Getting cows and heifers bred is only part of the challenge in beef and dairy production. Keeping them bred also requires careful management, especially during the summer. High heat index (combined temperature and humidity) is a common environmental factor in early pregnancy loss and can increase the risk well into the second and even third trimesters. Heat stress can also have a long-term effect on egg quality and, thus, embryo quality.
In July 2018, after a northern Missouri beef herd owner saw his bull breeding cows that were known to be pregnant from an earlier pregnancy check, University of Missouri Veterinarian Dr. Scott Poock took his ultrasound device to the field for rechecks of pregnancies. Overall, he found an average of 20% open in the herds he checked. The few exceptions were bred early in April prior to May heat. He also received reports of beef cows showing heats at 30 to 50 days after timed artificial insemination. These cows likely conceived but then lost their embryo.
That same summer, Poock found up to 25% loss of pregnancies after early diagnosis (30-32 days of gestation) at MU’s Foremost Dairy. He also found dead embryos from AI breeding from mid-May through June.
Heat-related pregnancy losses are caused by several factors, including increased internal temperature of the cow. The early embryo is sensitive to body temperatures above normal. At six to eight days, the embryo becomes heat tolerant. Early heat stress potentially leads to embryo loss within the first week after breeding; these cows come back into heat on schedule.
High temperatures also disrupt ovarian and uterine functions. Egg quality declines with oocytes being compromised. Fertilization occurs, but the fertilized egg does not develop normally. The embryo dies later. Such cows return to heat at strange intervals.
And, in some cases, it may not be the cow’s fault. Heat stress affects bulls, too. It can decrease sperm quality, which leads to fewer pregnancies.
Open cows or heifers are expensive. While there is a cost to pregnancy diagnosis, it is a valuable tool for managing or marketing cattle. Obtaining the highest value for every female is critical. Selling open cows or heifers prior to the seasonal cull cow market price decline in August and September has huge economic benefit. If forage availability is below normal, selling known open cows or heifers extends forage resources and reduces feed costs.
Consider the different pregnancy diagnostic options:
- Rectal palpation provides immediate results, allowing cows to be chute sorted at 35 days post-breeding. It requires significant experience and can cause early embryonic loss of 1-3%.
- Ultrasound is most expensive and requires a technician but can be performed at 28 days post-breeding. Depending on when it’s used, ultrasound is the most informative tool available. Results are immediate and allow you to identify the calf’s age and sex.
- Blood testing is the most inexpensive and least invasive method, with accurate results at 30 days post-breeding. Results are typically delayed two to four days, no calf information is available, and cows should be 90 days post-calving to avoid false positives.
The type of female being evaluated is important in your decision on what method to use. Since heifers don’t have a calf by their side, blood test and quick marketing is an option for those that aren’t pregnant. Conversely, for cow-calf pairs not being weaned early, palpation at a later date works.
For cows and heifers that are found to be pregnant, an early diagnosis allows you to make timely decisions to minimize heat stress and help protect the unborn calves through the summer. Heat abatement strategies such as ensuring adequate water and shade are critical. Watering stations need to be located conveniently to allow multiple cows access and keep up with hydration demands. Shade can be provided by trees, buildings, or shade structures. Evaporative cooling systems also can be used in barns to help beat the heat. Beyond reproductive benefits, minimizing heat stress also improves overall cow health, production and well-being during the summer season.
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