Spontaneous ovulation has been identified in several wild felid species, as well as in domestic cats, previously thought to undergo only induced ovulation.1,3,4 Limited studies have assessed ovulation patterns in tigers (Panthera tigris) and those have not found evidence of spontaneous ovulation in this species;2,6 however, uterine pathology typically associated with prolonged progesterone exposure has been identified in unbred tigers, suggesting spontaneous ovulation is occurring5. Ovaries from 47 tigers, previously submitted for histopathology, were reviewed. The presence or lack of corpora lutea (CL) was documented and compared with social housing condition for each animal. Social housing categories were: female housed alone; female housed with other females; female housed with one or more castrated males; and female housed with one or more intact males. Active CL 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 castrated male. The only female housed with an intact male did not have active CL. A chi squared test found that the presence of CL was independent of social housing condition. These results offer strong evidence of the potential for spontaneous ovulation in tigers that do not experience contact and/or breeding. This finding could impact assisted reproduction efforts as it suggests a luteal control protocol with an early luteolytic agent may have more success. It also supports spaying non-reproductive or post-reproductive female tigers to reduce the rate of uterine infections.
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