DOSE-RESPONSE TO EQUINE CHORIONIC-GONADOTROPIN AND SUBSEQUENT OVULATION IN LLAMAS

Multiple ovarian follicles were induced to grow and ovulate in llamas by administration of equine chorionic gonadotropin (eCG) followed by e ither copulation or injection of human chorionic gonadotropin (hCG). F orty-five parous female llamas were divided randomly into five treatme nt 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 dur ing the ovarian cycle, urinary estrone sulfate during the follicular p hase, and pregnanediol during the luteal phase. The number of follicle s was not different (P > 0.05) between control and females receiving 1 00 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 20 00 IU eCG, respectively. Concentrations of urinary estrone sulfate inc reased (P < 0.05) three-fold in animals with multiple follicles (101 n g mg(-1) creatinine (Cr)) compared with animals bearing single follicl es (29.7 ng mg(-1) Cr). Cystic follicles occurred in two, two, and nin e animals receiving 500 IU, 1000 IU and 2000 IU eCG, respectively. Twe nty 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, resp ectively. 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. D oses of 500 and 1000 IU eCG were optimal doses for inducing multiple f ollicle growth in llamas, while hCG administration was superior to cop ulation for stimulating ovulation.