Abstract
This study aimed to investigate the effect of three different doses of estradiol-17β on ovulation and subsequent luteal development and function in llamas. Twenty-three llamas were examined daily by transrectal ultrasonography until the detection of an ovulatory follicle (≥8 mm). Thereafter, animals were divided into five groups: Control (n = 3; treated with 1.6 ml of saline solution), GnRH group (n = 6, treated with an intravenous injection of 8.4 μg Buserelin), and estradiol groups that received 0.6 mg (E1, n = 4), 1 mg (E2, n = 4), or 1.6 mg (E3, n = 6) of estradiol-17β intravenously. Detection of ovulation was based on ultrasonographic visualization of disappearance of the largest follicle and subsequent presence of a newly formed corpus luteum (CL) and progesterone concentration exceeding 1 ng ml−1. Daily blood samples were collected to determine plasma progesterone concentration. Ovulation rate was 0% for control and E1 groups, 25% for E2 group, and 100% for GnRH and E3 groups. Differences in the mean CL diameter between GnRH and E3 groups were not statistically significant. Plasma progesterone concentration was similar between groups during the different days in ovulated animals. However, the day that the plasma progesterone concentration was above 1 ng ml−1 and the day that the highest plasma progesterone concentration was achieved differed among E3 and GnRH groups, occurring later in females treated with estradiol. In conclusion, an injection of estradiol-17β is capable of inducing ovulation in llamas and the response depends on the dose used. Most of the animals required the highest tested dose (1.6 mg) to induce the ovulatory process. Although the CL diameter in females induced to ovulate with estradiol was similar to that in llamas induced to ovulate with a GnRH analog, the rise in plasma progesterone concentration above 1 ng ml−1 and the peak progesterone concentration were attained 1 day later in the estradiol treated females.
Highlights
Unlike other species such as sheep and cattle, which ovulate spontaneously as part of their estrous cycle, female camelids are induced ovulators requiring an external stimulus in the presence of a follicle with a diameter ≥ 7 mm to elicit the ovulatory process [1, 2]
A corpus luteum (CL) was first detected after treatment between Days 4 and 5 in gonadotrophin-releasing hormone (GnRH) and E3 groups and on Day 4 in the only llama that ovulated in the E2 group
An effect of day was observed in both groups (P < 0.0001), and the highest plasma progesterone concentration was reached on Days 7, 8, and 9 post treatment (Figure 2). This is the first report demonstrating that an injection of estradiol-17β is effective to induce ovulation in llamas being the response dependent of the dose
Summary
Unlike other species such as sheep and cattle, which ovulate spontaneously as part of their estrous cycle, female camelids are induced ovulators requiring an external stimulus in the presence of a follicle with a diameter ≥ 7 mm to elicit the ovulatory process [1, 2]. Estradiol-17β Induces Ovulation in Llamas as beta nerve growth factor [4, 5] is present in the seminal plasma of males, which induces the LH secretion and ovulation around 30 h post-mating [6]. The administration of exogenous hormones that elicit LH release such as gonadotrophin-releasing hormone (GnRH) or hormones with LH activity such as human chorionic gonadotrophin (hCG) induces ovulation within an interval of ∼29 h [GnRH: [7]] or 26 h [hCG: [1]]. In spontaneously ovulating species, increasing plasma concentration of estradiol-17β, in the absence of plasma progesterone concentration from a corpus luteum (CL), induces the preovulatory surge of LH and, ovulation [8, 9]. Treatment of heifers with estradiol-17β, without exogenous progesterone or progestogen, is followed by a surge release of LH [10, 11]
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