Effect of Surgical Removal of the Residual Yolk Sac on the Development of the Digestive System and Immune Response in Broiler Chicks during Early Days Post-hatch

This study was designed to investigate the effects of the residual yolk-sac on the development of the digestive system and immune response of broiler chicks. Two experiments were conducted in this study. In the first one, 60 day-old broiler chicks (Lohmann) were allocated into three experimental groups according to the status of the residual yolk sac; deutectomized (surgicallyremoved residual yolk sac), sham operated and intact chicks. Five chicks from each experimental groups were randomly selected at days 2, 4, 6 and 8, weighed, euthanized and the different parts of their digestive tract and liver were weighed. The body weight of deutectomizd chicks at day 2, 4 and 6 post-hatch was significantly (P<0.05) lower compared to that of sham operated and intact chicks. At day 8, the body weights of all experimental groups did not significantly (P<0.05) differ from each other. The liver weight in deutectomizd chicks was significantly (P<0.05) lower at days 2, 4 and 6 post-hatch compared to that of the other experimental groups. At day 8 the liver weights in the different experimental groups did not show any significant difference. The weights of the different parts of the digestive tract (crop, gizzard, provenriculus, intestine), somehow, in deutectomizd chicks were significantly (P<0.05) lower at day 2, 4 and 6 compared to that of sham operated and intact ones. In the second experiment, 60 day-old broiler chicks (Lohmann) were allocated to the above mentioned experimental groups; 20 chicks per each. Thereafter, they were challenged with 10% sheep RBC suspension at day 2 and day 12 post-hatch. Ten chicks were randomly selected from each experimental group at day 12 and day 20 post-hatching, killed and their lymphoid organs (spleen, thymus and bursa of fabricius) were incised and sera were harvested from blood samples. The lymphoid organs were significantly (P<0.05) lower in deutectomized chicks compared to the two other experimental groups. The geometric mean titers (GMT) of antibodies against 10% sheep RBC suspension for primary and secondary immune responses in deutectomized chicks, were lower than that of sham operated and intact chicks. The results of this study revealed that the residual yolk sac is essential for the development of the digestive system and immune response in broiler chicks.