Influence of recombinant bovine interferon gamma and dexamethasone on pneumonia attributable to Haemophilus somnus in calves

Yu-Wei Chiang From the Department of Veterinary Microbiology and Preventive Medicine, (Chiang, Roth) and the Veterinary Diagnostic Laboratory (Andrews), College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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James A. Roth From the Department of Veterinary Microbiology and Preventive Medicine, (Chiang, Roth) and the Veterinary Diagnostic Laboratory (Andrews), College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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John J. Andrews From the Department of Veterinary Microbiology and Preventive Medicine, (Chiang, Roth) and the Veterinary Diagnostic Laboratory (Andrews), College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Summary

The influence of recombinant bovine interferon gamma (rBoIFN-gamma) treatment on resistance of clinically normal and dexamethasone-treated calves to Haemophilus somnus infection was evaluated. Four groups of 6 calves each were treated with saline solution (controls), dexamethasone (0.04 mg/kg of body weight/for 3 days), rBoIFN-gamma (2 μg/kg for 2 days), or dexamethasone and rBoIFN-gamma (aforementioned dosages). All treatments were started 24 hours before intrabronchial challenge exposure with 5 × 109 colony-forming units of H somnus. Rectal temperature and WBC count were monitored daily. Two of the dexamethasone-treated calves died of pneumonia 4 days after challenge exposure and were necropsied. All other calves were euthanatized and necropsied 7 days after challenge exposure. All calves had pneumonia of variable intensity. Dexamethasone-treated calves had increased volume of pneumonic lung (P < 0.05) and increased severity of pneumonia, compared with control calves. Recombinant bovine interferon gamma treatment resulted in reduction in pneumonic lung volume and severity of pneumonia in dexamethasone-treated calves (P < 0.05), although it did not influence severity of pneumonia in nondexamethasone-treated calves.

Summary

The influence of recombinant bovine interferon gamma (rBoIFN-gamma) treatment on resistance of clinically normal and dexamethasone-treated calves to Haemophilus somnus infection was evaluated. Four groups of 6 calves each were treated with saline solution (controls), dexamethasone (0.04 mg/kg of body weight/for 3 days), rBoIFN-gamma (2 μg/kg for 2 days), or dexamethasone and rBoIFN-gamma (aforementioned dosages). All treatments were started 24 hours before intrabronchial challenge exposure with 5 × 109 colony-forming units of H somnus. Rectal temperature and WBC count were monitored daily. Two of the dexamethasone-treated calves died of pneumonia 4 days after challenge exposure and were necropsied. All other calves were euthanatized and necropsied 7 days after challenge exposure. All calves had pneumonia of variable intensity. Dexamethasone-treated calves had increased volume of pneumonic lung (P < 0.05) and increased severity of pneumonia, compared with control calves. Recombinant bovine interferon gamma treatment resulted in reduction in pneumonic lung volume and severity of pneumonia in dexamethasone-treated calves (P < 0.05), although it did not influence severity of pneumonia in nondexamethasone-treated calves.

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