Genetic selection and crossbreeding to enhance reproduction and survival of dairy cattle
CALS Impact Statement
Unfavorable genetic correlations for first-lactation milk in the average American herd and age at first calving (AFC) and calving interval (CI) in the average Mexican environment were found (0.18 and 0.10). Regression coefficients of AFC in Mexican environments on American genetic gain in milk ranged from two to seven days, per 1,000 kg. However, the favorable predicted response in AFC from genetic gain in milk in Mexican environments, like those in average American herds, ranged from four to seven days per 1,000 kg (genetic correlation = - 0.20).
Decline in fertility of dairy cows prompted an investigation of the genetic relationships between two fertility traits and milk production in the United States and Mexico.
A data sets contained yields in first and second lactation, age at first calving (AFC), and calving interval (CI). There were 474 US sires in common between countries.
This unequal AFC response may indicate genotype by environment interaction in fitness performance or differential breeding management of high and low yielding Mexican cows. The potential effects of age at first service of breeding females need to be disentangled to accurately assess genetic improvement needs for Mexican Holstein herds.
R.W. Blake (Department of Animal Science)
E.G. Cienfuegos-Rivas (Universidad Autónoma de Tamaulipas)
H. Castillo-Juarez (Universidad Autónoma Metropolitana-Xochimilco)