Kinetics of the humoral immune response to multiple treatments with exogenous gonadotropins and relation to ovarian responsiveness in domestic cats

Objective - To investigate ovarian responses and kinetics of gonadotropin-binding immunoglobulin production in domestic cats repeatedly treated with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) at short or long treatment intervals. Design - Queens were treated 3 or 4 times with a standard eCG/hCG regimen at short (49 to 57 days) or long (130 to 135 days) intervals and subjected to laparoscopy after each treatment to evaluate ovarian follicular development. Serial serum samples were assessed by ELISA for the presence of eCG-binding immunoglobulins. Animals-11 clinically normal sexually mature female cats. Results - Queens repeatedly stimulated with eCG/hCG at long intervals typically had no decrease (P > 0.05) in ovarian follicle production or in maturity of recovered oocytes, whereas queens treated at short intervals had reduced (P < 0.05) follicular development and compromised oocyte maturity by the third stimulation. For both interval groups, ELISA data indicated individual variability in seroconversion after eCG/hCG challenge exposure. In general, queens treated at short intervals had higher peak anti-eCG immunoglobulin titer than did queens treated at long intervals; high titer at the time of eCG/hCG injection, or rapid increases in titer immediately after injection were predictive (P < 0.05) of poor ovarian responses. Conclusions - Results suggest that individual variability in immune responses and intervals between repeated gonadotropin treatments determine whether queens develop immunologically mediated ovarian refractoriness to exogenous gonadotropins. Intervals of at least 4 months between successive eCG/hCG treatments are recommended for assisted reproductive procedures in domestic and nondomestic cats.