The objective of this study was to evaluate the efficiency of cyclic and acyclic progesterone-treated recipient mares in a commercial embryo transfer program. Acyclic recipients were treated with decreasing amounts of estradiol cypionate (ECP® - Pfizer Saúde Animal, São Paulo, Brazil), followed by 1500 mg of a sustained-release progesterone injection (P4LA150® - Laboratórios B.E.T., Rio de Janeiro, Brazil). Out of all 1506 embryo recovery attempts performed, 59.36% were positive (894/1506). Pregnancy rates of cyclic and acyclic mares were, respectively, 44.12% (319/723) and 57.68% (139/241) - higher in acyclic recipients under progesterone treatment. Embryo loss was similar between groups (9.72% 31/319 vs. 11.51% - 16/139). When fertility data on acyclic mares treated with long-action progesterone were grouped in relation to the interval of the beginning of the treatment with progesterone to the embryo transfer, there was no difference in pregnancy rates at 12 days (51.28% - 20/39; 58.92% - 33/56; 60.52% - 46/76 and 58.57% - 41/70 for embryos transferred 3 (P3), 4 (P4), 5 (P5) and 6 (P6) days after the beginning of the treatment with progesterone). Groups P3, P4, P5 and P6 showed embryo loss rates of 20.00% (4/20), 12.12% (4/33), 2.17% (1/46) and 17.07% (7/41), respectively. These rates were similar in groups P3, P4 and P6. Pregnant recipients submitted to an embryo transferring procedure on P5 showed lower embryo mortality rates than on P3 and P6. P4 recipients tended to suffer higher embryo mortality rates than P5. Acyclic recipient mares under progesterone treatment can be satisfactoryly used in embryo transfer programs.
embryo loss; embryo transfer; mare; pregnancy
