Effect of altrenogest on pregnancy maintenance in unsynchronized equine embryo recipients

Non-surgical embryo recovery attempts were done on Day 7 after ovulation. Embryo recovery rate from mares of varied reproductive histories was 57% (38/67). Non-surgical transfer of these embryos into altrenogest-treated recipient mares that ovulated between 3 days before and 3 days after the donor resulted in a 30-day pregnancy rate of 77% (10/13). Transfer of embryos into altrenogest-treated recipients that ovulated between 4 days before and 6 days after the donor resulted in an overall pregnancy rate of 64% (16/25) at Day 30 of gestation. No recipients that were in oestrus at the start of treatment, nor recipients that ovulated 5 or more days before the donor, maintained pregnancy. Mean plasma progesterone concentrations of pregnant, altrenogest-treated, embryo-recipient mares; pregnant, altrenogest-treated, untransferred mares; and pregnant, untreated, untransferred mares were comparable (P greater than 0.05). Treatment of embryo-recipient mares with altrenogest appears to be beneficial in extending the degree of donor-recipient synchrony required for successful embryo transfer. Altrenogest treatment also seems to be conductive to pregnancy maintenance in recipients experiencing luteal dysfunction.