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Estimated Direct and Correlated Response to Selection for Performance Traits in Closed Hereford Lines under Different Types of Environments¹

University of Nevada, Reno 89507

Abstract

Five closed Hereford lines were established at two locations. In each line selection was practiced for a single trait. All progeny of both sexes (N=1488) were fed individually for 140 days postweaning. At one location (Line 1, postweaning gain; Line 2, feed efficiency; Line 3, yearling conformation) calves received 2 parts grass hay: 1 part concentrate during the postweaning period. Progeny at the other location (Line 4, gain; Line 5, feed efficiency) were fed a supplement plus grass hay ad libitum.

Inbreeding caused a reduction in postweaning performance of progeny under both sets of conditions. Maximum likelihood estimates of genetic trends based on differences between dam birth year groups indicated that positive changes had occurred in gain and gain/TDN in all lines during the period 1955 to 1969, although linear effects on these traits were statistically significant only in Line 4. Genetic changes in conformation score, with effects of body weight removed, were minimal. Regressions of gain/TDN on dam birth year in the gain lines were of about the same order of magnitude, or somewhat higher, as compared to values for lines in which direct selection was practiced for increased feed efficiency, suggesting that many of the genes which control the expression of growth rate of beef cattle are responsible also for efficiency of feed utilization.

¹ Contribution from the Agricultural Experiment Station, University of Nevada, Journal Series No. 175. The study was conducted in cooperation with Western Regional Project W-1, The Improvement of Beef Cattle Through the Application of Breeding Methods.

² The authors would like to thank Y. O. Koh. Statistician, College of Agriculture, University of Nevada for computer assistance, C. L. Probert and S. P. Hammack, former graduate students, for data collection and members of the Animal Science Division, particularly V. R. Bohman and W. C. Behrens, for participation in other parts of the study.

³ Professor, The Ohio State University, Columbus.