The presence of an ovulation-inducing factor (OIF) in the seminal plasma of llamas and alpacas (reflex ovulators) and cattle (spontaneous ovulators) has been reported previously (Ratto MH et al. 2006 Theriogenology 66, 1102–1106). The presence of this protein in unrelated species supports the hypothesis that OIF is a conserved factor among species. The objectives of this study were to determine if OIF was present in equine and porcine seminal plasma, and whether the proportion of test animals (llamas) that ovulated in response to treatment with seminal plasma was related to dose. In Experiment 1, female llamas were assigned randomly to four groups (n = 8 or 9 per group) and treated intramuscularly with 1 mL llama seminal plasma (positive control), 3 mL equine seminal plasma, 3 mL porcine seminal plasma, or 2 mL saline (negative control). Ovulation and maximum corpus luteum diameter were compared using ultrasonography and confirmed with blood samples taken on Day 7 (Day 0 = day of treatment) to determine plasma progesterone concentration. The diameter of the preovulatory follicle at the time of treatment did not differ among groups. Equine seminal plasma induced ovulations in 3/8 (38%) llamas compared to 0/8 (0%) llamas treated with saline or porcine seminal plasma (P = 0.1). The proportion of females that ovulated was lower in the equine group (P < 0.01) compared with those animals treated with llama seminal plasma (9/9; 100%). Of the animals that ovulated, maximum CL diameter did not differ between llama and equine seminal plasma-treated groups (mean ± SEM; 11.1 ± 1.1, 11.5 ± 1.5, respectively). Similarly, progesterone concentrations were not different among llamas treated with llama seminal plasma or equine seminal plasma (mean ± SEM; 3.1 ± 0.4, 3.7 ± 1.2, respectively). The design of Experiment 2 was the same, but the dose of equine and porcine seminal plasma was increased to 8 mL and 10 mL, respectively. The proportion of females that ovulated was less (P < 0.05) in equine (2/9) and porcine (3/9) seminal plasma groups compared with the group treated with llama seminal plasma (9/9). There were no ovulations detected in llamas treated with saline (0/8). Although differences between equine, porcine, and negative control groups did not reach significance, results provide some evidence for the presence of OIF in equine and porcine seminal plasma. The effect of dose of equine and porcine seminal plasma is equivocal, suggesting that the concentration of OIF in the seminal plasma of these species may be very low and the optimal dose for inducing ovulation in test animals had not been reached.