The project was carried out to study the effect of Mycoplasma gallisepticarn infection in chemically immuno-suppressed and normal broiler chicks by recording weight gain, calculating feed conversion ratio, detecting the immune response against Newcastle disease virus (NDV) vaccine and observing the pathological changes in lungs at gross and histopathological levels.

For this study 180 day-old broiler chicks were purchased. The birds were divided into three equal groups i.e. A, B and C having two replicates in each group. The birds of group A were subjected to immunosupression using cyclophosphamide and challenged with M. gallisepticum at day 14 of age. The birds of group B were not immuno-suppressed and only challenged with M. gallisepticum at the same day while the group C was kept as control. Weight gain and feed conversion ratio was studied at day 14 of age before inoculation and at days 24, 34 and 44 of age after the inoculation. The blood and lungs samples from each group were also collected at day 14 of age before inoculation and at days 24, 34 and 44 of age after the inoculation for detection of immune response against NDV vaccine and for observing the pathological alterations, respectively.

Lowest weight gain was recorded in birds of group A which was both immuno-suppressed as well as infected with M. gallispecticum (PcO.05) amongst the three treatment groups.

Similarly, feed conversion ratio of the group A was significantly lower (P
Geometric mean haemagglutination inhibition (GMHI) titers against NDV vaccine of immunosupressed and M. gallisepticum infected birds was lower than those of M. gallisepticum infected and control birds.

Gross pathological findings of the lungs of infected birds revealed congestion, consolidated spots, haemorrhages and accumulation of frothy material. The bronchi of the infected birds showed caseous exudates. Histopathological changes in lungs of infected birds depicted odema, hyperplasia of alveolar walls with massive mononuclear cell infiltration. This mononuclear cell infiltration was also seen in alveoli of infected lungs. However, these gross and histopathological changes were more severe in group A (immunosuppressed and M. gallisepticum infected) than that of group B (M. gallisepticum infected). No such gross or histopathological changes were observed in the control group C which was neither immunosuppressed nor infected with M. gallisepticurn.