Embryo Dysplasia in Obese Broiler Breeders Reduces Hatchability: Comparison of High and Low Abdominal Fat Lines

Hatchability is a key indicator of reproductive performance in broiler breeders. Obesity in broiler breeder hens results in a significant reduction in hatchability. Maternal obesity can impair embryonic development in mammals. However, whether maternal obesity reduces hatchability by compromising embryonic development remains unclear in birds. This study used the hens from 24th generation of the Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF), along with their corresponding hatching eggs. Hatchability, embryo malposition rate, embryo malformation rate, and embryonic development profiles were compared between the two lines. The results showed that hatchability of the fat line was significantly lower than that of the lean line (72.39% vs. 63.64%, P < 0.05), whereas embryonic malposition (20.64% vs. 26.59%, P = 0.049) and malformation rates (0.27% vs. 7.29%, P < 0.001) were significantly higher in the fat line. Further analysis showed that embryos from the fat line were developmentally delayed compared with those from the lean line at stages HH2, HH9, HH24, HH40, and HH43. The present study generates embryonic development profiles for genetically fat and lean broilers, highlighting that maternal obesity in poultry reduces hatchability by inducing embryonic malposition, malformation, and stage-specific developmental delay. These findings provide embryological insights into the causes of obesity-induced decline in hatchability.