Most producers who use a synchronization protocol do a pretty good job with first-service inseminations.
However, dealing with cows that did not conceive from the first service continues to confound many producers, says Paul Fricke,
That's where resynch protocols come into play. (See "Rapid resynch takes a bite out of time," in the September 2005 issue of Dairy Herd Management and "Resynch your synch program" in the October 2003 issue.) And new research from the
Previous recommendations called for all eligible cows to follow your prescribed synch protocol, then to receive 2 cubic centimeters (cc) of GnRH 26 days after insemination as step one. Cows were then pregnancy-checked according to your protocol. Those diagnosed as open received 5 cc of prostaglandin on day 33 following first insemination. Then, cows received another 2 cc-injection of GnRH 48 hours later, followed by timed A.I.
This protocol works. However, there's one small hitch. It does not necessarily account for early-pregnancy losses that occur, cautions Fricke. This means a significant percentage of cows diagnosed as pregnant on day 33 will not still be pregnant just two weeks later. Early embryonic losses take away about 15 percent of pregnancies.
A change in timing
Fricke's new research, which was reported in the June 2006 Journal of Dairy Science, indicates that you can increase the number of pregnancies from a resynch protocol by starting a week later. That is, follow your prescribed synchronization protocol with the initial inseminations, but wait an extra week before beginning your resynch protocol. This strategy offers you a way to manage for early-embryonic losses.
That means all cows receive GnRH injections on day 33 following initial insemination, rather than on day 26.
Conduct pregnancy checks a week later on day 40. All open cows should receive a prostaglandin injection and proceed through the resynch protocol. That means these cows should receive another GnRH injection 48 hours later. Breeding may occur at this time or within 24 hours, depending on labor scheduling and cow flow.
Repeat this step as many times as necessary to get the remainder of cows bred.
In Fricke's research, the strategy of starting resynch on day 33 resulted in a conception rate of 39.4 percent versus 28.6 percent for cows enrolled at day 26. Overall pregnancy rates were similar for the two treatments. And both of these groups of cows had better reproductive efficiency than those enrolled in a resynch protocol on day 19 following initial insemination.
Therefore, he concludes, that while it is desirable to get cows enrolled in a resynch program as soon as possible, you don't want to sacrifice effectiveness by beginning too soon. "If there were no embryonic loss, the earliest pregnancy check you could get would be best." Fricke says. "It's all a matter of timing."