Thermal requirements of young calves during standing and lying.

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.