Effects of feeding growing-finishing pigs with low crude protein diets on growth performance, carcass characteristics, meat quality and nutrient digestibility in different areas of China

Two experiments were conducted to assess the effects of reducing dietary crude protein (CP) within 3 percentage units, and crystalline amino acids (CAA) supplementation on growth performance, carcass characteristics, meat quality, and nutrient digestibility in growing-finishing pigs of northern and southern China. In Exp. 1, 288 pigs (initial BW 29.18 ± 1.47 kg; 24 pigs per pen; 6 pens per treatment) in northern China were randomly assigned to 1 of 2 diets: a high-CP (HP) or low-CP (LP) diet with 17% vs. 15%, 16% vs. 14%, and 15% vs. 13% CP for the growing phase (30–60 kg), growing-finishing phase (60–80 kg), and finishing phase (80–110 kg), respectively. In growing-finishing phase, pigs fed LP diet showed lower (P < 0.05) ADG, G:F and apparent total tract digestibility (ATTD) of dry matter (DM), gross energy (GE) and CP than that those pigs fed HP diet. However, in finishing phase, pigs fed LP diet showed greater (P < 0.05) beneficial impacts on ADG and ADFI than pigs fed HP diet. Notably, no influence on carcass characteristics and meat quality due to dietary CP levels was observed. In Exp. 2, 378 pigs (initial BW 24.96 ± 2.39 kg; 21 pigs per pen; 6 pens per treatment) in southern China were randomly assigned to 1 of 3 dietary treatments: the HP, LP, and LP diets supplemented with 0.10% N-carbamylglutamate (NCG) (LPG) diets. The HP and LP diets maintained same CP levels as Exp. 1 in the growing phase (25–60 kg), growing-finishing phase (60–90 kg), and finishing phase (90–110 kg), while different at the source of ingredients. Interestingly, pigs fed the HP, LP and LPG diets showed no difference on the growth performance, as well as the carcass characteristics, and meat quality, whereas lower concentration of serum urea nitrogen (UN) were observed in pigs fed LP and LPG diets than those pigs fed HP diets (P < 0.05). The values for ATTD of DM and GE that pigs fed the LPG diets were greater (P < 0.05) than the estimates of pigs fed LP diets in growing and growing-finishing phase, and no significant difference was observed in finishing phase. Additionally, pigs fed the LPG diets showed higher (P < 0.01) concentration of serum β-alanine and arginine, and tended (P = 0.09) to increase the loin-eye area of pigs compared with other groups. Taken together, the application of LP diets was affected by growth phase and environment, and NCG supplementation in LP diets may be a good choice to improve the nutrient digestibility and carcass characteristics of pigs.