The more we learn about progesterone, the more we realize the intricacies of how it affects various aspects of reproductive function.
In recent years there has been concern about the effects of increased milk production on progesterone in dairy cows. The increased metabolism resulting from high feed intakes and high milk production causes a decrease in circulating progesterone at critical periods for reproduction.
With suboptimal progesterone, the consequences can be low fertility, increased incidence of twinning and pregnancy loss.
Here are three key periods when progesterone has a known effect on cow fertility:
1. During follicular development. Each of a female’s many oocytes (eggs) are contained within a follicle on one of two ovaries from before birth.
Follicles are recruited throughout a fertile heifer or cow’s life to develop and grow during brief periods of time, called follicular waves. Many follicles and oocytes eventually die off, but a select few develop to the point of ovulation during an estrous cycle. An even smaller number of those oocytes will be subsequently fertilized.
The hormonal milieu during a follicular wave has a significant effect on the fertility and fate of an oocyte. Higher progesterone concentrations during follicular wave development correlates to healthier oocytes and more viable embryos.
In an experiment where researchers evaluated week-old embryos from super-stimulated cows, a higher number and percentage of embryos were classified as transferable and freezable in the treatment groups that received higher progesterone during development of the follicles.
Overall fertility is compromised when progesterone is low during development of a preovulatory follicle.
The risk of twinning is also related to progesterone. Double ovulation occurs more frequently in cows with low-circulating progesterone during development of a preovulatory follicle. The frequency of twinning increases with increased parity, increased milk production and the occurrence of multiple ovulations.
The risks resulting from low progesterone of a preovulatory follicle extend into the first couple of months of pregnancy. Rates of pregnancy loss between days 28 and 60 range from 3.5% to 26.3%, averaging around 12%, and one of the associated factors is low progesterone during growth of the preovulatory follicle.
When researchers used frequent measurements of milk progesterone to guide timing of AI and determine pregnancy status after AI, approximately 15% of cows were diagnosed as pregnant at 30 days post-AI but had a decline in progesterone by 55 days.
2. Just before AI. A standard timed AI protocol begins with gonadotropin-releasing hormone (GnRH) treatment.
Ideally, circulating progesterone will increase and remain high until prostaglandin F (PGF) treatment a week later. Optimum response to PGF treatment is a rapid decline in progesterone, remaining low until the final GnRH treatment and AI. If progesterone does not decline soon enough and low enough, fertility is compromised.
In a recent study, milk progesterone concentrations were greater than 0.5 nanograms per milliliter before AI at least 41.7% of the time, a predicament that was associated with reduced fertility.
3. After AI. Progesterone is essential for maintaining pregnancy after AI. Interestingly, efforts to supplement progesterone for improved retention of pregnancies have not resulted in consistently positive results.
Not only that, but supplemented progesterone between days 15 and 17 post-AI might also increase the increase the incidence of twins being carried to term.
Options for improving progesterone status in a herd can be quite varied.
For those who do not use timed AI there is value in frequently measuring progesterone in individual milk samples, but this isn’t always feasible. There are benefits to keeping good records of estrous activity soon after calving to determine if a cow has been cycling normally before insemination.
Another option to consider is simply using more timed AI, which just might cause the desired decrease in frequency of twinning in addition to more timely insemination, improved conception rates and reduced embryonic mortality.
For those using timed AI on a regular basis there are several things to consider: Progesterone issues become problematic when a timed AI protocol such as ovsynch is used with anovular cows (those not ovulating) or when it is initiated during the first follicular wave of the estrous cycle. In both cases there is not a large enough corpus luteum (CL) present at the beginning of the protocol, thus progesterone concentrations are not ideal.
Here are some protocol suggestions to consider:
For first insemination, use presynchronization protocols that include GnRH treatments to encourage development of luteal tissue and circulating progesterone prior to the final timed AI.
At the end of timed AI protocols, consider doubling up on PGF treatments. There seems to be enough evidence that two doses of PGF at least 24 hours apart on an ovsynch or cosynch protocol may be the most consistent method for causing complete CL regression and lowering progesterone concentrations near the time of AI.
Use CIDRs in the resynch protocol for open cows without signs of a CL. This can increase conception rates by 10%, improve embryo viability, decrease pregnancy loss and can reduce the odds of twinning.
If reproductive performance in your dairy herd needs improvement, take a close look at how suboptimal progesterone concentrations circulating through the cows might be limiting fertility. Investigate how protocol changes might improve progesterone status and reproductive success.
Sandeen is a dairy Extension educator in Indiana County, Pa.Source: Penn State Cooperative Extension, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset