Genomic evaluation of age at first calving

Area of Science:

• Animal Science
• Dairy Cattle Management
• Reproductive Biology

Background:

• Dairy heifers incur significant costs before their first lactation.
• Optimizing age of first calving (AFC) is crucial for economic viability and early productivity.
• Previous efforts focused on reducing pre-calving expenses and enhancing animal productivity.

Purpose of the Study:

• To determine the optimal age of first calving (AFC) for Holstein, Jersey, and Brown Swiss dairy breeds to maximize lifetime production.
• To analyze the association between AFC and key production, fertility, and health traits.
• To evaluate the impact of genetic selection and genomic testing on AFC.

Main Methods:

• Utilized phenotypic records from over 14 million US dairy cows (1997-2015).
• Analyzed associations between AFC and production, fertility, and stillbirth rates.
• Calculated genetic correlations and genomic predicted transmitting abilities for AFC.

Main Results:

• Mean AFC decreased since 2006 for Holstein and Jersey breeds.
• Lower AFC correlated with higher fertility and milk yield, except for the youngest group (18-20 mo).
• Unfavorable correlations observed between lower AFC and increased stillbirth rates in Holstein and Brown Swiss.
• Favorable genetic correlations found for lower AFC with lifetime merit and reproductive rates in Holstein and Jersey.

Conclusions:

• Optimal AFC for maximizing production: Holstein & Brown Swiss (21-22 mo), Jersey (20-21 mo).
• Balancing AFC is necessary to mitigate stillbirth risks associated with very young calving ages.
• Genomic testing enhances selection reliability for AFC in Holstein bulls.