Unless your dairy is terrible at detecting heats, breeding cows at second and later services based on visual signs will result in more pregnancies.
The reason: About 50% of cows have an abnormal pattern of return to estrus cycles following insemination. That’s due to a number of factors:
- Typically only 85% of cows are truly synchronized with timed AI protocols at first breeding.
- Fifteen percent of cows will have a short luteal phase after first breeding.
- Early embryonic loss after conception results in nearly 20% of cows with abnormal cycles.
Add these factors up, and it’s clear why it’s more difficult to get cows synchronized for rebreeding the next time around, says Ricardo Chebel, a reproductive specialist with the University of Minnesota.
As a result, rebreeding efforts on visual heats usually result in significantly more pregnancies at second and later breedings than following a conventional resynchronization breeding protocol.
New resynchronization programs are being investigated, including the use of an extra shot of presynchronizing GnRH and the use of CIDRs. These new synchronization strategies can improve pregnancies per AI by seven to nine percentage units. But they also add extra cost and further complicate compliance issues.
"Re-inseminating cows in visual estrus usually results in pregnancy per AI five to 10 percentage units greater than with resynchronization," Chebel says.
"We may implement new resynchronization protocols, but we should not recommend 100% timed AI [for rebreeding] unless heat detection accuracy is terrible or there are no means to do heat detection," he says.
- March 2011