Correlations among first and second lactation milk yield and calving interval

Area of Science:

• Animal Genetics
• Dairy Science
• Reproductive Biology

Background:

• Milk yield and calving interval are key economic traits in dairy cattle breeding.
• Understanding the genetic and phenotypic relationships between these traits is crucial for efficient breeding programs.

Purpose of the Study:

• To estimate genetic and phenotypic correlations between first and second lactation milk yields and calving interval in Holstein cows.
• To determine heritability estimates for milk yield and calving interval.
• To provide insights for optimizing breeding strategies balancing milk production and reproductive efficiency.

Main Methods:

• Utilized data from 15 New York State herds with approximately 144 AI-sired Holstein cows per herd.
• Employed a multiple-trait animal model including herd-year-season effects and numerator relationships.
• Estimated (co)variance components using the REML (Restricted Maximum Likelihood) method with the expectation-maximization algorithm.

Main Results:

• Genetic correlation between first lactation milk yield and concurrent calving interval was 0.17, and between second lactation milk yield and first calving interval was 0.10.
• Phenotypic correlations were 0.27 and 0.16, respectively.
• Heritability estimates were 0.27 for first lactation milk yield, 0.25 for second lactation milk yield, and 0.15 for calving interval.
• A genetic increase of 450 kg in milk yield may lead to an increase of 2 days in the first calving interval.

Conclusions:

• Milk records should be adjusted for the phenotypic effects of current and previous calving intervals.
• The genetic association between dairy cattle fertility and milk yield is relatively small.
• Breeding programs can pursue genetic gains in milk yield with a potentially minor impact on reproductive traits.