Season of Birth Affects Calf Growth on Great Plains

To everything, there is a season—even for ranchers raising herds of cattle out on America's Great Plains.

According to scientists with the Agricultural Research Service (ARS), calving season—the time of year when a cow gives birth to a calf—is an important factor in determining how healthy a cow and calf will be, how much weight they'll gain, and how much high-quality nutrition will be available to them.

ARS animal scientist Elaine Grings, along with colleagues at the agency's Ft. Keogh Livestock and Range Research Laboratory in Miles City, Mont., recently completed a three-year study investigating differently timed calving-season and weaning strategies and how they affect mother cows and their calves.

The researchers also wanted to see how certain calving times—late winter, early spring or late spring—affect the economics of livestock production.

In the northern Great Plains, which includes Montana, Wyoming and North Dakota, the primary inputs for raising cattle are the costs associated with providing ample nutrition to the animals. This feed comes in the form of supplements, winter hay, and the grasses that the animals graze.

In this semiarid region characterized by rolling hills and broken badlands, ranchers are accustomed to a narrow growing period that typically peaks in May and June, when temperatures and precipitation encourage new, cool-season grasses to sprout. According to Grings, this forage can be a vital source of food for lactating cows, which pass important nutrients on to their calves through their milk.

In choosing a calving season, a rancher changes the priority of how the most nutritious forage is used. The rancher can time the cows' reproduction so that the highest quality forage goes to boosting cows' weight gain during pregnancy, encouraging milk production for their nursing calves—or to nourishing the calves themselves, which need hardy forage to properly grow and develop.

Grings' calving study was published in the Journal of Animal Science.

ARS is the U.S. Department of Agriculture's chief scientific research agency.