ENERGY-COST OF STANDING AND CIRCADIAN CHANGES IN ENERGY-EXPENDITURE IN THE PRERUMINANT CALF

An experiment was conducted with four preruminant calves to measure th e energy cost and the diurnal pattern of physical activity in tethered , fed calves and to determine whether differences in activity could in terfere with the interpretation of circadian changes in heat productio n. Measurements were carried out in large respiration chambers (3,650 L of inner volume), and a computation method was presented that allowe d the calculation of the energy cost of standing for each standing per iod. This cost averaged 449 cal.kg BW-1.h(-1) (SE = 41.6, n = 4). It r epresented a 23 to 27% increase in heat production above that measured in the lying state. This estimate and its standard error were lower t han values obtained by regression (2,131 cal.kg BW-1.h(-1), SE = 862.2 , n = 8). The energy cost of standing was highest after meal times and lowest at night. These variations could reflect the nonuniform activi ty patterns of calves while standing. The time spent standing per hour showed the same variations during the day as the energy cost of stand ing. Noteworthy, the elevated energy expenditure measured in the Ist h after the morning meal was due to activity cost rather than to meal t hermogenesis. Standardization of diurnal heat production profiles to a given activity pattern thus seemed to be necessary.