Reproductive performance in genetic lines selected for high or average milk yield

Area of Science:

• Animal Science
• Genetics
• Reproductive Biology

Background:

• Selective breeding in dairy cattle aims to enhance milk production.
• High milk yield is often associated with potential trade-offs in animal health and reproduction.
• Understanding these trade-offs is crucial for sustainable dairy farming practices.

Purpose of the Study:

• To investigate the long-term effects of genetic selection for high milk yield on reproductive performance in dairy cattle.
• To quantify the relationship between increased milk production and key reproductive parameters such as days open and calving interval.
• To compare reproductive fitness between genetically divergent lines selected for milk yield.

Main Methods:

• Creation of distinct genetic lines of dairy cattle based on estimated transmitting ability for milk production.
• Long-term selection program spanning 24 years and up to eight generations.
• Analysis of reproductive records (days open, calving interval, days to first estrus) from nulliparous, first, and second parity animals.

Main Results:

• Higher milk yield was significantly associated with increased days open and calving intervals in both first and second parities.
• A 1000-kg increase in 305-day milk production correlated with approximately 7-day and 13-day increases in calving interval for first and second parity, respectively.
• Genetic lines selected for high yield exhibited longer days open and calving intervals compared to average lines, with differences up to 10 days in second parity.

Conclusions:

• Genetic selection for increased milk yield in dairy cattle has a modest, yet significant, negative impact on reproductive fitness.
• While high milk production is achievable, it necessitates careful management to mitigate adverse effects on reproduction.
• The study highlights the complex interplay between production traits and reproductive efficiency in breeding programs.