BREEDING VALUE AND PHENOTYPIC DIFFERENCES IN SEVEN CATTLE POPULATIONS SELECTED FOR CALVING EASE

Authors: Bennett, Gary

Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2006
Publication Date: 8/1/2006
Citation: Bennett, G.L. 2006. Breeding value and phenotypic differences in seven cattle populations selected for calving ease. Proceedings of the 8th World Congress of Genetics Applied in Livestock Production, August 13-18, 2006, Belo Horizonte, MG, Brazil. CD-ROM Communication No. 03-21.

Interpretive Summary: Calving difficulty in first-calf heifers is more common than in older cows. Simple selection for heifer calving ease would be slow primarily because the trait is only observed in calves born to heifers and heritability is low to moderate. However, a statistical technique for predicting breeding values for heifer calving ease can utilize birth weight which is highly correlated and information from relatives. Seven populations of cattle were selected for seven years for lower first-calf heifer calving difficulty score and targeted changes in weaning and yearling weights. The percentage of first-calf heifers requiring assistance at birth was reduced by 22%, birth weight was reduced by 3.6 kg, and targeted weights were maintained. Select line calves born to 2-year-old heifers had 10 to 13% better survival. Selection results show that breeders can select cattle for calving ease and still maintain moderate growth rates.

Technical Abstract: Seven populations were experimentally selected for seven years for lower first-calf heifer calving difficulty score (HCDS) and targeted changes in postnatal growth. Breeding values were predicted from multiple-trait BLUP. Select and control lines were selected for the same target yearling weight in each population. Select lines were also selected for lower HCDS breeding values. Averaged over the final two years, select lines had significantly lower direct HCD (-1.02) and direct birth weight (-3.44 kg) breeding values. Significant phenotypic differences were found for HCDS (-0.68), heifer calving assistance (-22%), and birth weight (-3.6 kg) but not for weaning and yearling weights. Select line calves born to 2-year-old heifers had 10 to 13% better survival than control line calves. In select lines there was little difference in survival between calves born to heifers and those born to older cows.