Haptoglobin response to clinical respiratory tract disease in feedlot cattle.

OBJECTIVE: To quantify haptoglobin response to respiratory tract disease in feedlot cattle, and to investigate its ability to predict disease outcome and response to antibiotic treatment. DESIGN: Randomized clinical trial. ANIMALS: 60 feedlot calves with clinical respiratory tract disease. PROCEDURE: Calves were randomly assigned to receive a standard antibiotic treatment regimen (TRT), or to observation pens without antibiotic treatment. Serum haptoglobin concentration was measured at initial and final examinations. Calves were examined for presence of gross pulmonary lesions at slaughter. RESULTS: Mean +/- SD serum haptoglobin concentration at initial examination was 67 +/- 108 mg/dl, with range of 0 to 508 mg/dl. Haptoglobin concentration at initial examination was similar for the TRT group and the group that did not receive antibiotic treatment, but at final examination, TRT-group calves had lower (P < 0.01) mean values. Calves receiving antibiotic treatment had haptoglobin concentration at or near zero at final examination. Calves not receiving antibiotic treatment had only slightly lower mean haptoglobin concentration at final examination, compared with initial examination. Within treatment groups, haptoglobin concentration was similar for cases with different outcomes. Calves with gross pulmonary lesions at slaughter had numerically higher, although statistically similar, haptoglobin concentrations at initial examination, compared with calves without lesions. CONCLUSIONS: Feedlot cattle with clinical respiratory tract disease have a large and variable haptoglobin response. Antibiotic treatment resulted in lower serum haptoglobin values, although low values were not required for full clinical recovery. CLINICAL RELEVANCE: Serum haptoglobin concentration may be an indicator of response to antibiotic therapy, although it appears to be unrelated to case severity or need for treatment.