Effects of an Anti-GnRH Vaccine Improvac on Estrous Activity, and Ovarian and Uterine Morphology in Adult Queens (Felis catus).

Reproduction can be avoided using immunocontraception. This research aims to study the effect of the anti-GnRH vaccine Improvac on clinical and reproductive function in colony-housed adult queens (Felis catus). Short-hair mixed-breed queens (n = 12) were housed together under a 14-h photoperiod. The treated group (TRT, n = 9) received 0.5 mL of Improvac, and the control group (CON, n = 3) received 0.5 mL of saline solution. Queens received two doses 30 days (D) apart. Animals were divided into 4 groups (G). Control queens (G1: n = 3) were ovariohysterectomized at 90 D. Treated queens were ovariohysterectomized at 120 D (G2, n = 3), at 270 D (G3, n = 3) and at 330 D (G4, n = 3). Data were analysed with GLIMMIX. The estrus was determined by behavioural observation and vaginal cytology. All CON queens displayed signs of estrus every 12-20 days. In the TRT group, seven queens (n = 7/9) did not display signs of estrus until the day of ovariohysterectomy (120 D [n = 2], 270 D [n = 2], 330 D [n = 3]). However, two queens (120 D [n = 1], 270 D [n = 1]) displayed signs of estrus after receiving the vaccine, at G1 on D10 and G2 on D45. The clinical, haematological and biochemical parameters of treated queens remained within the reference range for the species, supporting short-term tolerability of the vaccine. The TRT queens developed painless, soft tissue masses in the subcutaneous tissue at the vaccination sites. The masses appeared after the first dose but were not detectable at the end of the study. No histological abnormalities were detected in the endometrium or ovaries of control queens at 90 D. However, TRT animals exhibited altered follicular development, characterised by ovarian follicular cysts, while the endometrium predominantly showed atrophic changes. This vaccine is a promising alternative for reproductive control in adult queens.