THE VIRULENCE OF MYCOPLASMA GALLISEPTICUM INFECTIONS USING THAI ISOLATES IN BROILER CHICKENS

Abstract

Ninety 1-day-old-female broiler chickens were divided into groups as follows. Thirty birds were randomly selected to be bled from jugular vein for MG antibody assay and swabed at choanal cleft for MG DNA using PCR. The remaining birds were divided into 3 groups, 2 replicates in each group and 10 birds in each replicate. Group 1 was a sham negative control. Group 2, 3 received MG Thai isolates and MG S6 strains, respectively. All birds were injected into the left thoracic airsac, with 0.1 ml of broth or MG cultured broth (106 CFU). Each group was raised in a wire cage in separate isolation rooms. Clinical signs, death, feed conversion rates, and profits (Baht) were observed during 1 - 21 days. Dead birds were necropsied and swabbed from the left thoracic airsac for MG DNA by PCR and E. coli culture. At 21 days, all living birds were necropsied to determine the gross airsac and microscopical, tracheal lesion scores and simultaneously swabbed from the left thoracic airsac for MG DNA by PCR and E. coli culture. The results revealed that the number of birds that showed clinical signs, the number of that died, and the profits were significantly worse in group 2 than those in groups 1 and 3 (p<0.05) and the mean
microscopic tracheal lesion score was significantly worse in group 2 than that of group 3 (p<0.05). The mean gross airsac lesion scores of groups 2 and 3 were significantly higher than those of group 1 (p<0.05). MG PCR was only found in post infection in groups 2 and 3. No growth of E. coli was found in any groups.