Effects of high fibre and low protein diets on performance, digestibility, nitrogen excretion and ammonia emission in the heavy pig

An experiment was conducted to determine the effects of dietary fibre and protein contents and addition of bentonite on performance, nitrogen (N) balance and ammonia emission of heavy pigs from 80 to 170kg bodyweight. Pigs were fed 4 diets differing in the contents (g/kg as fed) of neutral detergent fibre (aNDFom) and crude protein (CP): 114 and 120 (diet C, control), 193 and 122 (diet HF, high fibre), 176 and 98 (diet HFLP, high fibre and low protein), and 175 and 99 (diet HFLPB, high fibre and low protein plus 10g bentonite/kg) for aNDFom and CP, respectively. Eighty pigs were randomly allotted to the 4 dietary treatments (4 pens for each treatment and 5pigs per pen). In addition, 6 pigs from each treatment were placed in individual metabolic cages for 7 days to determine total tract apparent digestibility (TTAD), N balance and ammonia emission from slurry. Dietary treatment did not affect average daily gain, feed conversion ratio and slaughter performance. The inclusion of fibre reduced TTAD of dry matter (P<0.001), organic matter (P<0.001), CP (P=0.026) and energy (P<0.001). Pigs fed the high fibre diets excreted more N in faeces than pigs fed the C diet (P=0.015). Urinary N was lower (P=0.007) for the low protein diets (17.8g/day, for both) compared to C (25.8g/day) and HF diets (23.8g/day). Nitrogen excretion was reduced by approximately 8.0% for each 10g/kg of dietary CP reduction. The pH values of slurries were not affected by diet. At the end of the monitoring period (14 days) pH was lower (P=0.046) for the low protein diets (8.26 for HFLP; 8.28 for HFLPB) in comparison with the C diet (8.82). Ammonia cumulative emission measured for 14 days was not affected by diet. Significant differences (P=0.048) were observed between diets C vs HF, HFLP and HFLPB when emission was expressed as the ratio between ammonia N emitted and initial N. It is concluded that increasing the fibre content of the diet together with a decrease of the protein content reduced N excretion without jeopardizing performance of heavy pigs. The inclusion of bentonite did not affect any of the traits studied.