Estradiol measurement after GnRH-stimulation as a method to diagnose the presence of ovaries in the female domestic cat

There is currently no method to reliably diagnose the presence of ovarian tissue in inactive intact female cats except laparatomy which is an invasive procedure. All available tests require that the queen is in estrus. Obvious overt symptoms of estrus are, however, not always observed and some queens may have only 2 estrus periods/year. Therefore this study was designed to evaluate if it is possible to diagnose the presence of ovarian tissue by measurement of estradiol before and/or after stimulation with a GnRH-analogue. Twenty-two female cats were divided into two groups; 11 females that were known to have been ovariectomized and 11 females that were known to be intact. From each cat a heparinised blood sample was collected from the cephalic vein for resting estradiol and progesterone measurements. All cats were treated with a GnRH-analogue buserelin (Receptal®, 0.4 μg/kg im). Two hours later a second blood sample was collected. Median estradiol increased after stimulation with buserelin in intact but not in ovariectomized females (11 range 5–21 vs. 20 range 12–41, P = 0.004 and 6 range 4–9 vs. 6 range 5–9 P = 0.8) and did not overlap between the two groups. The highest estradiol concentration post-GnRH in the ovariectomized group was 9 pmol/L while the lowest in the intact group was 12 pmol/L. Progesterone was basal in all cats except one both before and after GnRH-stimulation. In conclusion this study demonstrates that measurement of estradiol concentration in plasma 2 h after stimulation with a GnRH-analogue seems to be a reliable method to diagnose the presence of ovarian tissue in the female cat.