Effects of Copper Citrate and Copper Sulfate on Intestinal Health, Muscle Fiber Traits, and Antioxidant Capacity in Weaned Pigs

Copper (Cu) is an essential trace mineral additive in weaned pig diets. Copper citrate (CuCit) and copper sulfate (CuSO4) are common feed additives, yet their tissue-specific effects at different inclusion levels remain unclear. In this study, ninety pigs (six pens per treatment, three pigs per pen) with an initial body weight of 7.71 ± 0.15 kg were randomly assigned to five treatments for 28 d: a basal diet, and the basal diet supplemented with CuCit or CuSO4 at 20 or 100 mg/kg. The results show that CuCit increased slow-twitch fiber proportion in longissimus dorsi muscle (p = 0.009), whereas CuSO4 more markedly upregulated the expression of MyHC I (p = 0.005) and downregulated MyHC IIx (p = 0.006) and MyHC IIb (p = 0.033). Compared with the control group, CuCit and CuSO4 supplementation increased villus height and decreased crypt depth in ileum (p < 0.05). CuCit at 20 mg/kg showed higher ZO-1 expression than CuSO4 at 100 mg/kg (p < 0.05). Furthermore, CuCit showed greater T-SOD (p = 0.018) and CAT activities (p = 0.002) than CuSO4 in muscle, as well as greater T-SOD activity (p = 0.011) and lower MDA content (p = 0.001) in ileal mucosa. These results suggest that CuCit and CuSO4 exhibit different tissue-specific effects in weaned pigs, providing novel insights for precision Cu supplementation.