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Effects of Breeding System, Cow Weight and Milk Yield on Reproductive Performance in Beef Cattle¹

University of Guelph, Guelph, Ontario, Canada NIG 2W1

Abstract

Diverse breed types were used to analyze the effects of breeding system, cow weight and milk yield on reproductive performance of well-fed, confinement-housed beef cows. The five breeding systems were purebred Hereford, purebred Simmental, large rotational beef, small rotational dual purpose, and small rotational beef with 277, 85, 245, 92 and 75 successful matings, respectively. Simmental heifers had the highest age at first calving and days of pregnancy (P < .05). The Hereford, small rotational dual purpose and small rotational beef heifers had fewer services per pregnancy than the Simmental (P < .05) or large rotational beef heifers (P > .05). There were no differences (P > .05) among breeding systems for percentage of heifers pregnant by 18 mo, heifer gestation length, cow pregnancy rate, cow services per pregnancy, cow days to pregnancy and cow gestation length. A 100-kg increase in first lactation weight increased age at first calving by 11.3 d (P = .0004) and days to pregnancy by 3.8 d (P = .02). Increases in mature weight had no effect on the reproductive performance of cows. A 1-kg/d increase in the milk yield of heifers was associated with increased services per pregnancy (.017, P = .02) and days to pregnancy of heifers (1.08 d, P = .03) but did not affect any other trait measured for heifers or cows. Neither increased body weight nor increased milk yield had an effect on the reproductive performance of well-fed cows, but they did increase the time for heifers to become productive.

¹ The authors gratefully acknowledge the financial assistance of the Natural Sci. and Eng. Res. Council and the Ontario Min. of Agric. and Food and the assistance of O. B. Allen, M. R. McMorris, C. Watson, A. McBurney and the research station staff.

² Dept. of Anim. and Poult. Sci.