Newcastle disease virus (NDV) produces both gross and histopathologic changes in tissues and organs of infected birds. These lesions may cause increase or decrease in organ sizes especially lymphoid organs leading to immune suppression. Therefore, the effect of a velogenic NDV on the body and organ weights of vaccinated Shika brown (SB) cocks was studied. Forty SB cocks consisting of twenty control and twenty infected cocks were slaughtered at the age of thirty-two weeks after infection with a velogenic NDV. They were weighed before being sacrificed and their internal organs (liver, spleen, thymus, heart, bursa of Fabricius, brain and adrenal glands) were removed and weighed. Sections of these organs were taken and stored in Bouinâ€™s solution for 24 h and later sent for histology. The liver, spleen, thymus, heart and adrenal glands of the infected red SB cocks were heavier than those of the control red and white Shika brown cocks and infected white SB cocks. The weight of the spleen and brain of both the control and infected red and white cocks did not vary significantly (P>0.05). The infected red cocks had heavier adrenal glands, heart and liver weight than the control red and infected white cocks. The spleen and brain body weight ratio was similar for both control and infected red and white cocks. The control white cocks had the least thymus body weight ratio. The control white cocks had a higher bursa body weight ratio than the infected red and white cocks and the control red cocks. Only one infected white cock showed perivascular infiltration of lymphocytes and foci of glial cells. The increase in organ weights was seen mostly in the infected red cocks. It is recommended that chickens be routinely vaccinated against Newcastle disease to prevent atrophy of the bursa of Fabricius.
body weight, Newcastle disease, organ weight, Shika brown cocks, vaccination