Depending on who runs the numbers, the percentage of beef cattle grading Choice or higher has remained static or declined. This is despite an extraordinary amount of selection pressure apparently aimed at improving carcass quality. This is at a time when Angus and Red Angus cattle — noted for their marbling ability — represent at least two-thirds of the nation's commercial cowherd.

“Conventional wisdom says we've made great progress in the genetics for beef quality, but environmental factors have limited the genetic expression of it,” says Dan Moser, Kansas State University associate animal science professor. “In many cases, genetic improvement for marbling has been overstated.”

Moser analyzed the genetic progress in carcass quality traits for this year's Beef Improvement Federation (BIF) research symposium. He says the genetic trend for average marbling score is increasing — about 0.015 units of marbling score/year in Angus and 0.0075/year in other major breeds. At that rate though, Moser says it would take about 60 years to achieve enough improvement to move cattle from low Choice to mid Choice, say, or from Select to low Choice.

The trend indicates selection pressure is being applied to increasing marbling score directly or indirectly through the correlated trait of intramuscular fat (IMF). Unfortunately, the correlation between those two traits means selection pressure has been applied with less accuracy than some thought.

“When EPDs are presented for ultrasound IMF instead of for carcass marbling score, the associated accuracy values are overestimated because they reflect the accuracy of selecting for the correlated trait [IMF], not the true economically relevant trait of marbling,” Moser explains.

Ultrasound measures of IMF are being used by some breeds in addition to, or apart from, the actual marbling scores gleaned from carcass data.

Moreover, Moser points to the time lag between genetic pressure being exerted and phenotypic progress being made.

“It takes about five years for a generation of selection at the seedstock level, and another five years for a generation of selection at the commercial level, before we should expect to see much change,” he says. In other words, the ingredients and selection pressure may have been exerted, but there hasn't been enough time for it to show up phenotypically in the nation's annual average mix of quality grades.

Drought's effect

Back to the notion that environmental factors are impeding genetic progress in carcass quality, Pete Anderson, VetLife Benchmark Performance Program vice president, explains: “There's no obvious, non-genetic trend that would result in a significant increase or decrease in quality grade, with the possible exception of drought.”

The VetLife program collects live performance, carcass and financial data on about 40% of all U.S. fed cattle. Within this population, the percentage of steers and heifers grading Choice or higher has declined slightly since 1999.

It's occurred despite heavier harvest and carcass weights, and increased days on feed, Anderson says. “During this time, the percentage of carcasses receiving USDA Yield Grades of 4 or 5 has increased. All indications are that carcasses are heavier and fatter than a decade ago, yet USDA Quality Grade hasn't increased,” he says.

Anderson and Justin Gleghorn, also of VetLife, examined that company's database for non-genetic reasons that might explain the dearth of Choice progress. They looked at placement factors such as cattle age, sex and weight going on feed and seasonality. They examined cattle health, nutrition and management ahead of the feedyard, everything from the impact of photoperiod and the vitamin A of pasture forage. They looked at feedlot nutrition, health and management, everything from limit-feeding implications to the differences grain processing makes in energy availability.

They looked at the use of implants in steers and heifers and the impact of feeding heifers MGA (it increases grade, actually). Finally they looked at the relationship between using more corn co-products and differences in end-point selection.

Nothing suggested there should be a significant increase or decrease in quality grade, which leaves drought as the most likely environmental reason.

“Any nutritional insult impairs the ability to marble,” says Anderson, noting the drought still gripping wide sections of the nation has affected every section of cow country over the past five years.

“Since marbling deposition is a lifetime event, all segments of the industry will have to focus on quality in order to make significant progress,” Anderson says. “Research shows that early weaning and diets high in concentrates will increase marbling. The health status of cattle, especially early in the feeding period, appears to have an effect on performance and carcass characteristics. Growth promotants can affect marbling, but the effects are dependent upon sex and dosage of the product. End-point selection influences quality grade, yield grade and other economically important carcass traits.”

“The complexity of marbling allows some opportunity,” Anderson says. “While traditional wisdom states that marbling can be reduced by negative lifetime events, but not increased, recent research indicates that opportunity exists to increase marbling.”