Dietary Protein Levels Modulate the Antioxidant Capacity during Different Growth Stages in Huanjiang Mini-Pigs

Adequate crude protein (CP) levels in diets play potential roles in swine production. This study determined the impacts of different CP levels on the antioxidant capacity of pigs during different body weight (BW) stages. Three hundred and sixty Huanjiang mini-pigs were allocated to one of three independent experiments, including a 5–10 kg BW group, where CP levels included 14%, 16%, 18%, 20%, and 22%; a 10–20 kg BW group, where CP levels included 12%, 14%, 16%, 18%, and 20%; and a 20–30 kg BW group, where CP levels included 10%, 12%, 14%, 16%, and 18%. These independent experiments were conducted for 28, 28, and 26 days, respectively. Results showed that the 20% CP level increased (p < 0.05) the plasma CAT and GSH-Px activities and the GSH concentration of pigs than in the pigs supplemented with the 14–18% CP levels, and the 20% CP level up-regulated (p < 0.05) the ileal oxidative stress-related gene expression levels of pigs than in the pigs supplemented with the 14% CP level at the 5–10 kg BW. In addition, diets supplemented with 18% CP level increased (p < 0.05) the ileal GSH concentration of pigs than in the pigs supplemented with the 14% and 20% CP levels, and the 16–18% CP levels increased (p < 0.05) the jejunal SOD activity of pigs than in the pigs supplemented with the 14% CP level. At 10–20 kg BW, the 16% CP level presented the strongest jejunal and ileal antioxidant capacity, the 18% CP level had the lowest plasma concentrations of MDA and highest GSH, and the 14–16% CP levels increased the plasma CAT and SOD activities (p < 0.05). Moreover, the 16–20% CP levels up-regulated (p < 0.05) the oxidative stress-related gene expression levels. At 20–30 kg BW, diets supplemented with the 16% CP level increased the plasma CAT activity of pigs than in the pigs supplemented with the 12–14% CP levels, and the 14–16% CP levels decreased the MDA concentration compared with the 10% CP levels (p < 0.05). In conclusion, these findings indicate adequate CP levels of 20%, 16%, and 14% for Huanjiang mini-pigs at the 5–10, 10–20, and 20–30 kg BW stages, respectively.