Feeding Chicory-Plantain Silage and/or Se-Yeast Does Not Improve <em>Streptococcus uberis</em>-Induced Subclinical Mastitis in Lactating Sheep

The objective of this study was to evaluate the effects of feeding a combination of chicory-plantain silage and supplementing Se-yeast on the response of early-lactating ewes to induce subclinical mastitis. Polypay ewes were fed either chicory-plantain si-lage or grass silage and supplemented with 3.6 mg Se-yeast /ewe/day for approximately 2 months prior to the intramammary infection (IMI) by infusing Strep. uberis into both glands. The ewes had a typical subclinical mastitis response with an 8-fold in-crease in milk somatic cells within 24h post-IMI, a decrease in milk yield, and changes in all milk components measured. The ewes experienced a mild systemic inflammation post-IMI as determined by an increase in rectal temperature and decrease in feed and water intake and, in blood, by an increase in concentration of ceruloplasmin, hapto-globin, and myeloperoxidase and decrease of paraoxonase, Zn, advanced oxidation protein products, and hematocrit with no effect on pro-inflammatory cytokines. No effect of silage type or Se-supplementation was detected in response to IMI. In sum-mary, the subclinical mastitis model used was effective in mounting an inflammatory response, although this was mild; however, feeding chicory-plantain silage and sup-plementing Se-yeast had no significant effect on the response of ewes to mammary infection.