|dc.description.abstract||Three experiments were designed to gain an understanding of the role of ovulation-inducing factor (OIF) present in bovine seminal plasma. Within species, seminal plasma was pooled from 1 to 4 ejaculates per male (n=160 bulls, n=4 llamas in Experiments 1 and 2, and n=95 bulls in Experiment 3). The volume of seminal plasma used for treatment was adjusted to a total dose of 250 µg of OIF. Experiment 1 was done to verify the bioactivity of OIF in bovine seminal plasma. Mature female llamas were assigned randomly to be treated intramuscularly (i.m.) with either 10 ml of phosphate buffered saline (PBS, negative control, n=5), 50 µg GnRH (positive control, n=5), 6 ml of llama seminal plasma (n=6) or 12 ml of bull seminal plasma (n=6). Experiment 2 was done to determine the effect of OIF in bovine seminal plasma on LH-induced ovulation and luteal development. Beef heifers with a CL and a growing follicle ≥10 mm were given a luteolytic dose of prostaglandin followed by 25 mg pLH 12 h later. Heifers were assigned randomly to three groups and given 10 ml bovine seminal plasma i.m. 12 h after pLH treatment (n=10), bovine seminal plasma i.m. within 4 h after ovulation (n=9), or no further treatment (control, n=10).Experiment 3 was done to determine the effect of OIF in bovine seminal plasma on LH release, ovulation and luteal development. Ovulation in beef heifers was synchronized using a protocol with progesterone and estradiol. Six days after ovulation, , when a mature CL and a dominant follicle of 11-13 mm diameter were expected to be present, heifers were assigned randomly to four groups (n=8 per group) using a 2-by-2 design and treated with either pLH or phosphate-buffered saline i.m., followed 12 h later by treatment with either 10 ml bovine seminal plasma or phosphate-buffered saline i.m.; i.e., LH+PBS, LH+SP, PBS+SP, and PBS+PBS groups. In all experiments, ovulation and CL development were monitored by transrectal ultrasonography. In Experiment 1, llamas were scanned daily from treatment to Day 6 after treatment, while in the other two experiments ovulations were monitored every 4 h and CL development was monitored daily until the next ovulation. Ovulation rates were compared among groups by Fisher’s exact test, and continuous data were compared among groups by ANOVA for repeated measures. Single point data were compared by ANOVA. In Experiment 1, ovulation was detected in 0/5, 4/5, 4/6, 4/6 in PBS, GnRH, llama seminal plasma, and bovine seminal plasma groups, respectively (P<0.05). No difference was detected among groups in luteal development. In Experiment 2, all ovulations in the pre-ovulation treatment group occurred within a 4 h period, while the range for other groups was 22 h (P<0.0001). No difference was detected among groups in luteal development; however, plasma progesterone concentrations tended to be greater in the heifers treated with seminal plasma post-ovulation compared to the other two groups (treatment-by-day interaction, P=0.1). In Experiment 3, ovulations were detected in 5/8, 4/8, 0/7, 0/8 in pLH, pLH+SP, SP and control groups, respectively (P<0.05). Corpora lutea present at the time of treatment took longer to decrease significantly in size from the time they reached maximum size in heifers treated with seminal plasma (p=0.04), but, plasma progesterone concentrations did not differ among groups during this same period. Nevertheless, there was a more rapid increase in plasma progesterone concentration by 24 h after seminal plasma treatment than those not treated with seminal plasma (P=0.03). Results confirm the presence of bioactive OIF in bull seminal plasma and showed that bovine and llama seminal plasma have similar ovulatory and luteotrophic effects using a llama bioassay. Moreover, treatment of sexually mature heifers with OIF from bovine seminal plasma influenced the timing of ovulation and the duration of luteal function.