Approximately 4% of horses suffer from one colic episode per year. The outcome is fatal in 11% of cases. F2-isoprostanes are the "gold standard" for assessment of oxidative stress in vivo and have been used extensively to quantify lipid peroxidation in association with risk factors in various diseases in humans. Because horses with colic may have intestinal ischemia and/or inflammation characterized by oxidative stress and increased production of isoprostanes, measurement of isoprostane concentrations in colicky horses may be of clinical value.

The purpose of this study was to gather preliminary data on the feasibility of using urine isoprostane concentrations as an early screening tool for the severity of colic and to determine the need for surgery. The long term goal of this investigation is to reduce the number of deaths due to colic by developing a stall-side test capable of identifying horses needing surgery as early as possible and expediting their timely referral. We hypothesized that urine isoprostanes and isoprostane metabolites would be significantly higher in horses with colic compared to normal horses and that they can be used an indicator for the need for surgical intervention.

Urine samples were collected from 42 normal horses and 38 horses with colic (21 medical and 22 surgical). Urine isoprostane and isoprostane metabolite concentrations were measured by mass spectrometry and normalized by urine creatinine (Cr) concentrations. Statistical analysis was performed using a one way ANOVA (Tukey's post-hoc comparison) and a 2 sample t-test. Significance was set at P<0.05.

Mean (± SD) concentrations of isoprostanes and isoprostane metabolites were significantly higher in urine samples of horses with colic (2.94 ± 1.69 ng/mg Cr and 0.31 ± 0.22 ng/mg Cr, respectively) compared to healthy horses (1.89 ± 1.39 ng/mg Cr and 0.22 ± 0.08 ng/mg Cr, respectively). Urine isoprostane metabolite concentrations were significantly higher in horses undergoing surgery (0.38 ± 0.28 ng/mg Cr) compared to healthy control horses and medically treated colic horses (0.26 ± 0.11 ng/mg Cr). Non-survivors had significantly higher mean urine isoprostane metabolite concentrations (0.47 ± 0.39 ng/mg Cr) compared to healthy control horses and surviving colic horses (0.29 ± 0.24 ng/mg Cr).

Since urinary concentrations of isoprostane metabolites are increased in horses suffering from colic and in non-survivor colic horses, the measurement of urine concentrations of isoprostane metabolites may be an important prognostic indicator in equine colic.