Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2000
Publication Date: N/A
Interpretive Summary: Information on the association of ease of calving with other traits is important for two reasons. Traits that are highly correlated with ease of calving could be used to improve genetic evaluation of calving ease. Traits that are important for efficient beef production, but unfavorably correlated with ease of calving, need to be considered in predicting the consequences of selection. Six reproductive, skeletal, and carcass traits were analyzed to estimate their associations with ease of calving, birth weight, weaning weight, and gain after weaning. Estimates of genetic associations were used to predict genetic change in ease of calving from selection on each trait. All correlations of these six traits with calf or heifer genetic effects on calving ease were small to moderate. Predicted genetic change in ease of calving was greatest when selection was based on calving ease itself or on birth weight. Predicted genetic change resulting from selection on any of the other traits considered was less than half that of selection on calving ease or birth weight. The estimated genetic association of calving ease with percent retail product is small but unfavorable. This information will be useful in formulating selection plans when one of the objectives is improved calving difficulty.
Technical Abstract: Genetic, maternal and environmental covariances of six productive and reproductive measurements with calving difficulty, birth weight, 200-d weight, and 168-d post-weaning gain were estimated in 12 experimental populations of cattle. Calf (direct) genetic effects resulting in longer gestation length were associated with increased calving difficulty and birth weight. Maternal genetic effects of increased gestation length and heavier birth weight were significantly associated. Lighter birth weight and reduced calving difficulty were associated with earlier heifer age at puberty. Increases in calving difficulty, 200-d weight, and post-weaning gain were associated with small increases in scrotal circumference. Increased scrotal circumference was correlated with maternal effects that decreased calving difficulty and increased 200-d weight. Direct effects of the skeletal measurements, yearling hip height and heifer pelvic area, were positively correlated with direct effects of calving difficulty, birth weight, 200-d weight, and postweaning gain, positively correlated with maternal effects for birth weight and 200-d weight, and negatively correlated with maternal calving difficulty. Percentage of retail product was positively associated with calving difficulty and negatively with 168-d gain. Predicted genetic change in calving difficulty resulting from one standard deviation of selection for either calving difficulty score or birth weight was much larger than for any other traits. However, selection for reduced calving difficulty should be based on calving difficulty score and(or) birth weight because of their superiority in predicted genetic change.