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Nature or nurture? Study shows desert-born brangus cattle choose better diet, grazing patterns

August 9, 2010

[Source: Las Cruses Sun News“Eye on Research” is provided by New Mexico State University. This week’s feature was written by Christina Pheley of University Communications.

During a recent study, some of the subjects were natives, some were tourists and others were naive, but they were all brangus cows being tracked and monitored as they grazed the desert rangelands of New Mexico State University’s Chihuahuan Desert Rangeland Research Center north of Las Cruces.

The study compared the grazing distribution patterns and quality of forage selected by three groups of brangus cows:

•Native: those living their entire lives in the Chihuahuan Desert.

•Tourist: Cows born and raised in the desert, moved to the subtropical environment of Leona, Texas, for the previous three years and then returned to the CDRRC

•Naive: Cows born and raised in Leona, Texas, with no desert experience before coming to the CDRRC.

The findings are helping scientists tease apart the “nature versus nurture” puzzle by showing that an animal’s geographic experience affects its grazing behavior and diet choices in New Mexico’s harsh desert rangelands. The study will also help livestock producers make management decisions that are both profitable and sustainable in desert rangelands.

“In the extensive rangeland pastures of New Mexico and the West, there are many areas far from water, up steep slopes or at higher elevations that are grazed lightly or not at all, while other areas near water or on gentle slopes are often overgrazed,” said Derek Bailey, professor of range science and director of the CDRRC, which is operated by the College of Agricultural, Consumer and Environmental Sciences’ Agricultural Experiment Station.

“If we can find animals that are more willing to walk farther from water and use pastures on steeper slopes and at higher elevations, we can make grazing in those areas more sustainable, and ranchers will be able to graze more livestock in them. This approach is cheaper than adding water or building fences to extend grazing areas,” Bailey said.

“In our current research, we are putting GPS collars on the cattle and tracking them across the rangelands. CDRRC pastures are very large, some over 9,000 acres. The GPS collars allow us to watch where the cattle go and see how well they forage, how far they can walk for water and how well they can cover the landscape. We can determine their adaptability and how sustainable the grazing from these particular animals is,” he said.

“We know from the CDRRC’s multigenerational brangus breeding program that brangus cattle, which are three-eighths Brahman and five-eighths Angus, in general are well adapted to harsh desert rangelands,” Bailey said. “But this study documented that native brangus cows, those living their entire lives in the desert, had advantages over the other two groups.

“Native cows spent more time away from water, periods ranging from 24 to 48 hours, while naive and tourist cows spent 24 hours or less away from water. Also, native cows grazed and used areas farther away from water than either naive cows or tourist cows.

“On the other hand, naive cows, with no prior desert experience, used less area and stayed closer to water than tourist and native cows,” Bailey said.

The researchers found that cows with extensive desert experience – both native and tourist – chose a more nutritious diet during drought conditions than naive cows, which had no previous desert experience.

These results show that a cow’s experience does affect its ability to adapt to and thrive in the extensive rangeland pastures of the desert Southwest and that spending time away from the desert can affect an animal’s behavior and adaptability when it is returned to the desert rangeland.

For producers, the study’s results provide important information for making herd-

stocking choices and decisions about sustainable rangeland management.

“We can recommend that ranchers using desert rangelands stock at levels allowing them to keep a core herd of cows adapted to this environment in drought conditions so those cows can produce their own replacements. If ranchers purchase new animals, we suggest they choose animals developed with forages and environments similar to a rancher’s location,” Bailey said.

The study’s findings are also important for helping understand which of an animal’s characteristics and behavior result from genetics and which result from the animal’s experience and learning?

Milton Thomas, professor of animal science and the ACES 2010-2011 Gerald R. Thomas chair, is one of the study’s researchers. He focuses on molecular genetics and breeding, and since 1997, he has headed the CDRRC’s multigenerational brangus breeding program, which began in the 1960s.

“Today, because we can analyze DNA, we can tell if an allele (one part of a gene pair) comes from the Brahman parent or from the Angus parent. Therefore, we can know that the phenotype (a trait or characteristic) of an individual brangus is a certain way because of what it inherited from either the Angus or the Brahman,” Thomas said.

By combining Thomas’ genetic research with their recent studies using GPS collars to track cows and microhistological sampling (fecal matter analysis) to determine diet selection, Thomas and Bailey are acquiring unique data to help the historic brangus breeding program.

“It’s very important in rangeland management to understand how the animals can adapt or produce in certain environments,” Thomas said. “The cattle’s ability to understand the range itself is a part of the long-term selection process. Since we’ve been selecting the multigenerational brangus cattle for many years over many generations now, the cows have figured out what’s good to eat in the desert in different seasons.

“It’s really amazing. In some seasons when the grass is dead, you would think there’s nothing good to eat, but the brangus cows just seem to know how to go out and find what’s good to eat, and they eat a lot of stuff other than grass: forbs, like clover, sunflowers and milkweed, leaves off of shrubs, beans off of mesquite plants. They really have honed their foraging skills way beyond just eating grass,” he said.

Teasing apart the nature versus nurture puzzle is an important area of focus for Thomas and Bailey. “That’s a challenging part of science and one of the areas that Derek and I work at almost every day; when we look at traits like grazing distribution and diet selection, we really want to know how much of each trait is due to genetics and how much is due to learning.

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