Abstract
Heart rate (HR) and heat production (HP) were measured continuously using four Holstein heifers (285kg) to determine the effect of feed intake and behavior on the relationship between HR and HP. The effect of behavior on HP and its energy balance were examined under indoor (in stanchion) and outdoor (in paddock) conditions. Significant differences in the relationship between HR and HP within the animals and their behavior types were observed. The prediction error (Sy•x/y, %) of HP from HR could be reduced from ±9.4 to ±3.9% when using mean values measured every three hours using four heifers. ME intake, HP and energy retention were estimated from TDN intake, daily mean heart rate and average daily gain, respectively, which then used for evaluation of energy balance. It seems possible to evaluate the energy balance of growing heifers under free living conditions by measuring HR in addition to either ME intake or daily gain. In the evaluation of energy balance on free living animals, it is suggested that a control experiment should be done using housed animals which feed intake levels are controlled.
