Non-copulatory ovulation in cats during a non-surgical sterilization study

Introduction: Our original study was designed to evaluate a novel non-surgical spay technique for cats. An injectable lipid nanocomplex was developed that we hypothesized would reduce or eliminate estrus behaviors. We did not anticipate ovulations, as mating is considered necessary for ovulation to occur. But a small number of non-copulatory or “spontaneous” ovulations can occur. This study provided a unique opportunity to explore non-copulatory cat ovulations in a controlled setting. Materials and methods: Twelve 1-year-old female cats were housed together as a free-roaming colony. They were observed daily for five months and any signs of estrus behavior were documented. Blood progesterone levels were tested at four time points. Midway through the study, half of the cats were injected with the nanocomplex. At the end of the project, all cats were spayed and adopted. Ovarian histology was evaluated. Results: Our original hypothesis was not supported as all cats exhibited estrus, but one difference was observed. Ovulations occurred in 5/6 control cats producing corpora lutea (CLs) (83.3%), while only 1/6 of the treated cats ovulated (16.7%). The number of animals was small, and the differences were not statistically significant (Fisher’s exact test, p = 0.0801). Conclusions: Non-copulatory-induced ovulations were observed in the majority of control cats in this study. Although the numbers were small, these findings suggest that non-copulatory stimuli were possibly involved in inducing ovulations in these cats. Ovulations can present a problem as progesterone produced by these ovulations can lead to decreased fertility and possible reproductive disease.