Dairy producers have struggled with reproductive efficiency, perhaps due to less emphasis over the years on genetic merit for fertility vs. other desirable traits when making mating decisions.
A study conducted in Ireland compared ovarian and circulating hormone measurements, during one complete estrous cycle in cows, with good or poor genetic merit for fertility traits but similar genetic merit for milk production traits. The objective of the study was to characterize the estrous cycle of cows with similar proportions of Holstein genetics and similar genetic merit for milk production traits, but with good or poor genetic merit for fertility traits.
The results, published in the July 2012 Journal of Dairy Science, show that paying attention to genetic merit for fertility does make a difference.
The researchers found that superior genetic merit for fertility traits was associated with:
- A shorter estrous cycle.
- Fewer follicular waves.
- A larger corpus luteum.
- Greater circulating concentration of progesterone.
- A larger preovulatory follicle.
- Stronger behavioral estrus.
These results demonstrate, for the first time, that genetic merit for fertility has pronounced effects on these key reproductive parameters.