Endometritis in mares experimentally infected with three different strains of E. coli

The aim of this study was to describe the inflammatory response after intrauterine inoculation with three different strains of E. coli in the mare. Nine cyclic mares aged between 7 and 20 years old were selected and their estrous detected by transrectal palpation and ultrasound. Only clinically normal mares with negative cytology and bacteriology were used. Three different strains of E. coli obtained from: (UT) uterine swab of a mare with endometritis, (VE) vestibular swab from a healthy mare and (MA) from more manure, were used. Subsequently, the mares were submitted to intrauterine inoculation with 3x109 E. coli of one of the three different strains. All mares were challenged with each strain of E. coli in a randomized order in the subsequent different cycles. One day after infection, clinical examination of the genital tract by speculum, ultrasound, endometrial cytology and bacteriological cultures were performed. These procedures were repeated daily until negative culture and negative cytology were diagnosed. All mares had slight (<10/field) to severe (>20/field) endometrial neutrophils 24h after E. coli inoculation. In 25 of 27 mares (92.6%), vaginal clinical signs and intrauterine fluid (IUF) were detected. Severe vaginal signs with purulent aspect and hyperemic mucosa were observed in 17 mares and 8 presented mild signs. Only 59.2% of the mares (16/27) were E. coli positive 24h after the infection. The time needed for elimination of bacteria was in average 2.8 (+/-1.0) days. In conclusion, E. coli spp. provokes a positive cytology and most of the mares developed vaginal clinical signs of endometritis and IUF, with no difference among E. coli strains.