Strategic use of progesterone supplementation
Use strategy during timed AI programs to improve fertility in dairy cows
Reproductive efficiency is critical for the economic success of dairy herds. In view of that, timed AI programs have been developed to maximize submission to insemination and improve pregnancy rates in lactating dairy cows. The use of intravaginal inserts containing progesterone is an alternative to improve synchrony of ovulation and increase pregnancy per AI (P/AI) in cows subjected to timed AI protocols. Nevertheless, the benefit from progesterone supplementation is affected by a multitude of factors related both to the cow and the reproductive program implemented in the herd. Considering such aspects is important so that progesterone supplementation can be used in an effective manner.
A systematic review of the literature indicated that supplementing dairy cows with progesterone using a single intravaginal insert applied at the time of the initial GnRH and removed concurrently with the injection of PGF2α improved P/AI. However, this benefit was only seen when cows were not observed for signs of estrus throughout the synchronization protocol. Under such conditions, progesterone supplementation increased P/AI from 30.6 to 38.6%. Supplementation with progesterone had no effect on P/AI in herds where cows detected in estrus were inseminated before pre-scheduled timed AI. The underlying reasons for this interaction are related to synchrony of ovulation in response to hormonal treatments. It has been shown that 5 to 7% of the cows enrolled in a timed AI program display signs of estrus between the initial GnRH and the injection of PGF2α. If inseminated upon detected estrus, these cows are expected to have adequate fertility. On the other hand, failure to inseminate cows in estrus leads to asynchronous ovulation at the time of AI and reduces P/AI. Because supplementation with progesterone inhibits spontaneous estrus during the treatment period and increases synchrony of ovulation in cows subjected to timed AI programs, it represents an alternative to improve fertility responses in herds that do not implement estrous detection. In addition, progesterone supplementation during the timed AI program reduced the risk of pregnancy loss between the first and second month of gestation. Also important from a decision-making standpoint, similar responses to supplemental progesterone were observed in cows subjected to the first timed AI postpartum and to resynchronized timed AI.
The increasing use of ultrasonography for diagnosis of pregnancy in dairy herds provide a unique opportunity to target only the cows expected to benefit the most from progesterone supplementation as opposed to treating all cows subjected to timed AI programs. For instance, a low-fertility cohort of cows can be identified based on the absence of corpus luteum (CL) in a single ultrasound examination of the ovaries performed at the beginning of the synchronization protocol. Approximately 30% of the cows receiving the first AI postpartum and 22 to 46% of those receiving resynchronized AI lack a CL at the first GnRH injection and are 40% less likely to become pregnant compared with herdmates with CL. Progesterone supplementation using a single intravaginal insert increased P/AI by 16% in cows without CL at the initiation of the synchronization protocol whereas only a 5% increase was observed in cows bearing a CL at the first GnRH injection. Nonetheless, the increase in P/AI observed in cows lacking CL was observed primarily in herds that do not perform estrous detection concurrently with the timed AI program, also indicating improvements in synchrony of ovulation.
Another important concern related to current systems for delivery of progesterone is that the amount of hormone released increases concentrations in plasma by only about 1.0 ng/mL, which is insufficient to mimic the presence of a mature CL in high-producing dairy cows. Thus, the incorporation of a single intravaginal insert to timed AI programs has failed to restore P/AI in cows without CL to the P/AI observed in herdmates bearing a CL. Recent studies conducted by researchers at the University of Florida demonstrated that increasing the dose of supplemental progesterone by using two intravaginal inserts increased plasma concentrations by approximately 2.0 ng/mL and reestablished fertility in cows lacking CL at the initiation of the synchronization protocol. Progesterone supplementation increased P/AI in cows without CL from 28.6 to 43.7% during the 5-day timed AI protocol and from 28.9 to 37.2% during the Ovsynch protocol, which was similar to that observed in cows with CL in both programs (47.3 and 33.9%, respectively). Responses to supplementation with progesterone were not affected by service number, indicating that this strategy can be applied to cows subjected to the first timed AI postpartum as well as resynchronized timed AI.
In summary, progesterone supplementation during timed AI programs has the potential to improve reproductive performance in dairy herds, predominantly if heat detection is not implemented and all cows are inseminated at timed AI. A single ultrasonographic examination of the ovaries performed at the initiation of the synchronization protocol is sufficient to identify a low-fertility cohort based on the absence of CL, which represents approximately 30% of dairy cows subjected to timed AI programs. The use of two intravaginal inserts restored P/AI in cows without CL - a result that underscores the need for a progesterone delivery system optimized for high-producing dairy cows.