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Minimizing Open Cows This Breeding Season

by Wyoming Livestock Roundup

The number one determinant of profitability for cow/calf producers is successfully getting cows bred. It is commonly believed when cows and/or heifers come up “open” during preg test time, they simply did not breed up and failed to conceive. 

The truth is, 90 to 100 percent of females will be successfully fertilized, but not all females will maintain their calf. Embryonic losses during early pregnancy account for a significant portion of bad pregnancy rates and cost cattle producers millions of dollars each year. 

While not all pregnancy losses can be avoided, producers can make a difference in minimizing loss through good management during critical periods of production. 

This article details common causes of pregnancy loss and outlines some key considerations during critical periods of embryonic development, which can improve reproductive efficiency.

The first 42 days

The vast majority of pregnancy losses occur within the first 42 days of gestation.

Ovulation and fertilization happens 12 to 24 hours following breeding and standing heat. The embryo then moves into the uterine horn within the next three to five days and continues to develop. 

Around day 15 to 17, maternal recognition of pregnancy occurs. Approximately 80 percent of embryonic losses occurs before day 17. 

The embryo doesn’t implant on the uterus until around day 19, after conception. The placenta develops around days 22 to 25. The embryo is fully attached with a functioning placenta by day 42. 

Losses after day 42 are still possible, but they are much more rare in comparison.

Transportation stress

One of the easiest ways to stress cattle during the first 42 days is to load them on a trailer and ship them somewhere. 

When cattle are stressed due to handling and shipping, hormones like cortisol can be released into the uterus which can influence survivability of the embryo. 

Therefore, if shipping must take place following breeding, it should be done so immediately within the first three to five days before the embryo is in the uterus. Following day five, the embryo is very susceptible to environmental changes. 

One Colorado State University study found hauling between days five to 42 following insemination resulted in a 10 percent reduction in conception rates compared to cattle that were not hauled.

Nutritional plane

It’s well established cattle should have adequate body condition at calving, and protein and energy deficiencies going into rebreeding can be detrimental to fertility. 

However, it’s less known cattle should be managed on a positive plane of nutrition following breeding to establish pregnancy. Even cattle in good body condition can be sensitive to abrupt dietary changes during the first 42 days of pregnancy. 

A common example of this is heifers developed in a drylot setting and then turned out on pasture immediately following breeding. The change in diet and plane of nutrition, coupled with her increase in physical activity, can be enough to negatively affect the uterine environment and the heifer’s ability to maintain the pregnancy.

Heat stress

As temperatures increase, it is important to remember heat stress can also affect pregnancy losses. 

An Oklahoma State University study showed handling cattle in the middle of the day during early pregnancy can elevate body temperature and impact the uterine environment and circulating hormones. 

Therefore, if handling cattle must be done during early pregnancy, cooler mornings and evenings are the best time to do it. 

Additionally, ample access to cool drinking water, shade and good ventilation are good ways to minimize heat stress.

Herd health

Herd health plays an important role in reproductive efficiency. Pregnancy losses can result from disease, internal and/or external parasites and infections. 

It’s important to make sure good biosecurity practices are used to minimize exposure to potential risks and herd vaccinations are current. 

Testing and quarantining new animals before introducing them to the herd is a good way to avoid transmissible diseases. 

Treating all herd members for internal parasites and minimizing exposure to biting insects, such as biting flies and ticks, can decrease disease transmission.  


There are several reasons why a cow or heifer might have bred late or come up open. She usually gets the blame, but it’s not always her fault. 

By working towards improving the environment during early pregnancy, producers can give the cow the tools she needs to successfully maintain a pregnancy and maximize the reproductive efficiency of their herds.

Chance Marshall is a Fremont County University of Wyoming Extension educator. He can be reached at or 307-332-2363. 

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