WOOSTER, OHIO — Three years ago, only half of fed cattle graded U.S.D.A. Choice. The Choice/Select spread hit record highs in 2006, but the picture today is much different. In July, 60.1% of the harvest mix graded Choice the first half of this year, according to Certified Angus Beef LLC (C.A.B.).

C.A.B. animal scientists recently authored a research paper on those trends titled "Quality Grade: What is driving the recent upswing?" Written by Larry Corah and Mark McCully, the study addresses regional differences in beef quality, how it improved so quickly and why it changed.

The share of Choice-grading cattle nationwide increased 7.5 percentage-points in two years. "The main reason for that rapid shift is that a large number of cattle marbling scores are very close to the U.S.D.A. grading lines," said Mr. Corah, C.A.B. vice-president. "Just adding 20 more units of marbling, going from Slight-80 to Small-0, results in 5.71% more cattle grading Choice. That seemingly tiny change has an even greater impact on those qualifying for the Certified Angus Beef brand."

During this fiscal year, the C.A.B. brand will be more than 19.5% after a low of 14% acceptance in 2006. This represents almost a 40% increase in three years. The Central Plains show the greatest improvement and distillers grain byproducts might be part of the answer, although potentially part of the problem if they get above 40% of the dry-matter ration content. By 2007, these byproducts were fed in 82.5% of feedlot rations, but at a moderate 15% to 30% level.

Research shows that when held to those levels, distillers’ corn byproducts actually result in higher grades, partly by increasing appetite — and especially in starter diets. "Higher dry-matter intake, better calf health and higher daily gains support higher quality grade," said Mr. McCully, C.A.B. assistant vice-president. He added Elanco Animal Health Benchmark Program data reveals positive trends in all of these areas — that’s combined with herd liquidation, which has boosted the heifer share of the harvest mix to 37.4%, a few points above normal.

"Heifers tend to grade nine to 10 points better than steers, so that may account for at least a half a percentage point increase overall," he said.

Use of Angus genetics is up. At the same time, the expected progeny difference (E.P.D.) for marbling score in Angus has increased 7 points since 2004, C.A.B. reveals. "It only moved nine points in the first 25 years of the E.P.D.’s existence," Mr. Corah said. Angus bull usage increased from 39% to a 55% share of all bulls from 1994 to 2008, and nearly 70% of commercial cows are now considered primarily Angus.

Iowa feedlot futurity data shows only 52.7% of calves with less than a quarter Angus breeding grade Choice, compared to their counterparts that are at least three-quarters Angus, at 86.2% Choice and Prime. C.A.B. acceptance rate nearly quadruples with the greater Angus heritage.

If quality grades do not decline within a year, it could mean the infusion of higher-marbling genetics has had a lasting effect, Mr. Corah said. "Coupled with smaller cattle numbers, consumer demand in a recovering economy will likely drive the Choice-Select spread to higher levels," he added.