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Why cows don’t get pregnant

Andrew Sandeen for Progressive Dairyman Published on 10 August 2017
a mystery cow

No matter what, there is almost always a group of cows that don’t conceive on the first attempt. They are inseminated, but within a month or two, they have either required another insemination or unexpectedly turn up open. What is going on?

Why are there so many cows that don’t get pregnant? Even when careful attention is given to reproductive management, success rates can be disappointing.

There are many potential explanations: anovulation, genetic predisposition, improper timing of insemination, problems with semen storage, poor artificial insemination (A.I.) technique, embryonic death, infection, heat stress, metabolic issues. ... The list goes on. For this article, let’s focus on four overarching reasons why cows don’t get pregnant.

1. Is she in good health?

In terms of health, three things are clear: first, postpartum disorders are common in dairy herds; second, postpartum disorders lead to a cascade of other performance problems; and third, the relationships between different disorders and various production indices are complex. In a series of studies performed by Ribeiro et al., the carryover effect of postpartum disorders (retained placenta, metritis, mastitis, lameness, digestive problems or respiratory problems) extended more than four months in many cases. They documented negative impacts on embryo development, signaling for maternal recognition of pregnancy and the uterine environment. Cows diagnosed with a disorder between the time of calving and A.I. were 7 to 10 percent less likely to conceive than their healthy herdmates.

Bovine viral diarrhea (BVD) and chronic leptospirosis infection are two of the more troublesome infections that can lead to infertility and early pregnancy loss. Sound vaccination programs are important.

Body condition at a single point in time after calving may not be as significant as the change in body condition that takes place during the first few weeks after calving. A noticeable drop in body condition negatively impacts fertilization and embryo quality, whereas cows that are able to maintain body condition have more favorable reproductive responses.

Lactating dairy cows are particularly susceptible to heat stress. Their bodies produce a lot of heat, which, in combination with hot weather, can cause damage to oocytes and young embryos. Fertility can even be reduced as a result of heat stress that occurred several months before ovulation. Interestingly, the negative effects of heat stress can be circumvented with embryo transfer because a week-old embryo is past the vulnerable stages when heat stress causes most of its damage.

2. Did she ovulate?

Regardless of any other factors, if a follicle does not ovulate, there is no way for a pregnancy to be established. Anovulation, a term describing when cows fail to ovulate normally, can be a result of poor postpartum health but is also related to high milk production in the modern dairy cow. On average, anovulation persists in at least 20 percent of dairy cows beyond the common voluntary waiting period of 60 days.

Not only does a lack of ovulation mean oocytes aren’t available for fertilization, but it also usually means that circulating concentrations of progesterone are low during follicle development. It is becoming increasingly clear that the hormonal milieu during follicular development affects oocyte quality, and higher concentrations of progesterone in the days prior to ovulation have a positive impact on fertility.

3. Was she inseminated correctly with high-quality semen?

Sperm cells and ovulated oocytes both have a limited lifespan in the reproductive tract. However, sperm cells also need to spend several hours in the reproductive tract before they have fertilizing capability, during which time they make their journey from wherever they were deposited to the site of fertilization in the oviduct.

Though there is argument for some flexibility, proper timing of insemination is still critical. It can mean the difference between optimal and marginal fertility. Insemination based off of heat detection, regardless whether that is traditional methods of visual detection or more sophisticated methods using technological devices, should ideally be performed four to 16 hours after the onset of standing estrus or increased activity.

Using timed A.I., one misstep can seriously compromise all of the other efforts and expense. And though some of the recommended protocols are more complicated and less convenient, there is justification for their design. With appropriate compliance, some of the more complicated protocols work well and can lead to better results than the more convenient ones.

Though there are differences between individual bulls, as well as differences in how each bull stud packages semen, poor fertility with certain units of semen is more likely due to improper storage, thawing or handling of the semen. A semen tank should be in good repair and monitored for nitrogen levels. Exposure of semen straws to warm temperatures must be minimized. The temperature of the thaw bath and length of time semen is thawed should comply with recommendations from the supplier. And semen should be sanitarily deposited in the body of the uterus. Compromising any one of these details can have a negative impact on fertility.

4. Is it possible she was pregnant but lost the pregnancy?

Embryo loss is common and one of the biggest limitations for pregnancy in dairy cows. Fertilization takes place more often than we may think, but more than 20 percent of embryos don’t survive beyond four weeks. And even if embryos survive four weeks, an additional 12 percent are lost between day 28 and day 60 post-insemination.

What can be done?

A few key things can help improve fertility in a dairy herd:

  • Address any gaps in vaccination or transition cow feeding programs.
  • Seek effective heat abatement during hot weather months.
  • Consider using GnRH and CIDRs to ensure the presence of progesterone during follicular development, targeting problematic anovular cows.
  • Maintain A.I. equipment and be careful to follow good insemination practices.
  • And for embryo loss, accept that we can’t always stop it from happening, but be diligent to identify open cows and see that they are re-inseminated in a timely manner.  end mark

References omitted but are available upon request. Click here to email an editor.

Andrew Sandeen
  • Andrew Sandeen

  • Penn State Extension – Indiana County
  • Email Andrew Sandeen

PHOTO: Illustration by Kristen Phillips.

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