Heat Increment of Acetate and Corn and Effects of Casein Infusions with Growing Lambs

Abstract

The heat increment of a corn basal diet and ruminally infused acetate both with and without abomasally supplied casein was measured in two consecutive 4 × 4 Latin square total energy balance experiments with young lambs. Heat production was measured by open circuit indirect calorimetry. The increment of metabolizable energy (ME) resulting from the infusion of 400 to 500 kcal of acetate (0.25 Na acetate, 0.75 acetic acid) was utilized with an efficiency of 67.3 ± 5.1%, when infused with a corn basal diet fed at either 1.1 or 2.1 times the maintenance intake level. This was higher than the ME utilization of the basal diet for tissue deposition above maintenance which averaged 57.8 ± 3.2%. Acetate infusions significantly depressed CH₄ losses (P < 0.01) but had no effect on other parameters of energy digestibility or metabolizability. Although infusion of 15 or 45 g of casein plus 2% methionine into the abomasum doubled nitrogen retention, it had no effect on the heat increment of either acetate or the basal diet.