A New Classification to Diagnose Type of Anemia in Standardbred Horses: A Retrospective Study

Anemia is defined as a decrease in the erythrocyte content or oxygen-carrying capacity of blood as a consequence of a drop in packed cell volume (PCV), red blood cells count, or hemoglobin concentration to less than the lower limit of the reference interval. Anemia has usually been classified as mild, moderate, severe, and very severe based on PCV values, and as micro/normo/macrocytic and hypo/normo/hyperchromic based on mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC), respectively. This study aimed to propose a new classification based on hematological breed range to diagnose the types of anemia and to determine their incidence in Standardbreds in Italy. A retrospective study was carried out on 168 Standardbreds. Severity of anemia based on PCV (%) was classified as: slight (36%-34%), mild (33%-30%), moderate (29%-20%), severe (19%-13%), or very severe (<13%). The classification on the basis of the erythrocyte indices was: microcytic (MCV ≤ 39.9 fL), normocytic (40 ≤ MCV ≤ 44.9 fL), or macrocytic (MCV ≥ 45 fL) and hypochromic (MCHC < 36 g/dL), normochromic (36 ≤ MCHC ≤ 38 g/dL), or hyperchromic (MCHC ≥ 38.1 g/dL). Overall, 42.8% horses had slight anemia, 44% mild, and 13.2% moderate anemia. The most common form diagnosed was normochromic normocytic anemia. This new classification was able to identify as slight anemic Standardbreds which otherwise should have been considered still within the lower part of the normal range for hot blood horses. The proposed classification might be a useful first screening step for clinicians when faced with a Standardbred suffering from poor performance and anemia, to reach a correct diagnosis.