Genetic parameters for a multiple-trait multiple-lactation random regression test-day model in Italian Holsteins

Area of Science:

• Animal Genetics
• Dairy Science
• Quantitative Genetics

Background:

• Accurate genetic evaluation of dairy cattle is crucial for breeding programs.
• Understanding variance components for milk, fat, protein yields, and somatic cell score (SCS) is essential for improving dairy traits.
• The influence of foreign sire usage on genetic variance in Italian Holsteins requires investigation.

Purpose of the Study:

• To estimate variance components for test-day milk, fat, and protein yields and average daily SCS in Italian Holsteins.
• To assess the necessity of genetic heterogeneous variance adjustment based on foreign sire usage.
• To analyze genetic parameters across three lactations using a multiple-trait, multiple-lactation random regression test-day animal model.

Main Methods:

• Utilized a multiple-trait, multiple-lactation random regression test-day animal model.
• Employed Bayesian methods with the Gibbs sampler for variance and covariance estimations.
• Analyzed three subsets of Italian Holstein data based on foreign sire usage percentages (0-25% and 75-100%).

Main Results:

• Estimated genetic, permanent environmental, and residual variances were higher in herds with higher foreign sire usage (≥75%).
• Average daily heritability for milk, fat, and protein yields did not significantly differ among subsets.
• Heritability of SCS varied slightly, being highest in herds with lower foreign sire usage (≤25%).
• Genetic correlations across lactations for yields were similar, but for SCS, they were higher in specific foreign sire usage groups.

Conclusions:

• Adjustment for heterogeneous genetic variance based on foreign sire usage percentage is likely unnecessary for Italian Holsteins.
• The applied random regression test-day animal model adequately accounts for genetic variation across different sire usage scenarios.
• Further research could explore the biological basis for observed differences in SCS heritability and genetic correlations.