Calves that become chilled at birth and don’t immediately ingest colostrum have poor survival rates. If a calf fails to nurse, it doesn’t obtain energy (for keeping warm) or antibodies to protect against disease.

A calf’s ability to absorb antibodies from colostrum diminishes as its body temperature becomes colder. Even if you force-feed colostrum a few hours after birth, absorption rate will be less than that of a warm calf. Any stress – from cold or a difficult birth – can interfere with optimum absorption, leading to problems with scours, pneumonia and other infections.

Keeping newborn calves' warm

Robert Callan, professor of clinical sciences in the College of Veterinary Medicine at Colorado State University, says a newborn calf’s temperature is about 103° F. It drops to a “normal” of 101.5-102° within a few hours. “But if it drops below l01°, this means the calf can’t thermo-regulate and keep itself warm,” Callan says. If calves are born in cold, windy weather, their temperature drops faster.

You can tell when calves are really cold, and you can usually tell when calves will be alright, but borderline calves can be hard to evaluate, says Russ Daly, South Dakota State University Extension DVM. “Many ranchers stick a finger in a calf’s mouth to see how cold he is [if he hasn’t nursed, the inside of his mouth is cold], but I encourage use of a rectal thermometer. Any calf with a rectal temp below 100° will benefit from being warmed up and a supplemental dose of colostrum,” he explains.

A normal calf has a tremendous ability to thermo-regulate, especially if the cow licks him off quickly and helps him get dry, Callan says. A wet calf continues to chill (especially in a breeze) due to evaporation of moisture and more rapid heat loss.

“High-risk calves also chill quickly. These include calves that suffered prolonged birth, twins, and calves born to sick cows or cows in poor body condition. Cows deficient in energy and protein may give birth to weak calves that don’t have much reserve, and those cows’ colostrum has less energy and fewer antibodies,” Callan says. Calves born to well-nourished cows burn through glucose reserves, glycogen and fat more slowly than calves born to cows with inadequate nutrition.

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“If a calf doesn’t nurse, it starts depleting its blood glucose within 30-60 minutes. Its body tries to replenish this from liver glycogen stores but these can be used up within 4-6 hours, after which the calf becomes hypoglycemic. If calves fail to receive proper nutrition, they deplete their brown-fat reserves in 1-6 days and are starving,” Callan says.

Protein and energy are crucial, and supplying supplemental fat to cows during late gestation will help calves be better prepared to handle cold weather, he adds. Cows with adequate protein levels also produce better colostrum.