Genetic parameters for first lactation test-day milk flow in Holstein cows

Area of Science:

• Animal Genetics
• Dairy Science
• Quantitative Genetics

Background:

• Test-day milk flow (TDMF) is a crucial trait in dairy cattle breeding.
• Understanding genetic parameters is essential for effective selection programs.

Purpose of the Study:

• To estimate genetic parameters for TDMF in Holstein cows.
• To evaluate the potential for genetic improvement of TDMF through selection.

Main Methods:

• Utilized multiple-trait and repeatability models for 2175 first lactations.
• Employed the restricted maximum likelihood (REML) method for variance component estimation.
• Included direct additive genetic effects, contemporary groups, and age at calving in the models.

Main Results:

• Heritability estimates for TDMF ranged from 0.23 to 0.37, generally higher early in lactation.
• Positive genetic correlations (0.72 to 0.97) were observed between different TDMF measurements.
• Heritability was 0.27 with a repeatability of 0.66 using the repeatability model.

Conclusions:

• Milk flow exhibits sufficient heritability for successful genetic selection, leading to rapid genetic gains.
• Selection focused on TDMF around the fourth month of lactation could maximize genetic progress.
• Both repeatability and multiple-trait models are suitable for genetic evaluation, with the multiple-trait model offering more precise breeding value estimates.