Cushing’s Disease Challenges

Definition:

Cushing’s disease is a hormonal disease resulting from a benign tumor in the pituitary gland, and causing the disproportionate release of the hormone adrenocorticotropin or ACTH. This hormone fuels an increase in the quantity of cortisol hormones that are released into the bloodstream from the adrenal glands. This excess of these cortisol hormones leads to the typical Cushing’s disease clinical signs which include a long, shaggy, curly hair coat that doesn’t shed during the warm weather months, weight loss coupled with abnormal fat deposits over parts of the body, increased drinking and urinating, increased susceptibility to infections, and chronic laminitis. Some theorize that the clinical signs of Cushing’s disease are due to the pressure by the tumor on the hypothalamus, an area of the brain that produces hormones that controls the release of hormones by the pituitary gland. Affected horses are usually between the ages of 19 and 21 years. Ponies seem to be more susceptible than larger horses, and some studies would indicate that mares are more susceptible than gelding or stallions.

Diagnosis:

Horse with Cushing's DiseaseVeterinarians will often suspect Cushing’s disease just by the outward clinical signs, although a variety of blood tests can be used to confirm the diagnosis. The most common test is measurement of ACTH levels in the blood, ACTH levels in horses with Cushing’s disease having been reported to be approximately six times higher than those measured in normal horses. This test does require very careful handling of the blood samples. On the other hand, the most reliable test in the diagnosis of Cushing’s disease is the low-dose dexamethasone suppression test or LDD test. In this test, first the horse’s resting cortisol levels in the blood are measured, and then a dose of corticosteroid medication call dexamethasone is administered. In a normal horse, the dexamethasone suppresses the normal release of cortisol, which results in a lowered or “suppressed” resting cortisol measurement. However, in a horse with Cushing’s disease, the resting cortisol levels will remain normal since the normal feedback mechanisms that control the release of cortisol will not respond to the administered dexamethasone.

Since laminitis is a potential complication of dexamethasone administration, many veterinarians are reluctant to perform the LDD test on a horse that is already experiencing symptoms of laminitis lest it worsens the condition. In these cases blood tests can be used to help confirm the diagnosis.

Treatment:

Good basic care is the main element of a treatment plan for a horse with Cushing’s disease. This means clipping the hair coat during the hot weather months and making sure it does not becomes matted. Since Horses with Cushing’s disease are prone to dental problems due to their propensity to infections, regular dental care is very important. Laminitis being one of the chief complications of Cushing’s disease, special attention to foot care is necessary to minimize any chance of this problem occurring. A proper diet is also a requisite for keeping a horse suffering from Cushing’s disease as healthy as possible. Some recommend feeding hay with less that 10% total sugar plus starch

For now, there are two medications that can help treat the symptoms of Cushing’s disease: pergolide mesylate and cyproheptadine, the latter being less effective than pergolide.  In some cases, pergolide and cyproheptadine have been used in combination for maximum effectiveness, especially in horses that have developed a resistance to pergolide over a period of 2 to 3 years.

Conclusion:

In most cases, Cushing’s disease is a fairly benign condition with a few problems that can be easily managed. Nevertheless, when laminitis becomes a major component of the disease, it can then become life threatening being an extremely painful condition that can be difficult to control. When a horse has Cushing’s disease, the laminitis that accompanies it is often resistant to treatment and can easily spiral out of control.

The high levels of circulating cortisol in the horse’s system can also lead to complications since it causes the horse to be susceptible to infections. In particular, skin infections that are exacerbated by the long hair coat and excessive sweating that accompanies Cushing’s disease may require extra attention as well as any infections in the periodontal tissues that can lead to dental problems, including tooth loss and even sinus issues.

Allergies in Horses

Anyone with allergies knows how frustrating allergies can be, and how frustrating it may have been to find out exactly what you are allergic to. It is no less frustrating for horses and their owners; frustrating for the owners who are desperately seeking cause and remedy; frustrating for the horses who can find little relief from runny eyes, welts or itching.

Any dictionary will explain to you that an allergy is a strong abnormal reaction by the immune system to a normally harmless substance or substances located in the environment. These “allergens” can be introduced into the body by inhalation, ingestion, or skin contact, the reaction often manifested by itchy eyes, runny nose, wheezing, skin rash, or diarrhea. When first exposed to the allergen, the leukocytes or white blood cells produce antibodies to prepare the body’s immune system for its next encounter with the particular allergen in question. At this point, you don’t see any outward signs. The resulting antibodies attach themselves to what is known as a “mast” cell which is simply a large granular cell commonly present in connective tissue, capable of producing heparin, histamine, and serotonin. These mast cells are found in the respiratory system, the gastrointestinal tract, as well as the skin.

 Once the next exposure occurs, allergens will react with the antibodies releasing the chemicals that produce the allergic reaction. These symptoms can show up in other ways depending on the part of body affected, but are almost always in the form of an inflammation of some kind. In horses, the most typical manifestation is either a skin irritation like hives, welts, urticaria or a respiratory problem comparable to asthma in humans. Other allergic reaction symptoms include tearing eyes, runny nose, or digestive upset. Contact dermatitis is a result of exposure to foreign substances such as pesticides, heavy metals, dyes, topical medications, soaps, shampoos, blankets, wool, and poison ivy or poison oak. Atopy, or the tendency to be “hyperallergic” and SSRD (Seasonal Recurrent Dermatitis), which is a medical condition caused by hypersensitivity to insect bites, particularly midges, are also triggers for allergy-related symptoms.

 What are commonly called “protein bumps”, which resemble large BBs underneath the skin, are caused by an allergic reaction to a certain protein, usually a protein introduced by an insect bite. Scabby itchy outbreaks on the skin are the signs of another allergic reaction which causes the horse to rub the spot often enough to remove hair thus creating a sore or sores. A culture of the sores can assess whether it is an allergic reaction or a bacterial infection, in which case a treatment with antibiotics can alleviate the condition.

 Inhaled allergens are more likely to cause hives, teary eyes, runny nose, and coughing. These symptoms are often alleviated by replacing hay with a compete feed formulated to replace hay, thus decreasing the amount of dust and pollen from hay or submerging the hay in water before feeding. Wetting down stall bedding or completely changing the kind of bedding, and arranging for all the pasture time as possible, are the additional management choices available.

Attempting to determine the exact cause of an allergic reaction can be simultaneously frustrating and expensive, and usually ends up being an application of the “Trial and Error” test. In the matter of a food allergy, the sole reliable way of pinpointing which food is causing the allergy is an elimination diet. The difficult therein lies in the fact that finding a diet containing none of the suspect allergens and yet meeting a horse’s nutrition criteria is virtually impossible. One option is to place the horse on a hay only diet for a couple of weeks to see if the symptoms disappear. In the event the symptoms do not disappear, then it would be safe to conclude that the allergy is not food-related. Should the symptoms disappear, reintroduce each separate food one at a time until one triggers an allergic reaction.

Thrush: Causes and Treatment

Definition and causes

The Merck Veterinary Manual describes thrush as “a degeneration of the frog with secondary bacterial infection that begins in the central and collateral sulci”, the sulci being the valleys on either side of the frog and the small groove in the middle of the frog. The bacterium that causes thrush is found in the horse’s environment, and grows very well in wet, unsanitary conditions such as dirty stalls or muddy paddocks. It is an anaerobic bacterium that prefers a low-oxygen environment, and finds the clefts of the frog a perfect place to multiply. The infection can extend into the sensitive tissue all the way into the digital plantar cushion and, if left unchecked, into the navicular and coffin bones themselves. Although a number of bacterial species may be involved in causing thrush, Fusobacterium necrophorum seems to be the most common.

Symptoms

A hoof infected with thrush will have an offensive odor, the surface of the frog being white and crumbly, and a thick, dark colored discharge will be found in the cracks, depressions, or fissures in the horn of the frog. Although a horse with thrush is not necessarily lame, if the infection is allowed to invade the sensitive tissues of the frog lameness will ensue, especially if thrush has found its way to the central sulcus.

Treatment

The best treatment is good foot care. When thrush is found in a horse’s hoof the farrier or veterinarian will trim away the flaps of the frog to expose the infected area. From then on the following treatment recommended is as follows:

  1. Cleanse the foot, the clefts in particular, with warm water and disinfectant, using a wire brush.
  2. Clean up the horse’s living conditions, if necessary
  3. Treat with a germ-killing product. Some farriers recommend using iodine or a bleach-and-water mix, diluted 50-50. Of course, the product used will depend on how much sensitive tissue is exposed. If the infection was caught before it got very advanced and it’s only superficial, the diluted bleach would be fine. However, if the sensitive tissue of the frog has been compromised, the bleach would be much too caustic and would burn. If this case, the use of an iodine solution or commercial thrush lotion would be in order. Be careful not to use medications containing formalin if the frog is tender when cleaned out.
  4. Be careful when using a hoof pick to clean a thrush-infected hoof since you may be dealing with exposed sensitive tissue. Rather than a hoof pick, use a strip of gauze to clean a deep central sulcus, pulling it through the groove as you would dental floss.
  5. Bandage the hoof to prevent contamination.
  6. Treat the infection once a day for the first week, every other day for the second week, every third day for the third week, every fourth day for the fourth week, and then leave it alone for two weeks. Thrush usually disappears quickly and completely if the above steps are taken and seriously followed.
  7. A bar shoe may be used to promote frog regeneration