Spontaneous ovulation in cats-Uterine findings and correlations with animal weight and age.

Cats are considered induced ovulating animals but ovulations occur in the absence of mating (i.e., spontaneous ovulations). Factors that stimulate such ovulations remain largely unknown. In this study, ovaries and uterine horn segments from 89 post-pubertal queens presented for ovariectomy were evaluated morphologically and histologically. It was hypothesized that corpora lutea (CL) are present in non-pregnant cats and can be associated with cystic endometrial hyperplasia (CEH). Cats were assigned to three age groups (7-12 months, n = 32; 13-24 months, n = 26 and ≥ 24 months, n = 31) and three weight groups (2.1-2.8 kg, n = 28; > 2.8-3.3 kg, n = 32 and > 3.3 kg, n = 29). Uterine horn diameter and thickness of the endometrium and myometrium were determined. Corpora lutea were detected in 39.3% of the cats and presence did not differ between age groups. The percentage of queens with CL increased with bodyweight (2.1-2.8 kg: 14.3%; > 2.8-3.3 kg: 37.5%, > 3.3 kg: 65.5%; P < 0.01). In cats with CL, the thickness of all layers of the uterus were greater than in cats without CL (P < 0.05). Of the cats, 22.5% had CEH but there was no difference between cats without and with CL. The percentage of CEH increased with age (P < 0.001) but did not differ between weight groups. In conclusion, ovulations occurred in the absence of mating in approximately one third of all queens.