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Looking at cow size’s effect on production

cattle in field
COW SIZE MATTERS: Under managed grazing conditions, cow size makes a difference in efficiency, says Jason Rowntree, Michigan State University animal science professor.
A Michigan researcher and his team have been studying potential differences in cow size and efficiency on grass.

When Jason Rowntree, Michigan State University animal science professor, took the helm at the MSU research farm 10 years ago, he inherited a large cow herd, not in numbers but in animal size.

The crossbred cows weighed on average about 1,500 pounds, with a few specimens topping out at 2,200 pounds. For Rowntree, who wanted to get out of the haying business and research managed grazing, that cow size was too large to fit into his research goals. That’s why he liquidated the old herd and bought a new herd with a base of Red Angus, lowering the average cow size in the herd to 1,100 pounds.

Rowntree, who is the coordinator at Lake City and Upper Peninsula Research and Extension AgBioResearch Centers, talked about his challenges and experiences in transitioning his research at MSU when he recently visited Nebraska as part of the Nebraska Grazing Coalition’s annual traveling road show.

“One of the first things we did was to get fence around every acre and get water available,” Rowntree told producers at a meeting in Norfolk, Neb. “We really didn’t know what we were doing when we got started.”

He and his team of researchers sold their haying equipment, extended their grazing season and tried to figure out how best to utilize their forage resources through grazing management.

“We played with mob grazing and moving cattle multiple times each day,” he said. “Now, we just move once a day.”

Through research with grazing cows that are averaging about 1,100 pounds per head compared with large cows at 1,500 pounds, Rowntree realized a few facts that can be useful to producers under those managed grazing systems. The small cows ate about the same volume of forages as the large cows over the grazing period.

“There wasn’t much difference in utilization for the period of our trials between the small and larger cows,” Rowntree said. “But the small cows gained about twice the weight of the large cows during lactation on a per head basis. There was also very little difference in calf performance. Calves born from the bigger cows had a slight advantage in performance.”

That told Rowntree and his colleagues that small cows had the ability to convert forages better. From previous research, they realized that small cows had a greater potential to eat more low-quality forage than what they should have been able to do, which bodes well for producers in a low forage-quality environment.

In the long run, Rowntree has learned that his grazing management systems have been able to cut costs and increase production. Learn more by contacting him at

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