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An Analysis of Reproductive Traits in Beef Cattle¹

University of Nebraska, Lincoln 68503 and U.S. Department of Agriculture

Abstract

Analyses of data collected in a cross-breeding experiment conducted at the Fort Robinson Beef Cattle Research Station included first year reproductive performance of 315 daughters of 43 sires and reproductive performance of all heifers and cows mated to 70 bulls. Failure to conceive including embryonic loss that occurs prior to an early pregnancy diagnosis was the most important stage at which losses occurred. Thirty-one percent of heifers exposed for breeding failed to wean a calf. Two thirds of these represented failure to conceive or early embryonic loss. Eighteen percent of the second calf and older cows failed to wean a calf. Nearly half of these failures were not diagnosed pregnant.

Heritability estimates for all reproductive traits were low. The only traits where the heritability estimates exceeded their standard errors were (1) first service conception rate (h²=0.22±0.17) and (2) conceptions per estrous cycle exposed (h²=0.27±0.17). Comparison of correlations obtained suggests genetic variation in maternal environment was more important than variation in genotypes of the fetus for traits related to pre- and post-natal mortality.

¹ Department of Animal Science, published as Paper No. 3430, Journal Series, Nebraska Agricultural Experiment Station. Contribution from North Central Regional Project NC-1, Improvement of Beef Cattle Through Breeding Methods.

² Present address: Department of Animal Science, South Dakota State University, Brookings 57006.

³ U.S. Meat Animal Research Center, A.R.S., U.S.D.A., Clay Center, Nebraska 68933.

⁴ Dr. J. N. Wiltbank provided leadership for reproductive physiology data collected in this experiment.

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