Collection and transfer of multiple embryos in the mare

A pituitary extract was used to induce multiple ovulations in mares to determine whether day-7 embryos from multiple ovulators were viable as indicated by their ability to develop when transferred to recipients. There were more ovulations/donor for induced multiple-ovulating mares than for control single-ovulating mares (4.6 +/- 0.5 vs 1.0 +/- 0.0; n=14). The embryo collection rate per ovulation was similar for multiple ovulators (0.6 +/- 0.1 embryos/ovulation) and single ovulators (0.7 +/- 0.1). The embryo collection rate per donor, therefore, was higher (P<0.01) for the multiple ovulators (2.9 +/- 0.7 vs 0.7 +/- 0.1). The transfer success rate per embryo at day 21 was different (P<0.05) among recipients which received an embryo from control single-ovulating donors (7 8 ), multiple ovulators from which a single embryo was recovered (2 2 ), and multiple ovulators from which multiple embryos were recovered (9 19 ). The recipient pregnancy rate/donor at day 21 was 88% (7 8 ) for single-ovulating controls and 138% (11 8 ) for induced multiple ovulators. Results indicate that the survivability of day-7 embryos from multiple-ovulating donors was reduced. However, despite the reduced survival rate/embryo, the number of pregnant recipients/donor was increased by induction of multiple ovulations because of the increased number of embryos available for transfer.