eggs and soft 77 shelled eggs, egg weight and specific gravity every 2 weeks, and feed consumption by row every 4 weeks. 3.3.3 Laboratory Analyses Five layers were sacrificed at random and euthanized by cervical dislocation and carcasses from euthanized hens were dissected and meat removed from the femurs and tibias for determination of the percentage calcium content in the medullary bones before and after the molt. Also 24 layers (3 layers per treatment) were sacrificed and their tibias and femurs removed to determine the percentage calcium in relation to the treatment. The long bones (femur and tibia) were split longitudinally using a long knife and hammer and the moist medullary bone was separated from the cortical bone using a scalpel (Clunies et al., 1992). Medullary bone scraped from the shafts of the cortical bone was placed in a porcelain crucible and oven dried at 65°C and ashed at 600°C in a muffle furnace overnight. Medullary bone ash was then transferred to a 50 ml volumetric flask by washing the crucible with 10 ml of dilute hydrochloric acid and the solution was made up to the 50 ml mark using deionized water. Calcium concentration in mg/kg was then determined using atomic absorption spectrophotometry. 78 3.3.4 Chemical Analyses of Feed Calcium in the feed was determined by atomic absorption spectrophotometry (Heckman 1967) and phosphorus using the Shimadzu colorimeter method (Cavell 1955). Percentage of crude fat, (ether extract) in the feed sample was determined by the Goldfisch method as per the procedures outlined in (A.O.A.C, 1990). Percentage crude protein in the feed was determined by first determining the amount of nitrogen in the feed sample by the autoanalyser method (A.O.A.C. 1980) and then multiplying the percentage nitrogen with 6.25. An adiabatic bomb calorimeter was used to determine the energy content of the feed samples. Specific gravity was determined using sodium chloride solutions ranging in specific gravity from 1.065 to 1.100 in increments of 0.005 units (floatation method). 79 Table 3 . 3 Determined values for postmolt diets Dietl Diet2 Diet3 Diet4 Diet5 Diet6 Diet7 Diet8 Crude Protein % 17.85 18.47 17.54 16.33 15.69 17.00 19.31 17.92 Ether Extract % 1.97 2.2 5.35 5.57 2.52 2.71 4.39 3.94 Ash % 3.69 4.21 6.72 7.13 4.49 3.59 6.91 5.71 Calcium % 1.75 1.94 3.59 3.59 2.29 1.93 3.74 3.29 Available phosphorus % 0.35 0.20 0.39 0.42 0.38 0.20 0.32 0.24 3 . 3 . 5 Statistical Analysis Data was subjected to analysis of variance using the General Linear Models procedure of SAS software. Differences in means was detected by Tukey's Studentized range test (P < 0.05). Three way analysis of variance was done to study the interaction between calcium, phosphorus and protein on the different variables. 3 . 4 Results The hens were fed eight different postmolt diets followed by the layer diet during the experimental period. These diets were analyzed for crude protein, ether extract (fat content), calcium and phosphorus. The results are given in Table 3.3. 80 Fig. 3.1 shows the percentage hen day egg production starting from 55 weeks to 75 weeks of age. Eggs were collected daily and hen days were calculated to determine the weekly egg production. Hen days are days in which the hen is assumed to produce one egg per day. This is calculated using the daily mortality data. The lines in the graph are for the different treatments the hens were subjected to. There was no significant difference in the level of egg production for different treatments. Around week 69 there was a reduction in total egg production from hens subjected to treatment 8 which may be due to environmental stress. From the graph we can see that egg production declined as the age of the hen advances, the production being above 90% around week 65 and around 80% at week 75. In Appendix C Fig. C. 1 shows the percentage hen day production (gradable eggs) starting at 55 weeks to 75 weeks. The eggs that were collected were separated into cracked eggs, soft shelled eggs and total eggs. Those eggs that had a well developed egg shell could be marketed and hence were called gradable eggs. For calculating the percentage gradable eggs the daily mortality and hen days are to be determined. In Appendix C Fig. C.2 represents the effect of prelay diet on subsequent average egg weight. Every alternate week on two consecutive day's eggs were collected for determining egg weight. These data were used as a representative sample of all the eggs that were produced during the experimental period. The lines on this graph shows the average egg 81 weights for the different treatments. There was however no significant difference in egg weight among the treatments. Fig. 3.2 shows the effect of prelay diet on subsequent egg size. The eggs that were weighed alternate weeks on two consecutive days were then sorted into peewee, small, medium, large, extra large and jumbo based on their egg weight. All the eggs that weighed less than 42 g were grouped as peewee eggs, between 42 to 49 g as small, from 49 to 56 g as medium, between 56 to 64 g as large, from 64 to 72 g as extra large and eggs weighing over 72 g were classified as jumbo eggs. The stacked bar graph shows the percentage of different sizes of eggs produced for each of the eight treatments. Among all treatments, hens on treatment 4 produced more extra large eggs which is clear from Fig. 3.2. In general, all the hens subjected to the different postmolt diets produced more large and extra large eggs. Medium, small and peewee eggs contributed to less than 5% of the total egg production. These stacked bars for each of the treatments is a representative of all the egg produced during experimental period. Thus, one can use Fig. 3.2 to determine egg production by egg types for a given treatment. For example, in order to determine the number of small eggs produced with treatment 1, one can use the percentage value of small eggs from Fig. 3.2 and multiply by the total eggs produced for that treatment. 82 55 60 65 Age in weeks 70 75 — T r e a t 1 - - D- - • Treat 2 - -A - Treat 3 - -x - Treat 4 - -x- - Treat 5 - - o- - • Treat 6 - + - Treat 7 - - - Treat 8 Fig. 3.1: Effect of molt diet on total egg production Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein Table 3.4 Effect of postmolt diets on percentage egg grade Treat 1 Treat 2 Treat 3 Treat 4 Treat 5 Treat 6 Treat 7 Treat 8 Peewee 0.05 0.00 0.00 0.05 0.05 0.00 0.10 0.05 Small 0.20 0.05 0.26 0.10 0.05 0.00 0.48 0.15 Medium 2.05 1.30 1.24 0.79 1.48 2.38 2.27 2.12 Large 24.46 27.28 25.97 23.95 33.19 28.86 29.50 28.82 Extra large 59.08 55.41 56.98 62.86 53.58 54.10 56.74 53.20 Jumbo 14.16 15.97 15.56 12.25 11.65 14.65 10.91 15.67 Note: Treat- Treatment 84 N 100% 60% 40% r 20% 0% I— C N "* IT) «-> * J + H Cd Cd cd cd cd cd O O ( P OJ CD I H I H I H s- I H in H H H H H cd U S H H oo -4—I •cd U I H H IJ • EL • L E3M I S I P W l Fig. 3.2: Effect of molt diet on average egg size Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein 85 In Appendix C Fig. C.3 shows the effect of average specific gravity for all of the eight treatments. There was no significant difference in egg specific gravity between any of the treatments. There was a trend for reduced specific gravity as the age of the hen advanced. Fig. 3.3 shows percentage calcium in the medullary bones of tibia and femur. There was however no significant difference in percentage calcium in tibia and femur. Hens subjected to treatment 4 had a higher calcium content in the medullary bones of tibia and femur when compared to the other diets. From these results we can conclude that treatment 4 which contained 17% protein, 3.25% calcium and 0.25% phosphorus was beneficial in building the calcium reserves of the hen during the laying period. Table 3 . 5 Calcium content of the medullary bone before molt Premolt Mean dry Percentage Mean dry weight of dry weight of weight of cortical bone cortical bone medullary (g) (%) bone(g) Percentage Percentage of dry weight of calcium in the medullary medullary bone bone (%) (%) Tibia 6.88 Femur 4.08 88.8 83.8 0.87 0.79 11.2 16.2 6.64 8.10 Table 3 . 6 Calcium content of the medullary bone after molt Premolt Mean dry Percentage Mean dry Percentage Percentage of weight of dry weight of weight of dry weight of calcium in the cortical bone cortical bone medullary medullary medullary bone (g) (%) bone(g) bone(%) (%) Tibia Femur 5.94 4.02 89.9 84.6 0.67 0.73 10.1 15.4 0.73 1.08 86 Table 3.7 Effect of postmolt diets on medullary bone calcium content of tibia Treatment Dry Weight of Dry Weight of medullary bone medullary bone ( (g) Calcium in %) medullary bone (%) Dry weight of cortical bone(g) Dry weight of cortical bone(%) 1 0.39 5.31 1.82 7.20 94.69 2 0.50 8.99 2.11 5.25 91.01 3 0.37 5.23 2.84 6.80 94.77 4 0.39 5.06 3.14 7.22 94.94 5 0.38 6.82 3.25 5.25 93.18 6 • 0.41 6.16 2.68 6.25 93.84 7 0.40 5.49 1.61 6.95 94.51 8 0.43 5.68 1.55 7.15 94.32 SEM 0.1 1.6 1.1 1.0 1.6 Notes: Differences among means in each column are not significant (P > 0.05), SEM-Standard Error of Mean. 87 Table 3.8 Effect of postmolt diets on medullary bone calcium content of femur Treatment Dry weight of medullary bone (g) Dry weight of medullary bone (%) Calcium in medullary bone (%) Dry weight in cortical bone (g) Dry weight in cortical bone (%) 1 0.25 5.30 2.15 4.63 94.70 2 0.40 9.16 1.67 4.06 90.84 3 0.29 7.48 2.21 3.67 92.52 4 0.32 6.83 3.73 4.32 93.17 5 0.28 8.19 2.57 3.28 91.81 6 0.39 8.92 2.29 4.01 91.08 7 0.36 7.58 2.06 4.39 92.42 8 0.40 8.33 2.29 4.42 91.67 SEM 0.1 1.8 0.8 0.5 2.0 Notes: Differences among means in each column are not significant (P > 0.05), SEM-Standard Error of Mean. 88 Fig. 3.3: Effect of molt diet on percentage calcium in the medullary bones Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein 89 Tables 3.9 and 3.10 show the effect of dietary treatments on hen performance for two periods from 60-69 weeks and 70-77 weeks respectively. For each period, weekly percentage total egg production, gradable production, egg weight, egg mass and egg specific gravity were averaged and were subjected to statistical analysis for standard error of mean (SEM) and level of significance. The standard error of mean given in the tables are the maximum value among all the treatments. Since feed weigh back were performed monthly, feed per day and feed conversion were determined weekly by taking average of the monthly feed consumption data. The egg mass was calculated using average egg weight and percentage total egg production on a weekly basis. There were no significant difference among the means for different treatments. Table 3.9 The effect of postmolt diets on hen performance (60 to 69 weeks of age) Total egg production (%) Gradable egg production (%) Egg weight (g) Egg specific gravity Egg mass (g per hen per day) Feed/day FCR (g:g) Treat 1 63.7 63.4 66.7 1.089 46.7 135.2 2.90 Treat 2 62.8 62.5 66.4 1.089 45.8 135.7 2.97 Treat 3 62.9 62.7 66.9 1.089 46.4 136.8 2.95 Treat 4 61.6 60.8 66.9 1.089 45.1 132.6 2.94 Treat 5 62.7 62.5 65.8 1.089 45.0 133.9 2.97 Treat 6 62.3 62.2 66.4 1.089 45.0 135.3 3.01 Treat 7 61.9 61.2 65.8 1.089 45.4 133.9 2.95 Treat 8 61.5 61.1 66.1 1.089 45.3 133.3 2.95 SEM 11.6 11.5 1.1 0.0007 8.8 6.8 0.04 Notes: Differences among means in each column are not significant (P > 0.05), FCR- Feed conversion ratio. SEM-Standard Error of Mean. 91 Table 3.10 The effect of postmolt diets on hen performance (70 to 77 weeks of age) Total egg Gradable egg Egg Egg specific Egg mass Feed /day FCR production production weight gravity (g per hen (g:g) per day) (%) (%) (g) Treat 1 85.6 85.0 67.4 1.089 56.6 126.5 2.23 Treat 2 85.3 85.0 67.6 1.089 56.6 128.1 2.26 Treat 3 83.0 82.3 67.6 1.088 55.3 127.0 2.29 Treat 4 83.3 82.4 67.5 1.088 55.2 125.3 2.27 Treat 5 84.1 83.8 66.4 1.088 54.8 124.4 2.27 Treat 6 86.4 85.8 67.1 1.088 57.4 128.7 2.24 Treat 7 85.1 84.1 66.6 1.088 55.9 126.9 2.27 Treat 8 83.8 83.0 66.9 1.087 55.3 125.9 2.27 SEM 1.3 1.2 0.2 0.0005 1.2 6.6 0.004 Notes: Differences among means in each column are not significant (P > 0.05), FCR- Feed conversion ratio. SEM-Standard Error of Mean. 92 3 . 5 Discussion There are different methods of molting a flock. There is no one or optimal program due to differences in genetics, health, age, environment and previous flock history (Swanson and Bell 1971). In this particular study the birds were subjected to a 20 day molt, during which period the hens were fed cracked corn till the approximate body weight was achieved. The molting period was initiated by decreasing the day length to 1 hour for 10 days and 8 hours of light from day 11 to 20. The molt was continued till a target weight loss of 30% was achieved. The success of a molt depends on a accurate body weight monitoring which is an important criterion. In this molt study, there was no significant difference in egg production, average egg weight, egg specific gravity and egg mass which is clear from (Tables 3.9- 3.10) for both the periods. Feed intake during the postmolt period was not significantly affected by dietary calcium level. Hens under treatment 4 which had a dietary calcium content of 3.6%, 0.42% phosphorus and 16.3% protein produced eggs better in size when compared to the other treatments. However, the other treatments fed after the molting period to first egg did not significantly affect postmolt performance with respect to feed consumption, mortality, egg production or egg weight. Considering the level of protein again, treatment 4 had a crude 93 protein content of 16.3% and resulted in hens having better egg size as seen from Table 3.4 and Fig. 3.2 which agrees well with findings of Leeson and Summers (1988) that adequate protein is required for the onset of egg production and subsequent reproductive performance especially egg size. There are number of reports indicating reduced reproductive performance with low protein diets (Jensen et al., 1990 and Keshavarz 1991). In order to look at the hens' performance with regards to dietary protein contents, the diets were formulated to contain 15% and 17% protein. However, when the diets were analyzed for their protein contents it was found that all the molt diets contained 16-17% with the exception of treatment 5 and 7. Thus it was not possible to conclude that protein had any effect on egg weight or egg production. The molt diets resulted in hens producing more medium, large and extra large eggs which is evident from Fig. 3.2 compared to the first cycle which agrees well with the findings of (Leeson and Summers, 1987). There was an increase in egg size with the second cycle hens which may be due to the fact that the hens entering the second cycle had a higher body weight than when they had during the first cycle. Considering the medullary bone large amount of research has shown that the skeleton of the laying hens serves as a store for calcium which is utilized in egg shell formation (Simkiss 1961). Maintenance of such calcium stores is therefore important for maximum performance of the laying hen. Tables 3.5 and 3.6 show the percentage of calcium in the medullary bone before and after the molt. From these tables we can see that the medullary bone calcium 94 content is higher before molt because the hens were fed the layer diet containing 4.4% calcium, which was sufficient to build the calcium reserves until the time they were subjected to the molt. Whereas, after the molting there was a reduction in the medullary bone calcium content as there was no calcium supplemented while the hens were in the molting period, which did not allow for sufficient building up of calcium in the medullary bone. In this experiment, hens that were subjected to treatment 4 had higher percentage of calcium retained in the medullary bones of tibia and femur as seen from Tables 3.7 and 3.8 when compared with the other treatments, but there was no significant difference in the percentage calcium between the tibia and femur. This does not agree well with the findings of Clunies et al., (1992) that the largest reserve of calcium was found in femur followed by the tibia. Hurwitz (1964) reported that the turn over rate of medullary bone calcium differed for various bones. Hens fed 3.6% calcium as in treatment 4 had a higher percentage of calcium in their bones and this well agrees with the findings of Clunies et al., (1992) that birds fed 3.5% dietary calcium had the greatest amount of calcium in their medullary bones. They also found that with higher levels of calcium such as 4.5%, there was a decreased dependence upon medullary bone mineral to supply calcium for shell formation. Although hens under treatment 4 had higher percentage of calcium in the medullary bones of tibia and femur, there was no effect of dietary calcium levels upon individual medullary bones because the diets also contained different levels of available phosphorus and protein and the overall effect may be 95 due to the combination of calcium, phosphorus and protein rather than exclusively due to calcium. 3.6 Conclusions Based on the results of this trial we can conclude that there is a benefit from hens under treatment 4 which is a combination of 16.3 % protein, 3.6% calcium and 0.42 % phosphorus, as this diet resulted in hens producing more of large and extra large eggs when compared to the other treatments. The hens under treatment 4 also had a higher percentage of calcium in the medullary bone of the tibia and femur. Since the diets were a combination of protein, calcium and phosphorus it is difficult to conclude that the above effect may be due to the influence of calcium alone as there will definitely be an interaction of protein, calcium and phosphorus. More long term studies are required to confirm the relationship between dietary calcium and medullary bone calcium reserves. 96 Chapter 4 Discussion Three studies were conducted to study the effect of calcium on hens' performance. Two of the studies involved prelay trials and the third one was a molt study. In prelay study I only one strain was used namely the H&N strain. The same birds were subjected to molting at 57 weeks of age. Prelay study II was conducted to determine if there was any difference in hens' performance due to strain characteristics, hence two strains H&N and Hyline were used in this study. The determined calcium level in the developer, prelay diet, and layer diet are 1.0%, 2.6% and 4.4 % respectively compared to the expected values of 1.0%, 2.0% and 3.5%. This difference in the calculated versus the expected values could be due to many reasons like inaccuracies in dilution rates while making up the solutions for calcium determination, strength of the sample solutions and concentration of lanthanum used in the atomic absorption spectrophotometer, absorption of moisture during storage of feed. Weekly egg production or egg weight was not influenced by 1.0%, 2.6%, and 4.4% of calcium which agrees well with the findings of Brake et al., (1984) who found that diets containing 1%, 2.5% and 3.5% calcium did not affect the hen's performance in terms of egg production and egg weight. This is in contrast with the studies done by Roland et al., (1985), they noticed a significant decrease in egg production as the dietary calcium level decreased. 97 In another study by Keshavarz (1986), there was a tendency for decreased egg production with increasing dietary levels of calcium. In the present study however no such differences in egg production was noticed whether the dietary calcium levels increased or decreased. Furthermore, there was no difference in egg specific gravity for the weeks it was measured suggesting no difference in shell quality among the different treatments, although this is not in accordance with the study conducted by Roland et al., (1985) in which the egg specific gravity was significantly decreased in hens fed a 1% calcium diet than in hens under 4.4% calcium suggesting that egg specific gravity and shell weight are directly related to dietary calcium level. Feed consumption, feed conversion ratio, egg mass along with egg production and egg weight were calculated for two periods during the experiment. There was no significant difference among the means for different treatments (P > 0.05). This result however did not agree with the conclusions made by Roland et al., (1985) who found that the average feed intake of the laying pullets that were fed 1% calcium was significantly greater than hens fed a diet containing 3.75% calcium. They also found that feed consumption was 30% greater for hens fed 1% calcium during week 1 but was only 11% greater in week 3. In the present prelay trial no such differences in feed intake was noticed. Considering egg size, there was a difference in the distribution of egg size, which does not support the findings of Hamilton and Cipera (1981) who stated that prelay calcium diet 98 did not have any effect on egg size. Miller and Sunde ( 1975) found that hens fed a low calcium diet (0.5-0.6%) produced more larger eggs than hens fed a higher calcium diet (3%). In the current prelay study no such differences in egg size due to low dietary calcium level was noticeable, although hens fed a prelay diet containing 2.6% calcium produced more extra large eggs. Also after the introduction of the layer diet, shell formation was normal regardless of the prelay calcium treatment, which agrees with the work of Leeson et al., (1986). Nevalainen (1969) also reported that dietary prelay calcium concentration could influence maturity because inadequate levels of calcium would adversely affect the development of ovary and oviduct. Miller and Sunde (1975) and Gilbert et al., (1978) indicated that the dietary prelay calcium level had no effect on maturity and Lennards and Roland (1986) indicated that 0.58% calcium was adequate for ovulation but not for shell quality. In this study the prelay diet contained 2.6% calcium, which appeared to be sufficient to meet the calcium requirement of the bird for egg production, since there was no evidence of an adverse effect on subsequent egg production. The highest revenue was from the pullets receiving the prelay diet from 16 weeks to first egg. On the other hand when the prelay diet was introduced one week later i.e. at 17 weeks rather than at 16 weeks of age the net revenue per hen housed was similar to that of pullets receiving the grower diet until first egg. Feeding pullets a prelay diet with 2.6% calcium therefore appears to be beneficial. There was a reduced net revenue from those pullets which received the layer diet at 18 weeks rather 99 than at 16 weeks. This suggests that the net revenue was reduced the later the layer diet was introduced. Another advantage in feeding the prelay diet containing 2.6% calcium starting from 16 weeks of age is that the cost of the prelay diet is comparatively less than that of the commercial layer diet and appeared to be more economical than the layer diet that contained approximately 4.4% calcium. Feeding prelay diet is also beneficial as it supplies the bird with the required amount of calcium to build up its calcium reserves when compared to the excess provided by the layer diet thus reducing kidney damage caused by excess calcium. In the prelay study with two strains, there was a benefit in feeding the prelay diet at 1.8% calcium starting from 17 weeks of age until first egg in the case of Hyline and a prelay diet starting at 16 weeks in the case of H&N strains than the layer diet which contains approximately 3.3% calcium. Feeding the prelay diet, grower diet, and layer diet did not cause any significant differences in terms of egg weight, egg specific gravity, or egg production in both periods, but there was a difference in egg size. There was no difference in egg specific gravity although the hens were fed a diet containing 1.1%, 1.8% and 3.3% calcium. Feeding prelay diet with approximately 1.8% calcium was found to be beneficial in both the strains and that in the Hyline it should be introduced at 17 weeks and in the H&N at week 16. Also when comparing the feed cost the prelay diet had a lesser feed cost than the commercial grower or the layer diets. Considering the profit from both strains it appeared 100 that feeding the prelay diet at 16 weeks was found to be beneficial in the H&N strain which also correlates well with the first prelay trial where H&N strain of birds were used in the study. Feeding the prelay diet at 17 weeks of age was beneficial in the case of Hyline strain of chicken. All the same, irrespective of the time of introduction, whether it be 16 or 17 weeks the prelay diet was found to be beneficial in both the strains than the grower or the layer diets. From both the prelay trials it was seen that feeding a prelay diet with approximately 2% calcium not only helps building the calcium reserves in the medullary bone of hens thus resulting in eggs with good shell quality, but also that it is not detrimental to the health of the birds and that it can be given at 16 or 17 weeks. (i.e. prior to egg production) to give best result in terms of profit to the layer industry. In the molt study, the birds were subjected to a 20 day molt, during which period the hens were fed cracked corn till the approximate body weight loss of 30% was achieved. The success of a molt depends on a accurate body weight monitoring which is an important criterion. The molting period was initiated by decreasing the day length to 1 hour for 10 days and 8 hours of light from day 11 to 20. There was no significant difference in egg production, average egg weight, egg specific gravity and egg mass for all treatments in both periods. Feed intake during the postmolt period was not significantly affected by dietary calcium level for all treatments. Hens under 101 treatment 4 which had a dietary calcium content of 3.6%, 0.42% phosphorus and 16.3% protein produced eggs better in size when compared to the other treatments. Considering the level of protein again, treatment 4 had a crude protein content of 16.3% and resulted in hens having better egg size which agrees well with findings of Leeson and Summers (1988) that adequate protein is required for the onset of egg production and subsequent reproductive performance especially egg size. There are number of reports indicating reduced reproductive performance with low protein diets (Jensen et al., 1990 and Keshavarz 1991) indicating that protein is an essential constituent in the postmolt diets as it is required for ovary and oviduct development after the molt. In order to look at the hens' performance with regards to dietary protein contents, the diets were formulated to contain 15% and 17% protein. However, when the diets were analyzed for their protein contents it was found that all the molt diets contained 16-17 % with the exception of treatment 5 and 7. Thus it was not possible to clearly see the effect of protein on egg weight or egg production. The postmolt diets resulted in hens producing more medium, large and extra large eggs which is evident from compared to the first cycle which agrees well with the findings of (Leeson and Summers, 1987). There was an increase in egg size with the second cycle hens which may be due to the fact that the hens entering the second cycle had a higher body weight than when they had during the first cycle. 102 Considering the medullary bone large amount of research has shown that the skeleton of the laying hens serves as a store for calcium which is utilized in egg shell formation (Simkiss 1961). Maintenance of such calcium stores is therefore important for maximum performance of the laying hen. The medullary bone calcium content is higher before molt because the hens were fed the layer diet containing 3.5% calcium, which was sufficient to build the calcium reserves until the time they were subjected to the molt. Whereas, after the molting there was a reduction in the medullary bone calcium content as there was no calcium supplemented while the hens were in the molting period, which did not allow for sufficient building up of calcium in the medullary bone. In this experiment, hens that were subjected to treatment 4 had higher percentage of calcium retained in the medullary bones of tibia and femur when compared with the other treatments, but there was no significant difference in the percentage calcium between the tibia and femur. This does not agree well with the findings of Clunies et al., (1992 b) that the largest reserve of calcium was found in femur followed by the tibia. Hurwitz (1964) reported that the turn over rate of medullary bone calcium differed for various bones. Hens fed 3.6 % calcium as in treatment 4 had a higher percentage of calcium in their bones and this well agrees with the findings of Clunies et al., (1992 b) that birds fed 3.5% dietary calcium had the greatest amount of calcium in their medullary bones. They also found that with higher levels of calcium such as 4.5%, there was a decreased dependence upon medullary bone mineral to supply calcium for shell formation. Although hens under treatment 4 had higher percentage of calcium in the medullary bones of tibia and femur, there 103 was no effect of dietary calcium levels upon individual medullary bones because the diets also contained different levels of available phosphorus and protein and the overall effect may be due to the combination of calcium, phosphorus and protein rather than exclusively due to calcium. 104 Chapter 5 Conclusions Two prelay studies were conducted to determine the advantages of prelay diet especially in terms of egg production, egg shell quality and profit. In prelay study I only one strain of White Leghorn was used. From this trial it appeared that there was a benefit in feeding a higher calcium (> 1%) prior to the laying period and that this diet should be given at 16 weeks of age. Pullets fed the prelay diet with 2% calcium produced more extra large eggs than those on the grower or layer diets. Taking into account the profit, again the pullets fed prelay diet at 16 weeks yielded a higher profit than those on the grower or the layer diet. It was also found from this study that the profit was lowest when the layer diet was given at 18 weeks when compared to 16 or 17 weeks. In order to study if the same effect of prelay diet is seen in other strains of White Leghorns, prelay study II was conducted to determine if there was any difference due to strain. This study was done using H&N and Hyline strains. In this trial, both strains of birds were subjected to same lighting, and environmental temperature. From this trial it was seen that there was a benefit in feeding the prelay diet from 16 weeks to first egg in the case of H&N as in trial one, however feeding the prelay diet from 17 weeks was found to be economical in Hyline strain. With regard to feed cost, treatment 3 which involved feeding a 105 prelay diet from 17 weeks to first egg, was much less than for all the other treatments for both strains. Considering the overall performance of the layers, the Hyline strain performed better in egg production and feed conversion ratio during the first period and in the second period the H&N took over the Hyline in terms of egg production and feed conversion ratio. However, both the strains gave better profits when fed the prelay diet irrespective of the time of introduction of the diet whether given at 16 or 17 weeks of age than either the grower or layer diets. The profit was lowest from pullets fed the layer diet from 16 weeks in both the strains. From the point of view of layer industry or the egg producers, in order to get good returns it would be beneficial to rear a combination of the H&N and Hyline strains to meet the increasing demands of eggs for the market as during the initial laying period Hyline would give better returns with little feed consumption compared to the H&N strain. However there will be differences always due to strain characteristics like mortality, feed consumption, feed conversion ratio, body weight gain and egg production when more than one strain is involved. In the molt study the hens from the first prelay trial were subjected to molting. Here apart from studying the effect of molting on egg production, the effect of dietary calcium on medullary bones of tibia and femur was studied. The molted hens produced more large and extra large eggs than in the prelay trial. Peewee and small eggs contributed to about 5% of 106 the total egg production. After molting, the hens were fed eight postmolt diets with different levels of protein, calcium and phosphorus. Hence it was quite difficult to see the effect due to calcium as there will be an interaction of phosphorus and protein as well. Therefore, further research is recommended in this molting area with diets containing only two variables with a wider margin within the variables. Taking into account the medullary bone calcium content, the calcium content was higher in the femur and tibia in the five hens that were randomly sacrificed before the molt than those five hens after the molt. This is due to the fact that the five hens prior to the molt were on a layer diet so since the layer diet has around 3.5% calcium, this enabled the building of calcium in the medullary bones of the tibia and femur. Whereas, in the hens after the molt the calcium content was much lesser because the cracked corn fed during the molting period did not have sufficient calcium to build up the calcium reserves. This showed that there is a relationship between dietary calcium and medullary bone calcium reserves. During the post molt period the hens were fed eight postmolt diets with different levels of protein, calcium and phosphorus as mentioned earlier. Again, one bird per row was sacrificed and the medullary bones of tibia and femur were analyzed for calcium to study the effect of postmolt diets. It was found that hens under treatment 4 which had a higher amount of calcium had higher percentage of calcium in the medullary bones of tibia and femur compared to the other treatments. Both the tibias and femurs had more or less the same 107 amount of calcium for all treatments. Although the diets were formulated to contain two levels of protein at 15% and 17%, on analysis it was found that the protein content ranged between 16-17% for all treatments. Hence as said earlier further research is needed to study the effect of calcium or protein with regards to parameters such as egg shell quality and egg size with a wide range in the percentages of calcium or protein in the diets. Overall from this molt study it can be concluded that treatment 4 with 3.6% calcium, 0.42% phosphorus, 16.3% protein resulted in more large and extra large eggs and also the hens under this treatment had a higher percentage of calcium in the medullary bones of tibia and femur. Since only three birds were used per treatment it is difficult to see the effect due to treatments, hence it would be better to use more birds to study the effect of dietary calcium on medullary bone calcium reserves. 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Davis. C A . Swanson, M. H., and D. D. Bell, 1974 a. Force molting of chickens. 1. Introduction. Univ. of California. Coop. Ext. Bull. AXT-410. Taylor, T. G., 1965. Calcium endocrine relationship in the laying hen. Proc. Nutr. Soc. 24:49-54. Taylor, T G., K. Simkiss, and D. A. Stringer, 1971. The skeleton: its structure and metabolism. In Physiology and bio-chemistry of the Domestic Fowl, ed: F. M. Freeman. Pages 125-170. London academic Press. Taylor, T. G., and J. Kirkley, 1967. The absorption and excretion of minerals in laying hens in relation to egg shell formation. Br. Poult. Sci. 8:289-295. 117 Taylor, T. G., and J. M. Moore, 1954. Skeleton depletion in hens laying on a low calcium diet. Br. J. Nutr. 8:112-124. Taylor, T. G., T. R. Morris, and F. Hertelendy, 1962. The effect of pituitary hormones on ovulation in calcium deficient pullets. Vet. Rec. 74:123. Tortuero, F., and C. Centero, 1973. Studies of the use of calcium carbonate in the feeding of laying hens during summer months. Poultry Sci. 52:866-872. Vandepopuliere, J. M., and J. J. Lyons, 1992. Effect of inorganic phosphate source and dietary phosphorus level on laying hen performance and egg shell quality. Poultry Sci. 71:1022-1031. Van de Velde, J. P., N. Loveridge, and J.P.W. Vermeiden. 1984 a. Parathyroid hormone responses to calcium stress during egg shell calcification. Endocrinology 115:1901-1904. Van de Velde, J. P., J. P. W. Vermeiden, J. J. A. Touw, and J. P. Veldhudzen. 1984 b. Changes in activity of chicken medullary bone cell populations in relation to the egg laying cycle. Metab. Bone. Dis. Rel. Res 5:191-193. Voisey, P. W., and D. C. MacDonald. 1978. Laboratory measurement of egg shell strengh. 1. An instrument for measuring shell strength by quasi-static compression, puncture, and non-destructive deformation. Poultry Sci. 57:860-869. Whitehead, C. C , and D. W. F. Shannon, 1974. The control of egg production using a low sodium diet. Br. Poult. Sci. 15:429-434. Wideman, R. F., Jr., J. A. Closser, W. B. Roush, and B. S. Cowen., 1985. Urolithiasis in pullets and laying hens. Role of dietary calcium and phosphorus. Poultry Sci. 64:2300-2307. Wilson, H. R., J. S. Moore, A. W. O'Steen, J. L. Fry, and R. H. Harms, 1969. Forced molting of laying hens . Univ of Florida bulletin 728. Wood-Gush, D. G. M., and M. R. Kane, 1966. The behaviour of calcium deficient chickens. Br. Poult. Sci. 7:285-290. Zimmerman, N. G., and D. K. Andrews, 1987. Comparison of several induced molting methods on subsequent performance of single comb White Leghorn hens. Poultry Sci. 66:408-417. 118 Appendix A Egg Prices and Feed Cost Used in Economic Analysis Following table shows prices for different types of egg size that were used in economic analysis in chapter 2. Table A . l Egg price per dozen of eggs Type of Egg $ value of Egg (Chapter 2) $ value of Egg (Chapter 4) Peewee 0.25 0.25 Small 0.78 0.81 Medium 1.22 1.25 Large 1.28 1.31 Extra-large 1.28 1.31 Jumbo 1.28 1.31 Following table lists price of the feed used in economic analysis in chapters 2. Table A.2 Cost of feed per thousand kg Type of feed $ value of feed Grower 236.71 Prelay 242.83 Layer 245.83 119 Appendix B Graphs For Prelay Studies 0 *•=—' '— i 19 21 23 25 27 29 31 33 ; Age in weeks o Treat 1 -- D- -Treat 2 — -A -Treat 3 - -x - Treat 4 - -*- - Treat 5 - - o - Treat 6 35 Fig. B. 1: Effect of prelay diet on gradable egg production Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 120 two 65 60 55 JS •Sf * 50 (ae WO O) So 45 ea t-i tu < 40 35 17 19 21 23 25 27 29 31 33 Age in weeks —e—Treat 1 - - r> - • Treat 2 - -A — Treat 3 - -x - Treat 4 - -x- - Treat 5 . . o- - Treat 6 35 Fig. B.2: Effect of prelay diet on average egg weight Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 121 1.105 g 1.100 Of u s <u a 11.095 1.090 • -. • . *~ * ~*-*^. -* . • — •x _T77^r 1 i 19 20 21 * . u 22 Age i n weeks 23 — T r e a t 1 - -x- • Treat5 •D---Treat2 • o - • Treat6 - -A - Treat3 - -x - Treat4 24 Fig. B.3: Effect of prelay diet on average specific gravity Treat 1 = A commercial pullet grower diet (1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (2.6% Ca) from 16 weeks to first egg Treat 3 = A commercial pre-lay diet (2.6% Ca) from 17 weeks to first egg Treat 4 = A commercial layer diet (4.4% Ca) from 16 weeks Treat 5 = A commercial layer diet (4.4% Ca) from 17 weeks Treat 6 = A commercial layer diet (4.4% Ca) from 18 weeks 122 100 90 80 70 60 50 40 30 20 10 0 20 24 28 32 36 Age in weeks — « — H&N Treat 1 — B — H&N Treat 2 — A — H&N Treat 3 —X— H&N Treat 4 Hyline Treat 1 - - O- - • Hyline Treat 2 - • + - - Hyline Treat 3 - Hyline Treat 4 Fig.B.4: Effect of prelay diet on gradable egg production in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 123 65 Age in weeks •o— H &N Treat 1 — a — H &N Treat 2 —*— H &N Treat 3 >< H &N Treat 4 * - • HylineTreat 1 ••<>••• HylineTreat 2 -•+•-• HylineTreat 3 HylineTreat 4 Fig. B.5: Effect of prelay diet on average egg weight in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks 124 1.105 20 24 28 32 36 Age in weeks —e— Hyline Treat 1 —e— Hyline Treat 2 —*— Hyline Treat 3 —*— Hyline Treat 4 H&N Treat 1 - - o- - • H&N Treat 2 — i — H&N Treat 3 H&NTreat4 Fig. B.6: Effect of prelay diet on average egg specific gravity in H&N and Hyline Treat 1 = A commercial pullet grower diet (1.1% Ca) from 16 weeks to first egg Treat 2 = A commercial pre-lay diet (1.8% Ca) from 16 weeks to first egg Treat 3 = A commercial pullet grower diet (1.1% Ca) to 17 weeks of age and a commercial prelay diet (1.8% Ca) from 17 weeks of age until first egg Treat 4 = A commercial layer diet (3.3% Ca) from 16 weeks Appendix C Graphs For Molt Study .2 -•3 ja sa o i-s- W> a ^ on on 100 80 60 40 20 0 1 m- m wr i 55 60 65 70 75 Age in weeks —e—Treat 1 - - Q - - Treat 2 - -A -Treat 3 - -x - Treat 4 - -x- - Treat 5 - - o - • Treat 6 - •+ -Treat 7 • - - Treat 8 Fig. C.l: Effect of molt diet on gradable egg production Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein 126 55 60 65 70 75 Age in weeks —e—Treat 1 - - Q- - • Treat 2 - * -Treat 3 - * - Treat 4 - -x- - Treat 5 - - o - • Treat 6 - •+ - Treat 7 - - - Treat 8 Fig. C.2: Effect of molt diet on average egg weight Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein 127 1.091 1.091 h •£ 1.090 S, 1.090 ig 1.089 '§ 1.089 £ 1.088 h « 1.088 gi 1.087 1.087 ".// s , *.> 60 64 68 i 72 76 Age in weeks —e—Treat 1 - - Q - -• Treat 2 - -A - Treat 3 - -x - Treat 4 - - Treat 5 - - o- -• Treat 6 - + - Treat 7 - - • Treat 8 Fig. C.3: Effect of molt diet on average egg specific gravity Treat 1 = Molt diet with 1.8% calcium, 0.35% phosphorus, 17.9% protein Treat 2 = Molt diet with 1.9% calcium, 0.20% phosphorus, 18.5% protein Treat 3 = Molt diet with 3.6% calcium, 0.39% phosphorus, 17.5% protein Treat 4 = Molt diet with 3.6% calcium, 0.42% phosphorus, 16.3% protein Treat 5 = Molt diet with 2.3% calcium, 0.38% phosphorus, 15.7% protein Treat 6 = Molt diet with 1.9% calcium, 0.20% phosphorus, 17.0% protein Treat 7 = Molt diet with 3.7% calcium, 0.32% phosphorus, 19.3% protein Treat 8 = Molt diet with 3.3% calcium, 0.24% phosphorus, 17.9% protein 

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