Page 730 - The Veterinary Care of the Horse

diseases. T lymphocytes recognize and destroy cancer cells.

5 Monocytes are important cells in the immune system. In the presence of inflammation
VetBooks.ir from tissue damage or infection, they migrate from the blood into the tissues and

transform into macrophages. They engulf and digest bacteria, viruses, dead tissue and
foreign bodies.

Platelets

Platelets play an important part in the clotting mechanism of blood. This helps to ensure that
damaged blood vessels are quickly plugged and sealed to prevent serious haemorrhage.

Plasma

Plasma is the fluid in which the above cells are suspended and circulated around the body. It

is 93% water and approximately 6% protein and 1% minerals and salts. In the healthy horse
it is a clear straw colour. Whereas the blood cells and large protein molecules remain in the
circulation, the water component of the plasma with dissolved nutrients and gases can pass

freely through the thin capillary walls into the tissues where it forms tissue fluid. At the
arterial end of the capillary network, the pressure within the capillary from the pumping

action of the heart encourages the escape of fluid into the tissues. At the venous end the
pressure in the capillaries is smaller and most of the fluid is drawn back into the capillaries
due to an osmotic gradient caused by the large blood proteins such as albumin. Some of the

tissue fluid drains into a second network of vessels that form the lymphatic system. Once it
enters these vessels, it is called lymph.

BLOOD DISORDERS

Anaemia

Blood is made up of red blood cells, white blood cells and platelets, suspended in fluid called

plasma. If a horse has fewer red blood cells than considered normal for its breed and type, it
is said to be anaemic.

Red blood cells contain a pigment called haemoglobin. This pigment combines with
oxygen in the lungs to form oxyhaemoglobin. As the blood circulates around the body, the

oxygen is given up and used by the various tissues to produce energy.

There are several laboratory tests used to check whether a horse is anaemic.