Comparative analyses of laying performance and follicular development characteristics between fat and lean broiler lines

The deposition of high levels of fat in broiler breeder hens can have a profound impact on fol-licular development and laying performance. This study was formulated with the goal of comparing egg produc-tion and follicular development characteristics at differ-ent laying stages in the Northeast Agricultural University broiler lines divergently selected for abdomi-nal fat content (NEAUHLF). The egg production was analyzed using the birds from the 19th to 24th genera-tions of NEAUHLF; the follicular development charac-teristics were analyzed by hematoxylin-eosin staining and quantitative real-time polymerase chain reaction using the birds from the 24th generation of NEAUHLF. The results showed that the age at first egg of lean hens was significantly earlier than that of fat hens in this study. While no significant differences in total egg out-put from the first egg to 50 wk of age were noted when comparing these 2 chicken lines, lean hens laid more eggs from the first egg to 35 wk of age relative to fat hens, whereas fat hens laid more eggs from wk 36 to 42 and 43 to 50 relative to their lean counterparts. No dif-ferences in ovarian morphology and small yellow follicle (SYF) histological characteristics were noted when com-paring these 2 chicken lines at 27 wk of age. At 35 and 52 wk of age, however, lean hens exhibited significantly lower ovarian weight, ovarian proportion values, num-bers of hierarchical follicles, hierarchical follicle weight, and SYF granulosa layer thickness as compared to fat hens, together with a significant increase in the number of prehierarchical follicles relative to those in fat hens. Gene expression analyses suggested that follicle selection was impaired in the fat hens in the early laying stage, whereas both follicle selection and maturation were impaired in the lean hens in the middle and late laying stages. Overall, these data highlight that fat deposition in broiler hens can have a range of effects on follicular development and egg production that are laying stage -dependent.