Dose response to equine chorionic gonadotropin and subsequent ovulation in llamas

Abstract

Multiple ovarian follicles were induced to grow and ovulate in llamas by administration of equine chorionic gonadotropin (eCG) followed by either copulation or injection of human chorionic gonadotropin (hCG). Forty-five parous female llamas were divided randomly into five treatment groups: control ( n = 8), 100 ( n = 7), 500 ( n = 10), 1000 ( n = 10) or 2000 ( n = 10) IU eCG. Ultrasonography was used to monitor ovarian activity during the ovarian cycle, urinary estrone sulfate during the follicular phase, and pregnanediol during the luteal phase. The number of follicles was not different ( P > 0.05) between control and females receiving 100 IU eCG. Follicular growth was increased ( P < 0.05) seven days after treatment with doses of at least 500 IU eCG. A mean number of 4.7, 4.6, and 6.4 follicles was observed for doses of 500 IU, 1000 IU, and 2000 IU eCG, respectively. Concentrations of urinary estrone sulfate increased ( P < 0.05) three-fold in animals with multiple follicles (101 ng mg −1 creatinine (Cr)) compared with animals bearing single follicles (29.7 ng mg −1 Cr). Cystic follicles occurred in two, two, and nine animals receiving 500 IU, 1000 IU and 2000 IU eCG, respectively. Twenty females were induced to ovulate with either single copulation (11) or 750 IU hCG administration (9). Corpora lutea were observed in 59.9% and 78.8% ( P < 0.05) of females stimulated with single copulation or hCG, respectively. Mean number of corpora lutea was 3.4 and 5.4, respectively. Concentrations of pregnanediol were 9.3 and 7.7 ng mg −1 Cr, respectively, at day 7 after copulation or hCG. Although 2000 IU eCG provoked multiple follicle development, most of them became cystic. Doses of 500 and 1000 IU eCG were optimal doses for inducing multiple follicle growth in llamas, while hCG administration was superior to copulation for stimulating ovulation.