Different goals, common ground: A global perspective on dairy breeding objectives.

Area of Science:

• Animal Science
• Genetics
• Dairy Cattle Breeding

Background:

• Global dairy cow breeding objectives show convergence and divergence.
• Understanding these differences is key for international germplasm sourcing and genetic improvement programs.

Purpose of the Study:

• Compare Holstein-Friesian artificial insemination sire rankings across countries based on total merit index.
• Examine national genetic merit estimation methods and base population update frequencies.

Main Methods:

• Partial correlation analysis of 22 national indexes for 49,450 Holstein(-Friesian) sires (born post-2000, reliability >70%).
• Adjustment for genetic trends to compare sire rankings.
• Analysis of trait weighting strategies and genetic evaluation presentation (EBVs vs. PTAs).

Main Results:

• Partial correlations among sire rankings varied (0.24-0.87), with 41% >0.70 and 11% >0.80.
• Confinement-based indexes correlated weaker with grazing-focused indexes (0.48-0.50).
• Milk production subindexes showed higher average correlations (0.78), but varied widely (0.29-0.96).
• Trait weighting approaches differed: 38% used economic models, 29% desired gains, and the rest hybrid strategies.
• Eight countries assigned negative weights to milk yield; others varied or excluded it.

Conclusions:

• National breeding objectives are shaped by economic, biological, genetic, and policy factors.
• Differences in breeding objectives and evaluation methods influence international genetic trends and performance.
• Future breeding objectives increasingly consider health, environmental impact, and feed efficiency traits.