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Efficiency of Feed Utilization by Various Animal Species Fed Similar Rations

Department of Animal Husbandry, University of California, Davis, California

The relative response and efficiency of feed utilization by rats, chicks, pigs, sheep and steers were compared when two rations varying in fiber content made of the same natural feedstuffs were fed. Daily gains and feed intakes were characteristic of the species, considering the type of ration fed. Proportions of final body fat in rats and chicks were from 4 to 8%; in pigs 35 to 41%, and in ruminants from 21 to 26%. Body protein, however, was greatest in rats and chicks and lowest in pigs, sheep and steers. Body weight gain as fat was less than 10% in rats and chicks but from 40 to 50% in pigs, sheep and steers. The protein in liveweight gain was approximately 20% in rats, 29% in chicks, 10 to 12% in pigs and sheep and 18% in steers. Energy content of the weight gain was about 2,000 kcal/kg in rats and chicks but 4,500 to 5,200 in the larger animals. The total efficiency of feed utilization in terms of liveweight gain per unit of feed intake was lowest for ruminants; pigs and rats were intermediate, and chicks were the most efficient. Total efficiency of feed utilization measured as calories showed pigs to be most efficient, followed by sheep, steers, chicks, and rats in that order. Protein gain per unit of feed intake was greatest for chicks followed by rats, pigs, steers and sheep. Feed capacity played a major role in relative efficiency of feed utilization because less feed was used for maintenance when the animals gained faster. The correlation coefficient between feed capacity and efficiency of energy utilization in terms of energy gain was 0.91.