Uterine environment and early embryonic development in sheep

Uterine restriction during gestation can result in the birth of lambs that are smaller than those born from an unrestricted environment. The objective of this study was to examine whether this effect is present during the early embryonic period. Pure-breed embryos were transferred within and reciprocally between genotypically large (Suffolk: S) and small (Cheviot: C) sheep to establish four groups; SinS (Suffolk embryos in Suffolk dams), SinC (Suffolk embryos in Cheviot dams), CinS (Cheviot embryos in Suffolk dams) and CinC (Cheviot embryos in Cheviot dams). At Day 19, SinS embryos were longer (13.4 ± 0.53 mm) than SinC embryos (11.0 ± 0.57 mm; p < 0.05), whereas CinS embryos were longer (15.2 ± 0.68 mm) than CinC embryos (12.9 ± 0.53 mm; p < 0.05). There were fewer (p < 0.05) binucleate cells in SinC trophoblasts than SinS, and binucleate cells were larger (p < 0.05) in CinS than CinC trophoblasts. This study suggests that uterine environment regulates the development of embryos very early in gestation, when the physical capacity of uterus is not a developmental constraint, possibly via alteration in trophoblast binucleate cell number and structure.