There was a decline in the peripheral progesterone concentrations with increasing ration. The pregnancy rate in ewes fed a high ration was significantly reduced when compared with those of ewes fed a medium or low ration (48% vs 68 and 67% respectively; P < 0\m=.\05). In ewes fed the high ration exogenous progesterone increased the pregnancy rate from 48 to 76% (P < 0\m=.\01).Progesterone treatment did not influence pregnancy rates in ewes fed medium or low rations. The number of fetuses per ewe pregnant was not influenced by level of nutrition or progesterone treatment.
Embryos were collected from ewes on Day 6 after estrus (Day 0 = estrus), placed in M2 culture medium, and assigned to 1 of 4 treatment groups. Some embryos were transferred to recipient ewes on Day 6 of their estrous cycle either in pairs (group 1) or singularly (group 2) within 3 h of collection. The remaining embryos were individually cultured for 48 h in an atmosphere of 5% CO2 in humidified air in either synthetic oviduct fluid (SOF) medium (group 3) or SOF containing 1,000 U/ml of recombinant human leukemia inhibitory factor (hLIF) (SOF + hLIF: group 4). These embryos were then transferred to recipient ewes on Day 8 of their estrous cycle. The addition of hLIF to culture medium significantly improved the development of the embryos compared with control embryos prior to transfer (blastocysts hatching from the zona pellucida: group 3 = 16% vs. group 4 = 64%, p less than 0.05; those degenerative: group 3 = 27% vs. group 4 = 9%, p less than 0.05) and the subsequent pregnancy rates of the recipient ewes, receiving a single embryo, at Day 70 of pregnancy (group 3 = 16% vs. group 4 = 50%, p less than 0.05). The pregnancy rate of ewes given embryos cultured for 48 h in SOF + hLIF prior to transfer (50%; group 4) was similar to the group 2 ewes receiving a single embryo soon after collection (52%), but the pregnancy rate for both groups was significantly lower than that for the group 1 ewes receiving two embryos soon after collection (89%: 53% twins, 36% singles; p less than 0.05).
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