We have previously shown that feeding 50 ml of colostrum can increase the thermogenic activity of brown adipose tissue (BAT) in newborn lambs maintained at a warm (30¡C) ambient temperature. This study further examines the effect of ambient temperature on BAT and thermoregulation by investigating the response to feeding 50 ml of water. Immediately after vaginal birth, lambs were placed in either a warm (30¡C) or cool (15¡C) environment at ambient temperature and measurements of colonic temperature and heat production were recorded for 6 h. Lambs were fed 50 ml of water when 5 h old. The level of guanosine 5'-diphosphate (GDP) binding was higher, but adrenaline content lower in BAT sampled from lambs maintained at 15¡C compared with those at 30¡C. Feeding was associated with an increase in colonic temperature and plasma concentrations of glucose and non-esterified fatty acids in lambs maintained at 15¡C only. In this group plasma concentrations of adrenaline and dopamine declined after feeding, but noradrenaline concentrations were not influenced by feeding in either group of lambs. O2 consumption and CO2 production were higher in lambs maintained at 15¡C but were not influenced by ambient temperature or feeding. It is concluded that feeding a small volume of water can influence thermoregulation by a mechanism that is dependent on the ambient temperature at which the lamb is maintained.