PSI-1 Effects of Pre-Transit Diets and Road Transportation on Plasma, Salivary Cortisol, and Rumen Environment of Beef Heifers

Abstract Increased salivary cortisol in cattle may be detrimental to rumen bacterial diversity. Effects of transportation and diet before transportation on plasma and salivary cortisol and on rumen conditions of 20 ruminal-cannulated heifers (346 ± 16 kg BW) were evaluated. Heifers were fed ad libitum 40% Sorghum Sudan grass hay and 60% commercial pellet (64% TDN, 12.4% CP, DM basis) for 13 d before study initiation. Heifers were randomly assigned to a 2 × 2 factorial arrangement of 8-h transportation (TR) vs. no transportation (NT) and 100% Sorghum Sudan grass hay (HAY) vs. 30% hay and 70% pellets (H+P) fed ad libitum for 3 d before transportation. All groups were fasted during the 8-h transit period. Upon feedlot arrival at 8 h, cattle were fasted an additional 4 h. At 12 h, cattle were fed 30% wheat hay and 70% commercial feed (69% TDN, 16.6% CP, DM basis). Blood and ruminal fluid were sampled at 0, 8, 12, 24, 28 and 72 h. No diet × transport interactions were observed for any variable. Plasma cortisol was decreased for HAY vs. H+P heifers at 72 h (P < 0.05, diet × hour). Rumen pH and total volatile fatty acid concentrations did not differ between groups. Molar percentages of acetate increased, molar percentages of propionate decreased, and acetate-to-propionate ratios increased at 0 and 12 h for HAY compared to H+P (P < 0.05, diet × hour). At 0 h, molar percentages of butyrate were less for HAY vs. H+P (P < 0.05, diet × hour). Bacterial phyla richness was decreased for NT/HAY compared to NT/H+P and was increased for TR/HAY compared to TR/H+P heifers (P < 0.05, diet × transport). Proteobacteria relative abundances were less at 0 h for heifers fed HAY vs H+P (P < 0.05, diet × hour). Genera evenness was increased at 8 h for TR compared to NT cattle (P < 0.05, transport × hour). Genera Shannon-wiener indices were greater at 0 and 8 h for cattle consuming HAY compared to H+P (P < 0.05, diet × hour). Genera richness was increased at 0 h for cattle fed HAY compared to H+P (P < 0.05, diet × hour). Prevotella relative abundances were less for cattle fed HAY compared to H+P at 0 and 8 h (P < 0.05, diet × hour). In summary, due to negligible response to transportation, salivary cortisol effect on bacteria population and diversity were presumably minimal.