Your best cow is in standing heat this morning. Just two weeks ago, she was diagnosed pregnant. Bummer! The first thing you want to do is find someone to blame. Usually, the veterinarian is first on the list. Just so you know, it is not likely to be the veterinarian’s fault. Please don’t blame the veterinarian.
Perhaps an employee gave an injection of prostaglandin-F2α (PG) when they shouldn’t have. That happens, but the likelihood is it wasn’t that either, especially if injection compliance is excellent on your farm. So who is to blame for this dastardly deed? Unfortunately, you don’t have to look far. The high likelihood is that it was the cow’s fault.
There are three ways cows can lose pregnancies: disease, induced luteolysis with PG and physiological/developmental mechanisms. Clearly, certain diseases can cause pregnancy loss. This article will not discuss the impact of diseases such as bovine viral diarrhea virus (BVDV), Lepto hardjo-bovis or other diseases on pregnancy loss.
This article will discuss why healthy cows lose pregnancies and how you can manage to reduce these losses, in addition to making sure these cows are detected as soon as possible so they can be re-inseminated at the earliest possible time.
Higher progesterone levelsand lower pregnancy losses
Data from 2009 demonstrated an effect of the circulating levels of progesterone prior to A.I. on pregnancy losses. Cows lost significantly fewer pregnancies between first pregnancy diagnosis at day 29 post-A.I. and four weeks later if progesterone was higher in the cycle prior to breeding compared to cows with low progesterone during that time.
Since then, several papers have reported a positive correlation between higher progesterone levels prior to breeding and pregnancy. Another aspect to that study that was enlightening was the positive effect of progesterone on double ovulations. Most twins are the result of two ovulations following estrus or timed A.I.
Once again, the high-progesterone group had about half the number of double ovulations compared to the low-progesterone group. So does this mean twins might be a major culprit in embryonic losses? This study did not provide direct evidence, but it certainly provided the impetus for scientists to study this phenomenon more closely.
New data was presented this past summer at the American Dairy Science Association annual meeting on the effect of progesterone on pregnancy losses in lactating dairy cows. This study was conducted at Nobis Dairy, a 1,000-cow operation in St. Johns, Michigan.
The university researchers manipulated levels of progesterone prior to A.I. so that cows had either high or low circulating concentrations of progesterone prior to the final PG of Ovsynch. Then losses were evaluated at specific periods of pregnancy following A.I.
Higher losses in cowscarrying twins
It was quite clear from this double ovulations study, that likely produced twins were responsible for a significant amount of pregnancy loss. Cows were two times more likely to have pregnancy loss between days 35 and 56 post-A.I. if they had double ovulations compared to cows that ovulated a single follicle.
A majority of the losses in the double-ovulation group were due to cows with both ovulations on the same ovary. If twins develop from the double ovulations on the same ovary (unilateral), there would be more crowding in that particular uterine horn and a greater chance for loss compared to an embryo/fetus developing in each horn from ovulations from both ovaries (bilateral).
After day 56, there was no difference in losses between double and single ovulators, but the rate of loss of double ovulators was twice as likely in cows with unilateral ovulations compared to bilateral.
Other aspects of this study revealed twice the rate of losses from 28 to 56 days post-A.I. in single-ovulating cows with low progesterone prior to the final PG of Ovsynch compared to cows with high progesterone. It is not clear why levels of progesterone prior to A.I. during the growth of the ovulatory follicles affects loss in single-ovulating cows. But the likelihood is these losses are programmed at the time of fertilization.
Why this study is relevantto your dairy operation
Lactating dairy cows have about half the circulating concentrations of progesterone during an estrous cycle compared to when those cows were heifers. This dramatic reduction in progesterone is likely due to greater metabolism of progesterone.
Greater metabolism of progesterone is likely due to greater feed intake. It is clear that, on average, cows are consuming more dry matter than ever before. So a good proportion of your cows likely have reduced levels of progesterone, which in turn can create both an increase in twinning and an increase in pregnancy losses, both quite detrimental to the profit of your farm.
How to reduce twinningand pregnancy losses
So back to the cow that came into heat this morning that you thought was pregnant. First of all, breed her tonight. Then consider making potential changes to your reproduction program to reduce twinning and pregnancy losses. Here are just a few things to consider:
- Consider utilizing Ovsynch technologies such as Presynch-11, G6G or Double Ovsynch to increase progesterone prior to A.I. All three programs accomplish this and, in turn, these programs reduce twinning rates and pregnancy losses. Calendars for these programs can be found online.
- Consider pregnancy diagnosing cows early and often. The earlier cows are detected not-pregnant, the sooner these cows can be synchronized for re-insemination. An embryo with a beating heart can be identified by many veterinarians using ultrasound on day 28 post-A.I.
This is about the earliest most veterinarians will check. It is also a good time to determine the presence of twins and if the twins are being carried unilaterally. If so, these cows can be watched more closely and checked more often for pregnancy loss.
- Also, pregnancy-specific protein B (PSPB) or pregnancy-associated glycoproteins (PAG) in blood are very accurate in detection of pregnancy beginning 30 days post-A.I. These proteins are directly produced by the conceptus. These assays are virtually 100 percent accurate in cows that are or have been pregnant.
But these proteins have a long half-life and can remain in the bloodstream for approximately 10 days following the death of the embryo and cause a false positive reading. A positive indicator from these tests cannot determine if the embryo has a beating heart.
- It is critical to re-check pregnant cows around day 60 post-A.I. using palpation or ultrasound. As mentioned above, cows with twins have a greater chance of loss between 30 and 60 days post-A.I., especially if they are growing in the same uterine horn.
Consider re-checking pregnant cows at least once or twice prior to calving, e.g., 90 days and 180 days. A quick palpation by the veterinarian or a milk PAG would be in order at these times.
In summary, early pregnancy losses in healthy dairy cows are common and are primarily due to a low progesterone environment during the growth of the ovulatory follicle prior to A.I.
Growth of two embryos, especially in the same horn, is the primary reason for pregnancy losses between 28 and 56 days post-A.I. A more aggressive pregnancy diagnosis program will identify losses sooner and, in turn, will reduce days open in your dairy herd. PD
Dr. J. Richard Pursley is co-creator of the Ovsynch program. His current program focuses on enhancing fertility of dairy cattle.
References omitted due to space but are available upon request. Click here to email an editor.
J. Richard Pursley
- Department of Animal Science
- Michigan State University
- Email J. Richard Pursley