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Small, moderate cows most efficient in Wyo

by Wyoming Livestock Roundup

“The Wyoming environment is not a gentle environment on a cow. It’s harsh in terms of temperatures and topography. We need a cow that is still upright, on her feet that brings a calf to the pens every year,” notes University of Wyoming Extension Range Specialist Derek Scasta.

Pursuing an efficient Wyoming cow, Scasta and his team recently published an article in the Journal of Animal Science titled, “Drought Effect on Weaning Weight and Efficiency Relative to Cow Size in a Semiarid Rangeland.”

Arid environment

“If we ask the question, ‘What’s best, a large cow or a small cow?’ there is disagreement in the literature,” Scasta says.

Some studies suggest smaller cows have greater live weight production and net income, but many of those studies have been done in high production environments. Other studies show that larger cows are more optimal, but many of those studies have been done in feeding trials.

“There is a lack of ranch-level studies in our type of environment – arid, semi-arid and high elevation. That’s the reason I wanted to look at the UW beef unit data and determine optimal cow size,” he comments.


In their research, Scasta and his team looked at how cow size influenced weaning weights of calves in wet, average and dry years.

“We had three hypotheses. The first one was that in drier years, weaning weights would be lower. The second was that larger cows would maximize their potential for growth in wet years but not dry years, and the last was efficiency is greater for smaller cows,” explains Scasta.

From 2011-14, the team tracked a subset of 80 Angus-Gelbvieh cross cows, all of similar age, on the McGuire Ranch approximately 30 miles north of Laramie.

“In the driest year, the area grows about 600 pounds of grass per acre. In the wettest years, it grows about 1,300 pounds of grass per acre. Those estimates from NRCS (Natural Resources Conservation Service) give us an idea of production potentials,” he remarks.

Gathering data for their first hypothesis, the team determined there was a swing of about 90 pounds in weaning weights between wet and dry years. In the wettest year, calves weaned at an average of 560 pounds, while in the driest years, they averaged 476 pounds at weaning.

Weaning and stocking

“In the driest year, the smallest cows weaned the lightest calves, and the largest cows weaned the heaviest calves,” Scasta says. “This was a surprising result.”

In years with average precipitation, moderate-sized cows weaned the heaviest calves.

Exploring that data, Scasta comments, “For the largest cows, there really wasn’t a change in terms of the weaning weight, but as cows got smaller, the difference, or magnitude, between years got really large. Smaller cows weaned the smallest calves when there were really difficult conditions, but they had the greatest upside potential when the conditions were really good.”

He also explored data to determine the best stocking rate depending on cow size.

“For a 1,000-pound cow, we could have 100 head in a given area. If we only had 800-pound cows, when we match animal demand to forage supply and the forage needs of those cows, we could pick up an additional 18 head,” he explains. “If we got up into the 1,600-pound range, we would have to drop 30 head. We would only be able to carry 70 head.”


After compiling data from his own study, as well as data from many other comparative studies, Scasta concluded that small to moderate cows would likely prove to be the most efficient animals for a Wyoming operation.

“I’m not concerned with cows getting too small, but I am concerned with them getting too big. I want to rein it in a little bit and work more toward that moderate-sized cow. I’ve seen ranches in Colorado and Wyoming really aiming toward this, and I’m convinced that it is a good goal for the long-term sustainability of the cow/calf business,” he says.

Scasta spoke at the Progressive Rancher Forum in Casper on Nov. 30.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at

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