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Vitamin A’s Impact on Quality Grades

published: February 21st 2009
by: Beef Partner Connection
source: Troy Smith

What child hasn't been told to eat his or her carrots, because they promote good eyesight? It's true of foods containing carotenes and carotenoids which are precursors of Vitamin A. Students of animal science learn early that Vitamin A may be of most practical importance to ruminant nutrition for other reasons too. Vitamin A is essential to normal growth, reproduction and maintenance. It plays a big role in the utilization of other nutrients. But levels of Vitamin A in the diets of finishing cattle may also influence carcass quality grade.

Don't jump to conclusions. It's not about boosting dietary Vitamin A to enhance marbling and increase the percentage of carcasses that grade Choice or better. Rather, typical finishing diets may contain too much Vitamin A. That might actually inhibit marbling and, perhaps, prevent animals from achieving their genetic potential for quality grade.

It's an area of ongoing study at Ohio State University. Results of three separate feeding trials conducted there suggest restricting Vitamin A in finishing diets may improve marbling scores by up to 10 percent, without affecting animal health, performance or carcass yield grade.
Loerch

According to animal scientist Steve Loerch, the work at Ohio State was prompted by Japanese study of the relationship between blood serum Vitamin A levels and deposition of intramuscular fat (marbling). He says Japanese researchers are looking at how low Vitamin A diets can be applied to production of highly marbled Kobe beef.

"It's also well documented that high levels of Vitamin A inhibit fat cell development in laboratory animals," explains Loerch. "So we wanted to explore the effects of Vitamin A dietary levels as it applies to U.S. feeding systems."

Loerch notes how increased deposition of intramuscular fat can increase carcass value by $100. Conversely, deposition of excessive backfat brings the potential for discounting carcass value by $200, due to undesirable yield grade.

"If we can manipulate Vitamin A status, to promote intramuscular fat deposition versus backfat deposition, we may be able to increase marbling preferentially," he adds.

According to Loerch, supplementation of Vitamin A in beef cattle diets is based on the National Research Council recommendation established in 1976. He says the recommendation calling for 1,000 International Units (IU) per pound of feed was based on the limited data available at that time. But the recommendation has not been changed since then.

Furthermore, because supplemental Vitamin A is not very expensive, it's often supplemented at two to three times the recommended level. While it is an important nutrient, supplementing Vitamin A at excessive levels is a waste of money and may be detrimental to carcass value. The current research is focused on discovering what levels of Vitamin A might enhance marbling without creating a harmful deficiency.

Loerch says forages, and particularly green forages, are higher in Vitamin A precursors than grains. Consequently, animals coming off green forages have high levels of Vitamin A stored in their livers. If they are finished on a diet consisting of mostly corn, it should meet half of the recommended level of dietary Vitamin A, without additional supplementation. Researchers want to find out how long liver-stored Vitamin A will last and how long it hinders fat cells from filling with lipids.

"We think it takes 60 days to deplete liver stores, and another four months to fill fat cells to the extent they can be recognized as visible marbling. So manipulation of dietary Vitamin A probably won't have much application for short-fed cattle. It's likely to have the greatest impact on calf-feds and Holsteins," says Loerch.

"But let's be clear. This may be another part of the puzzle, but we are not recommending that Vitamin A be reduced or pulled from finishing diets to improve quality grade. This is an ongoing research project and we need to know a lot more.

Loerch warns against acting on too little evidence.