Objective: To compare the effect of a single parenteral injection of tilmicosin with that of a single dose of a long-acting oxytetracycline as treatment in the early stages of naturally acquired undifferentiated respiratory tract disease in young dairy calves.
Design: Prospective clinical trial, randomized block design.
Animals: 40 dairy calves.
Procedures: 78 calves from 5 farms were examined weekly until 3 months old. When respiratory tract disease was diagnosed by a veterinarian, the calf was assigned to 1 or 2 treatment groups. Transtracheal wash samples were acquired to characterize the pathogens. The veterinarian, who was unaware of treatment assignments, examined calves for 3 days after treatment and evaluated severity, using a scoring system. Growth rates were measured.
Results: On the basis of response to initial treatment, relapse rates, and effect on growth rates, the antibiotics were determined to be equally effective. Severity of clinical disease was significantly (P < 0.03) less for the tilmicosin-treated calves on days 2 and 3 after treatment. Findings from analysis of transtracheal wash samples indicated Pasteurella multocida (25/40), P haemolytica (4/40), Haemophilus somnus (4/40), Actinomyces pyogenes (3/40), and Aspergillus sp (2/40). Mycoplasma was isolated in association with bacterial isolates in 22 calves.
Clinical implications: Tilmicosin and oxytetracycline are effective in treatment of respiratory tract disease in young calves, even when Mycoplasma spp are involved. Tilmicosin is more effective in resolving clinical signs. Early treatment of dairy calves with respiratory tract disease may decrease detrimental effects on growth.