Selection of Beef Cattle for Single Traits

Abstract

Bulls selected from the Polled Hereford herd at Tifton (numbering 80 to 100 cows in size) were bred to four groups of similar grade Polled Hereford cows at Reidsville (the State Prison Farm) to produce from 17 to 44 calves per herd per year over a 7-yr. period. Seven bulls were used per herd in batteries of two per year in each year except the first. The herd designated as RG was bred to bulls selected for superior rate of gain on 168-day postweaning test; the herd WW-to bulls selected for high weaning weight; the herd TY-to bulls selected for high yearling type score; the herd AV-to bulls which were most nearly average in each of the aforementioned traits. Little or no selection was practiced among females. Phenotypic time trends for weaning weight were negative from 1958 to 1964, making a large negative environmental effect mandatory if genetic progress in this trait is to be postulated. Differences between performance levels of offspring of the herds varied with years for some of the traits studied but on the average, selection for RG and WW produced beneficial results in the form of increased weights. Least-squares constants for birthweight, weaning, postweaning weights and gains and scores were positive for the RG and WW herds and negative for the other herds. The regressions of deviations from the AV herd means on years were positive, generally, and different from zero in some cases but never significantly different (P>.05) for a given trait from herd to herd. Compared to the AV herd, improvements in birthweight and weanling traits were greatest in the TY herd, but these changes were not significantly (P>.05) different from changes in the other two herds. Mean postweaning daily gains of steers of the RG, WW and AV herds were similar, but all were greater (P<.05) than the TY mean. The RG and WW herds produced steer carcasses which weighed more (P<.05) than carcasses produced by the TY and AV herds (263 and 264 kg. vs. 239 and 244 kg.). Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science