Developmental changes in serum insulin-like growth factor-I and insulin-like growth factor binding proteins in the turkey embryo

The ontogeny of insulin-like growth factor-I (IGF-I) and ontogeny as well as the molecular nature of the insulin-like growth factor binding proteins (IGFBP) as they relate to embryogenesis and posthatch growth in the turkey have not been reported. In this study, serum samples were harvested from turkey embryos incubated under shell-less and shelled conditions from Day 12 to 28 of incubation. Samples from 3, 6, and 8 wk posthatch were also evaluated. Significant changes in serum IGF-I in shelled embryos were observed in that IGF-I was low in early incubation, peaked at mid-incubation, and returned to levels equivalent to early incubation at hatching. No mid-embryogenesis (Days 14 to 18) increase in serum IGF-I was noted in the shell-less cultures. Embryo weights diverge at Day 18 of incubation, with shell-less embryos being significantly lighter than their age-matched shelled embryos, suggesting a possible relationship between total circulating IGF-I and body weight gain. Three distinct IGFBP were identified in serum from turkey embryos, exhibiting molecular weights of 27, 29, and 69 kDa. During embryonic development, the 29 kDa IGFBP appeared to be the predominant species, with levels peaking on Day 24 of incubation, and being minimally detectable at hatching. Ontogeny of the 29 kDa IGFBP was similar in the shelled and shell-less embryos. The 69-kDa IGFBP-Like protein did not appear in the circulation until late in embryogenesis, Day 22 in shell-less and Day 26 in shelled embryos. The 27-kDa IGFBP appeared in late incubation. Similar IGFBP (28, 30, and 69 kDa) were observed in the growing male turkey. The 69-kDa protein did not vary across ages studied, whereas the 28-kDa IGFBP appeared to increase with age. This is the first report describing serum IGF-I and IGFBP in the developing turkey. Turkey IGFBP appear to be regulated by independent events during incubation and posthatch growth.