Each year, beef quality grade follows a seasonal pattern with a late-winter peak before a sharp drop in the spring. As measured by percent USDA Choice in the fed cattle harvest mix, quality improves a bit in midsummer but hits a second valley in September.
Let's look at some of the reasons for these variations.
“Calves coming off short periods on winter wheat pasture or lush spring growth are going to be loaded up with vitamin A,” says Steve Loerch, of The Ohio State University. That vegetation is high in beta-carotene, which is converted to vitamin A in the animal.
“Vitamin A inhibits the development of fat cells, which is great if you're a human,” he says. “It's not the best thing for a feedlot calf because the intramuscular fat [marbling] is caused largely by the development and multiplication of fat cells.”
Larry Berger, a University of Illinois animal scientist, says the load of vitamin A has a lingering, negative effect as yearlings enter a feedlot.
“It may take another three to four months after they go onto more normal vitamin A levels before the liver will become depleted,” he says.
Loerch suggests that the vitamin, which aids in immune system functions, is often supplemented at a too-high level.
“The NRC [National Research Council] recommendation may be double what it should be,” he says. “And since vitamin A is not very expensive, nutritionists tend to supplement it at twice what the NRC says, so many cattle get four times the requirement.”
Berger says some cattle may be in for a “double whammy” in the summer. High levels of vitamin A remain in the body while production of vitamin D races higher. Longer days under blue skies give animals more fuel for naturally synthesizing the “sunshine vitamin.”
Japanese work shows that vitamin D has an effect similar to that of vitamin A in keeping a lid on later beef quality grade.
“High levels of both appear to inhibit the differentiation of cells that eventually becomes marbling,” Berger says. “The biochemistry work was done in Japan, but it seems to be applicable across our breeds of cattle as well.”
Sun, health and heifers
Sunny days hurt marbling potential in more than one way, Loerch says.
“These animals that are getting up there in weight are going to be out in the sun all day long on hot summer days. Their intakes are going to be reduced and their maintenance energy is going to be higher as they try to combat that heat through increased respiration and other measures,” he says. “You end up with less energy available for growth and we see growth, intake and marbling deposition rates slide.”
Other unevenness in marketing to a finished endpoint can be attributed to calves that have to spend more time in the feedyard because of health issues or lack of performance.
“Your poorer genetics, your mismanaged calves are going to slide off into the summer,” Loerch says. “Calves that have been in an accelerated program that lets them marble will be harvested earlier.”
This constant ebb and flow of quality grade throughout the year might have a connection to percent of heifers in the harvest mix, too. Recent data show heifers may achieve CAB acceptance rates 8 to 10 percentage points higher than steers, but their supply varies seasonally.
“They're not as normally distributed throughout the year because the best heifers are kept back to breed,” Berger says. “Heifers kept back for breeding are typically grazed.”
Trends show total female slaughter as a percent of the steer slaughter is above 100% from October to March. In the summer months, that number can dip to as low as 80%. “Since heifers tend to grade better than herdmate steers, that may explain part of the seasonal variation,” Berger says.