Comparison of Criteria for Selecting Introduced Beef Sires

Abstract

Bulls selected from the Polled Hereford herd at Tifton (numbering 80 to 100 cows) were bred to four groups of grade Polled Hereford cows at Reidsville (the State Prison Farm) to produce from 10 to 38 calves per year over a 7-year period. Two bulls were used per herd per year. The breeding herd designated RG consisted of bulls selected for superior rate of gain on 168-day postweaning tests and daughters of sires which had been highly selected for the same criterion; the herd WW—of bulls selected for high weaning weight and daughters of bulls which had been highly selected for weaning weight; the herd TY—of bulls highly selected for yearling type score and daughters of sires which had been highly selected for yearling type score; the AV—of bulls which were most nearly average in the aforementioned traits and daughters of average sires. Female selection was not intense. Main effects (year, herd, sex and age of dam) and the interaction of herd and year were generally significant sources of variation in the analyses of birth and weaning data. Herd and final age of steer were important sources of variation in postweaning weights and gains. Weaning weight means were 179, 188, 180 and 181 kg in the RG, WW, TY and AV herds, respectively. Type score means were 10.16, 10.14, 10.63 and 10.47 for the herds in the order listed above. Postweaning rates of gain of steers from the RG and WW herds were comparable and greater than (P<.05) rates of gain of steers from the TY and AV herds. The WW herd was superior in carcass weight per day of age (P<.05). Three estimates of realized heritability of weaning weight, type score and postweaning average daily gain were in relatively good agreement, suggesting that response was obtained from selection in this study. In each case where the absolute value of the genetic correlation from offspring-sire regression was at least 0.4, the direction of observed correlated response and the sigh of the genetic correlation were in agreement.