Effects of a reduction in the dietary level of nonessential nitrogen in the female growing pig on feed intake growth performance and carcass characteristics according to energy concentration and energy substrates
Noblet, J.; Henry, Y.; Bourdon, D.
Annales de Zootechnie 29(2): 103-120
This experiment was performed on 63 female growing pigs between 25 and 100 kg live weight to study the influence of reducing the dietary level of nonessential N on feed intake, growth performance and carcass characteristics. Three groups of 9 animals (treatments 1, 3 and 5) received diets with protein levels corresponding to the usual recommendations [44 g of digestible crude protein/Mcal digestible energy (DE) up to 50 kg live weight], differing either by the energy concentration (treatment 1: maize-soybean meal; treatment 3: maize-soybean meal diluted with 6.5% vermiculite and treatment 5: barley-soybean meal). For other groups, i.e., treatments 2, 4 and 6 with 9 animals in each, the protein level was reduced (25%) by supplementing with the most limiting amino acids (lysine, tryptophan, threonine), in order to meet growth requirements. One treatment (treatment 7) consisted of threonine supplementation in barley-soybean meal diets and contained suboptimum levels of total protein. The pigs were fed individually ad lib pelleted diets. They were weighed at 2 wk intervals and after slaughter, at 100 kg live weight. Backfat measurements were taken and carcasses evaluated for lean and fat cuts. The addition of vermiculite in a maize-soybean meal diet reduced the digestibility of organic matter, energy and N. Digestibility coefficients were significantly lower with barley than with maize diets. In treatments 1, 3 and 5, the reduction of energy concentration by adding vermiculite or replacing maize with barley, induced an overconsumption of feed. The DE consumption was slightly reduced in both cases. The average daily gain (ADG) was not significantly affected by the energy concentration. The food conversion ratio (FCR) (Mcal DE/Kg gain) was reduced when the energy concentration was lower. Carcass adiposity was lower for the barley-soybean treatment but was not reduced significantly when an inert diluent was added to the maize-soybean meal diet. After a reduction of the N level, when the limiting essential amino acids were maintained at the optimum levels for growth, overconsumption of feed was observed mainly with the high level of energy concentration (maize-soybean meal). This effect was smaller for barley diets and null for maize diets diluted with vermiculite. The ADG was not affected by the level of nonessential N. The FCR ratio was higher for the low N diets, with the exception of barley diets. In all treatments, carcass adiposity was increased when the level of nonessential N was reduced. The addition of threonine in a low protein barley-soybean meal diet increased intake and ADG in growing females. The FCR ratio was significantly reduced. Threonine appears to be the 2nd essential limiting amino-acid after lysine, in a barley-soybean meal diet with a reduced protein level.