SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
In the horse CK is found mainly in skeletal muscle, the myocardium and the brain.
There appears to be little or no exchange of CK between the cerebrospinal fluid and
plasma. A significant increase in total plasma CK activity is, therefore, due to
cardiac and/or skeletal muscle damage. The plasma half-life of CK in the horse is
very short, 108 minutes, in contrast to the reports of 12 hours in man. The plasma
half-life of AST in the horse is 7-10 days, far longer than the 11.8 hours in man.
Exercise of all types produces an increase in plasma CK concentrations. Measuring
the CK and AST activities before and after a controlled period of exercise has been
suggested as an aid to the diagnosis of certain muscle disorders. A major difficulty
has been to establish exactly the "normal" enzyme response to exercise. There has
been much confusion regarding this, partly caused by the differences in the intensity
and duration of the exercise undertaken, the varying sampling intervals used, and
the inclusion of individuals with possible muscular problems. Generally, an increase
in CK activities occurs with hard exercise, whilst, with slower work, sometimes there
is no significant increase. Therefore, intensity is an important factor. However, it
has also been suggested that duration is equally or more important because values
are usually higher following prolonged endurance exercise.
Increases in AST activities of 35% have been reported following a 1,500 m canter
and 50% following strenuous exercise in previously rested animals. Often though,
there is little increase in AST following different types of exercise.
It is also widely held that less fit horses have higher CK and AST concentrations that
do their better conditioned counterparts. However, exceptions to this impression
have been noted. Large individual differences can exist in both resting and post-
exercise concentrations of CK and AST, so that while there may be a tendency for
values of these enzymes to decrease with training when a population is considered,
failure of an individual horse to display the same trend does not mean that it is less
fit or more prone to develop a myopathy. Consequently, the interpretation of the
result of a single test is difficult, as the effects of exercise on plasma muscle enzyme
activities may depend on the fitness of the animal, the intensity and duration of the
exercise, as well as the environment. Despite this, the following rule of thumb has
proven useful: increases of more than 100% in AST activity following exercise are
likely to be abnormal regardless of the intensity of the exercise or the fitness of the
animal. Also, if a short submaximal exercise test is carried out, the serum CK and
AST activities at 2 hours post-exercise should not rise to more than 250% and 50%
of the pre-exercise values respectively, regardless of fitness.
Other Factors Affecting AST AND CK Activities
Gender and Age
A group of thoroughbreds were sampled over a nine month period and it was found
that the two year old fillies showed more marked fluctuations in AST and CK
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