Circulatory System of a Horse

The horse belongs to the family Equidae and subspecies Equus ferus caballus. It has evolved from a small multi-toed creature to a large single-toed animal today. It has a well-developed sense of balance and a strong fight or flight instinct. A horse has a lifespan of 25 to 30 years and reaches adult development by the age of five. It is able to sleep both standing up and lying down. Horses are a grazing animal and mainly feed on good-quality forage from hay and pasture.

There are nearly 300 breeds of horses which can be differentiated into three categories on the bases of their temperament - cold bloods or draft horses like Belgian, Clydesdale for slow and heavy work; hot bloods or oriental horses like Akhal-Teke, Barb, Arabian Horse for speed and endurance; and warm breeds (cross between cold bloods and hot bloods) like Trakehner, Hanoverian for specific riding purposes.

The interaction between humans and horses is not restricted to sport competitions and recreational pursuits only, but horses are also beneficial in working activities like police work, entertainment, agriculture, assisted learning and therapy. Horses have been used for their by-products like milk, meat, hair, bone, hide and the pharmaceutical extracts from the urine of pregnant mares (female horses).

Circulatory System of a Horse

The circulatory system of a horse comprises of the heart, blood, blood vessels, spleen and the frog.

Heart
A horse's heart is made up of muscle tissues and is more rounded in shape as compared to the human heart. It pumps blood throughout the body and is divided into four chambers: the left and right atria, and the left and right ventricles. The average weight of a horse's heart is 3.6 kg or 8.5 lb, though sometimes it can be more than twice this size. The heart of a horse grows till the horse reaches an age of four years, but can also increase with proper conditioning.

Blood and Blood Vessels
The blood is formed of erythrocytes (red blood cells), leukocytes (white blood cells) and the plasma. The red blood cells are produced in bone marrow and are responsible for carrying oxygen to tissues and removing carbon dioxide through hemoglobin. The white blood cells are present in the body's immune system and protect against pathogens and foreign infectious materials. The plasma contributes to the blood volume and suspends the blood cells which contain clotting factors. The heart and blood vessels of an adult horse contain nearly 34 liters of blood.

Spleen
The spleen eliminates damaged red blood cells from circulation and holds extra blood cells. It releases these blood cells during exertion to increase blood volume and the quantity of oxygen carried to the tissues.

Frog
Each foot or hoof of a horse contains a structural component known as the frog. This frog covers the deeper structure of the foot called the digital cushion which is a vessel-filled tissue. When a horse puts weight on his leg, the ground pushes upward on the frog and compresses it along with the underlying digital cushion. This squeezes the blood out of the digital cushion and pumps it back up the leg which helps the heart to function against the gravity.

Around 4000 BC, humans began to domesticate horses, and since then besides being a great companion they are been used for different purposes throughout the world. Horses require regular hoof care and vaccinations to protect themselves against harmful diseases. Regular grooming of a horse helps maintain good health of their hair coat and underlying skin.