Effects of reduced dietary protein level and fat addition on heat production and nitrogen and 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 pro duction and energy balance in growing pigs. In trial 1, extreme variations in diet composition were obtained by using purified ingredients; convention al ingredients were used in trial 2. In each trial, three diets were prepar ed. Diet 1 had a conventional CP level (18.9 and 17.4% in trials 1 and 2, r espectively) 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 t rials, 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 die t 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 d iets (1.9 MJ NE per kg BW0.60). A reduction of dietary CP level (diets 2 an d 3 vs. diet 1) significantly reduced urinary nitrogen loss without impairi ng 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, mor e 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 BW0.60) 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.