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.

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Data from 131 calvings of Chianina crossbred cows (2 to 5 yr old) bred to Chianina bulls were used to compare stepwise multiple regression analysis (RA) and stepwise, two-group discriminant analysis (DA) for predicting dystocia. Variables (21) studied in relation to dystocia included both prebreeding and precalving cow and calf effects. Calving was categorized as either unassisted or assisted without regard to the severity of dystocia. During this study, 30 (22.9%) assisted births occurred. All variables were standardized to a mean of zero and a variance of one before statistical analyses. Models were developed based on precalving variables and with both precalving and postcalving variables with both RA and DA. Average discriminant scores (centroids) were different (P less than .01) between assisted and unassisted cows. Significant precalving DA variables were cow age and precalving pelvic height. This model correctly predicted 26 of 30 (86.7%) of the occurrences of dystocia. Significant precalving RA variables were prebreeding pelvic width and precalving pelvic height. The amount of variation accounted for by these two factors was 31.5%. Calf birth weight, calf chest depth, calf height, precalving pelvic area, cow age and precalving cow weight were selected by DA for use in the combined precalving and postcalving prediction model. Calf birth weight was 58% more important than either pelvic size or cow age. Percentage correctly classified with this model was 87.4. Significant postcalving variables selected by RA in order of importance were prebreeding pelvic width, calf birth weight and calf shoulder width (R2 = .399).(ABSTRACT TRUNCATED AT 250 WORDS)

Twelve mares fed altrenogest for 14 d were used to study the effects of a single injection of testosterone propionate on concentrations of follicle-stimulating hormone (FSH) during diestrus, and to relate the normal and perturbed patterns of FSH secretion to subsequent estrous characteristics and fertility. Seven of 12 mares received testosterone propionate at 200 micrograms/kg of body weight on d 5 of progestogen feeding. Mares were teased and blood samples were drawn daily; all mares were artificially inseminated at the first estrus after progestogen treatment. Testosterone propionate treatment caused a 50% reduction in concentration of FSH in plasma within 24 h, and this effect persisted through 48 h after injection. Within 4 d after the suppression of FSH secretion, concentrations of FSH rebounded and were significantly elevated compared with control values during the last 4 d of progestogen feeding. Testosterone propionate at this dosage also elicited estrous behavior in five of seven treated mares within 24 h after injection. After withdrawal of progestogen feeding, the interval to onset of estrus, duration of estrus, and magnitude of the luteinizing hormone peak were similar between groups (P greater than .05). Six of seven treated mares and three of five control mares became pregnant to breeding on the first estrus after progestogen treatment. Because manipulation of the normal pattern of FSH secretion during diestrus did not affect estrous characteristics or fertility of the subsequent estrus, such treatment may have potential as a means of synchronizing FSH surges during diestrus in the mare.