Investigation of virginiamycin to improve health of growing and finishing steers: I. Effects on ruminal acidosis and liver health*

Objective

Our objective was to observe the effects of the interrelationship among virginiamycin (VM) inclusion (240 mg/d), ruminal pH dynamics, and hepatic plasma metabolites on rumen and animal health during a 150-d feeding trial.

Materials and Methods

Steers (304 ± 27 kg; n = 120) were assigned randomly 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). All animals were orally administered 2 indwelling rumen pH and temperature recording boli on d 0 and 84. Blood samples were collected via jugular venipuncture on d −7, 28, 56, 84, 112, and 140, and plasma was analyzed for concentrations of albumin, alkaline phosphatase, direct bilirubin, total bilirubin, gamma-glutamyl transferase, and total protein using an automated blood analyzer. Concurrently, haptoglobin (HPT) was measured following a colorimetric method based on peroxidase activity. A random coefficients model with pen and animals within treatment as a random effect was used.

Results and Discussion

Animals that received VM for the first 100 d (T₁₁₀ and T₁₁₁) had greater mean ruminal pH during d 50 to 100 when compared with animals that did not receive VM (T₀₀₀ and T₀₀₁; 6.12 vs. 6.00, respectively). Moreover, T₁₁₁ tended to have less time under pH 5.8 (3.01 h/d) when compared with T₁₀₀ and T₀₀₁ (5.83 and 6.45 h/d, respectively). At slaughter, overall, 3.36% of cattle in the study were identified with liver abscesses (A and A−), and 24.3% had lung lesions. Plasma metabolite concentrations before slaughter did not predict the presence of liver abscesses (P ≥ 0.182). Based on acute phase responses, HPT was notably lower on d 84 after diet transition in VM-treated animals (46.1 vs. 68.9 mg/L). Additionally, VM inclusion boosted indicators of overall health with greater alkaline phosphatase levels and albumin-toglobulin ratios.

Implications and Applications

Virginiamycin has practical implications for rumen health and overall cattle health, where supplementation during the whole growing to finishing phases was more effective in capturing its full potential.