Utilization of dietary energy for maintenance, milk production and lipogenesis by lactating crossbred cows during their midstage of lactation.

1. Twenty-four energy and nitrogen balances were determined using twenty-four crossbred cows (Brown Swiss X Sahiwal) during their midstage of lactation. Energy balances were estimated by subtracting milk energy and heat production from the metabolizable energy (ME) intake. Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. The cows were given amounts corresponding to 90, 110 and 130% of the ME and 90 and 110% of the digestible crude protein (DCP) standards of the (US) National Research Council (1966). 2. Energy requirements were estimated by partitioning the ME intake for maintenance, milk production and energy gain or loss by multiple regression of energy balance values. Heat production (and thus energy balance) was corrected for excess N intake. 3. Energy requirements for maintenance were 585-18, 580-17 and 574-41 kJ ME/kg body-weight0.75 per d for cows in negative balance, cows in positive balance and for all cows, respectively. 4. The efficiency of utilization of ME for milk production was 68-52, 65-48 and 66-12% respectively, for cows in negative balance, for cows in positive balance and all cows. Energy required per kg fat-corrected milk production was 4-580, 4-791 and 4-746 MJ ME for the respective groups of cows. 5. The efficiency of utilization of ME for tissue gain was 67-67 and 64-86% for cows in positive balance and for all cows respectively.