In separate experiments, elevation of donor ewe plasma urea levels and IVC of embryos in serum have been associated with occurrence of large offspring syndrome (LOS). Fetuses displaying LOS also have abnormal expression of the imprinted gene IGF2R. The present study, therefore, examined the effect of variation in donor ewe nitrogen metabolism and embryo culture on fetal development. Zygote-donor ewes were offered a diet with either a 0% (LN) or 3% urea supplement (HN) for two weeks during which superovulation and artificial insemination (AI) took place. Zygotes were recovered 36 h after AI and cultured for 5 days in synthetic oviductal fluid (SOF) to which either steer serum (10%; SOFS) or albumin (0.4%; SOFA) was added. In vivo control (C) blastocysts were recovered (Day 5) from superovulated ewes offered diet LN. All embryos were transferred singly to recipient ewes; fetal tissues were recovered and snap-frozen at Day 125 of gestation. IGF2R expression was measured by semi-quantitative PCR in fetal heart and kidney and expressed as the ratio to 18S mRNA. Data were analyzed by ANOVA with donor ewe plasma urea-N prior to (preUN) and mean plasma urea-N during (meanUN) feeding as covariates. Correlation analysis was used to test relationships between variables. Heart IGF2R expression (see Table 1) was lower in SOFA than in SOFS fetuses (P = 0.003; preUN, P = 0.007), while kidney IGF2R expression was lower in HN than in LN fetuses (P = 0.04; preUN, P = 0.015; meanUN, P = 0.032). Overall the range of both heart and kidney IGF2R expression was greater for fetuses from cultured (1st/3rd quartiles; heart, 0.87–1.05; kidney, 0.77–1.10) than from C embryos (heart, 1.03–1.16; kidney, 0.84–1.00). In IVC fetuses, heart IGF2R expression was negatively associated with fetal body (r = -0.31; P = 0.003) and heart weight (r = -0.35; P = 0.008) whereas kidney IGF2R expression was not associated (r = -0.23; P = 0.089) with fetal body weight and not related to kidney weight. Heart and kidney IGF2R expression were only weakly associated (r = 0.26; P = 0.054). In conclusion, changes in IGF2R expression in both fetal heart and kidney were associated with donor ewe N status and IVC conditions. In this study, decreases in heart IGF2R expression were reflected in increased heart weight, but kidney IGF2R expression was not related to kidney weight.

This study was funded by Defra.