Inflammatory and degenerative changes in the endometrium of mares of the Crioulo breed

In order to study the causes of infertility in mares of the Crioulo breed, we examined 960 mares served at pasture by 33 different stallions. At the end of the breeding season, open mares (118) were separated by rectal palpation (pregnancy rote of 87.7%). Those mores were subjected to endometrial biopsy and uterine swab for bacteriological examination. Histologically, the endometria were classified in 4 grades according to Kenney and Doig (1986). Endometria classified as Grade I was observed in 49.2% of the open mares, grade II in 33.1%, grade III in 12.7% and grade IV in 5.1%. Severe inflammatory lesions were observed in 36/118 (30.5%) cases and degenerative lesions in 16.9% of the endometrium (20/118). In the following breeding season, the pregnancy rate of mares with or without inflammation was 59.3 and 85.5% respectively (P<0.01) and the pregnancy rate of mares with or without degenerative lesions, 47 and 84.8%, respectively (P<0.01). Old mares (> than 15) had a significantly (P<0.001) lower pregnancy rate (15/27, 55.5%) than young (= to or < than 15) mares (54/61, 88.5%). The frequency of inflammatory lesions was not significantly different (P>0.8) among older and younger mares (28.6 vs. 31.0 %, respectively), however, degenerative lesions were more frequent (P<0.001) in older mares than younger mares (40.0 vs. 7.0 %). We conclude that inflammatory and degenerative lesions are important causes of infertility in the Crioulo breed.