July 4, 2006

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COLLEGE STATION – A recent Texas Agricultural Experiment Station study indicates cattle fed longer on certain diets will produce beef with more of the "good" kind of fat.

Dr. Stephen Smith, Experiment Station professor of animal science in College Station, said the study showed the longer cattle were fed corn, the more monounsaturated – and less saturated – fat they produced. Monounsaturated fats are currently viewed as being healthier than other dietary fats, Smith said.

In the U.S., 8-month-old cattle are given a predominately corn diet until they are slaughtered at about 1,200 pounds. With adequate rainfall and good pasture, producers sometimes "background" their cattle on pasture until they are 1 year old, Smith said. After that, they are fed a corn-based diet until they weigh about 1,200 pounds.

"We've always had more corn in this country than we can consume, so we feed it to our livestock," he said.

U.S. consumers "like cattle young and marbled well," because of flavor, he said. Studies have found, however, the marbling and trimmable fat from cattle that are too young is high in saturated fats and trans fats, he said.

Japan, on the other hand, feeds cattle more grass and forage in the beginning. Calves are weaned at 8 or 9 months of age; producers then gradually increase the amount of grain in the diet until they are 28 to 30 months of age.

"They do it in steps," he said. "At the end, they feed corn concentrate."

For the study, 16 American Wagyu and 16 Angus steers were purchased as weaned calves. Eight from each breed were fed a high-energy corn-based diet. Eight were fed a diet of coastal Bermudagrass hay supplemented with a corn-based diet. The cattle were fed to 16 to 20 months of age (U.S. endpoint) or 24 to 28 months of age (Japanese endpoint).

The study tested three factors: breed type, diet and slaughter-age endpoint. Of the three, endpoint had the greatest effect on the adipose tissue lipid composition, Smith said. Lipids are organic compounds and include fats.

In an earlier study, researchers found the breed type did not affect marbling scores or the U.S. Department of Agriculture quality grades for Angus and Wagyu steers. The corn-fed steers had higher marbling scores than hay-fed steers of both breeds, Smith said. Steers raised to the Japanese endpoint had higher marbling scores and USDA quality grades than those raised to the American endpoint.

In the latest study, the corn-fed Angus steers raised to the Japanese endpoint "accumulated adipose tissues lipids that were remarkably unsaturated," according to the report.

Also, the adipose tissue from the Wagyu steers "contained higher concentrations of oleic acid and other monounsaturated fatty acids, regardless of diet or endpoint," it said.

"We're not sure that the trans fat in beef, trans-vaccenic acid, is completely bad for you," Smith said. "We need a human study (to determine that). It may be completely benign."

Smith and the other researchers theorized when Angus and American Wagyu steers were fed to the normal U.S. standards, the amount of monounsaturated fatty acids and cholesterol of the adipose tissue – the connective tissue that stores cellular fat – would be similar. The amounts would differ when fed to Japanese standards, they also theorized.

But they were proved wrong. Both breeds of steers produced more marbling and less trans and saturated fat the longer they were fed.

Wagyu cattle contribute only a small percentage to U.S. beef production. However, these results indicate that typical domestic cattle such as Angus can be raised to produce fat with a healthier composition, Smith said.

But what about completely grass-fed cattle? They have leaner carcasses, he said.

"The problem with (grass-fed cattle) is the U.S. consumer isn't accustomed to the flavor," Smith said. "It's very strong, and it's something we're just not accustomed to. And the other is that the fat that's produced from grass-fed cattle is higher in saturated fats and trans fatty acids."

Cattle fed longer on corn will have a better flavor, more marbling and monounsaturated fats. But there is a trade-off.

"There are more calories there," he said. "There's no question about that, and if you're watching your calories, grass-fed beef is lower in fat. And I can't argue with that."

The study was published in the international journal Meat Science this summer.