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Energy Level Effects on Growth and Conception Rates of Heifers

University of Kentucky, Lexington, 40506¹ ,^,2

Abstract

The relationship of growth and conception rates to the level of dietary energy was studied using weanling Hereford heifer calves. Forty-eight calves were randomly allotted to three groups that were twice replicated and fed equal quantities of corn silage and protein supplement plus one of the following levels of corn as a source of supplemental energy: (A) none, (B) 3.00 lb (1.36 kg) of ground shelled corn per head daily, or (C) 6.00 lb (2.72 kg) of ground shelled corn per head daily.

When compared with no supplemental energy, the addition of 3.00 lb (1.36 kg) of corn resulted in increased average daily gain, and 6.00 lb (2.72 kg) of added corn resulted in a further increase in gain. Average daily gains (ADG) of heifers in group C were greater (P<.05) than those of group A during the growing phase (phase I). From the termination of this phase until slaughter (phase II), ADG of heifers in groups A, B and C was 1.17, 1.36 and 1.63 lb (.53, .62 and .74 kg), respectively, and were different (P<.01) from each other. Significant differences were observed in carcass conformation, marbling, kidney fat, rib fat, yield grade, quality grade and carcass weight when the three dietary energy levels were fed these heifers from weaning until slaughter (273 days).

Reproductive measurements indicated that a diet fed to heifers containing only corn silage supplemented with protein, vitamins and minerals was adequate in energy for conception. Even though increased increments of supplemental energy resulted in fatter carcasses when the heifers were slaughtered at approximately 18 months of age, conception rates were not affected. The number of heifers pregnant in the respective groups was: (A) 15 of 16, (B) 16 of 16 and (C) 14 of 15. Also, no significant differences in fetal crown-rump length suggested that the time of first estrus and conception was similar for all groups of heifers.

¹ Department of Animal Sciences.

² This paper (76-5-25) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.