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Some Effects on Beef Cattle of Protein and Energy Restriction

U. S. Department of Agriculture

Abstract

The effects of rations of low protein as well as low energy value, fed between the ages of 6 months and one year, were studied with monozygotic beef-type cattle. The experiments were begun with 12 pairs of animals of which 10 pairs remained intact throughout the trials. Eight different pelleted rations were fed, ranging from a caloric maintenance ration that was only 2.5% digestible protein (ration 1) to rations of relatively high energy value liberally supplied with protein. During restriction, animals on ration 1 lost weight while those on the other rations made gains that ranged from slight increases to 1.9 lb. a day depending on the quality of the rations and the amounts fed. Slaughter of each retarded animal was delayed until its degree of fatness approximated the final condition of its co-twin; slaughter weights of co-twins were similar. In spite of the drastic treatments given some animals, efficiency of feed utilization and carcass and meat quality of co-twins, with one partial exception, were similar. The exception consisted of a lower degree of desirability of fat of 2 of the animals fed ration 1 as compared with the fat of their co-twins. Within one of the pairs this was likewise true of the lean meat while within the other pair it was not. When energy intake was held near maintenance, changes in bodyweight were positively correlated with level of protein intake. The existing need for an index of the minimum practical level of protein to be allowed young cattle on caloric maintenance rations is discussed and an allowance to meet this need is suggested on a tentative basis.

¹ Animal Husbandry Research Division, A. R. S., Beltsville, Md.

² Grateful acknowledgment is made of the assistance given by M. R. Irwin et al., Department of Genetics, University of Wisconsin, in whose laboratory the blood samples were analyzed.