Effects of a reduction in the dietary protein level in the growing pig on feed intake and growth performance according to amino acid balance and energy concentration
Noblet, J.; Henry, Y.
Annales de Zootechnie 26(3): 379-394
The influence of reducing the level of dietary protein on feed intake, growth performance and carcass characteristics according to amino acid balance and energy concentration was studied in Large White pigs. Six groups of 12 animals in each (half castrated males and half females) were compared according to a 2 .times. 3 factorial design. Two levels of dietary energy were used: 3400 and 3050 kcal digestible energy (DE)/kg air-dry feed, with diets based on maize and barley, respectively, in combination with soybean meal, so that dietary energy concentration was combined with a cereal source. Three levels of protein were utilized: a normal level, corresponding to the usual recommendations, on the basis of digestible crude protein per Mcal DE (43.5 g up to 50 kg live weight and 39.0 g afterwards) and 2 reduced levels (-25%), with or without supplementary lysine and tryptophan to meet the requirements for primary and secondary limiting amino acids. In all treatments the pigs were individually fed ad lib pelleted diets (5 mm diameter). They were weighed every 2 wk and after slaughter, at 100 kg live weight, backfat measurements were taken and carcasses were evaluated for lean and fat cuts. The daily DE intake was not significantly affected after replacing maize with barley in the diet (7.62 Mcal DE/day vs. 7.26 during the whole growth period, but in castrated males the average daily gain (ADG) was reduced (-12.5%) and feed conversion ratio (FCR) was increased (+11%). In both sexes, carcass adiposity was higher with the barley diets (loin/back fat ratio: 1.81 vs. 2.04; ham + loin: 51.3 vs. 52.9%). The overall reduction of protein level caused a compensatory hyperphagia in pigs fed maize diets (+ 8.5% DE intake/day). With both cereals a reduction in ADG was observed (-5.5 and -7.0% with maize and barley, respectively). This resulted in a deterioration of FCR, which was mostly apparent with maize diets (-16%), and carcass fatness was significantly increased (loin/back fat ratio: 1.62 vs. 2.04 and 1.72 vs. 1.85, with maize and barley diets, respectively. The overconsumption of feed observed in pigs fed maize diets with a low protein level was maintained after supplementing with limiting amino acids, but the effect was less pronounced in females (+2%) than in castrated males (+5.5%). With barley diets a reduction in the content of nonessential N did not seem to affect daily feed intake (7.61 vs. 7.62 Mcal DE per day), ADG (712 vs. 728 g) and carcass characteristics. A differential response according to sex was observed.