What is anaemia?
Anaemia is a deficiency in the number or quality of erythrocytes (red blood cells) that are circulating in the blood and that are stored in the body.
There are several types of anaemia, each with different causes and treatments. as treatments vary depending on the type of anaemia, it is important for the vet to advise you on the type of anaemia your horse is suffering. These include:
1. Blood loss anaemia
Ulcers, parasites, trauma, haemophilia.
2. Haemolytic anaemia
Infectious, toxic causes autoimmune, eg isoimmunisation of foals
3. Dyshaemopoietic anaemia
Selective depression of red cell production due to poor nutrition (deficiencies of iron, copper, cobalt, protein and B vitamins), parasites, viruses, bacterial toxins. in the case of horses having viral infections there is often bone marrow suppression and a subsequent anaemia and lymphopaenia (reduction in white cells) occurs. These are generally self limiting and with recovery the cell counts return to normal. extra iron supplementation is of no value in these kinds of anaemia.
4. Aplastic anaemia
Red and white cells are depressed as are platelets- typically caused by radiation poisoning, toxins (eg. pesticides, arsenic)
Anaemia can also be described by its appearance – cell size changes are described as normocytic, macrocytic and microcytic.
The haemoglobin content is described as normochromic or hypochromic. These descriptions can help to determine the cause of the anaemia.
What is the function of erythrocytes?
They are needed to transport oxygen from the lungs to all the cells and tissues of the body. Oxygen is the fuel that enables cells to function in order to maintain life. The life span of an erythrocyte is approximately 145 days in the horse. The cells are broken down in the liver, spleen and bone marrow. The proteins are conjugated in the liver and excreted in bile. The iron is stored in the liver and then transported to the bone marrow for the manufacture of new red blood cells.
How does a laboratory measure erythrocyte numbers?
The packed cell volume (pcv) is a percentage measure of the mass of erythrocytes in the fluid component of blood. A normal pcv is in the range of 32 – 53%. The spleen is a reservoir of erythrocytes should extra ones be needed in the circulation for exercise, trauma, shock and excitement. The pcv can be falsely elevated by splenic contraction and dehydration. a laboratory can also look at red cells in blood smears to check for their size, shape and colour. This then determines the type of anaemia that is present.
What causes anaemia?
Anaemia can be caused by blood loss, chronic inflammation and viruses. increased destruction of erythrocytes can occur with auto immune diseases and toxic chemicals. Reduced production of erythrocytes can occur with major nutritional deficiencies and cancer of the bone morrow. It is important to remember that anaemia is a symptom of an underlying primary problem that needs to be correctly diagnosed in order to ascertain the cause.
Dr. Jenene Redding BVSc (Hons)