452Pesq. Vet. Bras. 31(5): 452-458, maio 2011 RESUMO.-O presente estudo teve por objetivo avaliar a influência do exercício físico de alta intensidade e curta duração (provas de laço em dupla) sobre a lactacidemia e as concentrações séricas de aspartato aminotransferase (AST) e creatinoquinase (CK) em equinos durante competição realizada no estado do Espírito Santo. Para tal foram obtidas amostras de soro e plasma de 20 equinos, da raça Quarto de Milha ou mestiços, em três momentos assim definidos: no repouso, uma semana antes da prova atlética, já com o animal em treinamento (T0); antes da prova atléti-ca (T1) e imediatamente após o término da mesma (T2). As referidas amostras foram encaminhadas ao Laboratório Clí-nico do Centro Universitário Vila Velha (UVV) para as análi-ses. Na avaliação da lactacidemia, os resultados registrados nos momentos T0, T1 e T2 foram, respectivamente, de 0,49±0,24mmol/L, 0,93±0,16mmol/L e 9,86±2,09mmol/L. Na avaliação da atividade sérica de AST, os resultados registrados nos momentos T0, T1e T2 foram, respectiva- The aim of the present study was to evaluate the effects of high intensity and short duration physical exercise (roping team competition) on plasma lactate and serum AST and CK concentrations in horses during competition at Espírito Santo state, Brazil. Blood samples were obtained from 20 Quarter Horses, or cross-bred, in three moments: (1) at rest, one week before the competition, with the animals being trained, (2) just before the competition, and (3) immediately after the exercise. The samples were sent to Laboratório Clínico do Centro Universitário Vila Velha for analysis. Plasma lactate concentrations were 0.49±0.24mmol/L, 0.93±0.16mmol/L e 9.86±2.09mmol/L, respectively, on the moments rest and immediately before and after the exercise. Serum concentrations of AST were 189.1±43.6 IU/L, 210.2±46.7 IU/L e 173.1±33.5 IU/L, respectively, on the moments rest and immediately before and after the exercise. Finally, serum concentrations of CK were 110.9±35.2 IU/L, 51.8±15.4 IU/L and 88.2±33.5 IU/L, respectively, on the moments rest and immediately before and after the exercise. Results showed that the imposed physical exercise leaded to a significant elevation of plasma lactate and serum CK without alteration on AST. It was possible to conclude that horses were adapted to the level of exercise performed.