Age-At-First Calving To Be Added to Net Merit Index
An age-at-first calving (AFC) trait is expected to be added to the Net Merit $ index in 2019, says Paul vanRaden with USDA’s Animal Genomics and Improvement Laboratory.
Each day of earlier calving can save producers as much as $2.50, and research at USDA has shown there is a plus/minus genetic difference of up to 10 days, says vanRaden. See his abstract in the Journal of Dairy Science.
The trait will be added to Net Merit $, accounting for perhaps 3% of the index. Final details have yet to be worked out. When the trait is added, the emphasis on heifer conception rate will likely be lowered since it is correlated with age-at-first calving.
“We identified favorable genetic correlations of lower AFC with lifetime net merit, heifer conception rate, cow conception rate, and daughter pregnancy rate in Holstein and Jersey cattle, and favorable correlations for net merit and heifer conception rate in Brown Swiss,” says vanRaden.
“To maximize lifetime production and reduce the effects of AFC on stillbirth, the AFC that maximizes production for Holstein and Brown Swiss is 21 to 22 months, and for Jersey it is 20 to 21 months,” he says. “However, the effect of AFC on stillbirth reduces the benefits of calving at very young ages.”
The Council on Dairy Cattle Breeding notes that Dairy Herd Improvement Associations have accurate AFC reports dating back to 1960 on approximately 15 million records. The heritability of AFC is only about 2.7%, notes vanRaden, but the reliability is 66%.
