Effects of reduced dietary protein leveland fat addition on heat production and nitrogenand energy balance in growing pigs

Two trials were conducted in order to quantify the effects of reduction of dietary crude protein (CP) level, with or without fat addition, on heat production and energy balance in growing pigs. In trial 1, extreme variations in diet composition were obtained by using purified ingredients; conventional ingredients were used in trial 2. In each trial, three diets were prepared. Diet 1 had a conventional CP level (18.9 and 17.4% in trials 1 and 2, respectively) while diet 2 had a reduced CP level (12.3% and 13.9% in trials 1 and 2, respectively); diet 3 also had a reduced CP level (13.6 and 14.9%, respectively) and 3.5% (trial 1) or 4% (trial 2) fat was added. In both trials, diets 2 and 3 were supplemented with industrial amino acids in order to ensure similar ratios between digestible essential amino acids and net energy (NE) between diets while exceeding requirements of animals. Each diet was measured in 6 (trial 1) or 5 (trial 2) individually caged 60-kg pigs for digestibility, components of heat production (indirect calorimetry) and energy, protein and fat balances. Energy supply was standardised between diets (1.9 MJ NE per kg BW 0.60 ). A reduction of dietary CP level (diets 2 and 3 vs. diet 1) significantly reduced urinary nitrogen loss without impairing nitrogen gain in pigs. A reduction of dietary CP alone (diet 2 vs. diet 1) contributed to a significant reduction of total heat production and, more specifically, its component related to feed utilisation. This effect was accentuated when fat was added (diet 3 vs. diet 2). Fasting heat production (770 kJ per kg BW 0.60 ) and activity heat production (8% of ME intake) were not affected by dietary treatment. These results emphasise the interest of using an NE concept for estimating the energy value of pig feeds. pig / crude protein /crude fat / heat production / energy value Rsum -Effets de la rduction du taux de protines et de l'addition de matires grasses dans l'aliment sur la production de chaleur et le bilan d'azote et d'nergie chez le porc en croissance. Dans le but de quantifier les effets d'une diminution de la teneur en matires azotes totales (MAT) et de l'addition de matires grasses dans l'aliment chez le porc, deux essais ont t raliss.