Anhydrosis – Drycoat Syndrome & Puffs – Non Sweating Disorder

What is anhydrosis?

Anhydrosis is the partial or complete inability to sweat in response to high body temperature. It can also spontaneously reverse.

Some background:

The skin is the major organ of the body and it has a multitude of tasks. One of these tasks is to regulate the horse’s body temperature. This is achieved by the skin through sweating when the horse’s body temperature is too high. The sweat glands are densely packed in the skin – averaging 800 glands/cm2. They are a tubular coiled gland that exits the skin at the hair follicle. They have a rich blood supply and are surrounded by nervous tissue. They appear to be stimulated by both the nervous system and hormones in the blood stream.

Horses are unique in that their sweat (and saliva) contain latherin – a soap like protein that reduces surface tension and spreads sweat easily over the coat. The cooling effect comes from the evaporation of sweat. it is the latherin that causes the white foam seen on some horse’s coats when sweating. Horses can lose up to twenty litres of sweat per hour and can lose 4 -30 kg of body weight when exercising. Electrolytes are secreted in the sweat and consist of sodium, potassium, magnesium, calcium, chlorides, sulphates, phosphates and bicarbonates. They lose three times more sodium than people and ten times more potassium.

When a horse exercises it produces heat in the muscles which is absorbed by the blood stream. As the blood circulates through the lungs some of the heat is lost as the horse exhales. As the blood circulates in the skin it loses heat by radiating it out. If the core temperature continues to rise the hypothalamus in the brain sends hormones to the sweat glands to tell them to produce sweat.

What causes horses to overheat?

• Hot and humid weather is a major stressor for horses as the humidity effectively prevents evaporation of sweat.

• Overworked unfit horses will sweat profusely.

• Nervous and agitated horses will also sweat profusely as their core temperature increases.

• Dehydrated horses can overheat because they cannot sweat adequately to lower body temperature.

• Inappropriate rugging of horses in hot weather

• Horses unable to access shade and cool water will also overheat.


What causes anhydrosis?

It can occur in any breed at any age and can occur overnight. The exact cause is unknown but chronic or acute lack of electrolytes can trigger anhydrosis. The sodium and potassium losses associated with sweating actually cause a decrease in thirst and appetite which leads to further dehydration.

It is also thought that constant and continuous stimulation of sweat glands, especially in very hot weather, may cause them to shut down.

What are the signs of anhydrosis?

There is very little, patchy or no sweat present after work or on hot humid days. They have a higher than normal body temperature and an elevated pulse. recovery is slow after exercise and they may appear distressed. puffing is a response of the body in trying to compensate for the lack of sweating. Their coat may appear flaky and dandruffy if they have had the condition for some time.

How to manage anhydrotic horses.

• Hose with cool water before and after exercise.

• Keep hosing and scraping water until the respiratory rate returns to normal.

• Only exercise in the cool of the morning or late evening.

• Keep susceptible horses in stables with fans, cool water mists and regular sponging down.

• Very cool drinking water will help lower core temperature faster than warm water.

• Allow paddocked horses access to dams or creeks to stand in.

• Only rug if absolutely necessary and use white 100% cotton rugs.

• If a particular horse is absolutely non-adaptive to a hot humid environment then it would be in the horse’s best interests to relocate to a more temperate climate.

• Supplement with a complete mineral and vitamin product such as Equilibrium or LexveT to supply all the minerals needed for sweating.

Dr. Jenene Redding BVSc (Hons)

Anaemia and Nutrition

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)