Interactive effects of zinc and copper sources and phytase on growth performance, mineral digestibility, bone mineral concentrations, oxidative status, and gut morphology in nursery pigs

This study investigated the interactive effects of zinc (Zn) and copper (Cu) sources and phytase on growth performance, oxidative status, mineral digestibility, tissue mineral concentrations, and gut morphology in nursery pigs. A total of 288 weaning barrows [body weight (BW) = 5.71 +/- 0.81 kg], blocked by initial BW, were randomly allotted to one of eight dietary treatments, with nine pens per treatment and four pigs per pen. The eight dietary treatments were arranged in 2 x 2 x 2 factorial design, with two Zn sources [2,000, 2,000, and 100 mg/kg Zn from zinc oxide (ZnO) during phase 1 (days 1-14) and phase 2 (days 15-28), and phase 3 (days 29-42), respectively; 100 mg/kg Zn from zinc methionine hydroxy analogue chelate (Zn-MHAC) from phases 1 to 3], two Cu sources [150, 80, and 80 mg/kg Cu from copper sulfate (CuSO4) or copper methionine hydroxy analogue chelate (Cu- MHAC) during phases 1-3, respectively], and two phytase inclusion levels (0 or 500 FTU/kg). Results showed that ZnO supplementation at 2,000 mg/kg Zn significantly increased average daily feed intake (ADFI; P = 0.01) and average daily gain (ADG; P = 0.03) during phase 1 compared to Zn-MHAC group; however, Zn-MHAC supplementation tended (P = 0.06) to improve gain to feed ratio (G: F) during phase 2 compared to ZnO group. There were no differences (P > 0.10) between ZnO and Zn-MHAC groups in terms of ADG, ADFI, and G:F during the entire nursery period. Compared with CuSO4, Cu-MHAC tended to increase ADG (P = 0.07) and G:F (P = 0.08) during the entire nursery period. Phytase supplementation significantly increased ADG (P < 0.01), ADFI (P < 0.01), and G: F (P < 0.01) during the entire nursery period compared with no phytase supplementation. There was a significant interaction (P < 0.01) between Zn source and phytase on standardized total tract digestibility (STTD) of phosphorus (P), whereas there was no interaction (P = 0.21) between Cu sources and phytase on STTD of P. However, there was a significant interaction between Cu sources and phytase on calcium (Ca; P = 0.02) and P (P = 0.03) concentrations in metacarpal bones and G:F in phase 2 (P = 0.09). Furthermore, pigs fed diets containing Zn-MHAC tended to have lower ileum villus width (P = 0.07), compared with those fed diets containing ZnO, and pigs fed diets containing Cu-MHAC tended to have lower plasma malondialdehyde concentration (P = 0.10) compared with those fed diets containing CuSO4. In conclusion, under the conditions of the current study, ZnO supplementation at 2,000 mg/kg Zn was only effective in the first 2 wk postweaning, whereas Zn-MHAC supplementation at 100 mg/kg Zn could achieve better feed efficiency during phase 2 compared to pharmacological levels of ZnO, therefore, leading to no difference of growth performance in the entire nursery period. Low levels of Zn-MHAC may improve phytase efficacy on degrading phytate P compared to pharmacological levels of ZnO. Cu-MHAC may be more effective to promote growth compared to CuSO4, which may be partially driven by reduced oxidative stress. Results also indicated that Cu-MHAC might exert a synergistic effect with phytase on improving feed efficiency and bone mineralization.