Brown Adipose Tissue increases heat production in newborn calves and lambs

“Environmental stresses such as severe cold temperatures, wind, and moisture increase calf mortality,” states a Journal of Animal Science article published by Texas A&M University titled, “Ontogenic development of brown adipose tissue in Angus and Brahman fetal calves.”
Newborn calves have the ability to produce heat to maintain normal core body temperatures. However, calves are limited in their ability to conserve heat, so it must be constantly produced according to a Texas A&M University research paper by associate professor in animal nutrition Gordon Carstens titled, “Impact of Prenatal Nutrition on Cold Tolerance of Neonatal Beef Calves.”
According to Carstens, calves implement shivering thermogenesis in skeletal muscle tissue as one way to stay warm. However, nonshivering thermogenesis in brown adipose tissue (BAT) also contributes between 40 and 50 percent of cold-induced metabolism.
“A calf relies on his muscles shivering involuntarily, but that only makes up about half of newborn heat production. The other half comes from brown fat,” states Carstens.
Carsten’s article describes BAT as a lower lipid containing fat with a higher concentration of mitochondria and blood vessels as compared to white fat. It’s ability to generate heat comes from an uncoupling protein that causes cells to generate heat instead of producing chemical energy (ATP). It is highly sensitive to the sympathetic nervous system, which releases norepinephrine during cold exposure to activate BAT thermogenesis.
“Brown fat is very important in newborn calves or lambs to enable them to produce heat during the first week of life to offset heat losses to the environment,” explains Carstens.
BAT development undergoes major changes during late gestation. Additional Journal of Animal Science articles quoted in Carsten’s article found BAT thermogenic capacity in 130 day preterm lambs was only half that found in full-term lambs. They concluded that meeting energy and protein requirements of the dam during late gestation was crucial to ensure cold tolerance wasn’t compromised in offspring.
“If a pregnant dam is underfed protein or energy that results in the calf not having as much functional brown fat to help with the non-shivering component of heat production,” says Carstens.
Carstens article includes previous studies that found prenatal protein intake during the last 60 days of gestation was inversely related to weak calf syndrome. Calves from protein-restricted dams took longer to stand and produced 12 percent less heat.
“Make sure protein requirements are met. If calves are born to protein-deficient dams, that could easily impact their cold tolerance and passive immune transfer capabilities,” adds Carstens.
Carstens article also states that in one study, pregnant ewes were fed high and low-energy diets to determine if prenatal energy restrictions reduced perirenal fat. Results showed that perirenal fat was reduced by 17 percent in single lambs and 24 percent in twins at 125 days of gestation.
However, Carstens has found that pregnant cows exposed to cold stress typically have more cold tolerant calves.
“We know calves born to cows that have gone through cold stress are usually a little bigger when they’re born. Other research has shown those calves and lambs that are born to dams that have been cold stressed posses more brown adipose tissue, or brown fat. It’s a way for those calves and lambs to adapt in utero,” explains Carstens.
The article comparing Angus and Brahman calves found that Brahman calves had higher mortality rates, especially as the temperature dropped.
“Angus calves exhibit approximately 25 percent higher peak metabolic rates than Brahman calves, which may contribute to their greater cold tolerance. It was our hypothesis that reduced BAT thermogenesis in Brahman calves may be caused by limited BAT ontogenic development during the third trimester,” states the article.
Researchers also found that Angus calves had 60 percent more cells per gram of BAT, which consequently had 60 percent more adipocytes.    
Breed selection, nutrition and supplementation are all important factors that can be used to reduce cold stress and mortality and potentially increase BAT levels in newborns. As spring storms sweep across parts of the state, calf survival in cold temperatures is an important concern to many producers.
Heather Hamilton is editor of the Wyoming Livestock Roundup and can be reached at heather@wylr.net