Efficacy of Gamithromycin Injectable Solution for the Treatment of Mycoplasma bovis Induced Pneumonia in Cattle

Forty colostrum-deprived, cross-bred beef calves, including males and females 3 to 8 months of age, were procured and transported to the test facility 6 days before initiation of the study. On Day -2, each calf received 60 mL of challenge material by endobronchial infusion. Calves were randomly assigned to either Group 1 (saline at 2.0 mL/50 kg body weight by subcutaneous injection) or Group 2 (gamithromycin 6.0 mg/ kg [2.0 mL/50 kg body weight] by subcutaneous injection). Clinical assessments of depression scores, respiratory character scores, and rectal temperatures were conducted daily from Day -2 (prior to challenge) through Day 10. Calves were humanely euthanized and necropsy examinations were conducted on Day 10. Lungs were harvested and scored according to the percentage of pneumonic tissue. Each lung lobe was palpated and the percentage consolidation on the dorsal and ventral surface of each lung lobe was estimated and recorded. Calves treated with gamithromycin 6 mg/kg had lower mean depression scores, respiratory scores, and rectal temperatures than control calves from Day 1 through Day 10. On several posttreatment days, between-treatment differences were significant (P≤0.05). Treatment with gamithromycin also significantly reduced lung consolidation scores compared to untreated controls. Adverse reactions attributable to treatment were not observed from any calf treated with gamithromycin. It was concluded that a single subcutaneous injection of gamithromycin at 6 mg/kg body weight was effective in treating clinical pneumonia induced in young calves by endobronchial challenge with M. bovis.