Prenatal Stressors

A lot of thought and dollars go into ‌building a herd of cows with good phenotypes. But, it’s an investment ‌that may never pay dividends without an emphasis on low-stress management during gestation. Turns out, a stressed cow, regardless of her DNA, is still liable to produce an aggressive or difficult-to-manage calf.

Ron Randel, Texas A&M AgriLife Extension research physiologist, has been studying a phenomenon that shows there is an effect from a cow’s prenatal stress on gene expression in her calf. He recently began a three-year, federally financed research program to identify how prenatal stress alters expression of DNA, white blood cells and other tissues in calves.

PRODUCTION FACTORS. “One thing that makes this a timely topic,” Randel says, “is how common it is today for producers to transport pregnant females. We think nothing of loading them and moving them around during this phase of life. We don’t think of it as a stress because it is a normal thing. But, we are finding that prenatal stress, whether from transportation or other things, can alter those cows’ offspring negatively.”

He notes the technology now exists to be able to look into what causes these changes in the function of calves’ DNA.

“The environment is changing the methylation profile on the DNA,” he explains. “This, then, either increases or decreases function on the DNA as far as how it affects RNA. That, in turn, affects the many proteins that control what we see as the phenotype of that animal.”

DNA methylation is one of several mechanisms that cells use to control gene expression. Not all genes are active all the time. RNA (ribonucleic acid) is present in cells and is a messenger for the DNA.

All of the trials Randel has done in the past and will do during the next three years use the registered Brahman herd at the Overton, Texas, Extension center. The herd includes about 200 breeding females. Asked if the changes he’s seeing might be breed-specific, Randel says there is “little chance” and notes it may be species specific.

HISTORY AND STRESS. So, while a producer may purchase a replacement heifer with a set of EPDs (expected progeny differences) that look good on paper, Randel says the more known about that heifer’s history and exposure to stress while in utero, the more assured a buyer can be she’s a good addition to the breeding herd.

“It’s important to consider all the information you have,” he says. “If you’ve had a really bad drought, that is a nutritional stressor. And, it will have an impact. And, in the same way, frequent moving or poor management can create prenatal stress that will impact that calf. I would not consider those as prime prospects for replacements.”

Randel adds it’s unknown at this point if one stressor is enough to make a difference in the calf or if it takes several episodes.

“If it happens at a critical time in the development of a specific organ system, one time may be enough. We don’t know that yet.”

He hopes that a federal grant, totaling $382,800, will help him find answers and ultimately change the way producers manage cattle when prenatal stress might have negative consequences.

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