Effects of Genetic Line, Dietary Calcium and Non-Phytate Phosphorus and Age on Body Composition and Tibia Ash of Broiler Breeder Hens and their Progeny Determined by Dual-Energy X-ray Absorptiometry

Background and Objective: Body composition of broiler breeder hens changes dynamically throughout the rearing and laying periods, with alterations in lean tissue, fat and mineral reserves supporting growth and egg production. Broiler breeders utilize dietary calcium (Ca) and phosphorus (P) for eggshell formation, egg production and maintenance of skeletal integrity. However, limited information is available regarding the effects of dietary Ca and non-phytate phosphorus (NPP) on body mineral dynamics in broiler breeder purelines and their progeny. Therefore, this study evaluated the effects of genetic line, dietary Ca and NPP and age on body composition and tibia ash of broiler breeder hens and their progeny using dual-energy X-ray absorptiometry (DEXA). Materials and Methods: A total of 960 pureline broiler breeder hens, comprising 240 hens from each of four purelines (A, B, C and D), were fed six experimental diets containing increasing Ca concentrations in 0.25% increments, ranging from 2.25 to 3.25% Ca with 0.25% NPP, or 3.25% Ca with 0.40% NPP. These diets provided approximately 3.08 to 4.45 g Ca and either 340 or 550 mg NPP/hen/d at peak allocation. Ninety-six hens, comprising 24 hens per pureline and four hens per diet, were scanned using DEXA at 4-week intervals from 21 to 51 weeks of age. Progeny from the four purelines were scanned at hatch and 14 d of age. Body mineral content, fat mass, lean tissue mass and tibia ash were evaluated. Results: Pureline, dietary treatment and age significantly affected body mineral content, fat mass, lean tissue mass and tibia ash of the broiler breeder hens (p≤0.0003). Line C hens had the highest body mineral content (134 g; 3.8% of body mass), tibia ash (59.8%) and fat mass (726 g), whereas line A hens had the lowest body mineral content (99 g; 2.9%) and tibia ash (56.9%). Absolute body mineral content was lowest at 21 weeks of age, before sexual maturity and remained relatively stable thereafter. In contrast, body mineral content expressed as a percentage of body mass decreased from 3.8 to 2.9% as fat and lean tissue accumulated. Mineralization of the progeny followed the same line-specific ranking observed in the dams. At 14 days of age, progeny from line C dams had the highest body mineral proportion (2.72%), whereas progeny from line A dams had the lowest (2.45%; p<0.0001). Increasing dietary NPP from 340 to 550 mg/hen/d did not increase body mineral content or tibia ash in the pureline hens. Conclusion: Genetic line and age substantially influenced body composition and skeletal mineralization of broiler breeder hens and their progeny, whereas increasing dietary NPP within the tested range did not increase body mineral content or tibia ash. The consistent line-specific ranking of mineralization between breeder hens and their progeny suggests a genetic contribution to mineral utilization and deposition. These findings, together with companion studies demonstrating similar line differences in eggshell quality and progeny mineral utilization, indicate that genetic line should be considered when evaluating mineral requirements and skeletal development in broiler breeder populations.