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.