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Genetic Analysis of Postweaning Performance of Hereford Bulls^{1, 2, 3,}

North Carolina State University, Raleigh 27607

Abstract

The genetic parameters of and interrelations among postweaning performance traits were investigated using feedlot performance records of 695 individually-fed Hereford bulls from 72 sires. The data comprise two generations of selection for weaning weight (line 1), postweaning growth rate (line 2) and a random control (line 3).

Estimates of heritability from analyses of within-animal regression coefficients (regression of cumulative gain (B-WT) or feed intake (B-FEED) on the period of measurement) obtained from intermediate, 14-day measurements were higher than for total gain or total feed. Further, the heritability of the ratio of the two regressions (B-FEED/B-WT) was higher than for feed/gain. Heritabilities for B-WT, B-FEED, NEWEF (B-FEED/B-WT), PREDEF1 (total feed/B-WT)and PREDEF2 (B-FEED/total gain) were .41±.26, .52±25, .38±22, .33±.22 and .24±.21, respectively. Heritabilities of point estimates were: .23±.20, .44±.25, .26±25, .21±.23 and .49±28 for ADG (average daily gain), ADFC (average daily feed intake), FEEDEF (feed/gain), FAT(sonoray fat measurement) and FINWT (yearling weight), respectively.

High and positive genetic correlations were found between ADG and ADFC (.84), FINWT and ADFC (.55), FINWT and ADG (.71) and ADFC and FEEDEF (.72). FEEDEF and ADG were lowly correlated genetically (.23), whereas FINWT and FEEDEF were genetically independent (–.02). However, the regression coefficient approach produced different results regarding the associations among gain, feed consumption and feed efficiency. The genetic correlations between B-WT and B-FEED, B-WT and NEWEF and B-FEED and NEWEF were .19, –.06 and .12, respectively. Thus the antagonistic correlations were generally reduced by this approach. These results suggest that direct selection will be necessary to improve efficiency. Selection for NEWEF is suggested.

Heritability estimates from sire-son analyses were lower than those obtained from paternal half-sib correlations. Hence estimates of the covariance between direct genetic and maternal effects were negative for all traits.

¹ Paper No. 5386 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh.

² The authors express their appreciation to the personnel of the Agricultural Experiment Stations at Plymouth and Raleigh for their assistance in collecting the data.

³ Conducted in cooperation with the Southern Regional Project S-10, The Improvement of Beef Cattle for the Southern Region through Breeding Methods.

⁴ Present address: Agricultural Research Institute, Nicosia, Cyprus.