Pregnancy rates were evaluated at 15 days and pregnancy loss between 15 and 60 days on 430 embryo transfers (ET) in Mangalarga Marchador mares. Pregnancy diagnosis was performed between 15 and 60 days after ET. To evaluate the effects of the duration of the follicular phase of the recipient mare, three groups were formed: up to 3 days (<3d); 4 to 6 days (4-6d); 7 or more days (>7d). To evaluate the effects of the size of the pre-ovulatory follicle of the recipient mare, three other groups were formed: below or equal to 35mm (Ø<35); greater than 35 and below or equal to 45mm (35<Ø<45); greater than 45mm (Ø>45). The groups were compared by Chi-square test (P<0.05). Regarding the duration of the follicular phase, pregnancy rates were similar (<3d - 83.1%; 4-6d - 86.4%; >7d - 86.0%), and greater pregnancy loss in >7d (24.4%) than in <3d (12.0%) and 4-6d (13.3%), which were similar. Regarding the follicle size, pregnancy rates (Ø<35 - 86.4%; 35<Ø<45 - 86.5%; Ø>45 - 81.9%) and pregnancy loss (Ø<35 - 13.2%; 35<Ø<45 - 18.1%; Ø>45 - 10.5%) were similar. Reasons for the greatest pregnancy loss in the >7d group have not been elucidated, but we conclude that the duration of the follicular phase may be a factor for choosing recipient mares.
equine; embryo transfer; recipient mare; cyclical characteristics; pregnancy loss
