Response of dairy cows supplemented with antioxidants and/or chelated trace minerals to intra-mammary bacterial challenge

Abstract Text: The effects of chelated trace minerals (TM) of Zn, Cu, and Mn (MINTREX®, Novus International, St. Charles, MO) and dietary antioxidant (AGRADO® Plus, Novus International) supplementation on responses to experimental mastitis in lactating cows were evaluated. Sixty cows were blocked by parity, expected date of parturition, and initial BW. Cows were individually fed a basal diet formulated according to NRC (2001) from d -39.3 ± 4.6 prepartum until d 38 postpartum. Treatments were top-dressed as: 1) Negative control – no TM nor antioxidant (NEG), 2) TM provided with 100% sulfates without antioxidant (ITM), 3) TM provided with 100% sulfates with antioxidant (ITMAOX), 4) TM provided 50% of sulfates and 50% of chelated TM without antioxidant (OTM), and 5) TM provided 50% of sulfates and 50% of chelated TM with antioxidant (OTMAOX). Treatments were iso-mineral except NEG; all were iso-methionine. Animals were vaccinated against Escherichia coli (Enviracor J-5, Pfizer Animal Health) at drying-off, -27.3 ± 4.6, and 14 d from parturition, and against rabies (IMRAB, Merial) at parturition. On d28 after calving, the right front quarter of each animal was infused with 1.74 x 10⁴ CFU of E. coli P4:O32 diluted in 5 mL of sterile PBS and the contralateral quarter with the same volume of sterile PBS. Blood and milk samples were collected regularly during the experiment. Primiparous had higher rabies titers concentrations on d14 compared to multiparous cows, but no difference between parities on d28 (parity x time, P<0.001). OTMAOX showed the highest rabies titer concentrations compared to other treatments on d14 (treatment x time, P=0.04). Higher milk yield was observed for the first 3 days post-infusion in primiparous compared to multiparous cows (parity x time, P<0.05). Escherichia coli CFU were higher in infected quarters of multiparous cows (parity x quarter, P=0.03). Milk SCC were higher in AOX and OTMAOX in response to challenge than in other treatments (treatment, P=0.01). Additionally, SCC in primiparous peaked earlier and higher compared to multiparous cows (parity x time, P=0.004). Blood GSH:GSSG peaked at 48 h post-infusion (P=0.01). Blood GSH:GSSG in OTMAOX was highest in primiparous, but lowest in multiparous cows (P<0.05). Antibody titer and SCC recruitment results suggest OTMAOX may have improved some aspects of peripartal immune function. Additionally, the earlier and elevated milk SCC in primiparous cows may have limited the severity of E. coli infection, thereby allowing for increased DMI and milk production.

Keywords: Escherichia coli, mastitis, supplementation