Diurnal Variations of Blood Constituents in Young Thoroughbred Horses

Abstract

To delineate points to be attended to in utilizing blood constituents as parameters for diagnostic examination of race horses, serial changes of blood constituents were followed on a day of resting and a day of physical exercise in five 2-year-old Thoroughbred horses (2 males and 3 females) currently under a course of training equivalent to that for young prospective race horses. Of 31 blood constituent parameters assessed which are commonly measured in the clinical setting, 27 parameters revealed significant within-day variations (P < 0.05). Variations by 20% or more which are presumed to be of practical value from their nature were observed for 14 parameters: total leukocyte counts, neutrophil counts, lymphocyte counts, eosinophil counts, and serum levels of lactate dehydrogenase, glutamic dehydrogenase, total bilirubin, uric acid, glucose, triglyceride, potassium, inorganic phosphorus, triiodothyronine and thyroxine. Whilst the principal source of variations was physical exercise, there were several parameters which were inferred to be affected by such factors as feeding and daytime/night. Thus the present data indicated importance of due consideration of feeding conditions including quality and amount of physical exercise and of blood sampling time, for more accurate interpretation of data of hematologic and blood chemical tests. © 1995, Japanese Society of Equine Science. All rights reserved.