The objective ofthis study was to verify the effect of increasing soybean oil addition levelsin the concentrate, on the enzymatic activity CK (Creatine Kinase), LDH (LactateDehydrogenase), AST (Astarte aminostrafase), as an indication of energetic metabolism.Compond experimental diets were given with five oil levels (control, 6, 12,18 and 24% concentrate). Twenty Arabian equines, average weight 400 kg weresubmitted to a 80 km endurance race on a treadmill. The endurance was dividedinto four 20 km rings with an average duration of one hour and 10 minutes. Asignificant effect of oil addition and the covered distance was observed onthe variables AST, CK, LDH and they present the respective expressions AST and(7,045-0,2292x+0,007991x2+ 0,008517z- 0,0003282xz) CKand(8,06-,07020x+0,05546x2-0,001262x3+0,01204z+0,0006207xz), LDH and (6,624-0,3522x+0,03448x2-0,0008382x3+0,02401z-0,0007489xz). The oil is an important and well-used energy source for horses in exercise,because its addition to the diet of animals submitted to endurance test causemetabolic alteration that favored energy production. The animal metabolism saveits energy reserves derived from glucose and favored the use of the oil. Thesmaller plasmatic activity of the AST, CK and LDH, enzymes with the additionof oil to the diets indicated directioning of the energy metabolism to β-oxidation.As the enzymes show several isoenzymes, it was concluded that the enzymes studiedact widely on the energetic metabolism, favoring constant ATP reposition duringall exercise.
