Stress and Embryonic Mortality

After you've gone through all the work of a synchronization and AI the last thing that you want to do is jeopardize any potential pregnancies.  In a perfect world all the females would be AI bred out on summer pasture and there wouldn't be any need to move cattle to a new pasture or change feed, but in reality that is often not the case.  Since most of us don't live in the perfect world, I suggest reading the article "Understanding the Effects of Stress and Embryonic Mortality in Cattle," by Sarah Fields and George Perry from South Dakota State University.

 

Here are the key take home points that I took from the article:

• Fertilization rates are between 90-100% when semen is present at the time ovulation occurs, pregnancy rates are generally closer to 60-70%
• Poor oocyte quality, disease, and chromosomal abnormality are all contributors to pregnancy loss, but heat and shipping stress can play a large role
• Embryo development begins on day 0, the day of standing estrus
• Between days 5-6 the embryo migrates from the oviduct (where fertilization occurs) into the uterine horn
• One days 15-17, the embryo sends a signal to the cow to tell her she is pregnant
• By day 42 the embryo has fully attached to the uterus
• Between days 5-42 the developing embryo is most susceptible to changes in the uterine environment caused by the release of stress hormones
• Research suggests that shipping cows between 5 and 42 days can cause around a 10% decrease in pregnancy rates
• Shipping cattle between 45 and 60 days can result in 5% embryo loss

The authors recommend shipping females between days 1 and 4 for the best possible outcome.   If females cannot be moved during this time period it is best to wait until after day 45, and even better if you can wait until after day 60.  No matter when you ship, care should be taken to reduce stress to the animals being moved.

Understanding the critical embryonic development stages and how they are effected by stress can help you make more educated management decisions to achieve the most AI pregnancies possible.

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Author, Sarah Thorson, is our Beef Education Specialist. Sarah grew up in Eastern Montana on her family's ranch. She is a graduate of Montana State University and has been a member of the Genex team since 2004. Sarah works closely with the Genex Beef Marketing Staff, providing training to the cooperative's nearly 200 Independent Contractors. She also provides Artificial Insemination training for Genex members and customers and reproductive consulting.