Increasing Age Influences Uterine Integrity, but Not Ovarian Function or Oocyte Quality in the Cheetah (<I>Acinonyx jubatus</I>)

Abstract

Although the cheetah routinely lives for &gt;12 yr in ex situ collections, females &gt; 8 yr of age reproduce infrequently. We tested the hypothesis that reproduction is compromised in older cheetah females due to a combination of a disrupted gonadal, oocyte and uterine function/integrity. We assessed (1) ovarian response to gonadotropins, (2) oocyte meiotic, fertilization and developmental competence and (3) uterine morphology in three age classes of cheetahs (young, 2-5 yr, n = 17; prime, 6-8 yr, n = 8; older, 9-15 yr, n = 9). Ovarian activity was stimulated with a combination of eCG and hCG, and fecal samples were collected for 45 days before gonadotropin treatment and 30 days after oocyte recovery by laparoscopy. Twenty-six to 30 h post-hCG, uterine morphology was examined by ultrasound, ovarian follicular size determined by laparoscopy and aspirated oocytes assessed for nuclear status or inseminated in vitro. Although there was no influence of age on fecal hormone concentrations or gross uterine morphology (P &gt; 0.05), older females produced fewer (P 0.05) nuclear status and ability to reach metaphase II and fertilize in vitro. A histological assessment of voucher specimens revealed an age-related influence on uterine tissue integrity with &gt;87% and &gt;56% of older females experiencing endometrial hyperplasia and severe pathologies, respectively. Our collective findings reveal that lower reproductive success in older cheetahs appears minimally influenced by ovarian and gamete aging and subsequent dysfunction. Rather, ovaries from older females are responsive to gonadotropins, produce normative estradiol/progestagen concentrations and follicles containing oocytes with the capacity to mature and fertilize. A more likely cause of reduced fertility may be the high prevalence of uterine endometrial hyperplasia and related pathologies. The discovery that a significant proportion of oocytes from older females have developmental capacity in vitro suggests that IVF and embryo transfer may be useful for &#39;rescuing&#39; the genome of older, non-reproductive cheetahs.