Impact of chronic heat stress in broiler breeders on egg quality, hatchability, and day old chick quality.

Acute and chronic heat stress are critical stress factors in broiler breeder management. Acute heat stress not only can negatively impact maternal reproduction performance, but also their offspring's health and quality, whereas effects of chronic heat stress remains poorly understood. The aim of this study was to investigate effects of chronic mild maternal heat stress on egg quality, embryo development, and day-old chick quality. Broiler breeder hens (n = 144) were randomly assigned to either thermal neutral (20°C; TN) temperature or heat stress (32°C; HS) continuously for 8 weeks with 6 replicate pens per treatment. The HS treatment resulted from week 4 onward in lower egg weight, yolk weight, albumen weight and height, and eggshell thickness (all P < 0.05). Egg weight throughout incubation was lower in the HS treatment, but fertility ( P = 0.28) and hatchability of fertile eggs ( P = 0.32) did not differ between treatments. Physical chick quality at hatch did not differ ( P > 0.05) between treatments. However, at day 18 of incubation, chicks from the HS group had lower yolk-free body mass (YFBM) and breast muscle weight than the TN group. At pulling, they showed lower body weight, residual yolk sac weight, ileum weight, and higher liver weight (all P < 0.05) compared to the TN group. These results suggest that heat stress in broiler breeders not only negatively affects egg quality, but also has negative carryover effects on embryo development and day-old chick characteristics.