Relationship between egg productivity and insulin-like growth factor-I genotypes in Korean Native Ogol chickens

Endocrine factors, such as steroid hormones and growth factors, regulate egg productivity in terms of the quantity of egg production, egg weight, sexual maturity, and the number of small yellow follicles (SYF). Insulin-like growth factors (IGF) are involved in the regulation of ovulation rate and ovarian follicular development in chickens, and a relationship between IGF-I genotype and egg weight has been reported. However, the effect of IGF on egg productivity in Korean Native Ogol chickens (KNOC) has been little studied. Therefore, this study was conducted to identify the relationship among endocrine factors (IGF-I, IGF-II, estradiol, and progesterone), IGF-I genotypes, and egg productivity. Frequencies of IGF-I genotypes (AA, AB, BB) were 17.3, 26.9, and 55.8%, respectively, within a population. When compared with the IGF-I genotypes, the AB genotype had the highest serum levels of estradiol and progesterone at 40 and 30 wk of age, respectively; the highest IGF-II concentration in F1 follicles at 60 wk; and was positively associated with the number of SYF at 60 wk. The results showed that the A allele was associated with a higher IGF-II expression in the follicles and stimulated the development of follicles, indicating a positive association of the A allele with egg production and the number of SYF. Therefore, these results suggest that there is a possibility of IGF-I genotypes acting as a genetic marker for egg productivity of KNOC.