Production of exogenous gonadotrophin-neutralizing immunoglobulins in cats after repeated eCG-hCG treatment and relevance for assisted reproduction in felids

Combination regimens of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) are used in ovarian stimulation protocols for assisted reproduction of felids. In the present study, domestic cats exhibited decreased ovarian responsiveness after repeated administration of eCG-hCG and a possible immunological mechanism for this ovarian refractoriness was investigated. An ELISA was used to analyse sera from male, naive female and previously eCG-hCG-stimulated (1x, 3x and 4x) female cats for the presence of immunoglobulins binding to eCG, hCG and pig FSH (pFSH). The sera of cats receiving multiple eCG-hCG injections, at intervals of 44-50 days, displayed greater eCG and hCG-binding than did the sera of male, naive female or female cats stimulated once, and demonstrated variable affinity for pFSH. In preovulatory and postovulatory ovarian stimulation assays, mice injected with an eCG-antisera mixture had lower ovary masses than did mice injected with eCG-saline and fewer ovulated oocytes compared with mice treated with eCG-naive sera. Treatment of queens that were refractory to eCG-hCG with a pFSH-hCG regimen caused a rebound in development of ovarian follicles but not in oocyte maturity. These studies indicated that repeated treatment of domestic cats with eCG and hCG may cause an immunologically mediated refractoriness to ovarian stimulation. Although alternative gonadotrophin regimens may alleviate this refractoriness, a preferable strategy might be the avoidance of potential immunological complications through the cautious use of eCG and hCG in domestic and endangered nondomestic felids.