The effect of repeated administrations of llama ovulation-inducing factor (OIF/NGF) during the peri-ovulatory period on corpus luteum development and function in llamas

The objective of the study was to test the hypothesis that repeated administrations of OIF/NGF during the peri-ovulatory period (pre-ovulatory, ovulatory, early post-ovulatory), will enhance the luteotrophic effect in llamas. Female llamas were examined daily by transrectal ultrasonography in B- and Doppler-mode using a scanner equipped with a 7.5-MHz linear-array transducer to monitor ovarian follicle and luteal dynamics. When a growing follicle ≥7 mm was detected, llamas were assigned randomly to one of the three groups and given 1 mg of purified OIF/NGF im (intramuscular) (a) pre-ovulation (single dose; n = 12), (b) pre-ovulation and at the time of ovulation (2 doses, n = 10), or (c) pre-ovulation, at the time of ovulation, and 24 h after ovulation (3 doses, n = 10). The pre-ovulatory follicle diameter at the time of treatment, ovulation rate and the first day of CL detection did not differ (P = 0.3) among groups. However, maximum CL diameter was greatest (P = 0.003) in llamas in the 2-dose group, and smallest in the 3-dose group. Accordingly, the 2 dose-group had the largest day-to-day profile for CL diameter (P < 0.01), area of CL vascularization (<0.01), and plasma progesterone concentration (P = 0.01) compared to the other groups. Interestingly, the luteal response to 3-doses of OIF/NGF during the peri-ovulatory period was not different from a single dose. In conclusion, OIF/NGF isolated from llama seminal plasma is luteotrophic and the effect on CL size and function is affected by the number and timing of treatments during the peri-ovulatory period.