Energetic efficiency of starch, protein and lipid utilization in growing pigs

Mathematical models are increasingly used to predict: the response of an an imal to a changing nutrient supply. The objective of this experiment was to provide data that can be used in model development or evaluation and conce rns the energetic efficiency with which nutrients are used for protein and lipid deposition. A basal diet (D1), limiting in lysine supply, was fed at 1.7 MJ metabolizable energy (ME)/(kg BW0.60.d(1)) to growing pigs that weig hed similar to 60 kg, Four additional diets were formulated: the basal diet and a dietary supplement that consisted of starch (D2), starch and corn gl uten meal (D3), starch and casein (D4) or starch and lipid (D5). The latter four diets were fed at 2.55 MJ MV(kg BW0.60.d(1)) and ensured the same int ake of the basal diet across treatments; the difference was supplied by the supplement. Metabolic utilization of the basal diet and supplements was de termined using nitrogen and energy balances (indirect calorimetry). The N r etention was similar in pigs fed diets D1, D2, D3 and D5 but considerably h igher in those fed D4, A data analysis model was developed to account for d ifferences in ME utilization between nutrients. The ME not deposited as pro tein entered a common pool of energy, which was used for adenosine triphosp hate synthesis or lipid deposition. The energetic efficiencies of ME utiliz ation were 0.842, 0.520 and 0.883 for starch, protein and lipid, respective ly. Due to the energy cost of protein deposition (or protein turnover), the energetic efficiencies of depositing dietary protein as protein or lipid w ere similar.