Twenty-one years have passed since the development of Ovsynch, the synchronization of ovulation program used worldwide (Figure 1). The main objectives of Ovsynch were to produce an optimal time for artificial insemination (AI) without necessity of detection of estrus (or heat) and improve fertility of lactating dairy cows. In the first studies introducing Ovsynch for lactating dairy cows, cows inseminated after timed-AI (TAI) had similar conception rates compared with cows inseminated following heat detection (approximately 38%). Since then, Ovsynch went through several modifications to optimize conception rates following timed-AI; these improvements in the Ovsynch protocol were only possible due to a better understanding of the physiological parameters that affect the success of timed-AI in lactating dairy cows.
The key events for the success of the Ovsynch program and to increase the chance of pregnancy after timed-AI are: (1) ovulation after the first administration of gonadotropin-releasing hormone (GnRH) of the Ovsynch program; (2) presence of a corpus luteum (CL) at the beginning of the program or high circulating concentrations of progesterone during Ovsynch; (3) complete CL regression after prostaglandin F2 (PG) administration of Ovsynch; and (4) ovulation of an optimal size ovulatory follicle after timed-AI. Studies determined that a greater percentage of cows achieve these key events when the Ovsynch protocol is initiated on day 6 or 7 of the estrous cycle. Therefore, pre-synchronization programs were developed to increase the percentage of cows on day 6 or 7 of the estrous cycle at initiation of Ovsynch.
Figure 1: Original Ovsynch protocol in 1995. Ovsynch utilizes two hormone products: gonadotropin releasing hormone (GnRH) and prostaglandin F2α (PG). PG is also commonly called “lut” by dairy producers and workers in reference to the first commercial available PG product, Lutalyse. GnRH is used to cause ovulation of a follicle (ovarian structure that houses the egg) forming a corpus luteum (CL), which is a progesterone-producing ovarian structure in cows. PG has the function of regressing a CL, decreasing progesterone levels to basal or zero. TAI = timedAI.
Currently, most successful pre-synchronization programs are: Presynch-11 or 10, G6G and Double-Ovsynch (Figure 2, page 2). Studies showed that conception rates are greater for cows receiving first service timed-AI following these programs compared to Ovsynch without pre-synchronyzation or to AI following heat detection. A recent study showed that cows timed-AI following Double-Ovsynch had 10% points greater conception rates for first service compared with AI following heat detection (49% vs. 39%, respectively) with similar average days in milk (77 days) at first AI. A difference of 13% points was also found when a Presynch program was compared to Ovsynch without presynchronization (50% vs. 37%, respectively). Since these programs can enhance fertility of lactating dairy cows they are referred to as “fertility programs or treatments”.
Another modification on the Ovsynch program that was adopted to increase conception rates was the addition of an extra PG injection 24 hours after the PG of Ovsynch. This extra injection decreased the percentage of cows with lack of CL regression at time of timed-AI. Recent studies indicated that between 10 and 20% of cows do not respond to the last PG of the Ovsynch program and have a lack of CL regression. Chance of pregnancy for cows that do not respond to this last PG injection is close to zero. This extra PG injection significantly increased the percentage of cows with CL regression (96% vs. 85%) and resulted in an increase of 3 to 5% points in overall conception rate.
In summary, great improvements were made on synchronization of ovulation programs to enhance fertility of lactating dairy cows following timed-AI. Data from several controlled studies indicated that fertility treatments can achieve conception rates greater than 50% in high producing dairy cows. However, other factors such as heat stress, herd health and protocol compliance can contribute to the success of the program and need to be taken in consideration to enhance overall reproductive performance success.
Figure 2: Fertility program calendars: Presynch-10; Presynch-11; G6G; and Double-Ovsynch. Information on other reproductive management strategies is available from the Dairy Cattle Reproduction Council: http://www.dcrcouncil.org/protocols.aspx