Histology of the female reproductive tract of the cheetah (Acinonyx jubatus)

Abstract

Cheetahs are listed as vulnerable by the IUCN (International Union for Conservation of Nature) with their total worldwide population estimated at 6674 individuals. Ongoing habitat destruction, fragmentation, human animal conflict and predation threaten the survival of the wild cheetah population. Zoos and wildlife parks are tasked with maintaining a genetically healthy population as insurance against catastrophic extinctions. In contrast to reproduction in the wild, reproductive success in captivity has been poor, with only a handful of facilities achieving reasonable success. Much research has been done to try identify why. Both husbandry and spermatic factors have been investigated. Recently the focus has shifted to investigating the role of uterine health in reproductive success. Since the identification of pathology in any organ or system is made with reference to the normal, it was decided to investigate and document the normal histology of the female cheetah reproductive tract. Six captive female cheetah uteri, obtained from post-mortems after elective euthanasia of cheetahs aged 7-10.5 years, and one uterus, from a 3 year-old cheetah that died acutely, were sectioned and processed by routine histological methods. Histological sections were stained with haematoxylin and eosin and studied and photographed with an Olympus BX63 light microscope using bright field illumination and fitted with an Olympus DP72 digital camera. Very early signs of cystic endometrial hyperplasia were identified in 4 of the 7 uteri. These sections were disregarded and only sections with no pathological changes were included in the histological atlas. The histology of the female reproductive tract of the cheetah generally resembled that of the domestic dog, cat and African lioness. In the cheetah the suspensory ligament mostly branched in the region of the tubal pole of the ovary with the branch running in the mesosalpinx to join the tip of the uterine horn. The reproductive ligaments were comprised predominantly of smooth muscle, which was very well developed and supported the entire length of the uterus up to the cervix, similar to the African lioness. Cyst-like structures were found in the region of the UTJ. The uterine tube opened into the uterine lumen from a microscopic, well-defined papilla. The papillary glands were morphologically distinct to the uterine glands. The cyst like structures appeared to be dilations of the papillary glands, potentially acting as a storage cistern. The cyst-like structures are of importance to pathologists examining uterine sections in the UTJ region as they could easily be confused with cystic endometrial hyperplasia. It is therefore advised that sections for histopathology of the uterus of the cheetah be taken at least 5 mm distal to the UTJ to preclude accidental inclusion of these cyst-like structures. The Tunica muscularis of infundibulum to the ampulla, before increasing in thickness in the isthmus. The uterus and uterine glands were lined by a low cuboidal to cuboidal epithelium which contrasts with the dog and lioness. No ciliated cells were present in the uterus. The cervix displayed very few tertiary folds, no mucigenous nor goblet cells which is similar to the lioness but contrasts to the dog. The cervix contained no elastic fibres. Further research needs to be done to document the histology of the vestibule and clitoris as well as to determine the presence or absence of striated muscle in the distal two thirds of the round ligament as described in the lioness. The function of the papillary glands and significance of their cyst like appearance also needs to be further investigated.