It is a worrisome trend that Jared Decker, associate professor at the University of Missouri and Wurdack chair in Animal Genetics at the College of Agriculture, Food and Natural Resources, saw in 2013 when he joined the university.
Decker moved a few cows from the family farm in New Mexico, where it was hot and dry to Missouri, where it was also hot, but very humid.
“We moved five two-year-old cows,” said Decker. “Of those five, only one panned out. The others didn’t fare well. It’s challenging. It helps if there is a genetic adaptation and a physiological adaptation. If you can get a cow through the first year, then they can get their feet under them and get going. Over time they will physiologically adjust to the situation they are put in. But their genetic adaptation is the DNA variant they carry. Does it make them predisposed, or resilient, to the variant stressors?”
As a fourth-generation cattle farmer, Decker knows that cattle suffer from health and productivity issues when they are taken from an environment they are used to and put into a new environment — with a different climate, maybe a different elevation, and most likely different grasses.
But as a researcher he saw an opportunity to use science to solve the problem. The aim was to be able to give farmers the genetic information they need through a user-friendly DNA test to help their animals thrive.
“If you are in one of these really challenging environments and you are using an AI sire and produce 20 heifers out of it, half of them may not pan out,” he said. “You have wasted a lot of that investment on that semen or a bull whose offspring have not adapted. That’s the problem we are trying to avoid.”
Decker’s team analyzed six decades of bovine DNA data from tests of cryo-preserved semen produced by cattle breed associations. They found that, over time, while genes associated with higher productivity and fertility improved due to careful selection by farmers, many genes connected to environmental adaptations faded.
None of this is the fault of farmers because there is no cost-effective test that can be used to identify a cow’s suitability for any one particular environment.
But the study underlined the need for a practical, user-friendly DNA test that could highlight specific adaptations of cows to changes in natural feed, weather patterns, humidity or elevation.
Examples of adaptations include resistance to vasoconstriction, which is a narrowing of the blood vessels that can occur at high elevations, putting undue stress on the heart; resistance to a toxin in grass that can also cause vasoconstriction; tolerance for high heat or humidity, or changes in hair shedding.
He said when they were looking for signatures for selection in the DNA, there were pieces of DNA that appeared to be related to vasoconstriction or vasodilation, which would make the vessels narrower or wider. It was not just heat stress they were worried about but any sort of stressful environment.
“Hair shedding is how quickly cows shed out in spring,” he said. “When you start collecting those trait records it’s surprising how many cows fail to shed out in a timely manner. In some situations, they still haven’t fully shed out at the end of summer. That causes the animal to experience more heat stress. They end up struggling fertility-wise, they don’t get bred, or they calve later in the breeding season and tend to wean a younger, lighter calf.”
He said that hair shedding is a really complex trait and controlled by hundreds of DNA variants.
“The other thing with hair shedding is that it also paints a picture of the metabolic state of that animal. It could be something that would be a good companion to a body condition score for those cows struggling nutritionally and shedding later. But for hair shedding, the inheritability is quite high. Something in the range of 35-40 percent of the variation is due to genetics and the rest is due to environmental and management factors.”
The hair shedding trait has high merit to Decker. He said that in Missouri in winter they can run into a polar vortex event with abnormally cold weather. He wants cows to have a thick, furry coat to deal with the winter and then shed out efficiently for a desirable hair coat in the summer.
Under stressful conditions, some animals have a poor gene-by-environment interaction. Each cow’s genotype responds to an environmental variation in a different way and perhaps underperforms compared to what their genetic predictions would indicate.
“In the 1970s, some research showed there was significant re-ranking of animals across environments,” he said. “Researchers took a line of Hereford cattle from Montana and a line of Herefords from Florida and swapped a portion of them with some Florida cows going to Montana and vice-versa. In that research they showed there were significant gene-by-environment re-rankings, proving that genotypes by environment do exist.”
Today’s approach to breeding can include the application of artificial insemination. While it is selected from a bull with particular desirable traits and which itself had been bred in another part of the country, the semen brings with it the whole genetic package. Over time, the beneficial adaptations are going to decrease. Over generations, that cow herd will lose advantages that would have been useful to the farmer.
“While artificial insemination has improved genetic merits of the herd such as production traits, what we have tried to point out is that what is needed is a specific piece of information that allows producers to identify those animals that are specifically fit to deal with stressful forces in their local environment. We have lots of different animals that we have genotyped.”
The team is analyzing data to develop more tailored genetic predictions.
“If we look at our friends involved in crop production, all crops are produced with genetic-by-environment effects in mind,” he said. “They create specific varieties for specific climates. They are much more aware and intentional about creating crops that handle specific environments better.
“We need to create some of those things for livestock, whether it is genetic predictions tailored to specific environments or new traits.”
The study was recently published in the journal PLOS Genetics.
