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Nutritive evaluation of low=quality forages supplemented with different nitrogen sources in ruminant feeds Adeleye, Isaac Omotosho Adewale

Abstract

The utilization of low-quality forages in the feeds of ruminant animals takes on special importance because of the abundance of these materials and their potential value if supplemented with protein. The effect of the use of three different nitrogen sources, urea, biuret and poultry wastes, to replace a portion of soybean meal nitrogen in high roughage-rations of sheep was investigated using in vivo and in vitro techniques. The chemical composition of poultry waste was determined to study the feasibility of using it as a nitrogen source. There was a considerable variation in the chemical composition of poultry litter (bedding material plus droppings) as compared with the cage droppings. The litter contained 21.5 to 30.4% protein equivalent, approximately one-third of which was in form ' of uric acid nitrogen. The cage droppings contained 26.3 to 35.4% protein equivalent and about two-fifths of this was in the form of uric acid nitrogen. Before feeding trials were undertaken, attempts were made to reduce the number of pathogenic bacteria that might be present in the poultry wastes by heat treatment. Though autoclaving or steaming had no significant effect on the total nitrogen or uric acid nitrogen, these heat treatments however, were sufficient to destroy all the microflora in the wastes. No significant differences were observed in the digestibility coefficients of dry matter, crude protein, crude fiber or gross energy when approximately 50% of the soybean meal (SBM) nitrogen of the control ration was replaced by urea, biuret or poultry droppings in the rations of fattening lambs fed in the unpelleted form. However, similar replacement of 50% of the SBM nitrogen of the control ration by poultry litter, resulted in significantly lower nutrient digestibility coefficients of this ration when compared with the control. It might therefore by concluded that the presence of bedding material in the poultry litter hampered the availability of nitrogen from this source when fed to lambs. However, when the rations were offered in the pelleted form, the differences in nutrient digestibility coefficients, particularly between the control and the litter supplemented rations, were no Monger significant. Pelleting was found to increase the voluntary intake of the rations regardless of the source of nitrogen supplementation. Although all animals were in positive nitrogen balance, those fed the urea and poultry litter supplemented rations had significantly lower nitrogen retention than those fed the soybean, biuret and poultry droppings supplemented rations. This observation was also reflected in the lower body weight gains and feed efficiency of the animals fed the urea and litter containing diets. In experiments designed to determine the maximum level of poultry droppings that could be safely incorporated as an NPN source in high roughage rations, it was found that at levels of 18.7, 50.2 and 64.2% of the total nitrogen in the rations, there was no significant difference in the voluntary intake. This indicated that as a source of NPN, poultry droppings had an equally effective replacement value at all the three levels studied. In vitro tests were employed to determine the effect of alkali treatment on the nutritive value of low-quality forages. Treatment with NaOH or NH₄OH significantly increased cellulose digestibility. The type of nitrogen source (urea, biuret or uric acid) used in the basal medium did affect the cellulose digestibility. There appeared to be a positive relationship between the solubility of the nitrogen source and cellulose digestibility in vitro.

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