Effect of Serum IGF-I on Progesterone Concentration during Early Pregnancy in Korean Native Cattle (Hanwoo)

Insulin-like growth factor-I (IGF-I) is a polypeptide that has the function of regulating the expression of steroid hormones through endocrine, paracrine, and autocrine actions in reproductive organs. Moreover, IGF-I is involved in ovulation, implantation, maintenance of pregnancy, and development of fetuses in animals. Therefore, this study was conducted to investigate the effects of serum IGF-I concentration on progesterone ($P_4$) concentration and pregnancy rates in Korean native cattle (Hanwoo). Blood was collected at estrus (Day 0) and Day 11. Artificial insemination was performed at Day 0. Serum IGF-I and $P_4$ concentrations were measured by radioimmunoassay (RIA). Overall, $P_4$ concentration was higher at Day 11 than Day 0, whereas the pattern of IGF-I concentration was reversed. When animals were divided into two groups depending on the pregnancy status, $P_4$ concentrations of the pregnant group was significantly higher than that of the non-pregnant group at Day 0 (p