Effect of in ovo administration of insulin-like growth factor-I on composition and mechanical properties of chicken bone

The influence of in ovo administration of insulin-like growth factor-I (IGF -I) on long bone growth (tibiae and femora) of 42-d-old broiler chickens wa s investigated. Eggs were divided into three groups: uninjected control, ve hicle-injected control, and recombinant human (rh) IGF-I. Eggs were injecte d once with 100 mu L vehicle (10 mM acetic acid and 0.1% BSA) per embryo or vehicle containing 100 ng rh IGF-I/100 mu L per embryo (n = 555 eggs total ) on Days 1, 2, 3, or 4 of embryonic development. Males had greater bone le ngth and moment of inertia than did females for the tibia and the femur (P less than or equal to 0.01 for all). Although fracture load was significant ly affected by gender (P less than or equal to 0.02 and P less than or equa l to 0.006 for the femur and tibia, respectively), there was no treatment e ffect on these variables. However, when the fracture load was normalized wi th belly weight of the animal, treatment and gender effects were found for femora (P less than or equal to 0.04). Hydroxyproline concentrations of bon es from male broilers were increased by the treatment (P less than or equal to 0.02), whereas it had no effect on female broilers. There was no treatm ent effect on ash content, stiffness, yield load, yield deflection, and ult imate deflection and elastic, plastic, and total work for the femur or the tibia. We suggest that the effect of in ovo administration of IGF-I on bone mechanical properties was site-specific, and treated femora tended to have a lower fracture load relative to increased body weight.