| Abstract: | Estradiol and progesterone concentrations were evaluated from diestrous embryo transfer recipient mares (5 to 14 days post-ovulation) which were treated with an exogenous hormone regimen. Upon detection of the donor mare's ovulation (0 hours), 10 mg PGF2α was given to the recipient mare; at 12, 24 and 36 hours 20 mg estradiol cypionate; at 48 hours, 500 mg progesterone in oil and then 22 mg altrenogest at 60, 72 and 96 hours. Altrenogest (22 mg/day) was continued until end of the trial (detection of a fetal heart beat). Embryos were transferred non-surgically 6 or 7 days after the start of treatment.Plasma samples were evaluated over three periods; period 1-between recipient mare ovulation and prior to PGF2α period 2-between PGF and embryo transfer and period 3-post-transfer. During periods 2 and 3, estradiol was higher (P<.05) for mares which were 10 to 14 days post-ovulation (late diestrous) as compared to mares which were 5 to 9 days post ovulation (mid-diestrous) when treatment began. Progesterone concentrations were higher (P<.05) for the mid-diestrous mares in the same periods. The pregnancy rate was higher for the late diestrous mares than the mid-diestrous mares (58% (7/12) vs 10% (1/10)). However, no difference (P>.05) was detected in estradiol or progesterone in the late diestrous mares which were pregnant or open. During period 2, estradiol was higher (P<.05) in the pregnant than open mares. Whereas, during period 3, progesterone was higher (P<.05) in the open mares.These data suggest that estradiol is important for the establishment of pregnancy in the mare. Furthermore, hormone treatment developed in this study appears to have some potential in synchronization of diestrus mares to be used as embryo recipients. |
