What is Hypercalcemia?
Chronic renal failure, hyperparathyroidism, and even certain cancers can cause a persistent overabundance of calcium in the blood that can lead to increased thirst and urination, muscle weakness, and, in severe cases, cardiac arrhythmias. Known as hypercalcemia, this disorder may also be related to an excess of vitamin D or the ingestion of large quantities of specific plants known for inducing hypercalcemia when grazed upon. Prognosis for horses with this imbalance is dependent on the underlying cause and the speed of diagnosis.
Hypercalcemia, or an overabundance of calcium in the blood, can be an indicator of other conditions. Symptoms of hypercalcemia may be an indication of serious illness and should be evaluated by a veterinary professional.
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Symptoms of Hypercalcemia in Horses
Several symptoms are common to horses with hypercalcemia regardless of the cause of the hypercalcemia. They are, however, somewhat non-specific and further testing is required for a definitive diagnosis:
- Cardiac abnormalities
- Increased thirst
- Increased urination
- Leg stiffness
- Loss of appetite
- Muscle weakness
- Poor performance
- Weight loss
Calcium can enter the bloodstream of a horse in several different ways.
- Absorption - Most calcium absorption occurs in the ileum, the last and longest portion of the intestines; unlike most mammals, the intestinal absorption of calcium is mostly independent of vitamin D intake
- Excretion from kidneys - Both anion-bound and ionized calcium are filtered through an area of the kidney called the glomerulus, a group of tiny, intertwined blood vessels located within the kidneys; horses excrete a much larger percentage of absorbed dietary calcium in this manner than most other species
- Release from the bone - Calcium and phosphate are contained within the bones, and are released from the bone by stimulation from parathyroid hormone
Causes of Hypercalcemia in Horses
Chronic renal failure
The kidneys are particularly important for the excretion of calcium for horses. Kidneys that are functioning poorly may not be excreting enough calcium, causing it to build up in the blood.
Some plants can cause vitamin D to increase in the bloodstream, thereby increasing the amount of calcium in the blood stream, although feeds that are incorrectly formulated are a more common cause. Hypervitaminosis D is the only condition that causes increased levels of both calcium and phosphate.
Although this is not a well-understood syndrome, it is believed to be associated with placental insufficiency.
Many growths, including several types of cancer, can lead to increased calcium levels in the blood.
This is a rare condition in horses, but should be considered if other causes have been ruled out.
Diagnosis of Hypercalcemia in Horses
Hypercalcemia, or an overabundance of calcium in the blood, is usually diagnosed during comprehensive blood testing such as the biochemical profile and complete blood count. Several factors can cause the calcium test to be inaccurate, however, and these should be taken into account. For instance, certain anticoagulants can cause calcium levels appear to drop, particularly those containing citrate, EDTA, fluoride chelate calcium, or oxalate. Some disorders can also cause erroneous results; abnormalities in the albumen or protein concentrations can have an effect on the amount of calcium, falsely increasing or decreasing the amount of calcium reported in the circulatory system, although the correlation in horses is less than in other species.
High levels of fat in the blood or the rupture of red blood cells may also falsely raise total calcium levels. Acidosis is another condition known to interfere with a blood test involving calcium; although total levels of calcium will be accurate, the ionized calcium is increased due to a decrease in the amount of calcium that is bound to protein. The diagnosis of hypercalcemia is usually followed by additional testing in order to precisely determine the underlying condition.
Treatment of Hypercalcemia in Horses
If your horse is in distress when he is examined by the veterinarian, supportive treatments are likely to begin as soon as possible. Fluids and electrolytes will be administered intravenously in order to prevent dehydration, and if the underlying disorder is making it difficult to breathe as well, oxygen will usually be offered. There is usually an underlying cause of hypercalcemia that will require additional measures, such as the reduction of vitamin D in the diet or even surgery, before the increased levels of calcium will completely normalize.
There are treatment methods that will help with reducing the calcium concentrations in the meantime. These treatments will be focused on one of three approaches; reducing intestinal absorption of calcium, increasing the excretion from the kidneys, or lessening the amount of calcium released from the bone. The most common way to reduce the amount of calcium absorbed by the intestines is to cut back the amount of calcium in the diet itself. Diuretics may also be given, although thiazide diuretics should be avoided as it stimulates calcium reabsorption.
Recovery of Hypercalcemia in Horses
Initial treatments that reduce the calcium levels in the blood will ease many of the symptoms, the overall prognosis for horses that have elevated levels of calcium in their blood depends on the underlying causes. If the cause is an increase in vitamin D, the removal of the vitamin D from the diet should result in recovery, however, mineralization in the heart or kidneys worsens the prognosis. The outcome will also be influenced by how advanced the condition is particularly with kidney degeneration or cancers. Certain foods such as feeds high in protein or calcium should be avoided, and salt will most likely be restricted as well.