Penny Young, ASAS/ASAP Intern
Milking ability is a trait that many producers select for in their production systems, with the belief that it is one of the most significant influences on the weaning weight of a calf. However, a study by Edwards et al. from the University of Tennessee, recently published in Translational Animal Science has found that when beef cattle are raised in an environment where feed is highly available, greater milk production in the mother does not translate to improved weaning weight. In fact, all things considered, selecting for high milk production appears to have negative outcomes for reproductive efficiency.
The study aimed to investigate the effect of milk yield on a variety of markers, such as reproductive and calf performance, cow bodyweight, and circulating blood metabolites. The team collected data from 237 Angus-sired beef cows on three research stations in Tennessee; recording 24hr milk production on two dates post partum, as well as collecting samples of milk for analysis. The cows’ body weight and body condition score were collected weekly throughout breeding, and the calves’ bodyweights were recorded at birth, mid-weight (day 58) and at weaning.
The study found that the high milk-producing cows had the lowest timed-AI pregnancy rates, with no difference observed between the rates for Low and Mod milk producing cow groups. The high milk cows were also found to have the lowest overall pregnancy rate; the moderate milk producing cows having the highest. This negative effect on reproduction in high milk producing cows is most likely due to the increased energy demands for milk production competing with the reproductive demands.
The study found that milk yield did not have a significant impact on cow bodyweight or body condition scores despite the differences in nutrient demand. This perhaps suggests that in this study, the nutrition provided was sufficient to cover all the different requirements. It also was found to have no effect on the calf bodyweight at weaning (day 129 postpartum), despite what would have been greater nutrient availability for the calf over that time.
Thus the decision to select cows based on high milk production makes little sense from an economic perspective. Increased milk production comes with increased maintenance energy requirements, and given that food costs account for over 60% of annual cow cost (Miller et al., 2001), using milk production as a way of improving weaning weight of calves is inefficient when the small potential gains in calf weight is balanced against the greater costs of feeding their mothers. Hence overall, given it appears that high milk production reduces reproductive efficiency and there is no noticeable increase in calf body weight at weaning, producers should look elsewhere when selecting for genetics to improve weaning bodyweight.
To read the article in Translational Animal Science, click here.