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Grazing moldy fescue.

Lighter calves can be the result when a grass called fescue tangleb with the calf's "family tree."

A 3-year study has shown calves may weigh less at weaning if their mothers grazed fescue infected with a fungus - a common situation throughout the upper Midsouth. But the severity of the drop in weaning weights may hinge on the breed of the mother.

In the study, 160 purebred Angus or Brahman cows grazed pastures of either bermudagrass or fungal-infected fescue.

The cows were bred to Brahman or Angus bulls, and all the resultant crossbred calves shared the same genetic makeup: half Brahman, half Angus. But in some instances, the Angus blood came from the calf's mother, whereas other calves inherited their Angus blood from the father.

"On bermudagrass, the crossbred calves from Angus mothers weighed about 507 pounds at 205 days of age, compared with an average of 481 pounds for crossbred calves out of Brahman mothers," says Michael A. Brown, research leader at the ARS South Central Family Farm Research Center at Booneville, Arkansas, site of the study.

"On the infccted fescue, the gap between the two was not as large - 456 pounds for the calves from Angus mothers compared with 445 pounds for those from Brahmans. There was a more dramatic decline in weaning weight for calves from Angus mothers."

The culprit behind weaning weight losses is the fungal infection in the fescue. Infected forage can contain a toxin from the fungus that interferes with the animal's body temperature regulation and circulatory system.

Although this is hard on any breed, Brahmans are less affected than other breeds when it comes to grazing infected fescue. They are able to better dissipate body heat, so even though the toxin has reduced the outside blood supply to skin, ears, and tail, the animals can still cool themselves, says Brown.

In addition to monitoring the growth of the calves, the researchers regularly measured milk production of the mother cows.

Angus milk production dropped more than 3-1/2 pounds a day on infected fescue versus bermudagrass, whereas the fescue reduced Brahman milk production only about a pound a day.

"We're trying to show the effect of fescue as part of a grazing system," says Brown. "As we learn how to manage infected fescue, this study shows that breed of the mother is another component that cattle producers can work with in planning their herd management."
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Title Annotation:Agnotes; cows that eat grass infected with fungus
Author:Hays, Sandy Miller
Publication:Agricultural Research
Date:Nov 1, 1992
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