Impact of heat stress and a feed supplement on hormonal and inflammatory responses of dairy cows

摘要

The aim of this trial was to evaluate the effects of animmunomodulatory supplement (OmniGen AF, OG;Phibro Animal Health Corp.) and heat stress on hormonal,inflammatory, and immunological responses oflactating dairy cows. Sixty multiparous Holstein cowswere randomly assigned to 4 treatments in a 2 × 2factorial arrangement using 2 environments: cooled usingfans and misters, or noncooled, and 2 top-dressedfeed supplements (56 g/d): OG or a placebo (CTL).Temperature-humidity index averaged 78 during the8-wk trial. Blood was drawn to analyze cortisol, prolactin,and circulating tumor necrosis factor (TNF)-αand IL-10. Peripheral blood mononuclear cells (PBMC)were isolated and stimulated with hydrocortisone, prolactin,or lipopolysaccharide (LPS), individually or inseveral combinations, to assess induced proliferationand cytokine production. At d 52, 6 cows per treatmentwere injected i.v. with an LPS bolus (ivLPS) to assesshormone and cytokine responses. For cooled cows,feeding OG increased plasma cortisol concentrationrelative to CTL. Noncooled cows fed CTL had lowercirculating TNF-α concentrations than noncooled-OGand cooled-CTL cows, with cooled-OG intermediate.Hydrocortisone+LPS-stimulated PBMC from OGcows tended to proliferate more than CTL. Relativeto cooled cows, PBMC from noncooled cows producedmore TNF-α and IL-10 when stimulated with LPS. FollowingivLPS, cooled-OG cows had a greater cortisolresponse than the other treatments. In conclusion, OGsupplementation enhanced cortisol release under basalcondition and induced inflammation with cooling comparedwith CTL. This suggests that heat stress inhibitsOG-mediated cortisol release. Heat stress seemed to enhancethe inflammatory responses of PBMC from lactatingcows. However, OG supplementation promotedPBMC proliferation under stress, or in the presence ofhydrocortisone.