The effect of peri-conception nutrition on embryo quality in the superovulated ewe.

Evidence indicates that oocyte/embryo quality in the sheep is affected by nutrient status during the cycle of conception. This study aimed to determine, in the superovulated ewe, if there are stages during the peri-conception period (-18 days to +6 days relative to the day of ovulation [Day 0]) when quality is more likely to be influenced by nutrition. In Experiment 1, ewes were provided with either a 0.5 x maintenance (L), 1.0 x maintenance (M) or 1.5 x maintenance (H) diet (in terms of daily energy requirements) during the peri-conception period. Diet did not affect the mean ovulation rate (range: 15.4+/-1.47 to 16.1+/-1.55) nor the mean number of embryos collected per ewe (range: 10.9+/-2.05 to 12.4+/-1.82) but there was an increase (P<0.05) in the mean number of cells per blastocyst in the L diet (74.7+/-1.45) compared with either the M (66.4+/-1.29) or H (62.0+/-0.84) diets. This increase was due to an increase in the number of trophectoderm (Tr) cells, resulting in a shift (P<0.05) in the Tr:inner cell mass (ICM) cell ratio (range 0.69+/-0.03 to 0.73+/-0.04). In Experiment 2, six diets (HHH, MHH, MHL, MLH, MLL and LLL) were imposed during three 6-day periods commencing 12 days before and continuing until 6 days after ovulation. Although diet had minimal effect on the superovulatory response, both the mean number of cells per blastocyst and the Tr:ICM ratio were increased (P<0.05) when the L diet was provided after Day 0 (diets MHL, MLL and LLL). It is concluded that the ewe is able to respond to acute changes in nutrition imposed immediately after ovulation, resulting in changes in embryo development including cell lineage differentiation. The significance of these findings, in terms of fetal development, embryo-maternal signalling and the nutritional management of the ewe is discussed.