Effects of trace metal supplement form on markers of epithelial barrier competency during repeated intramammary challenges

Mastitis negatively affects milk composition, partly due to damage to mammary secretory epithelium. Trace metals are important cofactors for oxidative balance, immune cell function, and maintaining epithelial integrity. The objective of this study was to evaluate blood and milk indices of epithelial barrier integrity in cows supplemented with sulfate or methionine hydroxy analog chelate 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 composition was assessed at each milking throughout the challenge period, and blood composition was evaluated during the final challenge. The MTX-CHAL and SULF-CHAL cows had increased milk lactate and plasma lactose content. Milk concentrations of Na, S, and Mg increased, whereas Zn, Mn, P, and Fe decreased throughout the challenge period in MTX-CHAL and SULF-CHAL cows. Plasma concentrations of Zn, P, Fe, and Mg decreased during the final challenge in MTX-CHAL and SULF-CHAL cows. Results indicate that repeated infusions of formalin-fixed Staph. aureus did compromise epithelial barrier integrity; however, trace metal supplement form had minimal effect on indices of epithelial function.