Lifetime Effects of Winter Supplemental Feed Level and Age at First Parturition on Range Beef Cows

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Abstract
Ninety Hereford females were used in factorially arranged treatment groups to study the lifetime effects of three levels of winter supplemental feed and two ages at first parturition on the beef cow and her performance under range conditions. Winter supplemental feed level significantly affected winter and summer weight gains in the early years of the study. Mature cow size and body weight were not significantly affected by either winter feed level or age at first parturition. However, body weight and height were greatest for the later calving cows receiving the high level of winter supplemental feed, and least for those cows calving first at 2 years of age and receiving the low winter supplemental feed level. No differences in birth or weaning weights of the calves were noted; however, average calving date was delayed by the low winter supplemental feed level. The difference in the early years of the study being approximately 7 to 12 days later for the low level fed cows as compared to those receiving the high winter supplemental feed level. Percent calf crop born and weaned favored those cows receiving the low winter feed level, with the difference in percent calf crop weaned due to winter feed level approaching significance (P<.10). Total pounds of calf weaned per cow during her lifetime was significantly affected (P<.025) by winter supplemental feed level, with the average cow on the low winter supplemental feed level weaning 340 and 478 kg more calf than the average cow on the medium or high winter feed level, respectively. Although not statistically significant, the average cow calving first at 2 years of age weaned 154 kg more calf than the average cow calving first at 3 years of age. At the termination of the study, the average lifespan of cows on test was 14.65, 13.07 and 10.88 years for the low, medium and high winter feed level groups, calving at 2 years of age, respectively; and 13.51, 12.73 and 13.06 years, respectively, for the same winter feed level groups calving first at 3 years of age. Reasons for removal of cows from test, and the possible relationship between nutritional level and lifespan were discussed. Copyright © 1972. American Society of Animal Science . Copyright 1972 by American Society of Animal Science.

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