Endometrial hyperplasia and pyometra in captive lions (Panthera leo) and tigers (Panthera tigris).

Endometrial hyperplasia (EH) is a pathologic condition of the uterus with increased endometrial gland to stroma ratio compared to normal cyclic uterine proliferation. In domestic animals, EH often involves cystic distension of proliferating endometrial glands and may be concurrent with pyometra. In large captive nondomestic felids, an association between EH and pyometra is common; however, detailed species differences between the histological uterine findings in lions (Panthera leo) and tigers (Panthera tigris) and clinical manifestations have yet to be described. Uterine sections from 14 lions and 24 tigers with EH and/or pyometra were scored for several histological parameters and clinical histories were recorded. The percentage of endometrium affected by hyperplasia, endometrial gland to stroma ratio, and adenomyosis were significantly (P = .0385, P = .0008, and P = .0463, respectively) more severe in lions compared to tigers as univariate analytes. Although tubular complexity was not statistically significant (P = .3254), when combined as a proposed EH grading scheme, these 4 features confirmed lions had significantly (P = .0068) more severe EH compared to tigers. Endometrial hyperplasia severity significantly correlated with inflammation/pyometra severity when controlling for species (P = .0203). A significant correlation exists between pyometra-associated clinical sign severity and the presence of pyometra in tigers, (P = .0026) but not in lions (P = .1144). There was no statistical difference in the severity of clinical signs associated with pyometra between these species (P = .1986). This proposed grading scheme may have clinical utility in providing a more consistent and objective evaluation of EH in large captive felids.

HISTOLOGIC EVIDENCE OF SPONTANEOUS OVULATION IN TIGERS (PANTHERA TIGRIS).

Spontaneous ovulation has been identified in several wild felid species and domestic cats previously thought to undergo only induced ovulation. Two studies have assessed ovulation patterns in tigers (Panthera tigris) and have not found evidence of spontaneous ovulation in this species. However, uterine pathology typically associated with prolonged progesterone exposure has been identified in unbred tigers, suggesting spontaneous ovulation occurs. Ovaries from 47 tigers were reviewed with histologic examination. The presence or lack of active corpora lutea was documented and compared with social housing conditions for each animal. Social housing categories were as follows: female housed alone, female housed with other females, and female housed with at least one male. Active corpora lutea were identified in 66% (10/15) of females housed alone, 85% (6/7) of females housed with other females, and 58% of females housed with a male. A chi-squared test found the presence of active corpora lutea was independent of social housing condition. These results offer strong evidence of spontaneous ovulation in tigers. This finding suggests that a luteal control protocol with an early follicular inhibition agent may improve assisted reproduction efforts and supports spaying nonreproductive or postreproductive female tigers to reduce the rate of uterine infections.