Biostimulation with the ram effect increases the follicle recruitment, ovulatory diameter, and embryo viability rate in superovulated ewes.

The aim of this study was to compare the preovulatory follicular development and superovulatory outcomes in superovulated ewes which were either stimulated or not stimulated by placement with rams. The treatment regimen to super-stimulate ovarian follicular development was imposed to 28 ewes on "Day 0", from which 14 were stimulated with active rams for 48 h, starting at the time of the fifth FSH dose, with the ram being removed from the pen with the ewes and replaced which other ram every 12 h, using four different rams (group GRE). The other 14 ewes remained isolated from rams throughout the protocol (group GCON). All ewes were administered 133 mg of FSH, into six doses in decreasing quantities, every 12 h. The follicular development and number of ovulations were determined using ultrasonography. Biostimulation resulted in an increased number of large follicles, follicle diameter, and embryo viability rate (viable embryos/recovered structures∗100) was greater in ewes of the GRE than GCON group. The number of corpora lutea, follicular cysts, recovered structures, viable embryos, and degenerated and unfertilized structures was similar in ewes of the GRE and GCON group. Structures were recovered from more GRE than GCON ewes. In conclusion, biostimulation with rams during the last phase of the treatment regimen to induce superovulation enhanced the follicular growth and increased the embryo viability rate in ewes.