Exploiting genetic variability in the trajectory of lactation yield and somatic cell score with each progressing...

Area of Science:

• Animal Science
• Genetics
• Dairy Cattle Production

Background:

• Dairy cow breeding schemes have focused on reproductive performance, aiming to increase productive life by reducing involuntary culling.
• However, average productive life has not improved, suggesting other factors like yield or somatic cell score (SCS) influence culling, especially in older cows.

Purpose of the Study:

• To investigate the dynamics of lactation yields and SCS across parities in dairy cows.
• To quantify the potential for genetic selection to modify these trait trajectories and improve herd longevity.

Main Methods:

• Analysis of over 3.4 million lactation records (yields, composition, SCS) from 1.1 million dairy cows.
• Utilized random regression animal models to estimate genetic parameters and breeding values for traits across parities.

Main Results:

• Maximum milk, fat, and protein yields typically occurred by the fifth parity.
• Highest fat and protein percentages were observed in early parities (first and third, respectively).
• Somatic cell score (SCS) peaked significantly later, in the eighth parity, indicating a divergence from yield and composition trends.

Conclusions:

• Genetic correlations between parities for yield, composition, and SCS vary, with weaker correlations over longer intervals.
• Significant potential exists to alter parity profiles for milk yield, composition, and SCS through selective breeding.
• Modifying breeding goals to account for these parity-specific dynamics could enhance dairy cow longevity and health.