Effect of different dietary protein levels and amino acids supplementation patterns on growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs

BACKGROUND: This study was conducted to determine the effects of different dietary protein levels and amino acids supplementation patterns in low protein diets on the growth performance, carcass characteristics and nitrogen excretion in growing-finishing pigs. Forty-two barrows (25.00 ± 0.39 kg) were randomly assigned to 7 diets. Diet 1: the high crude protein diet with balanced for 10 essential amino acids (EAAs). Diet 2: the medium crude protein diet with 2% (approx) decreased protein level of Diet 1 and balanced 10 EAAs. Diet 3: the low crude protein diet with 4% decreased protein level of Diet 1 and balanced 10 EAAs. The protein levels of Diet 4, 5, 6 and 7 were the same as that of Diet 3. Diet 4 was only balanced for lysine (Lys), methionine (Met), threonine (Thr) and tryptophan (Trp); Diet 5 and 6 were further supplemented with extra isoleucine (Ile) or valine (Val), respectively; Diet 7 was further supplemented with extra Ile + Val. RESULTS: Over the 112 days trial, the reduction of dietary protein by 2% or 4% with balanced10 EAAs significantly decreased nitrogen excretion (P < 0.05), but had no effects on growth performance and carcass characteristics (P > 0.05). In low protein diet, Val supplementation significantly increased body weight gain at 25–50 kg phase (P < 0.05), while Ile supplementation at 75–100 kg phase and 100–125 kg phase significantly reduced the ratio of feed to gain (P < 0.05). No effect of different dietary protein levels and amino acids supplementation patterns in low protein diets on carcass characteristics was observed (P > 0.05). The total N excretion of pigs supplemented with only Lys, Met, Thr and Trp was numerically higher than that of pigs fed with extra Ile, or Val, or Ile + Val diets. CONCLUSION: In low protein diet, Val is more required than Ile in the early growing phage (25–50 kg), while Ile becomes more required in the late growing and finishing phage (75–125 kg). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s40104-019-0381-2) contains supplementary material, which is available to authorized users.