Hematologic and serum biochemical variables and plasma corticotropin concentration in healthy aged horses

Abstract

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 blood was collected from all horses, and CBC and serum biochemical analysis were performed for each horse. Plasma ACTH concentration was determined by radioimmunoassay. Student's paired t-test or the Mann-Whitney rank sum test was used to compare values between control and aged horse groups. Results - Compared with values for control horses, aged horses had significantly higher erythrocyte mean cell volume and mean cell hemoglobin. Aged horses also had significantly decreased total lymphocyte count. Five aged horses had lymphocyte count that was lower than the low reference limit as established for horses in our laboratory. Differences between control and aged horses for serum biochemical or plasma ACTH values were not significant. Conclusion - Compared with younger adult horses, those more than 20 years old have some hematologic differences, but there is no apparent effect of aging on baseline plasma ACTH concentration. Clinical Relevance - It is important to establish age-matched control values for optimal interpretation of clinicopathologic variables.