280 The Effect of Bromocriptine Mesylate and Heat Stress on Innate and Adaptive Immune Function in Beef Cattle

Abstract Injection of bromocriptine mesylate has been used to mimic the symptoms tall fescue toxicosis in beef cattle. Twelve steers (351 ± 11.82 kg) were investigate effect and heat stress on serum prolactin, rectal temperature, respiration rate, innate/adaptive immune function. Steers randomly assigned receive an injection saline (CON) or (BROMO; 0.1mg/kg BW) every three days. Animals housed for 22 d Brody Climatology Laboratory at thermoneutrality (TN; 19.5±0.26°C; 10-d) before transitioning (2-d) (HS; 27.2±0.26°C nighttime, 34.5±0.26°C daytime; 10-d). Cattle fed 1.8% BW (DM-basis) daily across two feedings. Rectal temperatures rates measured 0600, 0900, 1500, 1800 h. Serum plasma harvested from blood collected 1, 9, 21 (9th stress, respectively) analyzed prolactin cytokines. Dry-matter intake was not affected by treatment (P=0.52) temperature (P=0.78). Prolactin concentrations decreased (P=0.02) throughout trial (P< 0.01) with BROMO. rate greater BROMO during TN HS. increased Pro-inflammatory cytokine (TNF-α, IFN-α, IFN-γ, IL-1α, IL-1β, IL-17, IL-18) than CON. Heat pro-inflammatory cytokines exception IL-18 (P=0.98) regardless treatment. Anti-inflammatory (IL-13, IL-1-F5, IL-21, IFN-β, LIF) 0.07) IL-10 (P=0.58). Regardless IL-13, IL-10, LIF 0.05) These results demonstrate that successfully mimicked toxicosis. Innate adaptive responses influenced potentially affecting cattle competency.