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 research physiologist, has been studying a phenomenom that shows there is an effect from a cow's prenatal stress on gene expression in her calf. He has just started a three-year, federally-funded research program to identify how prenatal stress alters expression of DNA, white blood cells and other tissues in calves.
"One thing that makes this a timely topic," said Randel, "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 noted 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 explained. "This then either increases or decreases function on the DNA, as far as how it effects 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, or 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 over 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 said there is "little chance" and noted it may be species specific.
So while a producer may purchase a replacement heifer with a set of EPDs that look good on paper, Randel said the more that is known about that heifer's history, and exposure to stress while in utero, the more assured a buyer can be that she's a good addition to the breeding herd.
"It's important to consider all the information you have," he said. "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 added, 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 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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