Fasting heat production and energy cost of standing activity in veal calves.

Metabolic body size of veal calves is still calculated by using the 0.75 exponent and no data were available to determine energy cost of physical activity during the whole fattening period. Data from two trials focusing on protein and/or energy requirements were used to determine the coefficient of metabolic body size and the energy cost of standing activity in male Prim'Holstein calves. Total heat production was measured by indirect calorimetry in ninety-five calves weighing 60-265 kg and was divided using a modelling approach between components related to the BMR, physical activity and feed intake. The calculation of the energy cost of standing activity was based on quantifying the physical activity by using force sensors on which the metabolism cage was placed and on the interruption of an IR beam allowing the determination of standing or lying position of the calf. The best exponent relating zero activity fasting heat production (FHP 0) to metabolic body size was 0.85, which differed significantly from the traditionally used 0.75. Per additional kJ metabolizable energy (ME) intake, FHP 0 increased by 0.28 kJ; at a conventional daily 650 kJ/kg body weight (BW)0.85 ME intake, daily FHP 0 averaged 310 kJ/kg BW 0.85. Calves stood up sixteen times per day; total duration of standing increased from 5.1 to 6.4 h per day as animals became older. The hourly energy cost of standing activity was proportional to BW 0.65 and was estimated as 12.4 kJ/kg BW 0.65. These estimates allow for a better estimation of the maintenance energy requirements in veal calves.