Consequences of selection for milk yield from a geneticist's viewpoint

Area of Science:

• Animal Breeding and Genetics
• Dairy Science
• Livestock Production

Background:

• Annual genetic trend for milk yield in US Holsteins has accelerated significantly since the 1960s.
• Dairy industry selection programs prioritize yield traits for profitability, impacting Holstein cow conformation and physiology.
• Increased selection intensity has led to greater genetic relationships among animals.

Purpose of the Study:

• To analyze the genetic trends in milk yield and other traits in US Holstein populations.
• To evaluate the impact of intensive selection programs on Holstein cow characteristics and potential health issues.
• To address the rising levels of inbreeding in commercial Holstein populations.

Main Methods:

• Analysis of historical genetic trends for milk yield in Holsteins.
• Review of selection goals and their impact on type traits and body size.
• Assessment of genetic relationships and potential for inbreeding.

Main Results:

• Milk yield genetic trends show a continuous acceleration, with significant increases across decades.
• Selection has favored larger body size and angularity, potentially increasing susceptibility to metabolic problems.
• High selection intensity has resulted in increased genetic relationships, leading to elevated inbreeding risks.

Conclusions:

• Intensified genetic selection in US Holsteins has driven milk yield increases but also altered physical traits and increased inbreeding.
• The emphasis on specific traits may compromise cow survival, efficiency, and health.
• Crossbreeding is suggested as a strategy to manage inbreeding and potentially improve overall herd resilience.