Merck Manual

Please confirm that you are a health care professional

honeypot link

Introduction to Blood Disorders of Horses


Susan M. Cotter

, DVM, DACVIM (Small Animal Internal Medicine and Oncology), Tufts University

Last full review/revision Mar 2019 | Content last modified Apr 2019
Topic Resources

Blood cells form and develop mostly in the bone marrow, that is, the tissue located in the cavities of bones. Blood performs a variety of important functions as it circulates throughout the body. It delivers oxygen and vital nutrients (such as vitamins, minerals, fats, and sugars) to the body’s tissues. It carries carbon dioxide to the lungs to be exhaled and waste products to the kidneys and liver to be eliminated from the body. It transports hormones, which are chemical messengers, to various parts of the body, allowing those parts to communicate with each other. Blood also includes cells that fight infection and platelets that control bleeding.


Types of Blood Cells*

*See chapter text for descriptions and functions.

There are 3 cellular elements of blood: red blood cells, white blood cells, and platelets. Basically, red blood cells supply the body with oxygen; white blood cells protect against infection; and, platelets start the formation of blood clots.

Blood is a complex mix of plasma (the liquid component), red blood cells, white blood cells, and platelets.

Blood is a complex mix of plasma (the liquid component), red blood cells, white blood cells, and platelets.

Blood disorders are quite diverse. They can occur as normal responses to abnormal situations; for example, a significant increase in the number of white blood cells in response to an infection or disease. They may also occur as primary abnormalities of the blood; for example, a deficiency of all cellular elements of the blood due to bone marrow failure. Furthermore, abnormalities may be quantitative (too many or too few cells) or qualitative (abnormalities in the way cells function). It is helpful to understand what the names of some blood disorders mean, as they often provide a description of the disorder itself (see Suffixes table below). Like people, horses have different blood groups or types. Researchers have identified 8 blood types in horses: A, C, D, K, P, Q, U, and T. Groups A, C, and Q are considered the most important. Horse owners and breeders will often have a record of their horse’s blood type. This should be included in the medical records for your horse.


Suffixes Used in Names of Blood Disorders





Increase in blood levels of that type of cell



An abnormal increase in blood levels of that type of cell; can also refer to a disease process



Decrease in blood levels of that type of cell



Destruction of that type of cell



Denotes the presence of a substance in the blood



To stop or stabilize


For More Information

Also see professional content regarding blood and blood disorders.

Others also read

Also of Interest

Become a Pro at using our website