PS1-13. Changes in Serum Immunological Markers in Beef × Dairy Steers in Response to A Liver Abscess Challenge and Pre-Weaning Plane of Nutrition.

Abstract Liver abscesses (LA) continue to be a costly problem for the beef industry with prevalence rates of 50% in beef × dairy cattle. Predictive and diagnostic tools are needed for targeted prevention strategies. However, currently there are no reliable blood-based biological markers of LA. Therefore, a study was conducted to evaluate metabolic and immune markers that have the potential to differ between cattle with and without LA. A secondary objective was to evaluate metabolic and immune markers relative to different pre-weaning planes of nutrition (PON). Steers (n = 43) were randomly assigned to low (LOW; 0.68 kg/d milk replacer; 22% CP, 20% fat, 11.98% milk solids twice daily; ad libitum textured starter, 20.3% CP DM) or moderate (MOD; 0.82 kg/d milk replacer, 26% CP, 20% fat, 14.2% milk solids twice daily; ad libitum textured starter, 25.4% CP DM) PON. Steers were transported to a BSL-2 level facility in the Livestock Issues Research Unit 29 d post-weaning (initial BW = 109 ± 2.2 kg) where they underwent two 3-d acidotic diet cycles (d -5 to -3 and d 2 to 4) and two intraruminal inoculations (d 0 and 6) with Fusobacterium necrophorum subsp. necrophorum (1.5 x 1010 CFU per calf) and Salmonella enterica serovar Lubbock (6.1 x 1010 CFU per calf). Steers were humanely euthanized and necropsy performed on d 27. Blood was collected and serum isolated on d -13, 0, 13, and 27. Complete blood counts were determined on whole blood, and serum samples were analyzed for haptoglobin (Hp) and the D2Dx immunity test to assess immune health. Data were analyzed using the MIXED procedure of SAS specific for repeated measures, with steer as the experimental unit. There was no difference in LA prevalence between LOW and MOD steers (57.1 vs. 63.6, respectively; P = 0.67). There was a tendency (P = 0.07) for red blood cell counts to be greater in steers without a LA than with a LA. Additionally, red blood cells, hemoglobin, hematocrit, platelets, white blood cells, including lymphocytes, were greater in MOD than LOW steers. Serum Hp concentrations were not affected by LA or PON (P ≥ 0.18). However, D2Dx immunity test values were greater (P = 0.04) in steers with LA than without. Additionally, LOW steers had greater (P = 0.05) D2Dx values than MOD steers. Greater D2Dx values indicate greater immune activity/inflammation. These data indicate that the D2Dx immunity test may be a valuable tool to identify cattle with liver abscess. Further, differences in immune status are evident in steers fed a LOW pre-weaning PON, which may affect responses to later health challenges. However, additional studies should be conducted in cattle with naturally occurring liver abscesses outside of a challenge model.