Experimental reduction of eggshell conductance during incubation. I. effect on the susceptibility to ascites syndrome

Two hundred-four fertile broiler chicken eggs were obtained from a commercial source and divided into three equal groups. On day 1 of incubation, 68 eggs were selected randomly and four strips of vinyl tape were applied to the shell below the air cell (tape-day 1) to reduce eggshell conductance. This procedure was repeated with an additional group of 68 eggs on day 14 (tape-day 14). Sixty-eight eggs were incubated without treatment, as controls. One week after hatch, 20 chickens from each treatment group and control group were placed into a hypobaric chamber (simulated altitude of 2500 m) for 5 weeks. The remaining chickens in each group were maintained under normobaric conditions. The hematocrit and the mean frontal resultant electrical vector (MRV) of the heart were measured following 1 week, 3 weeks, and 5 weeks of hypobaric or normobaric exposure. Surviving chickens were euthanized at the end of 5 weeks. The weight ratio of right ventricle to left ventricle plus septum (the hypertrophy index [HI]) and the cardiac index, the HI divided by body weight, were determined. All mortality during the study was subjectively scored for the presence of ascites syndrome lesions. The percentage of chickens dying during, or exhibiting ascites syndrome at the completion of, the 5-week hypobaric exposure was 16.7%, 66.7%, and 58% for control, tape-day 1, and tape-day 14 treatments, respectively. MRV values of birds following hypobaric exposure were significantly different between treatment and control groups of the hypobaric exposure and between the two tape treatments. These results suggest that reducing conductance of the eggshell during incubation significantly potentiates the development of ascites syndrome in the broiler chicken.