Mateusz Perkowski/Capital Press
Keeping young beef heifers penned over winter tends to delay puberty compared to letting them out on pasture, according to a new study.
Slowing a cow’s reproductive maturity may impair her ability to get pregnant in the first breeding season, which is economically undesirable for ranchers.
Only 32 percent of heifers kept in pens over winter reached puberty by late spring, compared to 67 percent that remained on pasture, the Oregon State University study found.
Among the cows that did reach puberty, those in pens achieved maturity 33 days later than those on pasture and they were 100 pounds heavier on average.
The stress of being kept penned was likely the reason that fewer heifers timely reached puberty and their maturity was delayed, said Reinaldo Cooke, who co-wrote the study.
“That may be taking a toll on the reproductive development of those females,” he said. “They like to walk around and graze and they don’t have that in the pen.”
Cows kept on pasture got more physical activity, averaging 20,000 steps a week, compared to 3,100 steps for penned heifers. Their hair also had lower levels of cortisol, a hormone associated with stress in cattle.
Pens probably make young heifers uncomfortable because they’ve spent their early lives on rangeland before weaning and are unaccustomed to being confined, said Cooke.
“That abrupt change in environment is pretty stressful,” he said.
Ranchers often keep young heifers in pens over winter because they’re easier to feed and check on, Cooke said. In some cases, cattle producers may not have enough property available to keep them on pasture.
“I’m not saying confinement is bad,” he said. “Many times it’s necessary. It’s the only option.”
However, ranchers should keep in mind that pens may prevent timely puberty, so they can try to reduce negative effects by avoiding overcrowding.
The half-year study compared 30 Angus and Hereford cows kept in pens with 30 heifers of the same breeds left out on pasture, with all the animals being fed the same diet.
Cooke was an animal scientist at OSU when the research was conducted in late 2015 and early 2016 but was recently hired as an associate professor of beef cattle production at Texas A&M University.
Researchers decided to conduct the study after noticing that penned heifers generally had poorer reproductive performance compared to those on pasture, Cooke said.
“Wow, maybe there’s something going on here,” he said.