The metabolic and body weight changes in two non-pregnant beef cows were studied during prolonged exposure to warm (20 ± 3 °C, relative humidity 50–70%) and cold (−10 ± 2 or −25 ± 4 °C) temperatures. Other factors including daily food intake were held constant throughout each 8-week exposure. During cold exposures, metabolic rate, blood hematocrit, and plasma concentrations of glucose and free fatty acid were elevated and respiratory frequencies and skin temperatures decreased. Resting metabolic rates measured at 20 °C, i.e., without the direct influence of cold, were 83.4–95.3 litres O2 per hour when the cows were cold acclimated, at either −10 or −25 °C, and 30–40% greater than when the cows were warm acclimated. The resting metabolic response and the concomitant reduction in intensity of shivering is indicative of metabolic acclimation to cold in these animals of greater than 500 kg body weight.As well as the expected changes in body weight with changes in energy metabolism there were losses in weight (13–24 kg) during the first 3 days of each cold exposure. Weight gains occurred when the cold stress was abruptly removed. These short term weight changes were associated with changes in water intake and apparent shifts in body fluid content.