Effects of trace metal supplement form on production performance, antioxidant status, and mammary tissues during repeated intramammary challenges

Mastitis negatively alters milk composition, partly due to oxidative damage to the mammary secretory epithelium. Trace metals are important cofactors involved in oxidative balance and immune function. However, trace metal absorption is affected by its supplement form. The objective of this study was to evaluate milk composition and indicators of oxidative balance in cows supplemented with sulfate or methionine hydroxy analog chelates of Zn, Cu, and Mn at isometal levels during sterile mastitis. A total of 36 mid-lactation multiparous Holstein cows were used. Cows received either (1) sulfate-bound trace metals and intramammary infusions of saline (SULF-CON; n = 9), (2) sulfate-bound trace metals and intramammary infusions of formalin-fixed Staphylococcus aureus (SULF-CHAL; n = 12), or (3) methionine hydroxy analog chelates of Zn, Cu, and Mn and intramammary infusions of formalin-fixed Staph. aureus (MTX-CHAL; n = 12). The study lasted 6 wk, and cows were repeatedly intramammarily infused every 3 d during the final 2 wk to elicit chronic mastitis. Milk yields and components were measured at each milking (twice daily) throughout the challenge period. Blood samples were collected during the final challenge, and mammary tissue biopsies were performed at the end of the study. Milk yields and DMI were similar between treatments. Milk SCS was markedly increased in the MTX-CHAL and SULF-CHAL cows in response to challenge. Milk lactose content decreased in MTX-CHAL and SULF-CHAL cows but tended to be greater in MTX-CHAL cows. The plasma ferric reducing antioxidant power values of SULF-CHAL cows were lower than SULF-CON, whereas the values of MTX-CHAL cows were intermediate. Histological evaluation of mammary tissue structure and markers of lipid peroxidation did not differ between treatments. Results indicate that repeated infusions of formalin-fixed Staph. aureus negatively affected milk composition, and that trace mineral supplement form may better maintain antioxidant status and some markers of epithelial barrier competency during mastitis.