Maintenance requirements for energy in cross-bred cattle.

1. Twenty-seven energy and protein balances were done using nine cross-bred (Brown Swiss times Sahiwal) mature bullocks in a series of three balance trials. The bullocks were fed 75, 100 and 125 percent of the metabolizable energy (ME) and digestible crude protein standard values recommended by the (US) National Research Council (1966). Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. 2. Utilization of energy for maintenance and fat production was estimated by computing regression of energy balance v. digestible energy (DE) and ME separately on a metabolic body size (kg body-weight (W)0-75) basis. Maintenance energy requirements and efficiency of utilization of ME for lipogenesis were estimated using multiple regression of ME intake, also. Heat production (and thus energy balance) was corrected for excess nitrogen intake. 3. An attempt was made to measure basal heat production of bullocks so that the net energy requirements for maintenance could be estimated. Extrapolation of the regression line of energy balance v. ME intake below maintenance on a W0-75 basis gave a basal metabolism of 348-09 kJ/W0-75 per d. 4. Energy requirements for maintenance were (kJ/kg W0-75 per d): 539-43 DE, 448-81 ME and 348-09 net energy. The results of multiple regression gave a requirement of 432-15 kJ ME/kg W0-75 per d for maintenance. 5. The efficiency of utilization of ME for maintenance was 81-34 percent while for lipogenesis it was 54-5 percent.