57 Evaluation of Virginiamycin Inclusion in the Diets of Feedlot Steers: Interplay between Rumen pH and Liver Health

Abstract

Abstract In the beef cattle system, liver abscesses are the most common liver abnormality and are the leading cause for condemnations at slaughter. Virginiamycin (VM) has been used to prevent sub-acute ruminal acidosis (SARA) and subsequently control liver abscess incidence. This study observed the interrelationship between VM inclusion (240 mg/hd/d), ruminal pH dynamics, and hepatic blood metabolites over a 150-d feeding trial. Housed in a Calan gate system, 120 Angus crossbred steers (291 ± 28 kg) were randomly assigned to 1 of 6 dietary treatments: no VM (T000); VM for the last 50 d (T001); VM for the last 100 d (T011); VM for the first 50 d (T100); VM for the first 100 d (T110); and VM for 150 d (T111). Steers were orally administered 2 indwelling smaXtec rumen pH and temperature recording boluses on d -4 and d 84. On d -7, 28, 56, 84, 112 and 140, blood samples were collected via jugular venipuncture and all plasma samples were analyzed for concentrations of albumin, alkaline phosphatase, direct bilirubin, total bilirubin, gamma-glutamyl transferase, and total protein using an automated blood analyzer (Carysta High Volume Chemistry Analyzer; Zoetis). Haptoglobin (HPT) was measured following a colorimetric method based on peroxidase activity. Data were analyzed using a random coefficients model with the pen as a random effect and animals within treatment as the subject. Results indicated that VM did not convalesce hepatic function (P > 0.05), but HPT had increased concentrations on d 84 for VM excluded treatments (42.75 vs. 93.25 mg/L). Comparatively, T111 tended to have less time under pH 5.8 (2.50 h/d) when compared with T001, T100, and T000 (5.27; 4.94; and 4.23 h/d, respectively; P = 0.107). Therefore, VM should be fed from the growing phase to slaughter to capture the full potential of the product on animal health status.