THERMAL REQUIREMENTS OF YOUNG CALVES DURING STANDING AND LYING

A study of 23, 6-d-old Holstein-Friesian male calve was conducted to e valuate 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 period s was derived from the continuous measurement of physical activity. Fo r both standing and lying, heat production was increased at 5 and 9-de grees-C compared with 13 and 18-degrees-C. This increase in heat produ ction 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.d-1 at 5, 9, 13, and 18-degrees-C, respectivel y). The time spent standing was not affected by ambient temperature. T he thermal requirements of the calves were dependent on the posture. L ower critical temperature was 13.5-degrees-C during lying and 17.0-deg rees-C during standing. The rate of increase in heat production below the lower critical temperature was 7.47 kJ.kg-.75.d-1.C-degrees-1) dur ing lying and 11.24 kJ-kg-.75.d-1.C-degrees-1) during standing. These results indicate that the increase in heat loss upon standing in the c old is greater than the increase in heat production upon standing at t hermoneutrality. Consequently, young calves require increased cold-ind uced thermogenesis when they are standing.