Adding a presynch step will boost fertility but may also increase breeding interval.

by Dennis Halladay, Hoard's Dairyman Western Editor

Many years and growing use of managed heat protocols by dairy producers continue to generate ways to fine-tune their use, as was discussed by Texas A&M University Extension Dairy Specialist Todd Bilby (pictured) at the 7th annual Dairy Cattle Reproduction Council annual meeting in Sacramento, Calif. The meeting concludes today.

Bilby explained that the addition of a presynchronization component before resynchronization improved fertility in a joint study involving researchers in Texas, Minnesota and New York. The improvement was 7 to 9 percent. However, some programs that were used also saw an increase in breeding interval of 7 to 13 days.

The researchers found that use of GnRH (Gonadotropin-releasing hormone) reduced estrous detection in dairy animals, while prostaglandin increased estrous detection. And he asked the question, "Do we really need to wait 11 days after prostaglandin if we are using estrous detection?"

His take home messages for the audience were:

1. Presynchronization before resynchronization improves fertility.

2. GnRH will reduce estrus and prostaglandin will promote it, so don't use protocols that reduce estrus if estrus is what you are trying to detect.

3. Initiating resynch with GnRH/hCG (human Chorionic Gonadotropin) before Day 25 will greatly reduce estrus and not improve fertility.

4. Dairy producers must take into account both estrous detection and timed A.I. fertility.

5. Their economics is a balance between interbreeding A.I. interval, the proportion of cows that are reinseminated after estrous detection, and the fertility rates of both estrous detection and timed A.I. protocols.

6. Shortening the resynch interval is good but not at the expense of reducing fertility.

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