Try protocol for timed AI in heifers
We spend a lot of time talking about improving fertility within the milking herd, but we tend to overlook heifer fertility. One reason for this oversight is that the national average conception rate for heifers is 57%, a number producers can only dream of achieving in lactating cows.
Conception rate, however, does not show the whole picture. You also need to take into account estrus detection rate, or service rate. Using both conception rate and service rate, you can calculate pregnancy rate. You also can evaluate reproductive success in heifers by average age at first calving.
Missing the mark
In April 2008, data from 4,437 AgSource herds was analyzed to determine heifer benchmarks. The average age at first calving was 26.4 months, but the recommendation is to have an average age at first calving of 22 to 24 months. This means if you’re the average farm, there is room for improvement.
Often, improper semen handling or AI technique can cause poor fertility. Periodic re-training of those responsible for AI can help. Estrus detection is more complex because we not only rely on heifers to show us estrus, but we also have to correctly interpret the signs of behavioral estrus. Until recently, if you failed to detect heifers in estrus, then you couldn’t inseminate them, and they couldn’t get pregnant!
Current protocols for synchronization of ovulation and timed AI in lactating cows result in poor fertility in dairy heifers compared to AI after a detected estrus. The reason for this difference is the ovarian physiology between these two groups of animals differs. The standard seven-day interval between GnRH and PGF does not work well, even when a CIDR is used during those seven days.
Researchers at the University of Florida recently published a new variation of the Ovsynch protocol for use in non-lactating heifers. In this protocol, the interval between GnRH and PGF was shortened to five days, compared to the traditional seven-day interval, and heifers also received a CIDR device during those five days. The final GnRH was administered along with timed AI 72 hours after PGF (i.e., Cosynch). The conception rate for this group was 53%.
A second study used the same five-day CIDR sync protocol, but with the addition of a second PGF injection 12 hours after the first injection for half of the heifers. Although this second PGF injection has proved to be critical for synchronizing lactating dairy and beef cows, there was no difference in conception rate (50% for both groups) after protocols with one or two injections of PGF.
In addition, several studies compared use of conventional vs. sex-sorted semen with timed AI after this protocol. The reduction in fertility due to sexed semen was similar to previous studies comparing conventional vs. sex-sorted semen after a detected estrus in dairy heifers. Thus, this synchronization protocol can be used in conjunction with sexed semen rather than having to detect heifers in estrus.
In summary, yes, the conception rate for even the most successful heifer synchronization protocols still falls short of the national average heifer conception rate. If fertility is good in your heifers and you do not have problems with estrus detection, by all means, keep up the good work! However, if good estrus detection is a problem on your farm, the five-day CIDR sync protocol can boost your service rate and also provide acceptable conception rates to help you work toward the goal of an average age of 22 to 24 months at first calving.
Brusveen is the Sauk County Extension agriculture agent.
This article published in the July, 2010 edition of WISCONSIN AGRICULTURIST.
All rights reserved. Copyright Farm Progress Cos. 2010.