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.