“So, cows have gotten bigger, and we’ve documented how much bigger, and we want to stay in that 1,200-1,400 lb. range. That’s where management comes into play in terms of a producer deciding where his perfect range is, where he wants to be within that range, and what would provide acceptable carcass sizes,” Olson notes.

Knowing actual cow size is a critical first step in managing cow weight, he continues. While many ranchers don’t have access to a scale, Olson encourages getting a mature cow weight if at all possible. Looking at cull-cow weights, and adjusting that weight based on how those cows compared to a herd’s average, is another way ranchers can get a general idea of how big their cows are.

“Of course, bigger cows need more nutrients. The neat thing is nutrient requirements don’t go up in direct proportion to the size of the cow. They actually go up at a ¾ powers ratio, or 75%, not one to one. So, the maintenance energy required by the 1,400-lb. cow is about 11% higher than that required by the 1,200-lb. cow, despite the fact that she is about 16% heavier,” Olson explains.

But, what about finding the additional feed resources to maintain that bigger cow?

“Annual dry matter intake will be 9,353 lbs., and 10,406 lbs. for the 1,200- and 1,400-lb. cows, respectively. There is that 11%, or 1,053-lb., difference for the larger cow. So, you’re going to have to allocate more resources, if your environment allows that. But, that bigger cow is going to have to do something to pay that bigger feed bill. How much more does she need to produce?”

To determine the answer, Olson divided the 9,350 lbs. of feed consumed by a 1,200-lb. cow by a 500-lb. weaning weight, which resulted in that size cow using 18.7 lbs. of feed to produce 1 lb. of weaned calf. A 1,400-lb. cow will produce a 550-lb. calf at a rate of 18.9 lbs. of feed/1 lb. of calf weaned.

“The conclusion I draw is, as you add 200 lbs. to the cow, you need to add 50 lbs. more weaning weight to the calf just to break even on the additional feed cost you’re going to put in that cow, Olson says, adding that his conclusion is based on the additional feed being the same forage, and not a more expensive supplement.

Producers also need to consider their ranch environment, and what impact larger cows have on stocking rates, he says.

“Simply put, if cows weighed 1,200 lbs. in the past, and they now weigh closer to 1,400 lbs., that’s a 17% increase in size and an 11% increase in forage intake. Therefore, those cows should get a similar increase in pasture allocation (adjusted stocking rate), or pasture productivity needs to have increased in a similar proportion.

“The bottom line is that production systems need to be considered on an integrated approach. As we make adjustments to genetics, we need to consider the ramifications on all other aspects of the operation, including range management, and feed/nutrient supplies, if we want the system to be productive and profitable,” Olson says.

Heather Hamilton is a freelance writer based in Lance Creek, WY.