Nutritional studies with Bos Taurus and Bos Indicus calves
Black, David Hamilton
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Milk substitute diets whose dry matter contained 10 %, 20% and 30ft added fat were fed to Bos taurus calves in Scotland and !3os indicus and Bos taurus calves in Trinidad. Bos taurus calves adapted readily to the system of artificial rearing used, but considerable difficulty was experienced in training Bos indicus calves to drink either milk substitute or whole milk diets from a bucket, and as a consequence their daily intake of milk was considerably less than that of Bos taurus calves of comparable body weight. The food intake of Bos indicus calves was increased markedly by allowing them to suck milk from nurse cows, and under these conditions their intake was similar to that of Bos taurus animals of comparable body weight.The apparent digestibility of the components of the milk substitute diets by Bos indicus and Bos taurus calves was similar irrespective of the fat content of these diets, but Bos indicus calves appeared to retain more magnesium than Bos taurus calves. This high level of magnesium retention may have resulted from the low rate of water intake and urine excretion by Bos indicus calves and could have been responsible for the occurrence of urolithiasis in some of the Bos indicus calves, Although none of the Bos taurus calves exhibited symptoms of urolithiasis, 33% of those Ros indicus calves which survived until weaning died within six weeks of weaning as a result of urinary calculi formation and the calculi obtained from those Bos indicus calves which died had a very high magnesium content.The apparent digestibility of the components of the milk substitute diets was higher by Bos taurus calves in Trinidad than by Bos taurus calves in Scotland. This finding was most apparent when calves were fed the milk substitute diet containing 30% added fat. The use of this diet was discontinued in Scotland because a large percentage of the calves on this treatment died, but in Trinidad Boa taurus calves digested this diet without difficulty.The digestible energy requirement for maintenance of each kilogramme of body weight was found to be considerably less for Bos taurus calves reared in Trinidad than for Bos taurus calves reared in Scotland.The apparent digestibility of nitrogen by Bos indicus and Bos taurus calves in Trinidad was similar, but the digested nitrogen required for the maintenance of body weight was greater for Bos indicus calves than for Bos taurus calves, because of a high endogenous nitrogen excretion rate in urine by Bos indicus calves.With all calves the arynarent digestibility of fat and the apparent absorption of calcium were positively correlated irrespective of the fat content of the diet fed. This uresumably indicates that fatty acids excreted in the faeces were in the form of calcium soaps.The heart rate of calves was shown to be affected by the fat content of the diet fed and the level of food intake, but Bos tau-rus and Bos indicus calves with similar levels of food intake had similar heart rates.Partial alopecia was exhibited between five and eight weeks of age by all Bos indicus calves, but by no Ras taurus calf.Under the conditions of this experiment, the major difference between ßcs indicus and Ros taurus calves was the behavioural response by Bos indicus calves to the system of artificial rearing practised which resulted in these calves having a low voluntary food and water intake. It is not clear to what extent this low voluntary food and water intake affected the other minor differences which were observed between those ",os indicus and Bos taurus calves used in these experiments, but no justification has been obtained that, in general, Bos indicus calves differ from Ros taurus calves in their nutrient requirements.