The high prolificacy sheep group (HP, n = 3, litter size = 3) and low prolificacy sheep group (LP, n = 3, litter size = 1) were selected from the nucleus herds of Hu sheep at Taizhou Sheep Industry according to their littering records (three consecutive lambing records) and polymorphism analysis of FecB [17 (link)], two groups of sheep in this study had similar numbers of dominant follicles and FecB genotype. All sheep were housed under the same conditions with free access to feed and water. Synchronous estrus of sheep was conducted according to previously described [18 (link)]. The estrous cycles of the ewes were adjusted by intravaginal progestagen sponges (30 mg; Ningbo Sansheng pharmaceutical Co., LTD, Zhejiang, China) for 11 days. Estrus was monitored by presentation of a buck fitted with an apron three times one day following sponge removal. The sheep were deeply anesthetized by intravenous administration of 3% pentobarbital sodium (30 mg/kg; Solarbio, P8410, China), and sacrificed by exsanguination in a healthy physiological stages at the second estrus (natural estrous), and endometrium was collected from the mid-part of uterine horns, and immediately frozen in liquid nitrogen for RNA extraction.
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