Relationships between conformation and calving interval in Holstein cows.

Area of Science:

• Animal Science
• Dairy Cattle Genetics
• Reproductive Performance

Background:

• Holstein Association of Canada type information and Agriculture Canada's Record of Performance calving interval data were used.
• The study analyzed 22,791 records from first calf heifers across 9,272 herd-round classification groups.

Purpose of the Study:

• To investigate the relationship between physical type traits and calving interval in Holstein cattle.
• To determine the heritability of calving interval and various type traits.
• To assess the efficiency of direct versus indirect selection for improving calving interval.

Main Methods:

• Matched type information with calving interval records.
• Calculated heritability estimates for calving interval and type traits.
• Estimated phenotypic and genetic correlations between type traits and calving interval.

Main Results:

• Heritability of calving interval was low (.04), while type trait heritability varied (0.06 to 0.33).
• Phenotypic correlations between type traits and calving interval were negligible.
• Favorable genetic correlations with calving interval were observed for chest floor, rear udder, and capacity.

Conclusions:

• Direct selection for calving interval is more efficient than indirect selection using type traits.
• While some type traits have genetic links to calving interval, they are not primary targets for selection to improve reproductive efficiency.