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A study of 23, 6-d-old Holstein-Friesian male calves was conducted to evaluate the thermal requirements of young calves in relation to their posture (standing or lying). Calves were housed individually and were assigned to one of four ambient temperatures: 5, 9, 13, or 18 degrees C. Heat production of each calf was measured continuously every 9 min by indirect calorimetry for 5 d. The posture during these 9-min periods was derived from the continuous measurement of physical activity. For both standing and lying, heat production was increased at 5 and 9 degrees C compared with 13 and 18 degrees C. This increase in heat production was larger during standing than during lying. Consequently, the energy cost of standing was affected by ambient temperature (173, 189, 144, and 114 kJ.kg-.75 x d-1 at 5, 9, 13, and 18 degrees C, respectively). The time spent standing was not affected by ambient temperature. The thermal requirements of the calves were dependent on the posture. Lower critical temperature was 13.5 degrees C during lying and 17.0 degrees C during standing. The rate of increase in heat production below the lower critical temperature was 7.47 kJ.kg-.75 x d-1 x Co-1 during lying and 11.24 kJ.kg-.75 x d-1 x Co-1 during standing. These results indicate that the increase in heat loss upon standing in the cold is greater than the increase in heat production upon standing at thermoneutrality. Consequently, young calves require increased cold-induced thermogenesis when they are standing.

Heat production, dry matter, and water loss in the body and yolk sac of neonatal broiler chicks were measured during 24 h exposure to constant temperatures from 30.8 to 38.8 C. Average initial body and yolk sac weights were 41.6 and 4.4 g, respectively. Chicks housed at 30.8 C lost 3.5 g/day and chicks housed at 38.8 C lost 5.7 g/day of total body weight. Between 30.8 and 35.1 C, weight loss of the yolk sac was 1.9 g/day. At 38.8 C, weight loss of the yolk sac was 1.4 g/day. Weight lost from the yolk sac consisted of equal amount of dry matter and water. Water loss from the remainder of the chick's body (the total body without yolk sac) increased from 1.8 to 4.4 g as environmental temperature was raised from 30.8 to 38.8 C. This increase occurred mainly above about 35 C. Chick heat production increased with ambient temperature. Heat production as determined per subsequent 3-h period decreased with increasing duration of exposure from 34.6 to 28.2 kJ/kg per hour (1 kJ = .239 kcal) at 30.8 C and from 44.1 to 35.5 kJ/kg per hour at 38.8 C. The upper critical temperature was derived from regression of heat production on temperature. Results showed that this critical temperature was between 36 and 37 C.

Circadian rhythm in total and activity-free heat production (H and Hacf, respectively) was studied in Norwegian Landrace (N), Finnish Landrace (F), Dutch Landrace (D), and Great Yorkshire (Y) barrows. Animals, weighing 26 kg at the start of the study, were kept in groups for 18 2-d periods in climate respiration chambers at environmental temperatures (Tenv) between 11 and 26 degrees C. Measurements of H and physical activity of the pigs were done in 12-min intervals for 36 h per breed per Tenv. Feeding level of animals in a group was 93 g.kg-.75 x d-1 (2.5 times maintenance) and based on mean BW. Circadian rhythm in H and Hacf with data excluding the feeding periods was assessed using a sine wave with a 24-h periodicity per breed and per Tenv. With respect to H, the intercepts and amplitudes for the three Landrace breeds were similar, but the Y pigs had a lower intercept and a lower amplitude. The intercepts increased with decreasing Tenv. In N pigs, but not in F, D, or Y pigs, the amplitude increased with decreasing Tenv. With respect to Hacf, all breeds had similar intercepts and amplitudes. The Hacf varied less within a day than did H. In all breeds, the intercepts were increased with decreasing Tenv. The amplitudes were not affected by Tenv.

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