A Possible Mechanism for Double-Yolked Eggs in the Early Stage of Egg-Laying in Zhedong White Goose–Function of IGF1 and LHR Signaling

SIMPLE SUMMARY: The reason that birds produce double-yolked eggs is not clear. However, double-they often occur in the early egg-laying stage. We detected and recorded the proportion of double-yolked eggs, the number of abdominal follicles, and the changes of key ovulation-related genes in Zhedong white geese. We proposed that, in the first egg-laying stage of geese, high plasma concentrations of insulin like growth factor 1 (IGF1) stimulate the development of pre-hierarchal follicles, causing more than one follicle to be selected at the same time, to mature at the same rate under the same gonadotrophin milieu, and to ovulate at the same time to produce double-yolked eggs. ABSTRACT: The cause of double-yolk (DY) egg production in birds is unclear, but it is related to body weight and adiposity. We explored the causes of the high proportion (up to 26%) of DY eggs in the first clutch of Zhedong white geese. We recorded the egg production of Zhedong white geese during the first egg-laying cycle and counted the proportion of DY eggs. We found that 30% of geese had 3 sets of double or triple follicles of the same diameter in the abdomen, which was close to the DY egg rate. In addition, the mRNA expression levels of the steroidogenic acute regulatory protein (StAR) and luteinizing hormone receptor (LHR) genes in granulosa cells were similar within the same set of follicles. Furthermore, the IGF1 concentration in geese that had at least 3 sets of follicles of the same diameter was significantly higher than that in birds with 0–1 set of follicles of the same diameter. Thus, we proposed that, in the first egg-laying stage of geese, high plasma concentrations of IGF1 stimulate the development of pre-hierarchal follicles and cause more than one follicle to be selected at the same time, mature at the same rate under the same gonadotrophin milieu, and ovulate at the same time to produce DY eggs.