High eggshell temperatures during incubation decrease growth performance and increase the incidence of ascites in broiler chickens

High eggshell temperatures (EST; >= 38.9 degrees C) during the second half of incubation are known to decrease the body and organ development of broiler hatchlings. In particular; relative heart weights are decreased by a high EST, and this may increase the incidence of metabolic disorders that are associated with cardiovascular development, such as ascites. The current study investigated the effects of a high EST on chick quality, subsequent performance; and the incidence of ascites later in life. Eggs were incubated at a normal (37.8 degrees C) or high (38.9 degrees C) EST from d 7 of incubation onward. After hatching, the chickens were housed per EST in pens; and a normal or cold temperature schedule was applied during the grow-out period. Hatchability, hatchling quality, BW, feed conversion ratio, total mortality, mortality associated with ascites, slaughter characteristics, and ascites susceptibility at 6 wk of age were evaluated. Except for total ventricle weight, no interaction was found between EST and the grow-out temperature. Hatchability was comparable between the EST treatments, but the percentage of second-grade chickens was 0.7% higher at the high EST. Yolk-free body mass was 3.0 g lower, and heart weights were 26% lower at hatch in the high compared with the normal EST treatment. Body weight continued to be less during the grow-out period after the high EST incubation. However, breast meat yield was 1.0% higher in the high than in the normal EST. Feed conversion ratio did not differ between EST treatments. Total mortality was 4.1% higher and mortality associated with ascites was 3.8% higher in the high compared with the normal EST treatment. The ratio between the right and total ventricle was 1.1% higher in the high compared with the normal EST treatment at slaughter age. In conclusion; a high EST from d 7 of incubation onward decreased hatchling quality and growth performance; but increased breast meat yield. Furthermore, high EST incubation increased the incidence of ascites, which may be related to the reduced heart development at hatch.