SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
activities than the three year old fillies and colts . Unfortunately , no two year old colts were studied . In a later study of sixty-six 2 and 3 year old thoroughbred racehorses in training , it was found that fillies were more likely to have high CK and AST activities than colts , and two-year-olds more likely to have raised ASTs than the three year olds . The effect of age on the incidence of raised muscle enzyme activities was thought not to have been caused by the natural loss of 2 year olds from training with high enzyme activities , especially as several of these raced and won . It may be that certain animals have physiologically higher plasma activities or their muscle enzymes are more slowly removed from the circulation . Alternatively , they may be more sensitive to the various insults that cause permeability changes in muscle fiber membranes . A genetic contribution to these observations has not been ruled out , and age and / or training could have a dampening effect on these muscle membrane changes .
Time of Year and Training
Several workers have suggested that AST plasma activities increase in the early stages of training and then decrease as the training progresses . Time of year has been shown not to have a significant effect on the number of animals with normal or with high AST and CK activities . However , an increase in the mean activities to a peak in April and May followed by a decrease to a low in September was shown in this group of thoroughbred racehorses in the Northern hemisphere . The very high mean activities found in April , May and June were accompanied by very high standard deviations which made definitive conclusions difficult . Such large standard deviations were also found in another study on thoroughbreds in training . On an individual basis , a change in AST activities does not always seem to occur with training . Changes in the serum levels of AST concentrations have not been thought to be good indicators of peak fitness or slight overtraining .
In a recent study of AST activities in a small number of barren and pregnant standardbred mares , evidence for a diurnal rhythm was found , with the lowest activities occurring in the early hours ( 0400-0600 ) and the maximal ones at night ( 2200-2400 ). The mean levels increased from September-November until March . A circannual cyclicity was found but the pattern differed between the two groups . In the barren animals the arcophase appeared to occur in the second half of January whereas for the pregnant animals it occurred in September ( approximately month 5 of pregnancy ). The error fields were , however , quite broad .
Relationship to Performance
It has been stated that elevated CK and AST activities decrease a horse ' s chance of winning . However , a group of 500 standardbred trotters with a recent history of equine rhabdomyolysis and raised plasma muscle enzyme activities , had a significantly better racing record compared to a large , comparative group of apparently unaffected horses . 50 % of the horses with high median AST activities raced and won at least once in another study . It is , however , obviously not possible 66