HEMATOLOGIC AND SERUM BIOCHEMICAL VARIABLES AND PLASMA CORTICOTROPIN CONCENTRATION IN HEALTHY AGED HORSES

Objectives-To compare hematologic and serum biochemical variables and plasma ACTH concentration between healthy horses 5 to 12 years old and those more than 20 years old. Animals-30 healthy horses 5 to 12 years old and 30 healthy horses more than 20 years old. Procedures-Venous b lood was collected from all horses, and CBC and serum biochemical anal ysis were performed for each horse. Plasma ACTH concentration was dete rmined by radioimmunoassay. Student's paired t-test or the Mann-Whitne y rank sum test was used to compare values between control and aged ho rse groups. Results-Compared with values for control horses, aged hors es had significantly higher erythrocyte mean cell volume and mean cell hemoglobin. Aged horses also had significantly decreased total lympho cyte count. Five aged horses had lymphocyte count that was lower than the low reference limit as established for horses in our laboratory. D ifferences between control and aged horses for serum biochemical or pl asma ACTH values were not significant. Conclusion-Compared with younge r adult horses, those more than 20 years old have some hematologic dif ferences, but there is no apparent effect of aging on baseline plasma ACTH concentration. Clinical Relevance-It is important to establish ag e-matched control values for optimal interpretation of clinicopatholog ic variables.