Increasing Age Influences Uterine Integrity, But Not Ovarian Function or Oocyte Quality, in the Cheetah (Acinonyx jubatus)1

Abstract

Although the cheetah (Acinonyx jubatus) routinely lives for more than 12 yr in ex situ collections, females older than 8 yr reproduce infrequently. We tested the hypothesis that reproduction is compromised in older female cheetahs due to a combination of disrupted gonadal, oocyte, and uterine function/integrity. Specifically, 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 equine chorionic gonadotropin and human chorionic gonadotropin (hCG), and fecal samples were collected for 45 days before gonadotropin treatment and for 30 days after oocyte recovery by laparoscopy. Twenty-six to thirty hours 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 no influence of age on fecal hormone concentrations or gross uterine morphology was found (P > 0.05), older females produced fewer (P < 0.05) total antral follicles and oocytes compared to younger counterparts. Regardless of donor age, oocytes had equivalent (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 more than 87% and more than 56% of older females experiencing endometrial hyperplasia and severe pathologies, respectively. Our collective findings reveal that lower reproductive success in older cheetahs appears to be minimally influenced by ovarian and gamete aging and subsequent dysfunction. Rather, ovaries from older females are responsive to gonadotropins, produce normative estradiol/progestogen concentrations, and develop follicles containing oocytes with the capacity to mature and be fertilized. 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 in vitro fertilization and embryo transfer may be useful for "rescuing" the genome of older, nonreproductive cheetahs.

Ultrasonographic and laparoscopic evaluation of the reproductive tract in older captive female cheetahs (Acinonyx jubatus)

“…The study populations' median age placed them within a cohort ideal for evaluating the effects of aging reportedly associated with markedly decreased reproductive competency where older cheetahs were classified as 9 to 15 years of age [13]. Ultrasonographic evaluation of the reproductive tract, uniquely enhanced by the concurrent direct laparoscopic visualisation of structures, provided a valuable insight into the reproductive status of cheetahs.…”

“…Laparoscopically the absence of an enveloping ovarian bursa obscuring the felid ovary (as found in Canidae) enabled complete visualization of the ovary, its associated structures and adnexa. Laparoscopic visualization of the cheetah ovary had previously only been reported for assessing the effects of exogenous gonadotropin administration and oocyte retrieval [13].…”

“…Previous studies reporting effects of GnRH agonists including deslorelin in various domestic and non-domestic felids were limited by indirect methods such as laboratory-based serological and faecal steroid metabolite assays for evaluating cyclic ovarian activity when compared with direct ultrasonographic evaluation of ovarian and uterine appearance [2,13,14]. Inconsistent responses to GnRH agonists may make ultrasonography an ideal modality for monitoring any indication for additional administration of these agents in captive wild felids under field conditions [14].…”

“…The utilization of ovarian imaging to observe changes in ovarian function in domestic felids is partially limited by the small size of the ovarian structures but has been reported as an adjunct to oestrous monitoring in non-domestic felids [5,6,8,[10][11][12][13]. Ultrasonography provides a non-invasive, practical and relatively uncomplicated means to rapidly assess reproductive status in both free-ranging and captive animals.…”

“…Ultrasonography provides a non-invasive, practical and relatively uncomplicated means to rapidly assess reproductive status in both free-ranging and captive animals. Laparoscopy facilitates direct visualization of the ovaries and uterus thus enabling evaluation of the dynamic changes associated with follicular and luteal phases of the oestrous cycle as well as for the diagnosis (and staging) of pregnancy and pathologies of the reproductive tract of wild felids [5,6,13]. Additionally, uterine changes may also be indicative of the different stages of the reproductive cycle.…”