Effects of different levels of dietary crude protein on growth performance, blood profiles, nutrient digestibility, pork quality and odor emission in growing-finishing pigs.

This experiment investigated the effects of varying dietary crude protein (CP) levels on growth performance, blood profiles, nutrient digestibility, pork quality, and odor emission in growing-finishing pigs. A total of 210 growing ([Yorkshire × Landrace] × Duroc) pigs (39.93 ± 0.080 kg body weight [BW]) were assigned to 1 of 6 treatments with 5 replicates of 7 pigs per pen. Diets with different CP levels (%) for early growing, late growing, early finishing, and late finishing phases, respectively, were as follows: CP1411: 14, 13, 12, 11; CP1512: 15, 14, 13, 12; CP1613: 16, 15, 14, 13; CP1714: 17, 16, 15, 14; CP1815: 18, 17, 16, 15; CP1916: 19, 18, 17, 16. Overall average daily gain decreased with increased dietary CP (linear, p < 0.01), while average daily feed intake increased during the late finishing period (linear, p < 0.01). Final BW increased as dietary CP decreased (linear, p < 0.01). Total protein concentration increased with higher CP levels at the 7^th, 11^th, and 13^th weeks (linear, p = 0.02; p < 0.01; p < 0.01; respectively). Lower CP levels decreased creatinine concentration at the 4^th and 13^th weeks (linear, p = 0.03; p < 0.01; respectively). Blood urea nitrogen and urea concentrations decreased with lower CP (linear, p < 0.01). Emissions of ammonia, amine, mercaptan, and hydrogen sulfide decreased with lower CP (linear, p < 0.01; respectively). Excreted nitrogen in urine increased with higher CP (linear, p < 0.01). No significant differences were observed in carcass characteristics, pH, or pork color among treatments. Reducing CP levels in the diet did not negatively impact growth performance and improved protein metabolism, reducing odor emissions from feces and urine in growing-finishing pigs.