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Background: Horse welfare is a priority in the equine sport of endurance riding. Identification and reduction of risk factors associated with elimination and lameness have been the focus of research to date, however, this has centred on international competition. National federations recognise there is a need to consider risk factors for elimination at a more local level. Objectives: Determine current risk factors associated with horse eliminations, specifically lameness eliminations within British endurance. Study design: Retrospective cohort study. Methods: Data were extracted from the Endurance GB database, for open and advanced horses, competing in rides >64 km in the 2017 and 2018 competitive seasons. Variables were analysed via univariable models which informed subsequent multivariable binary logistic regression modelling. Two models were completed: (A) horse eliminated vs. not eliminated and (B) horse lame vs. not lame. Results: One thousand seven hundred and forty‐seven competitive starts were analysed; 542 horses were eliminated. Lameness accounted for 56.1% (n = 304) of eliminations. Multivariable analysis identified decreased odds of lameness in graded rides compared with race rides (adjusted odds ratio, OR 0.6; 95% confidence interval, CI 0.4–0.8). There were increased odds of elimination (OR 4.7, CI 3.5–6.5) and increased odds of lameness (OR 1.9, CI 1.2–3.06) when competing in FEI competitions of 2* and above, compared to rides run under national rules. Horses and riders who had not competed as a combination previously had increased odds of elimination (OR 2.2, CI 1.5–3.02). Main limitations: Variables which can influence performance such as speed, environmental and topographical conditions were not recorded in the data set. Only two seasons of data were analysed. Conclusions: Competitive history of horses, including the number of previous starts, previous eliminations and the category of ride entered are significant in establishing the likelihood of elimination and more specifically lameness elimination in British national endurance. [ABSTRACT FROM AUTHOR]

Oxidative stress occurs when antioxidant defense mechanisms are overwhelmed by free radicals and may lead to DNA damage, which has been implicated in processes such as aging and diseases such as cancer. The two main techniques presently used to quantify DNA damage are measurement of 8-hydroxydeoxyguanosine and the Comet assay (also known as single-cell gel electrophoresis). The aim of this study was to apply the comet assay to equine peripheral blood mononuclear cells (PBMCs) and identify two conditions in which we hypothesized that oxidative DNA damage would be increased in PBMCs: aging and equine recurrent airway obstruction (RAO, a condition similar to human asthma). The images obtained were similar to those previously published for humans, cats, and dogs. The optimum concentration of [H.sub.2][O.sub.2] to estimate susceptibility to exogenous damage was 50 [micro]M. Mean intraassay coefficients of variation were 4.7 and 9.7% for endogenous and exogenous tail-DNA quantities, respectively, and 7.3 and 8.3% , respectively, for interassay coefficients. There was no significant difference in either endogenous or exogenous percentages of tail DNA for samples collected from six ponies on three consecutive days. There was no significant difference in endogenous, exogenous, or exogenous (corrected for endogenous) oxidative DNA damage between mature and aged ponies. However, young pony foals had significantly less endogenous DNA damage than mature or aged ponies (P < 0.05). RAO-affected horses without airway inflammation (i.e., in clinical remission) had significantly greater endogenous damage compared with non-RAO-affected control animals (P = 0.009). There was a significant correlation between endogenous percentage of tail DNA in PBMCs and red blood cell hemolysate glutathione concentration (r = 0.720; P < 0.001). In conclusion, the comet assay appears to be suitable for investigating DNA damage in equine PBMCs. J. Nutr. 134: 2133S-2140S, 2004. KEY WORDS: * single-cell gel electrophoresis * horse * recurrent airway obstruction * aging * foals

Prolonged low-medium intensity exercise is associated with increased oxidative stress in humans. We hypothesized that competitive equine endurance racing would induce changes in circulatory antioxidants and produce systemic oxidative stress. Forty horses competing in a 140-km endurance race in warm conditions [shade temperature 15-19[degree]C; 62-88% relative humidity (%RH)] were sampled before (Pre), immediately after exercise (End) and at approximately 16 h into recovery (+16 h). Plasma ascorbic acid concentration was not different between Pre [11.1 (median); 4.6-20.3 [micro]mol/L (range)] and End [9.7; 3.0-38.9 (range) [micro]mol/L] but was significantly decreased at + 16 h (5.5; 2.8-15.5 [micro]mol/L; P < 0.05). Total red cell hemolysate glutathione (TGSH) concentration was significantly reduced by exercise (Pre 1261; 883-1532 [micro]mol/L; End 1065; 757-1334 [micro]mol/L; P < 0.05) and at +16 h recovery (1032; 752-1362 [micro]mol/L; P < 0.05). Glutathione redox ratio was unchanged by exercise but was significantly decreased at +16 h compared with that at both Pre and End (P < 0.05). The concentration of total barbituric acid reactive substances (TBARS) in plasma was increased compared with that at Pre (309; 66-1048 nmol/L), both at End (408; 170-1196 nmol/L; P < 0.05) and + 16 h (380; 99-1161 nmol/L; P < 0.05). [alpha]-Tocopherol was unchanged by exercise or recovery. Mean race speed was 16.5[+ or -]1.6 km/h and ranged from 13.9 to 19.7 km/h. Mean speed during competition in horses that completed the full 140 km (n = 28) was significantly correlated with end of exercise ascorbic acid (r = 0.622; P = 0.0004). Although there were increases in creatine phosphokinase (CK), aspartate aminotransferase (AST) and TBARS and a loss of TGSH, this study failed to demonstrate evidence of classical oxidative stress. Key Words: * horse * reactive oxygen species * antioxidants * prolonged exercise