How much muscle do we need in a commercial beef cow?
That question intrigues Oklahoma State University Extension beef cattle specialist David Lalman, who believes ranchers need to be cautious in any program that's aggressively selecting for muscle and growth. The natural outcome is often greater weight and less body fat in mature cows, a combination that can hurt reproductive performance.
"The trend for more muscle is continuing, and some producers and researchers are now starting to recognize the potential antagonism between more muscle and reproductive performance," Lalman says.
The relationship between lean muscle mass and reproduction isn't well defined, although there does seem to be a minimum body fat composition required for reproductive success, he notes. "Muscle or leanness can probably be successfully increased in some breeds, although specific selection pressure for fertility will need to be applied at the same time. Increasing muscle is relatively simple, and significant change can be achieved in a generation or two, because it is a highly heritable trait."
Producers don't want market discounts because calves aren't stout enough, which has led to excessive Yield Grade 4 and 5 carcasses. However, there are ways to avoid this without an overly muscled cow herd.
"Cross-breeding with a terminal sire is one of the best ways," Lalman notes. "Match the cow to the environment, and match the bull to the market."
Similar to muscle and growth, there's also a trend of aggressive selection for milk production, especially in Angus and Hereford cattle. "In many cases, we're selecting animals that have more genetic potential than our forage can support," Lalman says. "Why would you want to have a cow in Oklahoma, Wyoming, Iowa or some other state where you have to artificially modify the environment with expensive inputs to keep from having a 70% pregnancy rate?"
He urges producers to challenge their cows. "Let the cows tell you which ones fit your environment and which ones don't," he says. "If your ranching operation is designed to maximize use of home-grown forage with minimal external inputs, selecting for more production may be a waste of time. A low-input forage-production environment may not be able to support more production."
In 1968, producers in Oklahoma, on average, fed 1,500 pounds of harvested hay per beef cow. Lalman says today, that number is nearing 4,500 pounds of hay per cow annually.
"That's a very big difference, but it really hasn't impacted weaning weights in commercial operations," he stresses. "Input costs are higher today because we have artificially modified the environment."
A study from University of Wyoming range specialist Derek Scasta, Oregon State University livestock and range specialist Leticia Henderson and Lalman, examined cow sizes from 1,000 to 1,400 pounds. The researchers found only the smallest cow was weaning 50% of her body weight on the semiarid Western rangelands. Scasta concludes: "More small cows equate to more weaned pounds of beef, and a growing number of producers in many areas of the country are capitalizing on this."
For More Information:
"Drought Mitigation for Grazing Operations: Matching the Animal to the Environment": www.bit.ly/2fs10dH
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