Ovarian Function, Including Steroid Production Patterns and Oocyte Quality, in the Aged Cheetah (Acinonyx jubatus) Is Similar to Younger Counterparts.

Reproductive success is low in cheetahs managed in captivity, especially in females ≥ 9 y of age. This study examined age-related reproductive fitness, testing the hypothesis that aged cheetahs experience reduced ovarian activity and poorer oocyte quality than younger counterparts. The objectives were to evaluate: 1) estrous cyclicity before eCG stimulation (assessed by fecal estrogens); 2) formation of functional corpora lutea (CL) after oocyte aspiration (measured by fecal progestagens, PG); and 3) correlation of PG to oocyte quality. Cheetahs were divided into three age classes (young, 2-5 y, n = 8; adult, 6-8 y, n = 6; aged, 9-15 y, n = 5) and given 300 IU eCG (i.m.) followed 82 to 86 h later by 150 IU hCG (i.m.). Fecal samples were collected (4-5/week/female) for 45 to 47 days before and 32 to 35 days after eCG/hCG. At 26 to 32 h post-hCG, total follicle number (≥ 2 mm diameter) and vascularization (score 0-3; 3 = most vascular) were determined by laparoscopy, and oocytes were recovered by aspiration. Oocyte quality was assessed by grade (1-4, 1 = excellent) and fertilizing ability. Oocytes were inseminated with cryopreserved sperm and cultured in Ham's F10 with 5% fetal calf serum. Fecal samples were lyophilized and boiled in ethanol to extract steroid hormones for EIA analysis. Baseline hormonal concentrations were calculated using an iterative process for each female, excluding values that exceeded the mean + 1.5 SD. An estrogen peak was the highest value within a group of samples > 1.5 x baseline. Estrous cycles were defined as the interval between estrogen peaks ≥ 5 days apart. Anestrous periods were defined as those with no estrogen peaks for > 28 days. Data were analyzed by Pearson correlations and GLM procedures. There was no effect (P> 0.05) of age on the average number of estrogen peaks before eCG (range, 3-4 peaks) or the average number of days between peaks (range, 13-17 d). Females in each age group exhibited anestrous periods, with no differences (P> 0.05) among groups. Young cheetahs produced more (P< 0.05) follicles in response to eCG/hCG than aged females, but follicle number was not correlated (P> 0.05) with estrogen concentrations before eCG. Post-aspiration luteal PG concentration did not correlate with follicle number, but was positively related to vascularization score (r = 0.57, P< 0.05) and number of grade 1 and 2 oocytes recovered (r = 0.59, P< 0.05). There also was a positive relationship between PG concentration after oocyte recovery and percentage of fertilized oocytes that cleaved in vitro (r = 0.82, P< 0.05), although this proportion did not differ (P> 0.05) among age groups. There was no influence (P> 0.05) of age on follicular vascularization, oocyte quality grade or PG concentration after aspiration. Results demonstrate that the fertility decline in older cheetahs is not due to a compromised ability to produce normal ovarian steroid concentrations or patterns. Younger cheetahs are capable of producing more follicles (and, thus, more oocytes) in response to eCG/hCG, but oocyte quality is comparable among age groups. This similarity in ovarian steroid and gamete capacity indicates that cheetah age-related infertility has another etiology, perhaps related to as yet undetermined physiological declines. The recovery of high quality, fertilizable oocytes from older cheetahs offers opportunities for rescuing genetic material from unrepresented individuals.(poster)