Hormonal synchronization protocols have been incorporated widely into reproductive management programs by dairy farmers (Caraviello et al., 2006; Norman et al., 2009). The initial impact of timed AI protocols on 21-day pregnancy rates in U.S. dairy herds has been to increase the AI service rate (Norman et al., 2009); however, a deeper understanding of the physiology underlying the Ovsynch protocol has allowed for a dramatic increase in fertility to timed AI.
In the Fertility Programs to Achieve High 21-day Pregnancy Rates in High-Producing Holstein Dairy Herds (paper or presentation), UW-Extension Dairy Reproductive Specialist Dr. Paul Fricke refers to the latest iteration of hormonal synchronization protocols as fertility programs for lactating dairy cows.
Take home messages include:
- The key factor affecting fertility in an Ovsynch protocol is the response to each of the three sequential hormonal treatments that can be defined using progesterone profiles.
- Cows with the greatest fertility to timed AI have mid-level progesterone concentrations at the first GnRH treatment, high progesterone at the PGF2α treatment, and low progesterone at the last GnRH treatment of the Ovsynch protocol.
- Presynchronization strategies that incorporate a combination of GnRH and PGF2α to tightly control ovarian function optimize progesterone concentrations at the first GnRH and PGF2α treatments of the Ovsynch protocol, thereby increasing fertility.
- Cows that initiate an Ovsynch protocol in a low-progesterone environment ovulate to the first GnRH treatment at a high rate, but fail to undergo complete luteal regression by the last GnRH treatment resulting in dramatically decreased fertility to timed AI (TAI).
- Addition of a second PGF2α treatment 24 hours after the first in an Ovsynch protocol decreases progesterone concentrations at the last GnRH treatment, thereby increasing fertility, particularly for cows that initiate Ovsynch in a low-progesterone environment.
- An aggressive reproductive management strategy that incorporates these concepts can result in an annualized 21-day pregnancy rate that exceeds 30% in healthy, high-producing dairy herds.