Llamas are considered to be reflex ovulators. However, semen from these animals is reported to be rich in ovulation-inducing factor(s), one of which has been identified as nerve growth factor (NGF). These findings suggest that ovulation in llamas may be elicited by chemical signals contained in semen instead of being mediated by neural signals. The present study examines this notion. Llamas displaying a preovulatory follicle were assigned to four groups: group 1 received an intrauterine infusion (IUI) of PBS; group 2 received an IUI of seminal plasma; group 3 was mated to a male whose urethra had been surgically diverted (urethrostomized male); and group 4 was mated to an intact male. Ovulation (detected by ultrasonography) occurred only in llamas mated to an intact male or given an IUI of seminal plasma and was preceded by a surge in plasma LH levels initiated within an hour after coitus or IUI. In both ovulatory groups, circulating β-NGF levels increased within 15 minutes after treatment, reaching values that were greater and more sustained in llamas mated with an intact male. These results demonstrate that llamas can be induced to ovulate by seminal plasma in the absence of copulation and that copulation alone cannot elicit ovulation in the absence of seminal plasma. In addition, our results implicate β-NGF as an important mediator of seminal plasma-induced ovulation in llamas because ovulation does not occur if β-NGF levels do not increase in the bloodstream, a change that occurs promptly after copulation with an intact male or IUI of seminal plasma.

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The objective was to evaluate the developmental competence of cumulus-oocyte complexes (COC) collected by follicular aspiration in llamas treated with FSH or eCG. Llamas were assigned randomly to two groups (n = 16 per group) and treated, at the time of ovarian follicular wave emergence, with either: 1) 25 mg of FSH im, twice daily for 4 d; or 2) 1000 IU of eCG as a single i.m. dose. The start of gonadotropin treatment was considered Day 0. Both groups were given 5 mg of Armour Standard LH im on Day 6, and COC were collected by follicle aspiration on Day 7. Expanded COC collected from FSH- (n = 157) and eCG-treated llamas (n = 151) were fertilized in vitro using epididymal sperm, and presumptive zygotes were in vitro cultured in SOF medium for 8 d. The FSH and eCG treatment groups did not differ with respect to: the number of follicles ≥7 mm (16.0 ± 2.7 vs 14.0 ± 1.9, respectively; P = 0.5); the number of COC collected (11.5 ± 1.9 vs 9.7 ± 1.2; P = 0.4); the number of expanded COC (9.8 ± 1.4 vs 9.4 ± 1.2; P = 0.8); or the percentage of presumptive zygotes which developed into 2 to 8 cell stage embryos (65.3 vs 63.1), morulas (46.2 vs 42.5), or blastocysts (23.1 vs 20.5; P > 0.05). In conclusion, FSH and eCG treatments were equally effective for recovery of a high number of expanded COC which were used directly for in vitro fertilization. Furthermore, rate of embryo development was not significantly affected by the gonadotropin treatment used.

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The type of stimuli triggering GnRH secretion has been used to classify mammalian species into two categories: spontaneous or induced ovulators. In the former, ovarian steroids produced by a mature follicle elicit the release of GnRH from the hypothalamus, but in the latter, GnRH secretion requires coital stimulation. However, the mechanism responsible for eliciting the preovulatory LH surge in induced ovulators is still not well understood and seems to vary among species. The main goal of this review is to offer new information regarding the mechanism that regulates coitus-induced ovulation. Analysis of several studies documenting the discovery of β-NGF in seminal plasma and its role in the control of ovulation in the llama and rabbit will be described. We also propose a working hypothesis regarding the sites of action of β-NGF in the llama hypothalamus. Finally, we described the presence of β-NGF in the semen of species categorized as spontaneous ovulators, mainly cattle, and its potential role in ovarian function. The discovery of this seminal molecule and its ovulatory effect in induced ovulators challenges previous concepts about the neuroendocrinology of reflex ovulation and has provided a new opportunity to examine the mechanism(s) involved in the cascade of events leading to ovulation. The presence of the factor in the semen of induced as well as spontaneous ovulators highlights the importance of understanding its signaling pathways and mechanism of action and may have broad implications in mammalian fertility.

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