PS12-2. Lipopolysaccharide (LPS) Challenge Alters Oxidative Stress Markers in Dairy-beef Breeds.

Abstract The objective of this study was to evaluate dairy cross-breeding influence on oxidative stress incurred when subjected to a lipopolysaccharide (LPS) challenge. Steers (n = 30; 194 kg ± 40 kg) were transported to the USDA- Livestock Issues Research Unit where they were housed in individual pens with ad libitum access to a receiving ration and water. Breed differences were established as crossbred beef steers (NAT; n = 9), Charolais × Jersey crossbred steers (CHAR; n = 10), and Holstein × Angus crossbred steers (HOL; n = 11). Steers were fitted with jugular catheters and indwelling rectal thermometers on d -1. On d 0, steers were challenged i.v. with LPS (0.15 μg/kg BW) and blood samples were collected at -2, 0, 1, 2, 4, 6, 8, 12, 24, 36, and 48 h relative to administration of LPS. Blood was further processed for plasma and analyzed for lipid oxidation via thiobarbituric reactive substance (TBARS) and total antioxidant capacity (TAC). Data were analyzed as a repeated measure using the GLIMMIX procedure of SAS. There was a breed effect on malondialdehye (MDA) concentrations via TBARS (P = 0.05), where concentrations were lowest in NAT steers when compared to HOL (P = 0.02) and CHAR (P = 0.06). There was a main effect of time on MDA (P < 0.001), where concentrations reached their lowest at 2 h post-challenge, but increased after 4 h (P < 0.001), where concentrations were then similar from 6 h until 36 h (P ≥ 0.05). From 36 to 48 h post-challenge, concentrations decrease again to levels similar to those at h 2 (P ≥ 0.12). An interaction occurred between breed type and time for TAC (P = 0.03). By 6 h, CHAR had the greatest TAC compared to NAT (P = 0.03) and HOL (P = 0.06). This continued to 8 h, where CHAR had a greater TAC compared to NAT (P = 0.04). These data suggest that breed type may influence the ability to manage oxidative stress during an immune challenge, which can have further impacts on feedlot performance, management practices, and meat quality as terminal breeds.