EFFICACY OF TILMICOSIN IN THE CONTROL OF EXPERIMENTAL MYCOPLASMA-GALLISEPTICUM INFECTION IN CHICKENS

This study was conducted to evaluate the efficacy of 5-day, ''in water '' tilmicosin medication for the prevention of experimental Mycoplasma gallisepticum (MG) disease in 10-day-old specific-pathogen-free (SPF) chickens. Birds were inoculated intratracheally and into the sinus wi th the MG R-P10 strain. A limited dose titration of the antibiotic ove r the expected effective range was included, using six groups of GO bi rds each: UI: uninfected untreated group; IUT: infected untreated grou p; IT1 to IT4: four infected treated groups, which were administered 5 0, 100, 200, or 300 mg/liter of tilmicosin. The birds were given tilmi cosin from 8 to 13 days of age and were inoculated at 10 days of age. The birds were observed for 11 days postchallenge before terminal post mortem examination was completed including, assessment of lesions and sampling for mycoplasma culture and serology. Body-weight gains of the different groups were compared. The results showed that tilmicosin me dication at dose levels of 50-300 mg/liter significantly decreased gro wth losses and respiratory signs due to MG infection (P < 0.05). Signi ficant reduction in air sac and peritonitis lesions were obtained by t reatment with 100, 200 or 300 mg/liter for 5 days (P < 0.05). A signif icant reduction in the proportion of MG-culture-positive birds was obt ained at a dose level of 50 mg/liter (P < 0.05). Increasing the dose r esulted in a further decrease in the number of MG shedding chickens to the extent that with the two highest doses of tilmicosin, no bird was serologically positive on day 21, compared to 46/58 positively infect ed untreated birds (day 21).