Chapter 62 Pyometra in Large Felids

Pyometra is well described in domestic cats, but is relatively uncommon. However, pyometra appears to occur more often in large exotic felids.⁹ It has been diagnosed in leopards, lions, tigers, and a liger, with lions being at an increased risk.^1,^2,⁹ Most large felids that develop pyometra are older than 10 years, although it has been seen in a 5-year-old lion.⁹

Pyometra in domestic carnivores is associated with cystic endometrial hyperplasia,^3,⁶ which also appears to be the case in large felids.^9,¹⁰ In the development of pyometra, cystic endometrial hyperplasia is followed by secondary bacterial overgrowth of normal vaginal flora that enters the uterus during proestrus and estrus. The incidence of cystic endometrial hyperplasia in exotic felids increases with age.¹⁰ Unlike with domestic felids, it is uncommon to spay large exotic felids in zoo collections for the prevention of pregnancy, but more common to contracept them. Historically, melengesterol acetate implants were commonly used for this purpose, although they are used less frequently now because of associated side effects. Cystic endometrial hyperplasia has been reported in felids both with and without a history of melengesterol acetate contraception.¹⁰

Pyometra is less common in the domestic cat than in the dog,⁶ presumably because of cats being induced ovulators. In induced ovulators, uterine tissue is exposed to progesterone only after copulation or artificial stimulation. The uterus is not, therefore, exposed to progesterone in every estrous cycle, which reduces the risk for the development of cystic endometrial hyperplasia.

An early work suggested that lions are spontaneous ovulators,¹² but a more recent study has suggested that most lions are induced ovulators.¹³ Like in the domestic cat,^5,⁸ spontaneous ovulation may occur with varying frequency in lions housed singly or with other females.^2,¹³ The same appears to be true for the tiger.⁴ In contrast, the leopard has been shown to ovulate in the presence of other females, but not when housed singly. This suggests that they do not require intromission but do require stimulation for ovulation to occur.^2,¹¹

Histopathology of the reproductive tracts of large felids with pyometra has demonstrated at least one corpus luteum in most cases, indicating that ovulation had taken place within a few weeks prior to surgery.⁹ One lion was housed only with other females, which confirms the previous findings that intromission is not required for ovulation in the lion. Additionally, one of two tigers and a liger were housed alone and also had multiple corpora lutea, supporting the occurrence of spontaneous ovulation in at least some large exotic felids.