Chronic cold exposure has no effect on brown adipose tissue in newborn lambs born to well-fed ewes

It has been previously shown in twin-bearing ewes fed only 60% of their metabolizable energy requirements for late pregnancy that chronic cold exposure induced by winter shearing of the ewes results in larger lambs with more brown adipose tissue. This effect appears to be primarily due to prevention of a decline in fetal body and tissue weights between 145 days' gestation and 2 h after birth (i.e. 147 days' gestation) in lambs born to underfed shorn ewes. The present study therefore examined the impact, in ewes that were well fed (i.e. received 100% of their metabolizable energy requirements) during the final month of gestation, of chronic cold exposure induced by winter shearing on lamb birthweight and perirenal adipose tissue composition as measured 2 h after birth. Perirenal adipose tissue was analysed for its thermogenic activity (i.e. GDP binding to mitochondria) and catecholamine content. These observations were combined with similar measurements made in near-term (i.e. 145 days' gestation) fetuses sampled from well-fed unshorn ewes. There was no difference between lambs born to shorn or unshorn ewes with respect to birthweight or perirenal adipose tissue weight and composition. Perirenal adipose tissue weight was higher in lambs born to unshorn ewes than in fetuses. The thermogenic activity of adipose tissue was 2-fold higher in lambs born to unshorn ewes compared with 145-day-old fetuses. Epinephrine was detectable only at very low levels in fetal perirenal adipose tissue, increasing 10-fold after birth, with no difference between lambs born to shorn or unshorn ewes. In newborn lambs, plasma growth hormone concentration was lower and insulin concentration higher in shorn compared with unshorn groups. In conclusion, chronic cold exposure induced by winter shearing had no effect on brown adipose tissue development in lambs born to well-fed ewes.