Is an ovulation-inducing factor (OIF) present in the seminal plasma of rabbits?

The objectives of this study were (1) to determine the effect of rabbit seminal plasma on LH secretion and ovulation using the llama animal model as an in vivo ovulation bioassay and (2) to determine the effect of llama or rabbit seminal plasma on ovulation induction in the rabbit model. In Experiment 1, llamas with a growing follicle ≥8 mm in diameter were assigned randomly to one of three groups (n = 5 per group) and given an intramuscular dose of 1 mL of: (a) llama seminal plasma, (b) rabbit seminal plasma, or (c) phosphate buffered saline (PBS; negative control). Blood samples for LH measurement were taken every 15 min from 1.5 h before to 8 h after treatment (Day 0: starting of treatment). Llamas were examined by ultrasonography every 12 h from treatment to ovulation, and then every other day until Day 16 after treatment to evaluate corpus luteum (CL) development. Blood samples for progesterone measurement were taken every other day from Day 0 to Day 16. Ovulation was detected in 4 of 5, 5 of 5, and 0 of 0 llamas treated with llama or rabbit seminal plasma and PBS, respectively (P < 0.001). After treatment, plasma LH concentration increased and decreased (P < 0.01) in the llama and rabbit seminal plasma group but not in the PBS-treated group. No differences were observed on CL development (P ≥ 0.3) and progesterone secretion (P > 0.05) between both seminal plasma treated groups. In Experiment 2, receptive female rabbits (n = 5–7 per group) were given an intramuscular dose of: (a) 0.5, (b) 1.0 and (c) 2.0 mL of either rabbit or llama seminal plasma, (d) 0.5 mL PBS (negative control), or (e) 25 μg of gonadoreline acetate (GnRH; positive control). Does were submitted to laparotomy 24–36 h after treatment to determine the ovulatory response and the presence of antral and hemorrhagic anovulatory follicles. Ovulation sites (7.0 ± 0.6) were only detected in GnRH-treated does (P < 0.01). There was an increase (P < 0.01), in the total number of follicles (antral plus hemorraghic follicles) in those females treated with 1 mL of rabbit seminal plasma and there was a tendency (P = 0.08) for more hemorrhagic anovulatory follicles in does treated with 1.0 and 2.0 mL of either rabbit or llama seminal plasma. Results document the presence of OIF in the seminal plasma of rabbits. The differential ovulatory response between species, however, requires further investigation.