Obesity has been associated with uterine dysfunctions in the pregnant mare (Sessions-B et al, Biology of Reproduction, 2018: 99(4), 761-772). This study hypothesized that obesity itself (body condition score, BCS) affected parameters associated with post-breeding endometritis. Mares (n=17) were classified by their BCS (Henneke et al., 1983) in obese (>7, n=6) and normal-weight (<7, n=11) and age group in mature (5 to 14 years, n=9) and aged mares (15 to 21 years, n=8). Transrectal ultrasonography was performed every day and oedema score and intrauterine fluid diameter were determined at insemination and 8 hours afterwards when a low volume (50 mL) uterine flush with PBS was performed (lavage). Neutrophils were counted using a Neubauer camera and the flush was centrifuged; the supernatant was frozen for metabolite determination by spectrophotometry. Blood samples were taken at this moment also for metabolite determination. Data were analyzed with PROC MIXED (SAS) including BCS and age as fixed effects. Data not normal was log-transformed. Obese mares tended to present greater neutrophil counts than normal-weight mares (43.6±8.3 vs 28.8±5.7 × 106/mL P=0.08); aged mares had greater counts than mature mares(46.7±7.7 vs 21.0±6.3 × 106/mL P=0.02). No effect of age or BCS was found on oedema and IUF at insemination or lavage. In serum, glucose, triglycerides, albumin, and urea concentrations were unaffected. Serum cholesterol concentrations were affected by BCS (P<0.01) and tended to be affected by age (P<0.09). Serum globulin concentrations were not affected by BCS, but aged mares had greater concentrations than mature mares (P=0.05). In the intrauterine fluid, BCS did not affect albumin or glucose concentration nor did age affect them. No effect was observed in cholesterol or triglyceride concentrations in the IUF. Although urea concentrations in the IUF were not affected by BCS, aged mares had greater concentrations than mature mares (1.22±0.23 vs 0.37±0.19 mM, P=0.016). Although the number of animals is limited, data shows that obesity and age are associated with greater neutrophil counts in the uterine lumen 8 hours after insemination, suggesting an altered uterine clearance in these mares. As far as we know this is the first description of metabolites in IUF according to obesity and age, showing significantly greater urea concentrations in the aged group.