Penned beef heifers stressed, sedentary and experience delayed puberty

CORVALLIS, Ore. – Beef heifers raised in close quarters are under more stress and don’t get as much physical activity as heifers raised on pasture, according to an Oregon State University study.

The findings, published in the journal animal, could offer guidance for cattle ranchers who want to improve the efficiency of their herds and assure the public they are interested in the welfare of the cows, said Reinaldo Cooke, a former animal scientist OSU’s College of Agricultural Sciences and corresponding author on the study: Impacts of stocking density on development and puberty attainment of replacement beef heifers.

“People want to know that beef is coming from animals that are well-treated,” said Cooke, now an associate professor of beef cattle production at Texas A&M University. “We found that the heifers in the pens weren’t comfortable.”

In U.S. spring-calving cow-calf herds, heifers are weaned in the fall, spend the winter together in pens or pastures, so they are protected against the elements, and exposed to their first breeding season the following spring.

Beef cattle producers count on replacement heifers to become fertile cows. In a six-month experiment, researchers in OSU’s College of Agricultural Sciences determined that cows clustered together in industry-standard dry-lot pens experienced delayed puberty despite adequate age and body weight development.

Heifers must reach puberty at an early age to ensure high conception rates in their first breeding season, so a delay in their sexual maturity holds economic disadvantages for cattle ranchers, Cooke said.

The OSU research team monitored the growth, physical activity and stress-related physiological responses of heifers from September 2015 to March 2016 at OSU’s Eastern Agricultural Research Center in Burns.

The researchers dispersed 60 Angus and Hereford heifers into three 450-square-foot dry-lot pens and three 60-acre pastures, with 10 heifers in each pen and 10 in each pasture. The number of heifers kept in a pen influences whether the heifers thrive and go on to produce healthy calves, Cooke said.

On the first day of the experiment, they measured each cow’s temperament with, among other things, how the animal handled being squeezed through a chute. They fitted each heifer with a pedometer placed inside a patch behind the right shoulder. They also collected hair samples from the animal’s tail switch to analyze cortisol concentrations. The concentration of cortisol, a stress hormone, in hair from the tail switch is a biomarker of stress in cattle.

At the end of the six-month period, the cows kept in pastures took on average nearly 20,000 steps a week, compared to about 3,100 for the penned heifers. The pasture heifers had lower cortisol concentrations and were better behaved than their pen-raised counterparts. These outcomes were independent of heifer nutritional status and growth rate because all the cows were on the same diet.

“Out on the pasture, there is snow everywhere and little to graze on. But they learn how to survive,” Cooke said. “We found that our heifers on pasture, as we expected, exercised more, which is important for reproductive maturation.”