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Influence of constant enthalpy on broiler growth rate Kennedy, Brian James 1971

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INFLUENCE OF CONSTANT ENTHALPY ON BROILER GROWTH' RATE by BRIAN JAMES KENNEDY B.S.A. UNIVERSITY OF SASKATCHEWAN, 19 69 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of A g r i c u l t u r a l Mechanics We accept t h i s t h e s i s as conforming to the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1971. 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of AGRICULTURAL MECHANICS The University of British Columbia Vancouver 8, Canada Date O c t o b e r 28 , 1971. _ X -ABSTRACT An experiment was designed to t e s t the hypothesis that enthalpy could be used as an i n d i c a t o r of the s u i t a b i l i t y of the environment f o r growing p o u l t r y . Growth-rates and body weights of the b i r d s were used as a measure of t h e i r performance under d i f f e r e n t enthalpy c o n d i t i o n s . The e x p e r i -ment t e s t e d three enthalpy treatments, ranging from 29.3 to 33.3 BTU/lb of a i r , each treatment being r e p l i c a t e d three times. Male U n i v e r s i t y of B r i t i s h Columbia New Hampshire chickens from nine hatches (120 b i r d s per hatch) were used. They were grown from hatch to seven weeks of age i n three groups. Two of the groups were r a i s e d from hatch to three weeks of age i n c o n t r o l l e d environment brooders. The t h i r d group was r a i s e d i n a n o n - c o n t r o l l e d environment i n a f l o o r pen, and used as a check or c o n t r o l group. The r e s u l t s of the analyses i n d i c a t e d that f u r t h e r study would be necessary before e n t h a l p i e s i n the range studied could be used to p r e d i c t environmental c o n d i t i o n s f o r p o u l t r y . LIST OF CONTENTS ABSTRACT ACKNOWLEDGEMENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS INTRODUCTION REVIEW OF LITERATURE Heat Loss and Homeothermy Heat Loss by the Animal Body P h y s i o l o g i c a l Mechanisms f o r Thermo-regulation Thermo-regulation i n Bi r d s Enthalpy Growth Response of P o u l t r y to T h e i r Environment Mathematical Modelling of Heat Loss from a B i r d MATERIALS AND METHODS EXPERIMENTAL DESIGN MANAGEMENT OF BIRDS DISCUSSION AND RESULTS CONCLUSIONS SUGGESTIONS FOR FUTURE WORK LITERATURE. CITED / - i i -ACKNOWLEDGEMENTS The c o n t r i b u t i o n s of the f o l l o w i n g persons to t h i s study are g r a t e f u l l y acknowledged: Pr o f e s s o r L.M. Staley and Dr. C.W. Roberts f o r t h e i r guidance and encouragement. Dr. G.W. Eaton f o r a s s i s t a n c e i n preparing the computer programs to do the analyses. Douglas Bernon, Janet Gehring, the s t a f f of the p o u l t r y farm and a l l others who a s s i s t e d w i t h t h i s p r o j e c t . - i i i ; -LIST OF TABLES TABLE PAGE 1. ' Degrees of Freedom and Expected Mean Squares 26 f o r the Experimental Model. 2. Weekly Mean Body Weights f o r Enthalpy 30 Treatments. 3. Weekly Mean Body Weights f o r Each Group. 30 4. Mean Growth-rates f o r each of the Growth 31 Peri o d s . 5. ANOVA Expressed as Percentage Sums of Squares 31 f o r 1 and 7 week Weights and 1-3 and 3-7 week Growth-rates. 6. Mean Body Weights and Growth-rates f o r 34 Selected Growth Periods. 7. Percentage Sums of Squares f o r Body Weight 36 Analyses. 8. Percentage Sums of Squares f o r the Growth- 37 ra t e Analyses. - i v -LIST OF FIGURES FIGURE - ' PAGE 1 Psychrometic Chart Showing Selected 1° RelationshiDS. LIST OF SYMBOLS body weight surface area pure number -f a c t o r approximately equal to 2/3 but var y i n g w i t h species e q u i v a l e n t diameter ( f t ) f a c t o r depending on animal's age and s i z e enthalpy enthalpy of moist a i r (BTU/lb) enthalpy of water vapor (BTU/lb) work eq u i v a l e n t of heat constants c o e f f i c i e n t s f o r r a d i a n t , convective and evaporative heat l o s s e s r e s p e c t i v e l y mass r a t e flow of dry a i r (lbs.mass/min.) mass r a t e flow of water (lbs.mass/min.) exponent r e s p i r a t i o n r a t e pressure vapor pressures of s k i n and a i r r e s p e c t i v e l y atmospheric pressure ( l b s . / i n ) conductive heat exchange (BTU/hour) heat l o s s by conduction and evaporation convective heat exchange evaporative heat l o s s heat l o s s - v i -^met m e t a b o l i c h e a t o r o d u c t i o n 0 heat l o s s t o t h e environment 'P Qr r a d i a n t heat exchange 0 h e a t l o s s ^ by r e s p i r a t i o n R c o e f f i c i e n t r r a d i u s T a b s o l u t e t e m p e r a t u r e (°K o r °R) T , T a b s o l u t e t e m o e r a t u r e s o f s k i n and r a d i a n t s u r f a c e s s ' r x t , t s k i n and a i r t e m p e r a t u r e s r e s p e c t i v e l y (°C o r °F) s a t t i m e v a i r v e l o c i t y 3 • t i d a l volume ( c c o r i n ) V s p e c i f i c volume s W h u m i d i t y ( l b w a t e r / l b a i r ) W w e i g h t o f b i r d ( l b s ) p d e n s i t y o f a i r a p d e n s i t y o f w a t e r u i n t e r n a l energy INTRODUCTION The environment of an animal i s the sum t o t a l of th e f f e c t s of i t s surroundings, Esmay (14). An animal's performance such as:; growth, milk p r o d u c t i o n , o r egg produc-t i o n , i s a f f e c t e d by s t r e s s and genetics which are functions: of environment.. Researchers are attempting to determine optimal environmental c o n d i t i o n s f o r various c l a s s e s and genetic s t r a i n s . One of the most obvious s t r e s s e s i s the i n t e n s i t y of the thermal environment which i s a f f e c t e d by temperature, wind v e l o c i t y , humidity and r a d i a t i o n i n t e n s i t y . Under n a t u r a l c o n d i t i o n s animals have developed behavioural mechanisms, as w e l l as p h y s i o l o g i c a l mechanisms, i n order to f i n d comfortable environments. Since man has domesticated animals he has hindered t h e i r b ehavioural mechanisms f o r choosing a s u i t a b l e environment by c o n f i n i n g them i n a r e l a t i v e l y s m a l l area to f a c i l i t a t e t h e i r husbandry. These mechanisms i n c l u d e m i g r a t i o n and roaming over l a r g e areas i n search of food, water or shade. In order to. o b t a i n optimum production from h i s l i v e s t o c k man must compensate f o r these mechanisms by p r o v i d i n g s u i t a b l e environments f o r h i s l i v e -stock. In many cases he has found environmental c o n d i t i o n s that allow him t o approach optimum pr o d u c t i o n , but t h i s s t i l l leaves the q u e s t i o n , "What are optimum environmental c o n d i t i o n s f o r various c l a s s e s of l i v e s t o c k ? " . Research has been conducted i n t o various aspects of p o u l t r y environment i n order to improve p o u l t r y production Combinations of temperature, r e l a t i v e humidity and d i e t have been s t u d i e d w i t h respect to p o u l t r y . Researchers have noted t h a t p o u l t r y hatched and reared i n w i n t e r have grown more r a p i d l y than those hatched and reared i n the s p r i n g or summer, (Adams, et a l . 1). Diet has e f f e c t s on the growth of b i r d s i n various temperature ranges, but r e l a t i v e h u m i d i t i e s between 35-75% have not shown demonstrable e f f e c t s over temperature, (Adams, et a l . 1, and Smith, et a l . 25). Studies w i t h human volunteers have i n d i c a t e d t h a t enthalpy (a com-b i n a t i o n of temperature and humidity) might be used as a p r e d i c t o r of the s u i t a b i l i t y of the environment. Suggs (31 and 32) showed th a t when subjects e x e r c i s e d at a constant r a t e the same p h y s i o l o g i c a l responses were produced as measured by heart r a t e , f o r d i f f e r e n t temperature humidity combinations on a constant enthalpy l i n e . In the heat range s t u d i e d h e a r t - r a t e ( p u l s e ) , used as a measurement of heat s t r e s s , increased l i n e a r l y w i t h enthalpy, (Suggs .31). B i r d s reared i n a c o n t r o l l e d environment during t h e i r e a r l y growth (hatch to 21 days) perform b e t t e r , as measured by body weight and growth-rate, during e a r l y and l a t e r growth p e r i o d s , (Roberts 22). This study was designed to t e s t the i n f l u e n c e of enthalpy on p o u l t r y growth-rate. Due to equipment l i m i t a t i o n s enthalpy extremes were chosen from 29.3 BTU/lb to 33.3 BTU/lb a i r . The t h i r d enthalpy of 31.3 BTU/lb of a i r was chosen to b halfway between the extremes. Population d e n s i t y , l i g h t i n g arid d i e t were the same f o r each t r i a l i n the experiment. As there was a time f a c t o r between t r i a l s , t h i s , introduced the p o s s i b i l i t y t h a t there could be a change i n the p o p u l a t i o n being sampled, or changes i n other f a c t o r s that were impossible to c o n t r o l . Every attempt was made to keep the environments . i d e n t i c a l except f o r the enthalpy treatment. 4 . '/' . / • • ' REVIEW OF-, LITERATURE Heat Loss and Homeothermy A l l o b jects whether l i v i n g o r n o n - l i v i n g come i n t o thermal e q u i l i b r i u m with t h e i r environment. The mechanisms f o r accomplishing t h i s are: conduction, convection, evapo-r a t i o n , and r a d i a t i o n . In l i v i n g o b jects a s e r i e s of. chemical r e a c t i o n s that produce heat are necessary to m a i n t a i n ' l i f e . Animal species have developed two c l a s s e s w i t h respect to body heat management: p o i k l i o t h e r m s and homeotherms. The body temperature o f po i k l i o t h e r m s f l u c t u a t e s with environmental temperatures. Homeotherms, which i n c l u d e p o u l t r y , maintain a constant body temperature by a d j u s t i n g t h e i r heat production to equal heat l o s s e s . Heat Loss by the Animal Body Environmental, as w e l l as p h y s i o l o g i c a l f a c t o r s govern heat l o s s from the animal. Some of the environmental, f a c t o r s a f f e c t i n g heat l o s s are: a i r temperature, humidity, temperature of the surroundings, and wind speed. Factors such as animal age, surface area, d e n s i t y of coat and c o l o r of the coat a l s o a f f e c t heat l o s s , (Esmay 1 4 ) . When an animal i s i n thermal e q u i l i b r i u m w i t h - i t s environment heat produced by metabolism equals heat l o s t . Heat i s l o s t by four methods: r a d i a t i o n , conduction, convec-t i o n and evaporation. Thermal r a d i a t i o n i s heat energy t r a n s f e r from one body to another by electromagnetic waves. Radiant energy t r a n s f e r i s dependent on the.emissive c h a r a c t e r i s t i c s of an o b j e c t , the view of the surroundings, and i s p r o p o r t i o n a l to the f o u r t h power of the absolute temperature of the body. Conductive heat t r a n s f e r does not play a l a r g e part i n heat l o s s from an animal to i t s environment, but i s more important i n heat movement w i t h i n the. animal. Convective heat t r a n s f e r i s "the movement.and mixing of f l u i d p a r t i c l e s . Perhaps the most important heat l o s s mechanism f o r an animal, p a r t i c u l a r l y at h igher environmental temperatures, i s . evaporation. Most domestic animals and p o u l t r y , i n p a r t i c u l a r , are non-sweating. Any evaporative heat l o s s t h a t they experience comes from v a p o r i z i n g water from the lung surfaces by panting. An i animal can c o n t r o l ( w i t h i n l i m i t s ) the amount of heat l o s t by evaporation. These heat l o s s mechanisms must remove a l l of the heat produced by an animal's metabolic processes, (Hammond 15). P h y s i o l o g i c a l Mechanisms f o r Thermo-regulation Any thermo-regulatory system must have a temperature sensor and c o n t r o l l e r . In an animal the t h e r m o s e n s i t i v i t y and temperature c o n t r o l i s a f u n c t i o n of the hypothalamus, ( B l i g h 4). A very small increase or decrease i n the tempera-t u r e of the blood f l o w i n g i n t o the hypothalamus causes i t to t r i g g e r responses to change body temperature, (Hardy 16). In man t h i s change i s i n the order of 0.01°C, (Benzinger 3). A p o s s i b i l i t y that there are separate c o l d s e n s i t i v e organs a l s o e x i s t s , ( B l i g h 4). An animal's body has two thermal g r a d i e n t s : 1) from the body core to the s k i n s u r f a c e , and 2.) from the s k i n surface to the environment, (Hardy 16). I n s u l a t i o n i s provided by the f u r or feathers and the l a y e r of s t i l l a i r around the animal. Cold exposure causes the r a t e of heat l o s s from the body to i n c r e a s e . The hypo-thalamus senses t h i s heat l o s s and t r i g g e r s the appropriate responses. There are two l e v e l s of response: 1) p h y s i c a l , which i n c l u d e increased muscular a c t i v i t y and movement to a warmer environment, and 2) chemical,.which i s accomplished by i n c r e a s i n g the metabolic r a t e . The p h y s i o l o g i c a l response to hot environments i s to increase heat l o s s and decrease heat production. There i s convective and conductive heat t r a n s f e r from the body core to the body s u r f a c e , causing more heat to be l o s t to the environment. Heat l o s s by the t o t a l of a l l the heat t r a n s f e r mechanisms i s increased. Evaporative heat l o s s i s incr e a s e d most because i n hot environments the temperature d i f f e r e n c e decreases between the surroundings and the body which decreases heat l o s s by conduction, convection and r a d i a t i o n , w hile the l a t e n t heat of evaporation remains r e l a t i v e l y constant. In non-sweating animals panting i s the mechanism used to increase evaporative heat l o s s from the lung surface t o cool the animal. Thermo-regulation i n Bi r d s -During e a r l y development the embryo can not r e g u l a t e i t s own temperature although a f t e r .19 days the embryo can respond to a lowering of the environmental temperature (S t u r k i e ' 30, chapter 8). At hatch : the chick i s at the incuba t o r temperature of 102°F, (King 18). A f t e r drying the body temperature r i s e s and continues to r i s e f o r about 1.4, days, at which time i t reaches adult l e v e l s (106 to 107°F). As adult temperature l e v e l s are reached the b a s a l metabolic r a t e per u n i t of surface area i n c r e a s e s . At hatch the young b i r d can respond to a c o l d s t r e s s by i n c r e a s i n g heat produc-t i o n . Young b i r d s pant at lower temperatures than a d u l t b i r d do, ( S t u r k i e 30). He a l s o i n d i c a t e d that there i s a very high water l o s s from the young b i r d s during t h e i r f i r s t day of l i f e . This high water l o s s occurs because of high r e s p i r a t i o n r a t e s and a high cutaneous water l o s s . This evaporative l o s s decreases a f t e r the f i r s t day, but i s high again a f t e r two to three weeks due to increased metabolism. B a s i c a l l y the thermo-regulatory a b i l i t y of a b i r d depends on age, degree of f e a t h e r c o v e r i n g , musculature development, and s i z e and development of the c e n t r a l nervous system. The body temperature of adu l t b i r d s i s a f f e c t e d by s e v e r a l f a c t o r s , some of which are: 1) nervous c o n t r o l of heat production (hypothalamus), 2) . i n s u l a t i o n of s k i n and f e a t h e r s , 3.) energy metabolism, 4) evaporation ( p a n t i n g ) , / ' . 5) heat storage, 6) p h y s i c a l a c c l i m a t i z a t i o n , 7) genetic a c c l i m a t i z a t i o n , and 8) the^behaviour of the b i r d s , (Hammond 15). The b i r d ' s s t a t e of h e a l t h and i t s n u t r i t i o n a l s t a t u s a l s o a f f e c t i t s body temperature. Body s t r u c t u r e s , such as the comb, are a l s o i n v o l v e d i n thermo-regulation, ( S t u r k i e 30). At high temperatures water i n t a k e i s in c r e a s e d , e f f e c t i n g s e n s i b l e c o o l i n g , and f a c i l i t a t i n g evaporative c o o l i n g . Behaviour, such as seeking a c o o l e r o r warmer environment, al s o plays a part i n thermo-regulation. Sex does not appear to a f f e c t body temperature, though s i z e does. Light breeds are more heat t o l e r a n t than heavy breeds. B a s i c a l l y the response of b i r d s to t h e i r thermal environment i s an attempt to e q u a l i z e heat produced and heat l o s t . I f the l i m i t s over which the b i r d s can respond are exceeded, the' b i r d i s thermally s t r e s s e d . I f the time i s s h o r t , the b i r d recovers; i f i t i s l o n g , t h i s s t r e s s may cause death. Enthalpy . Thermodynamically the enthalpy of a substance i s a composite energy term, defined bv the f o l l o w i n g equation: PV h = y + • [ l ] . A i r enthalpy i s a t h e o r e t i c a l psychrometric property. For normal environmental temperatures (between about 20-110°F) the constant enthalpy c o n d i t i o n has a s i m i l a r r e l a t i o n s h i p to dry bulb temperature as does the constant thermodynamic wet bulb c o n d i t i o n . The observed wet bulb and the thermo-dynamic wet bulb temperatures deviate very l i t t l e f o r normal atmospheric temperatures and pressures. Very l i t t l e e r r o r i s i ntroduced i n t o t h i s sytem by assuming t h a t the enthalpy c o n d i t i o n corresponds to the observed wet bulb c o n d i t i o n , ( T h r e l k e l d 33). The enthalpy of moist a i r i s given by the f o l l o w i n g equation: ( f o r . t h e B r i t i s h system of u n i t s ) h = 0.24t + W.h . '• [2] a a g where h = 1075.5 + 0 .4.5 (t-32) [31 g where 1075.5 BTU/lb i s the energy r e q u i r e d to vaporize 1 l b of water at 32°F. By combining equations [2] and [3] an expression f o r the enthalpy of a i r at a given dry bulb temperature i s given: h = 0.24t •+ W(0.45t + 1060.8). [4] a a a The l i n e AB .in Figure 1 i s defined by t h i s equation. q _Q o tt ~~U £ I FIGURE 1. T r — — i T A i r T e m p e r a t u r e (wet a n d d r y b u l b ) (°F) Psychrometic Chart showing Selected Relationships O 11. Work using human volunteers has suggested t h a t enthalpy can be used as a measurement of the i n t e n s i t y of the thermal environment, (Suggs 31). In another study Suggs (32) has shown t h a t enthalpy can be s u b s t i t u t e d f o r a i r temperature i n the heat l o s s equation, as f o l l o w s : Q" . = K ( T 4 - T 4) + K / v ( t - t ) + xmet r s r c s a K e ^ ( P s " V - [ 5 ] Omitting r a d i a n t heat l o s s e s , convective and evaporative l o s s e s become: Q . = K / v ( t - t ) + RK /v(P - P ); [6] xc+e c s a c s v K where R = and the humidity r a t i o i s c P W = 1.605 IP - P ). C 7 ] a v By combining equations [4] and [7] 1.876h + 1060.8 t = »*.-17h - Pv(Q7gggp r-LT7065P K t 8 ] a v S u b s t i t u t i n g equation [8] i n t o [6] and s i m p l i f y i n g : Q _ = K / v ( t + RP - 4.17h ). [9] c+e e s s a Equation [9] i s the expression f o r heat l o s s by convection and evaporation, w i t h enthalpy s u b s t i t u t e d f o r a i r temperature. Suggs (31) has v e r i f i e d by experimental work tha t enthalpy can be used as an i n d i c a t o r o f heat s t r e s s . Growth The mature weight o f an animal and the s l o p e o f i t s growth curve are g e n e t i c c h a r a c t e r i s t i c s under a given environment, (Brody 7). Growth can be d e s c r i b e d as an i n c r e a s e i n the s i z e o f an organism (weight) d u r i n g a s p e c i f i c t i m e . p e r i o d , (Cole 9). The growth process i n c l u d e s one or a l l o f : 1) c e l l m u l t i p l i c a t i o n 2) c e l l enlargement, and 3) i n c o r p o r a t i o n o f m a t e r i a l taken from the environment, (Brody 7). G r a p h i c a l l y growth can be shown as an asymmetrical s i g m o i d a l o r S-shaped curve. I t i s d i v i d e d i n t o two phases: s e l f - a c c e l e r a t i n g and s e l f - i n h i b i t i n g . Environmental and g e n e t i c f a c t o r s determine the p o i n t of i n f l e c t i o n , which separates the two growth-phases. The growth curves of i n d i v i d u a l s and of p o p u l a t i o n s are remarkably s i m i l a r because both are made up o f d i s c r e t e u n i t s ( c e l l s and i n d i v i d u a l s r e s p e c t i v e l y ) , (Brody 7). I t has been demonstrated t h a t environment a f f e c t s the e a r l y growth of growing b i r d s , ( S t a l e y , et a l . 27). Growth-rate can be used t o measure the e f f e c t i v e n e s s o f environmental c o n d i t i o n s , (Roberts 21). The f u n c t i o n Y = at* 3 can be used t o d e s c r i b e the i n i t i a l p o r t i o n o f the growth curve when Y i s body weight at time t (measured from c o n c e p t i o n a i s body weight at time zero, and b i s a pure number, defined as growth-rate, (Roberts 21). The r e l a t i v e importance o f the c o n t r i b u t i o n s of growth during d i f f e r e n t time periods towards the f i n a l body weight has been demonstrated, (Roberts 2 2 and Roberts, et a l . 23). Response of P o u l t r y to T h e i r Environment The response of p o u l t r y to t h e i r environment i s a f f e c t e d by many f a c t o r s , the e a s i e s t to measure being the response to the•thermal environment: made up of temperature, humidity and wind v e l o c i t y . As temperatures r i s e v o l u n t a r y food intake drops, but can be compensated f o r by n u t r i t i o n , (Saihsbury 24). High temperatures r e t a r d the growth-rate of p o u l t r y , (Huston and Carmon 17). The e f f e c t of a i r v e l o c i t y on b i r d s i s not c l e a r l y understood, (Longhouse, et a l . 19) sin c e in. the wi n t e r b i r d s avoid d r a f t s and i n the summer they seek them. There i s a s u s p i c i o n that high a i r v e l o c i t i e s may enable the b i r d s to t o l e r a t e high a i r tempera-t u r e s , (Drury and S.eigel 13). R e l a t i v e humidity i s not s i g n i f i c a n t i n improving growth, but b i r d s ( b r o i l e r s to three weeks) can sense changes from a comfortable l e v e l , about 50%, ( P r i n c e , et a l . 20 and Longhouse, et a l . 19). However, high r e l a t i v e h u m i d i t i e s aggravate the e f f e c t s of high temperatures (Drury and S e i g e l 13). Tolerance to hot environments appears to be g e n e t i c a l l y i n f l u e n c e d . For a given breed of b i r d s (White Leghorns) f a m i l i a l d i f f e r e n c e s i n heat t o l e r a n c e have been found, (Wilson, et a l . 34). B i r d s w i t h a high growth-rate are best able to withstand high temperatures,. (Huston and Carmon 17). Further research on the s u r v i v a l of b i r d s i n hot environments i n d i c a t e s t h a t both temperature and r e l a t i v e / • -humidity are important f a c t o r s to con s i d e r , (Dorminey, et a l . 12). The p r e s e n t l y accepted c o n d i t i o n s f o r growing b i r d s are a 90-95°F (32 ..2-35°C) s t a r t i n g temperature which i s lowered 1°F (5/9°C) per day u n t i l a temperature of 65-70°F (18.3-22°C) i s reached, (Farm B u i l d i n g Standards 8 and Esmay 14). For mature b i r d s a temperature range of 32-85°F (•0-29.. 5°C) i s a l l o w a b l e , with the optimum being 55-60°F (12,8-15.5°C) , (Farm B u i l d i n g Standards 8 and Esmay 14). I t is.hoped that by d e f i n i n g the environmental c o n d i t i o n s of p o u l t r y more p r e c i s e l y , p o u l t r y production can be made more e f f i c i e n t . 1 6 . Mathematical M o d e l l i n g o f Heat Loss from a. B i r d In o r d e r to understand the h e a t . l o s s mechanism and t h e r m o - r e g u l a t i o n i n animals ,' mathematical models, have been proposed; ( B o u c h i l l o n , e_t a l . 6, and Becket and V i d r i n e 2). . Such models should prove u s e f u l when s t u d y i n g an animal's performance under v a r i o u s environmental regimes. Optimum-environments c o u l d then be p r o d i c t e d . At the p r e s e n t time s t r e s s e s o t h e r than thermal can not be accounted f o r , even though they are p r e s e n t . Equation [ 1 0 ] shows metabolic heat p r o d u c t i o n and the pathways through which i t i s d i s s i p a t e d : c o n d u c t i o n , c o n v e c t i o n , r a d i a t i o n and e v a p o r a t i o n . In o r d e r to p r e d i c t h e a t l o s s by each o f these pathways we must e s t a b l i s h the shape and s i z e of the c h i c k e n . Heat l o s s i s a f u n c t i o n of s u r f a c e area, heat p r o d u c t i o n i s a. f u n c t i o n o f body weight. 0- . = 0 , + Q + Q + 0 . [ 1 0 ] •met -cd. x c v  <v e The t h e o r e t i c a l c h i c k e n i s c o n s i d e r e d to be s p h e r i c a l and has an e q u i v a l e n t diameter as d e s c r i b e d by: ( B o u c h i l l o n e t a l . 6) D = [ 1 1 ] e TT p w The equations f o r heat l o s s by r a d i a t i o n , c o n d u c t i o n and c o n v e c t i o n are given below Q r = A e a (TJ - T 4 ) , [ 1 2 ] Q . = -KA ~ , [ 1 3 ] < c d d r ' Q_v = K A v n ( t x - t 2 ) , [ 1 4 ] 17. Heat i s also l o s t by r e s p i r a t i o n and must be accounted f o r . This heat i s l o s t by two processes? the sensible heat of respired a i r and evaporative heat. The following equations give an estimate of t h i s heat l o s s , (Bouchillon et a l . 6): C- = M9w\ - M.W. - mh , [15] rp 2 2 1 1 g-M = P AV TN R, [16] and m = M(W2 - V^). [17] Mathematically the heat loss from a chicken can be represented as Q = A e bCT 4, - T 4) + (-KA^) + hAv n(t , - t ) xp ch s dr ch s + (P AV TN R) (W2 - W1) (1 - h ), [18] and Q . = FWtd, (Brody 7). [19] met Heat production can also be calculated from oxygen consump-t i o n of the chicken,(Esmay 14). The chicken attempts to adjust Q . = Q . J xmet xp As the temperature changes the chicken can adjust ph y s i o l o g i c a l mechanisms to balance heat l o s s . It can change the i n s u l a t i n g value of the feathers by f l u f f i n g or preening them. It can increase surface area by spreading i t s wings, or decrease surface area by squatting and folding i t s head under i t s wing. The r e s p i r a t i o n rate can be increased or decreased, as can feed consumption, depending on environmental conditions. The rate of metabolism can also be changed. Changes i n age-, feather cover, and p h y s i o l o g i c a l conditions 18:1 / a l s o a f f e c t the chicken's thermoregulatory a b i l i t y . A l l of these f a c t o r s should be considered i n a complex model of the chicken's•thermoregulatory system. A simple model (as presented above) provides an i n s i g h t i n t o a chicken's response to i t s thermal environment. 19. MATERIALS AND METHODS In t h i s study two 4-foot square c o n t r o l l e d e n v i r o n -ment p o u l t r y brooders were used, ( S t a l e y and Roberts 2 6 and S t a l e y , e_t a l . 28). The a i r c o n d i t i o n i n g u n i t f o r the brooders was designed to handle 90 b i r d s from hatch to three weeks of age. This u n i t maintained the d e s i r e d psychrometric c o n d i t i o n s w i t h i n the brooders. A i r entered at the top of the brooder, was drawn down, over the b i r d s , then removed at the bottom f o r f i l t e r i n g and measuring of i t s s t a t e p o i n t s . I t was then 1 cooled to the dew p o i n t , s a t u r a t e d , reheated and returned to the brooders. About one-quarter of the a i r i n the system was exchanged hourly f o r f r e s h a i r . A i r was moved through the system at about 280 cubic feet per minute. Hot and c o l d water were used to heat and c o o l the a i r . A spray of water at the d e s i r e d dew point temperature was used to sa t u r a t e the a i r . The flow o f hot and c o l d water was c o n t r o l l e d by a pneumatic c o n t r o l l e r and p r o p o r t i o n a l flow c o n t r o l v a l v e s . A n t i f r e e z e was added to the c o o l i n g water to prevent freeze-up when a l a r g e c o o l i n g c a p a c i t y was r e q u i r e d . The brooders were constructed of plywood, i n s u l a t e d w i t h two inches of styrofoam, and aluminum l i n e d . They were connected to the a i r c o n d i t i o n i n g u n i t by i n s u l a t e d ductwork. View ports were provided so that the b i r d s could be v i s u a l l y checked. Feed was introduced i n t o the brooders through a i r -l o c k f e e d e r s , water was s u p p l i e d by an automatic watering system (Hart cups) and b i o l o g i c a l gloves were provided so that the b i r d s could be cared f o r without breaking the environment. The brooder f l o o r s were wire mesh and had p r o v i s i o n s f o r r a i s i n g and lowering,. ( S t a l e y and Roberts 25). For t h i s experiment the height of. the f l o o r was set. i n i t i a l l y and h e l d at a constant height from the feeder throughout a l l of- the t r a i l s . Continuous l i g h t i n g was provided by four corner' mounted. 8-inch f l u o r e s c e n t tubes i n each chamber. The l i g h t . i n t e n s i t i e s i n the chambers, as measured by the photometer-, -were the same at about 33 foot candles. A hot wire anemometer detected a d i f f e r e n c e i n a i r v e l o c i t y between the chambers, 6.2 feet/ s e c f o r brooder one-as compared to 7.1 f e e t / s e c f o r brooder two. This equipment was l o c a t e d i n an a i r c o n d i t i o n e d room. The windows of t h i s room were covered w i t h metal f o i l to prevent s o l a r r a d i a t i o n from e n t e r i n g , ( S t a l e y et a l . 27). Temperatures i n the a i r c o n d i t i o n i n g apparatus were measured by thermocouples and recorded on a m u l t i - p o i n t recorder. Brooder temperatures were measured by a black globe thermometer. These i n t e g r a t e the environmental c o n d i t i o n s and give an i n d i c a t i o n of the comfort sensed by non-sweating animals, (Bond and K e l l y 5). Regular maintenance of the equipment was necessary f o r proper o p e r a t i o n . Iron-constantan thermocouples were used as tempera-^ ture sensors. There were 24 s t a t i o n s to be monitored f o r temperature on t h i s equipment, two of which were i n two inch black globes. A Texas instrument 24 p o i n t M u l t i - R i t e r r ecorder was used to record the temperatures from s e l e c t e d 21. s t a t i o n s . A Powers pneumatic c o n t r o l l e r and p r o p o r t i o n i n g valves were used to c o n t r o l the thermodynamic s t a t e p o i n t s of the a i r to an accuracy of + 1°F. EXPERIMENTAL DESIGN The experiment c o n s i s t e d of three l e v e l s of enthalpy each r e p l i c a t e d three times, i n three time b l o c k s . Each treatment was represented once i n each time block. The order of the treatments was randomized w i t h i n each time block with" the a d d i t i o n a l r e s t r i c t i o n that a given treatment could not appear i n the corresponding c e l l of e i t h e r of the other time b l o c k s . The l e v e l s of enthalpy used were 29.3, 31.3 and 3 3.3 BTU/lb of a i r ; corresponding to 64, 6-6 1/2 and 69°F wet' bulb temperature r e s p e c t i v e l y . These enthalpy treatments were chosen because they were extremes that could be maintained by the a i r c o n d i t i o n i n g equipment over the range o f dry bulb temperatures r e q u i r e d . The enthalpy of 31.3 BTU/lb of a i r was halfway between the extremes. P r i o r to p l a c i n g the b i r d s i n the brooders the d e s i r e d environmental c o n d i t i o n s i n the brooders had been reached and s t a b i l i z e d . A l l t r i a l s s t a r t e d at 90°F (32.2°C) J dry bulb and the d e s i r e d wet bulb temperature f o r the enthalpy c o n d i t i o n being t e s t e d . The wet bulb temperature was h e l d constant during the t r i a l . The dry bulb temperature dropped three degrees Fahrenheit every three days u n t i l a temperature of 70°F (21.2°C) was reached. The b i r d s used f o r t h i s study were random-bred New Hampshires from the U n i v e r s i t y of B r i t i s h Columbia f l o c k . Ten males and 60 females were used as parent stock. A f t e r four hatches the o r i g i n a l parent b i r d s were replaced by younger b i r d s of the same genetic l i n e . Eggs were c o l l e c t e d and stored i n a c o o l e r at 5 5°F (12.8°C) f o r approximately two weeks before being incubated. At hatch the ch i c k s were, sexed, and only the males were used f o r experimental purposes. Females were used when there were not enough males to make up the d e s i r e d population d e n s i t y i n two of the nine t r i a l s . The female b i r d s were not considered i n the subsequent analyses of the experiment. The male b i r d s were randomly d i v i d e d i n t o three equal groups. Forty i n d i v i d u a l s from each group were randomly s e l e c t e d , subsequently wingbanded and weighed. Each of the three groups was then randomly assigned to one of the treatment areas -- brooder one, brooder two, or a 9 foot by 12 foot f l o o r pen ( i n the U n i v e r s i t y of B r i t i s h Columbia p o u l t r y environment l a b o r a t o r y b u i l d i n g ) . The b i r d s were weighed at weekly i n t e r v a l s f o r the seven weeks of the t r i a l . The experimental r e s u l t s were based on the analyses of body weight and growth-rates of the b i r d s . I t has been shown that growth-rate i s an independent v a r i a b l e , even though i t i s obtained from body weight, (Roberts 21). Growth-rates were c a l c u l a t e d using"the f o l l o w i n g equation: l o g (Y /Y ) b ; l o g (t2/t|)» [ 2 0 ] where: b i s a dimensionless r a t i o defined as growth-rate, Y^ and are body weights at times 1 and 2, and t ^ and t ^ are times 1 and 2 (measured from conception). • > / . This equation i s f o r the f i r s t p o r t i o n of the growth curve to the point of i n f l e c t i o n , (Roberts 2 1 ) . The po i n t o f i n f l e c t i o n corresponds to puberty f o r i n d i v i d u a l s or the 'coming of age' f o r p o p u l a t i o n s , (Brody 7 ) . The experiment was analyzed on a weekly b a s i s using the model: Y. .. . = u + C. + R. + T, + E. + G, l j k l m 1 ] k 1 3 k 1 + TG. , + F. ., , + H...,, , [ 2 1 ] k l 13 k l l j k l m " "th x. 1 where: Y. .. , r e f e r s to the m i n d i v i d u a l of the 1 i jklm "t h group f o r the k treatment, u r e f e r s to grand mean. C\ i s the e f f e c t of the i " * " ^ column, R. i s the e f f e c t of the j row, 3 k T, i s the e f f e c t of the k treatment, "th G^ i s the e f f e c t of the 1 group, and E,F,H are the appropriate e r r o r terms f o r the design. The e f f e c t s of columns, rows, groups and treatments were f i x e d . Treatments were f i x e d by d e f i n i t i o n . Groups were f i x e d by the design of the equipment. Rows and columns were time e f f e c t s and t h e r e f o r e considered to be f i x e d . E r r o r s E and F were a l s o f i x e d . E r r o r H was considered to be random because i t represented i n d i v i d u a l s . Table 1 gives the degrees of freedom and the expected mean squares of the model. Due to the b i o l o g i c a l nature of t h i s study and. the. deaths of some of the i n d i v i d u a l s the data were not propor-t i o n a l . P r o p o r t i o n a l i t y was achieved by randomly d i s c a r d i n g i n d i v i d u a l s from the c e l l s . A p r o p o r t i o n a l design was d e s i r e d because a non-proportional design introduces b i a s i n t o the a n a l y s i s of v a r i a n c e , ( S t e e l and T o r r i e 29). A f t e r a c h i e v i n g p r o p o r t i o n a l i t y 72 0 i n d i v i d u a l s were l e f t i n the experiment. The analyses were c a r r i e d out using s t a t i s t i c a l r o u t i n e s developed by Dempster et a l . (11) on an IBM 360/67 d i g i t a l ' computer. TABLE 1. DEGREES OF FREEDOM AND EXPECTED MEAN SOUARES, FOR. THE„ EXPERIMENTAL MODEL Source o f V a r i a t i o n Degrees Freedom o f Expected Mean Squares-Column (C) ( r - 1) a 2H + n 'a 2F + g' n' 'a 2E + r ' ' t ' g ' n' . 2 •0 C Row (R) ( r - 1) a 2H + n ' c 2 F g* n 1 0 1 a"E + c 1 " t ' g 1 n' 2 Treatments ( T ) ( r - 1) a 2H + n •a 2F + g' n' 'a 2E + c" ' t ' r ' n! 0 E r r o r (E) ( r - l ) ( r - 2) a 2H n •a 2F + g' n 1 Groups (G) (g - 1) a 2H + n •a 2F + r ' c 1 't'n'0 2G T x G ( r - l ) ( g - 1) a 2H + n •a 2F + r ' c 1 'n*9 2TG E r r o r (F) r ( r - l ) ( g - 1) a 2H + n •a 2F E r r o r (H) ( z n _ i ] klm 2 •r g ) a2 H T o t a l i j k l m 1) n', r ' , t ' , g', c', are a d j u s t e d numbers, p r e d i c t e d on p r o p o r t i o n a l sample s i z e . MANAGEMENT OF BIRDS When the b i r d s were placed i n the brooders, one g a l l o n d r i n k i n g fountains w i t h an a n t i b i o t i c s o l u t i o n (Terramycin) were provided. These were l e f t i n the brooders u n t i l they were empty and the b i r d s had learned to dr i n k from the automatic watering cups provided i n the brooders. The feces were c o l l e c t e d on a p l a s t i c sheet and removed weekly. 1 Feed was i n the feeders and some feed had been placed on a paper on the f l o o r to encourage the b i r d s to s t a r t e a t i n g . From t h i s time u n t i l they were removed from the brooders the b i r d s always had access to feed and water (except when vaccinated f o r Newcastle-Bronchitis at ten days of age). The 40 b i r d s that were assigned t o the f l o o r pen were placed i n a pen w i t h clean shavings as l i t t e r . The same f l o o r pens were Used throughout the experiment. The l i t t e r was not changed during the seven weeks that the t r i a l was being run. For approximately h a l f of the t r i a l s a card-board enclosure was used to r e t a i n the c h i c k s . I t was removed a f t e r two weeks so that the b i r d s had the run of the pen. Heat lamps were provided and feed was i n a three foot l i n e a r feeder and a l s o on a paper on the f l o o r when the young b i r d s were f i r s t placed i n the pen. A one g a l l o n d r i n k i n g f o u n t a i n w i t h an a n t i b i o t i c s o l u t i o n (Terramycin) was a l s o i n the pen. A f t e r the a n t i b i o t i c was consumed the d r i n k i n g f o u n t a i n was cleaned and f i l l e d w i t h f r e s h water d a i l y . After three to four weeks the birds were trained to use- the automatic waterers (Johnson cups) i n the pen and the one gallon drinking fountain was removed. At the end of the three weeks the birds i n the brooders were placed on the f l o o r with the group that had started there. At t h i s time the l i n e a r feeder was.replaced by two 20-pound hanging feeders.. The birds were fed a commercial chick s t a r t e r ad. l i b . for the entire seven weeks that they v/ere on the experiment. DISCUSSION AND RESULTS. The observed body weights f o r treatments averaged over r e p l i c a t e s , are shown i n Table 2 (Weekly Mean Body Weights f o r Enthalpy Treatments). There was no apparent d i f f e r e n c e -between treatments, however an i n t e r e s t i n g trend appeared-. The-enthalpy treatment of 33.3 BTU/lb was heaviest from week 2 u n t i l the end of the experiment where i t weighed 753 grams. The middle treatment of 31.3 BTU/lb was the- l i g h t e s t at 72 3 grams and the low treatment of 29.3 BTU/lb was between these two at 7 36 grams. Tables 3 and 4 (Weekly Mean Body Weights f o r Each Group and Mean Growth-rates f o r Each of the Growth Periods) show the e f f e c t s o f : a c o n t r o l l e d versus a n o n - c o n t r o l l e d environment. Table 3 shows that a l l groups s t a r t e d at the same weight at hatch (42 grams). By one week of age the b i r d s i n the brooders were hea v i e r than t h e i r contemporaries on the f l o o r (64 and 6 8 grams versus 59 grams). The brooder reared b i r d s maintained t h i s weight advantage f o r the e n t i r e seven weeks. Table 4 shows that i n the f i r s t weekly growth p e r i o d (H - 1) the brooder reared b i r d s grew much f a s t e r , as evidenced by a higher growth-rate (1.45 and 1.66 as compared to 1.12). During the next two growth periods (1 - 2 and 2 - 3) there was very l i t t l e d i f f e r e n c e between the brooders and the f l o o r . At three weeks Of age the brooder b i r d s were t r a n s -f e r r e d to the f l o o r . The s t r e s s imposed by t h i s move shows d r a m a t i c a l l y i n the 3 - 4 and 4 - 5 week growth periods 30. TABLE 2. Weekly Body Weights f o r Enthalpy Treatment's Growth Enthalpy Treatments (BTU/lb) P e r i o d 2 9.3 31. 3 33.3 (Weeks) (grams) (grams) (.grams) Hatch 42 44 41 1 65 64 62 2 125 . 123 126 3 214 221 216 4 302 307 314 5 417 412 4 3'6 6 578 572 589 7 736 72 3 753 TABLE 3. Weekly Mean Body Weights f o r Each Group Growth G r o u p s Pe r i o d Brooder 1 Brooder 2 F l o o r (Weeks) (grams) (grams) (grams) Hatch 42 42 42 1 . 64 68 59 2 127 133 113 3 224 232 193 4 312 315 292 5 42 3 428 410 6 579 5 89 568 7 736 748 726 TABLE 4. Mean Growth-rates f o r each of the Growth Periods. Growth Per i o d Brooder 1 Brooder 2 F l o o r H-l 1.45 1.66 1...12 1-2 3 .08 3.00 2.9 2 2-3 3.13 3. 05 2.9 5-3-4 2.14 1.99 2.68 4-5 2.26 2.27 2.5 2 5-6 2.6 8 2.73 2.79 6-7 2.29 2.26 2.. 32 TABLE 5. ANOVA Expressed as Percentage 1 and 7 Week Weights and 1-3 r a t e s . Sums of Squares f o r and 3-7 Week Growth-Source of Variance df 1 Week Wt. Growth Rates 1-3 3-7 7 Week Wt. Rows 2 5.46 6.92 8.68 1.56 Columns 2 2.40 3.42 2.08 4 . 38 Treatments 2 0.60 4.5 9 0.22 1.33 E r r o r (E) 2 8.29* 2 .86 10.49* 3.40* Groups 2 12 . 88* 5 . 84* 15.25* 0.90 1,2 vs 3 1 10.14* 4.42* 14.65* 0 .66 1 vs 2 1 2.74* 1.42 0.60 0.24 T x G 4 5.56 2.82 .3.21 1.23 E r r o r (F) 12 6.64* 7.84* 10.09* 5.21* E r r o r (H) 693 58.17 65.71 49.97 81.99 T o t a l 719 9 9.98 99.63 .99.99 100.00 T o t a l SS 84161 - 60 32 6662100 * S i g n i f i c a n c e : P < 0.05 (2.14 and 1.9 9 versus 2".6'8 i n the 3 - 4 week growth p e r i o d and 2.26 and 2.27 versus 2,52 i n the 4 - 5 week growth p e r i o d ) . The d i f f e r e n c e i n favor of the f l o o r s t i l l e x i s t s i n the 5 - 6 and 6 - 7 week growth p e r i o d s , however i t i s very s l i g h t . Tables 5, 6, 7, and 8 show the analyses o f the data. Tables 5, 7, and 8 show the sources of v a r i a n c e , the degrees of freedom, a weekly breakdown of the analyses and the s i g n i f i c a n t e f f e c t s . Table 5 i s a summary of Table 2 and 8 and in c l u d e s 1-week weight, 1-3 week growth-rate, 3-7 week growth-rate and 7-week weight. One-week weight, 1-3 week growth-rate and 3-7 week growth-rate e x p l a i n the ma j o r i t y of the v a r i a b i l i t y of 7-week body weight, ( S t a l e y , et a l . 30). The. growth-rate from 1.-3 weeks of age i s the simple average of the growth-rates between one and three weeks o f age. The growth-rate from 3-7 weeks i s the simple average of the weekly growth-rates between three and seven weeks of age. Table 5 (ANOVA Expressed as Percentage Sums of Squares f o r 1 and 7 Week Weights and 1-3 and 3-7 Week Growth-rates) shows t h a t Rows, Columns and Treatments are n o n - s i g n i f i c a n t . N o n - s i g n i f i c a n t Row and Column e f f e c t s show that there was no hatch e f f e c t nor a time e f f e c t . I f e i t h e r Row o r Column e f f e c t s had been s i g n i f i c a n t i t would have i n d i c a t e d that the b i r d p o p u lation t h a t was sampled f o r t h i s experiment was not the same over time. As these e f f e c t s were n o n - s i g n i f i c a n t i t i n d i c a t e d that there was no e f f e c t of changing parent b i r d s ( o l d b i r d s f o r young b i r d s of the same genetic l i n e a f t e r the f o u r t h hatch). This was confirmed by Table 3. At Hatch the average weights of the b i r d s i n brooder one, brooder two and the f l o o r were the same. I t i s i n t e r e s t i n g to note t h a t E r r o r (E) was s i g n i f i c a n t f o r 1-week weight, 3-7 week growth-r a t e and 7-week weight. This i n d i c a t e s t h a t there was a l a r g e variance i n t h i s term. Groups were s i g n i f i c a n t f o r one week weight and 1-3 and 3-7 week growth-rates. The orthogonal breakdowns show that most o f the variance was between the brooders and the f l o o r , however there was a s i g n i f i c a n c e betwee the. brooders at one week of age. Table 6 (Mean Body Weights and Growth-rates f o r Selected Growth Periods) shows that at one week of age brooder one weighed 64 grams and brooder two weighed 68 grams. The f l o o r was l i g h t e s t at 5 9 grams. During the 1-3 week growth p e r i o d , the brooder reared b i r d s had s u p e r i o r growth-rates (3.11 and 3.02 f o r brooder one and two r e s p e c t i v e l y as compared to 2.94 f o r the f l o o r , Table 6). During the 3-7 week growth p e r i o d the f l o o r reared b i r d s had a s u p e r i o r growth r a t e (2.65 as compared to 2.50 and 2.46 f o r brooders one and two r e s p e c t i v e l y ) . This r e v e r s a l , with the f l o o r reared b i r d s performing b e t t e r , i s probably due to the s t r e s s imposed on the brooder reared b i r d s by moving them to the f l o o r at three weeks of age. By seven weeks of age there was no. s i g n i f i c a n t d i f f e r e n c e , although the brooder reared b i r d s have a weight advantage (7 36 and 748 grams f o r brooders one and two r e s p e c t i v e l y as compared to 726 grams f o r the f l o o r reared b i r d s ),• 34. TABLE 6. Mean Body Weights and Growth-rates f o r Selected Growth Periods Growth Period Brooder 1 Brooder 2 Fl o o r 1 Wk Wt 1-3 Week Gr. 3-7 Week Gr. 7 Wk Wt 64 grams 3.11 2.50 7 36 grams 6 8 grams 3.02 2.46 74 8 grams 59 grams 2.9 4 2.6 5 726 grams 35. The r e s u l t s of the-body weight analyses are shown i n Table 7 (Percentage Sums of Squares f o r Body Weight Analyses). There was no s i g n i f i c a n t d i f f e r e n c e f o r one week f o r Rows, Columns or Treatments. E r r o r (E) was s i g n i f i c a n t f o r three of the eight weekly p e r i o d s (Hatch, 1 and 7). Groups were s i g n i f i c a n t f o r weeks 1, 2, 3, and 4. The orthogonal break-downs show that t h i s d i f f e r e n c e was between the brooders and the f l o o r . At one week of age there was a l s o a d i f f e r e n c e between brooders one and two. The Treatment by Group i n t e r -a c t i o n was n o n - s i g n i f i c a n t , however, i t was i n t e r e s t i n g to note that the variance i n E r r o r (F) i s s i g n i f i c a n t f o r a l l weeks except Hatch. This a n a l y s i s shows that Treatments are not s i g n i f i c a n t , although i t should be noted (Table 2) that a f t e r two weeks of age Treatment three (33.3 BTU/lb of a i r ) was the h e a v i e s t and that Treatment two (31.3 BTU/lb of a i r ) was the l i g h t e s t , 126 and 123 grams r e s p e c t i v e l y . From t h i s time u n t i l completion of the experiment, Treatment three was always h e a v i e s t . A Sign t e s t (Crow, Davis and M a x f i e l d 10) i n d i c a t e d s i g n i f i c a n c e . This suggested t h a t enthalpy t r e a t -ments d i d have an e f f e c t on the b i r d s ' growth. In order to provide more convincing evidence, more studi e s w i l l be necessary. For the f i r s t four weeks the brooder reared b i r d s maintained s i g n i f i c a n t l y h e a v i e r body weights than the f l o o r reared b i r d s . By f i v e weeks of age, the s t r e s s of moving the brooder reared b i r d s to a new environment had depressed TABLE 7. Percentage Sums of Squares f o r Body Weight Analyses. WEEK Sources o f Variance df Hatch 1 2 3 4 5 6 7 Rows 2 8.17 5.46 2.24 1.10 0.74 0.22 0.18 1.56 Columns 2 8.5 3 2.40 1. 35 1.09 1.82 10. 82 3.20 4 .38 Treatments 2 7.83 0.59" 0.29 0.82 1.19 2.45 0.7 8 1.33 E r r o r (E) 2 4.39* 8. 29* 4.25 3.44 4.17 0.61 0.60 3.40* Groups 2 0.36 12.88* .16.54* 25.13* 5.6 3* 1.53 1.31 0.90 1,2 vs 3 1 0.19 10.14* 15.2 8* 24.24* 5.5 3* 1.41 1.04 / 0.66 1 vs 2 1 0.17 . 2.74* 1.25 0.89 0.10 0.12 0.27 0.24 T x G 4 0.35 5.56 2. 25 2.10 0.90 1.11 1.15 1.23 E r r o r (F) 12 1.17 6.64* 15.4 7* 7.71* 7.2 6* 7.5 0* 6.0 9* 5.21* E r r o r (H) 693 69. 29 58.16 57. 61 58.61 78.21 75.75 8 6.70 81.9 9 T o t a l 719 100,00 99.98 100 .00 100.00 99.92 99 .99 100.00 100.00 T o t a l SS 12842 84161 307500 798860 1326100 2630500 4107800 6 662100 * S i g n i f i c a n c e : P < 0.05 TABLE 8. Percentage Sums of Squares f o r the Growth-rate Analyses GROWTH PERIOD WEEKS Sources o f Variance df H- 1 1-2 2-3 3-4 4--5 5-6 6- 7 Rows 2 4. 15 2. 77 3. 42 3. 12 0, ,58 4 . 65 8. 10 Columns 2 2. 42 2. 74 0. 43 2. 20 18. ,67 21. 26 3. 81 Treatments 2 2 . 78 3. 05 7 . 72 2. 73 4. ,07 4. 41 0. 55 E r r o r (E) 2 5. 9 4* 1. 61 2. 54 3. 66 14. , 27* 3. 64 , 27. 37* Groups 2 13. 8 8* 1. 73 3. 08 27. 6 3* 4. , 67* 0. 89 0. 25 1,2 vs 3 1 11. 9 8* 1. 22 2 . 45 26. 44* 4. , 66* 0. 73 0. 21 1 vs 2 1 2. 02@ 0. 51 0 . 63 1. 19 .0. ,01 0. 16 0. 0 3 T x G 4 6. 89 .11. 38 6. 90 1. 48 0. , 87 0. 74 0. 78 E r r o r (F) 12 6. 99* 24. 11* 27. 54* 6 . 11* 2. ,82* 6. 0 8 * 1. 4 8* E r r o r (H) 693 56. 83 52. 60 48. 36 51. 96 54. . 04 58 . 33 57. 66 T o t a l 719 99. 88 99. 99 99 . 99 99. 72 99 . ,99 100. 00 10 0. 00 T o t a l SS 250 169 135 228 2. .7 153 148 * S i g n i f i c a n c e : < 0.05 @ Approaching s i g n i f i c a n c e at the 5% l e v e l . 38. t h e i r growth enough so th a t body weights were not s i g n i f i -c a n t l y d i f f e r e n t , from those of the f l o o r b i r d s , even though-the brooder reared b i r d s were s t i l l h e a vier. The growth of the brooder reared b i r d s was depressed f o r two weekly growth periods (3-4 weeks and 4-5 weeks) due to the s t r e s s of changing environments at 3 weeks o f age. However, the weekly growth p e r i o d 3-4 weeks had the most severe e f f e c t on the b i r d s . The H-l week growth, p e r i o d was the most important i n improving the b i r d s ' growth. In the next two weeks growth-r a t e s were not. improved by the c o n t r o l l e d environment, but the body weight was increased due to the increased growth i n the f i r s t week. CONCLUSIONS The data i n these analyses have shown that the range of enthalpy treatments (29.3 t o 33.3 BTU/lb of a i r ) used d i d not s i g n i f i c a n t l y a f f e c t the growth-rate or the seven week'body weight of the b i r d s . The data demonstrated that the f i r s t week of growth has the most e f f e c t on the b i r d s ' l a t e r * p e r f o r -mance as measured by growth-rate and body weight. The d i f f e r e n c e between brooder one (the o r i g i n a l brooder) and brooder two (a l a t e r a d d i t i o n ) i n t h i s growth p e r i o d ( H - l week) was probably due to a chance environmental s t r e s s i n brooder one which reduced growth i n t h i s p e r i o d . This would not seem to be too important s i n c e i t i s only observed once. I t was t h e r e f o r e concluded that the environments i n the brooders were e s s e n t i a l l y the same. A f t e r the b i r d s were removed from the brooders (at three weeks of age) and placed on the f l o o r , i t took two weeks f o r the shock o f t h i s move to d i s s i p a t e . Obviously most of t h i s s t r e s s occurred i n the growth p e r i o d immediately f o l l o w i n g t r a n s f e r (3-4 weeks). By the 5th week the d i s t i n c t advantage of the c o n t r o l l e d environment had disappeared, due to the s t r e s s of p l a c i n g the b i r d s i n the new environment at three weeks of age. At seven weeks of age there was no s i g n i f i c a n t d i f f e r e n c e i n the performance of the brooder reared b i r d s as compared to.the f l o o r reared b i r d s , although the brooder -reared b i r d s were c o n s i s t e n t l y h eavier. Because the brooder reared b i r d s were hea v i e r than 40. the floor reared birds, i t i s possible that controlled environment poultry brooders might be economically j u s t i f i e d for commercial production. The same argument could be applied to justify the use of a high enthalpy environment. Because enthalpy i s a function of temperature and relative humidity a high relative humidity might be used instead. SUGGESTIONS FOR FUTURE WORK Some improvements .to the experiment could probably 'be?-made. A low energy d i e t was fed to the b i r d s . I f a higher energy d i e t had been used, i t i s p o s s i b l e that the d i e t a r y s t r e s s could have aided i n g i v i n g more d e c i s i v e r e s u l t s to t h i s experiment. Probably the b i r d s should not have been vaccinated f o r Newcastle and B r o n c h i t i s . Vaccina-t i o n imposes a s t r e s s on the b i r d s and i f t h i s were removed the a d d i t i o n a l growth might show which treatment was more e f f e c t i v e . One aspect of the b i r d s ' environment t h a t should be considered i n the next experiment i s the genetic back-ground source of the b i r d s . The b i r d s should be pedigreed and f u l l s i b l i n g s compared i n each enthalpy treatment. A d d i t i o n a l i n f o r m a t i o n on whether or not the genetic back-ground i n f l u e n c e s the e f f e c t of enthalpy would then appear. From the in f o r m a t i o n c o l l e c t e d during t h i s e x p e r i -ment i t has been suggested that a high and a low enthalpy should have been chosen, with the t h i r d treatment c l o s e r to the high enthalpy than'the low enthalpy. A l l of these m o d i f i c a t i o n s i n the experimental design can be made wit h the e x i s t i n g equipment. I f the equipment were a v a i l a b l e a l l three treatments and t h e i r r e p l i c a t e s should be run at one time. This would remove any time e f f e c t s . 4 2 . LITERATURE CITED 1. Adams, R.L.,-Andrews, F.N., G a r d i n e r , E.E., F o n t a i n e , W.E., and C a r r i c k , C.W., 1962..'The E f f e c t s of E n v i r o n -mental Temperature on Growth and N u t r i t i o n a l Require-' ments of the Chick. P o u l t r y S c i . , V o l . 41, 588-594. 2. Beckett, F.E., V i d r i n e , C.G. A Mathematical M o d e l l i n g of. Heat T r a n s f e r i n a P i g . ASAE Paper No. 69-4 37. 3. Benzinger, T.H., 1961. The Human Thermostat. S c i e n t i f i c American, V o l . 204:1, 134-197. "4. B l i g h , J . , 1966. The. T h e r m o s e n s i t i v i t y of the Hypothalamus and Thermoregulation i n Mammals. Bio. Rev., V o l . 41, . ' 317-367. 5. Bond, T.E., K e l l y , C.F., 1955. The Globe Thermometer i n A g r i c u l t u r a l Research. A,g. Eng. V o l . 36:4 , 251-2 55 . 6. B o u c h i l l o n , C.W., Reece, F.N., Deaton, J.W. Mathematical M o d e l l i n g of Thermal Homeostasis i n a Chicken. ASAE Paper No. 69-436. 7. Brody, S., 1964. B i o e n e r g e t i c s and Growth. Hafner P u b l i s h i n g Company. 8. Canadian Code for.Farm B u i l d i n g s , 19 70. N a t i o n a l Research C o u n c i l , Ottawa. 9. Cole, H.H. I n t r o d u c t i o n t o L i v e s t o c k P r o d u c t i o n , 2nd E d i t i o n . -W.H. Freeman and Co. 10. Crow, E.L., Davis, F.A., M a x f i e l d , M.W. S t a t i s t i c s Manual. Dover- P u b l i c a t i o n s Ltd. 4 3 . 11. Dempster, J.R.H., Starkey, J.E., Coshow, B., 1970. UBC MFAV A n a l y s i s of Variance. 12. Dorminey, R.W., Wilson, H.R. , Ross, I . J . , Jones, A.E.-, 1967. Temperature and Humidity E f f e c t s on S u r v i v a l of Chickens. Quarterly J o u r n a l of the F l o r i d a Academy of Sciences, V o l . 30:4, 316-320. 13... Drury, L.N., S e i g e l , H.S., 1965 . A i r V e l o c i t y and Heat Tolerance of Young Chickens. Trans. ASAE, Vo l . 19:4, 583-585. 14. Esmay, M.L., 1969. P r i n c i p l e s of Animal Environment, AVI Publ. Corp. 15. Hammond, J . , 1954. Progress i n the Physiology of Farm Animals. V o l . 1, Butterworth's S c i e n t i f i c P u b l i c a -t i o n s , London. 16. Hardy, J.P., 1961. Physiology of Temperature Regulation. P h y s i o l . Rev., V o l . 41, 521-606. 17. Huston, T.M., Carmom, J.L., 1958. Some P h y s i o l o g i c a l and Genetic E f f e c t s I n f l u e n c i n g Heat Tolerance i n Domestic Fowl. World's Congress. 18. King, J.O.L., 1956. The Body Temperature of Chicks During the F i r s t Fourteen Days of L i f e . B r i t i s h V e t e r i n a r y . J o u r n a l , V o l . 112:4, 155-159. 19. Longhouse, A.D., Ota, H., Emerson, R.E., Heishman, J.D. .Heat and Moisture Design Data f o r B r o i l e r Houses ASAE Paper No. 67-422. P r i n c e , R.P., Whitaker, J.H..., Matterson, L.D. ,. Luginbuhl, R.E.,.. 1965 . Response: of Chickens to Temperature and R e l a t i v e Humidity Environments. P o u l t r y S c i . V o l . 44, 7 3-77. Roberts, C.W., 1964. Esti m a t i o n of E a r l y Growth Fate i n the Chicken. P o u l t r y S c i . V o l . 43, 238-252, Roberts, C.W., 1965. One-week Body Weight to a 7-week Body Weight i n the Chicken. P o u l t r y S'ci: V o l . 44, 947-952. Roberts, C.W. , Crober, D.C, H i l l , A.T., 1966 . The Response of 1-week Body Weight and 1 to 7-week Growth Rate to S e l e c t i o n f o r 7-week Body Weight i n ' the Chicken. P o u l t r y S c i . V o l . 45, 897-900. Sainsbury, D.W.B., 1966. C o n t r o l l e d Environment P o u l t r y Housing. The T h i r t e e n t h World's P o u l t r y Congress, 474-479. Smith, R.M., Kan, J . and Rokeby, T.R.C., 1962. The E f f e c t s of P o u l t r y Housing on B r o i l e r Weight, Feed Conversion and M o r t a l i t y . P o u l t r y S c i . V o l . 41, 594-607. S t a l e y , L.M., Roberts, C.W., 1969. Design and Develop-ment of C o n t r o l l e d Environment Brooders f o r P o u l t r y . Can. Ag. Eng. V o l . 11:2, 71-73. S t a l e y , L.M., Roberts, C.W. ,. Crober, D.C. , 196.7 . The. E f f e c t of Thermal Radiation on E a r l y Growth of the New Hampshire Chicken. Can. Ag. Eng. Vo l . 9:1, 1-4 45. 28. S t a l e y , L.M., Roberts, C.W. , Paulson, S., 1970. Improved Growth of P o u l t r y U t i l i z i n g C o n t r o l l e d Environments. Can. Ag. Eng. V o l . 12:2, 76-79. 29. S t e e l e , R.G.O., T o r r i e , J.H. , 1960. P r i n c i p l e s and Procedures of S t a t i s t i c s . McGraw-Hill Book • Company Inc. 30. S t u r k i e , P.D., 1965. Avian Physiology. Comstock P u b l i s h i n g A s s o c i a t e s . 31. Suggs, C.W., 1966. Role of Enthalpy i n Heat Loss. Trans. ASAE 9:3, 322-325. 3.2. Suggs, C.W. , 19 67. Temperature and Enthalpy Equivalence of Thermal R a d i a t i o n . Trans. ASAE 10:6, 727-729. 33. T h r e l k e l d , J.L., 1970. Thermal Environmental Engineer-i n g . P r e n t i c e - H a l l , 2nd E d i t i o n . 34. Wilson, H.R., Armas, A.E., Ross, L.J.', Dorminey, R.W. , Wilcox, C.J., 1966. F a m i l i a l D i f f e r e n c e s of S i n g l e Comb White Leghorn Chickens i n High Ambient Temperature. P o u l t r y S c i . V o l . 45, 784-7 88. 

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