Select Sires

When Heat Detection Isn’t a Good Option, Consider a Modified Ovsynch Program
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired May 23, 2002

In our last segment, we discussed the possibility for reducing the cost per pregnancy to Ovsynch by substituting heat detection for GnRH. However, in many large dairies, heat detection is simply not a good option. Today I’d like to mention a couple other options for improving Ovsynch efficiency that do not involve heat detection. The first is to modify Ovsynch to a system that has become known as Cosynch in the beef cattle industry. With Cosynch, one animal handling is eliminated by administering both the last GnRH and the fixed time A.I. at the same time. In beef cows, most research has focused on a 48-hour interval after PGF for breeding and GnRH. In our research with Cosynch, we based insemination timing on the typical estrus response observed when cows are allowed to express estrus after the prostaglandin injection. The cows tell us the appropriate timing for a Cosynch treatment is closer to 60 to 64 hours after prostaglandin. Compared to Ovsynch, a 64-hour Cosynch has the same insemination timing relative to Ovsynch, but again reduces animal handling by backing the GnRH injection up to the time of A.I. We have a number of beef cattle studies and are wrapping up a large dairy cow study that shows no fertility benefit to the extra cattle handling of Ovsynch, so why bother. Other recent studies have suggested conception rates with half doses of GnRH are comparable to full doses. This could obviously significantly reduce the cost of an Ovsynch program. However, I’m hesitant to broadly recommend a switch to half doses. Number one, in statistical research, just because the results of a particular study cannot conclusively prove that two treatments are different, that does not automatically prove that the two are equal. I think a still unknown is, how well does the half dose of GnRH induce cyclicity in the anestrous cow? Additionally, procedural differences in syringe size; needle size and injection site from farm to farm will likely influence how much of this small dosage is actually delivered to and retained in the cow. A recent study in beef cows by Dr. John Hall at Virginia Tech, found the average fertility with half doses of GnRH was not different, but the variation from herd to herd was much greater with half than with full doses. This suggests in some places it works and in some places it doesn’t and tends to make me want to associate half doses of GnRH with petting strange dogs; most of them probably won’t bite but some of them do. So if you want to try it, you’ll need to exercise a little caution and common sense Watch out, keep the pulse on your results to be sure half doses are working as well as full doses.

Copyright 1996-2002 Select Sires Inc. Last updated 15-Jul-2002.

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