Although the United States cow herd has decreased from nearly 45 million head in 1974 to 31 million head in 2011, the total pounds of beef produced annually has been maintained at nearly 50 billion pounds over that same time frame. To maintain production at that level, cattle have had to steadily increase growth potential and size, according to Ken Olson, beef specialist with South Dakota State University.
During the last 20 years, cow size has increased over 200 pounds. As cow size increases, producers need to be more aware of their cow's nutritional requirements. During his presentation at the Range Beef Cow Symposium, Olson asked producers if they knew what their cows weigh. "If everyone had a scale at their ranch, this would be known," he said. Instead, producers must rely on other alternatives such as the scale weights of their cull cows, adjusted for any differences between the culls and the cows that remain in the herd. Another alternative is estimating mature cow size based on the live weight of their finished offspring. "The general rule of thumb is that mature cow weight and live weight of their progeny at slaughter should be similar," Olson explained. "In 1990, the average market weight for slaughter cattle was 1,180 pounds," Olson said. "By 2009, it had increased to 1,340 pounds. Mature cow weights were comparable at 1,220 and 1,380 pounds, respectively."
Olson also showed producers data from the USDA Germplasm Evaluation Program being conducted by the Meat Animal Research Center near Clay Center, Neb. Based on head-to-head comparison of several sire breeds, the average cow weight across all breeds was 1,390 pounds in 2009. The data also indicated British breeds have surpassed continental breeds in mature cow size. In the data, the mature cow weight of a Hereford was 1,419; Angus, 1,410; Red Angus, 1,409; Simmental, 1,404; Gelbvieh, 1,323; Limousin, 1,391; and Charolais, 1,371. "This may be a function of genetic trends that are changing the size of cows in each breed at different rates," Olson explained of the data. "The breeds that produce the bigger cattle may still be changing," he noted.
With mature cow size averaging 1,300 to 1,400 pounds, producers need to manage the size of their cows so they don't get any larger. "A 1,000 pound cow produces carcasses that are too small for the packer, while a 1,600 pound cow will produce carcasses that are too big with huge discounts from the packer," Olson explained.
Since most of the cows in the region meet their nutrient requirements by grazing, it is important to remember that as cow size goes up, producers need to manage their grazing land to make sure they have adequate feed resources available, Olson said.
Fortunately for producers with bigger cows, nutrient requirements don't increase in proportion to cow size, he continued. "The maintenance energy required by a 1,400 pound cow is about 11 percent higher than the energy required by a 1,200 pound cow, despite the fact she is about 16 percent heavier," he explained. "A 1,400 pound cow will also need to yield a calf that is 50 pounds heavier to have the same feed efficiency as a 1,200 pound cow, he added.
"Larger size or high milk production dramatically increases the cow's nutrient requirements," Olson continued. "Producers need to pay close attention to matching the type of cows they have to the nutrient supply the resources or range provides," he explained. "Forage quality can really differ. Producers need to allow more forage for cows that have higher intake. They may also need to adjust the stocking rate, or reduce the number of cows grazing per section if the animals are larger."
"Bigger cows need more feed to meet their nutrient requirements," he said. "Not all cows may fit into the limited range resources we have in this area." If a 1,000 pound cow needs 20 acres to graze for eight months, Olson said a 1,200 pound cow would need 23 acres, and a 1,400 pound cow would need 26 acres. "It basically increases three acres for every 200 pounds larger the cow is," he explained.
Olson encouraged producers to constantly monitor their cows for weight and body condition score and not be afraid to adjust the stocking rate based on what they determine. "You can't manage what you don't measure," he said.