Size does matter, at least when it comes to cattle, according to Kenneth Olsen,range beef cow/calf specialist at South Dakota State University.
Olsen said today’s fed cattle (steers and heifers) compared to 1990 are 14 percent larger at slaughter, spend eight more days on feed, gain weight 16 percent faster, are 7.6 percent more efficient and require 0.50 less pounds of feed per pound of gain. (Although Olsen said this at a cattle symposium a couple of years ago, I think this information is still relevant.)
He said even though they grow faster to larger weights than they did 20 years ago, today’s livestock have the same characteristics and marbling, according to data collected by Kansas State University where they followed over 10,000 cattle from 1990 to 2010.
After evaluating current genetic trends, Olsen concludes that cows are also getting bigger, on average, weighing about 200 pounds heavier than they did in 1990. The average mature cow weight for seven popular breeds is around 1,400 pounds. The British breeds used in Olsen’s research included Angus (1,410 lbs.), Hereford (heaviest at 1,419 lbs.) and Red Angus (1,409 lbs.). British breeds averaged heavier weights than Continental breeds, which included Simmental (1,404 lbs.), Gelbvieh (1,323 lbs.), Limousin (1,391 lbs.) and Charolais (lightest at 1,371 lbs.)
Olsen said producers have to consider a cow’s size when planning the size of its expected offspring. “Cow weight correlates to steer carcass weight,” he said. For instance, a 1,000 lb. cow produces a hot (dressed) carcass which is too small. A 1,600 lb. cow, he said, produces a carcass that weighs over 900 pounds. A hot carcass weight of 900 pounds or more is typically discounted for being too heavy.
“It’s important to manage cow sizes,” he said. “Everyone should know what their cows weigh.” However, as the size of a cow increases, he said nutrient requirements also increase. Nutrient requirements are not calculated in direct proportion to their weight, he said, but by their surface area in square inches of skin. As an example, he said, a 1,400 pound cow may weigh 16 percent more than a 1,200 lb. cow, but requires only 11 percent more nutrients.
“A 1,200 lb. cow eats 9,400 pounds of forage annually, a 1,400 pound cow eats approximately 10,000 pounds of forage annually,” he said. Therefore, Olsen said, a 1,400 lb. cow would need to raise a calf weighing 50 lbs. more at weaning to match the feed efficiency of a 1,200 pound cow.
“A heavier cow needs more feed to wean a bigger calf and needs to be able to pay the producer back for that 11 percent difference in nutrient requirements,” he said.
Olsen said biological types and numbers of cattle need to be matched to forage resources.
To help determine stocking rate, Olsen said, a 1,000 lb. cow needs approximately 20 acres of forage per eight month growing season; a 1,200 lb. cow needs 23 acres and a 1,400 lb. cow needs 26.
He said with this in mind bigger cows may not fit limited range resources. The ideal situation, he said, would be to have cows that top out at about 1,200 lbs., but produce a calf that has the potential to top out at 1,400. He said management of sires is also important as the proper bull can put the desired growth on a calf by genetically prompting rapid weight gain and earlier maturing.
He encourages producers to weigh their cows for better management, to cull out the larger ones and develop a nutrient management plan for heifers.
“You can’t manage what you can’t measure,” he said.