Research articleEffect of purified llama ovulation-inducing factor (OIF) on ovarian function in cattle
Introduction
Spontaneous ovulators, such as cattle, are species capable of ovulating without copulatory stimulation. In the presence of low plasma progesterone concentrations, estradiol secreted by the preovulatory follicle has a positive feedback effect on the hypothalamus, leading to a surge release of LH [1] and initiation of the ovulatory cascade [2]. Conversely, induced ovulators, such as llamas, alpacas and camels, are species that, in the absence of copulation, will not ovulate or do so at a very low incidence (e.g., 5% in alpacas [3], [4], [5]). Although the role of seminal plasma in the induction of ovulation has been examined in some induced ovulators [6], [7], [8], [9], [10], [11], few reports were found regarding the influence of seminal plasma on ovulation in spontaneously ovulating species. In pigs, intrauterine administration of seminal plasma was associated with a reduction in the interval between the LH peak and ovulation [12]. Although no effect on ovulation was detected in another study in pigs [13], administration of seminal plasma was associated with an increase in CL size and progesterone secretion in vivo, and increased LH responsiveness and progesterone secretion of granulosa and theca cells from preovulatory follicles in vitro. No references were found to studies of the effect of seminal plasma on ovulation in cattle.
Results of recent studies on the effects of bovine, equine, and porcine seminal plasma on ovulation in llamas suggest that an ovulation-inducing factor (OIF) may be widely conserved among induced and spontaneous ovulators [14], [15]. After intramuscular treatment with an equivalent volume of seminal plasma from llamas, alpacas and bulls (i.e., 1 mL), ovulation was induced in 19/19 (100%), 19/19 (100%) and 5/19 (26%) female llamas, respectively, all of which were significantly more frequent than in the control group 0/19 (0% [14]). In an earlier study on Bactrian camels, 3/5 females ovulated after intrauterine or intramuscular treatment with bovine seminal plasma [8].
In both llamas and camels, the ovulation-inducing effect of seminal plasma was attributed to a surge release of LH from the pituitary [6], [7], [14], [16]. Further, results of a recent dose–response study in llamas were consistent with the hypothesis that OIF affects ovulation and CL function in a dose-dependent manner, at physiologically relevant doses, i.e., 1/25 to 1/100 of the amount of protein normally present in an ejaculate [17]. Results of recent studies document that OIF in seminal plasma is a protein molecule with a molecular mass of 14 kDa that is resistant to heat and enzymatic digestion with proteinase K [18], [19].
The objective of the present study was to determine the effects of purified OIF on ovarian function in cattle, as a representative species of spontaneous ovulators. We tested the hypothesis that OIF will induce ovulation and affect CL form and function in cattle (Experiment 1). Based on the results of Experiment 1, we subsequently tested the hypothesis that OIF, given at various stages of development of the first follicular wave, will induce atresia of the dominant follicle and hasten emergence of a new follicular wave (Experiment 2).
Section snippets
Materials and methods
All animal experiment protocols were reviewed and approved by the University of Saskatchewan animal care committee.
Experiment 1—effect of OIF in prepubertal heifers
No effect of replicate was detected for any endpoint; therefore, data from Replicates 1 and 2 were combined. The diameter of the dominant follicle at the time of treatment did not differ among groups, but the proportion of heifers that ovulated in response to treatment (i.e., within 3 d of treatment) was greater (P < 0.05) in the GnRH-treated group than in the OIF- and saline-treated groups (Table 1). The interval from treatment to wave emergence was earlier in GnRH- and OIF-treated heifers
Discussion
Two experiments were conducted to determine the effect of OIF in cattle. Prepubertal heifers were used as a first approach, to avoid the confounding effects of spontaneous ovulation and elevated circulating concentrations of progesterone, and as an attempt to imitate the physiological conditions of the unmated llama—an induced ovulator. Although no ovulations were detected, OIF treatment was associated with suppression of the existing dominant follicle, a subsequent rise in circulating FSH
Acknowledgments
The project was supported by grants from the Natural Sciences and Engineering Research Council of Canada, the Alpaca Research Foundation and donations from members of the Canadian Llama and Alpaca Association.
References (36)
- et al.
Neuroendocrine regulation of GnRH release in induced ovulators
Front Neuroendocrinol
(2000) - et al.
Comparison of the effect of ovulation-inducing factor (OIF) in the seminal plasma of llamas, alpacas, and bulls
Theriogenology
(2006) - et al.
Seminal collection, seminal characteristics and pattern of ejaculation in llamas
Theriogenology
(1996) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding
Anal Biochemestry
(1976)- et al.
Ovarian synchronization following ultrasound-guided transvaginal follicle ablation in heifers
Theriogenology
(1994) - et al.
Composition and characteristics of follicular waves during the bovine estrous cycle
Anim Reprod Sci
(1989) - et al.
Effect of LH or GnRH on the dominant follicle of the first follicular wave in beef heifers
Anim Reprod Sci
(1999) - et al.
Plasma progesterone concentrations in heifers and cows treated with a new intravaginal device
Anim Reprod Sci
(1991) - et al.
Fertility in beef cattle given a new or previously used CIDR insert and estradiol, with or without progesterone
Anim Reprod Sci
(2004) - et al.
Form and function of the corpus luteum in llamas
Anim Reprod Sci
(1991)