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Many varieties of pasture mixture include white clover (Trifolium repens) and red clover (Trifolium pratense) due to their high protein and calcium content as well as their palatability. Occasionally, a variety of clover known as Alsike clover (Trifolium hybridum) will be added into mixes for their hardiness or will be found growing wild. The Alsike clover can induce photosensitivity or liver trouble for horses who snack on it. This clover is made all the more dangerous due to its palatability, as horses will often consume large quantities.
Although most clovers are a safe and valuable addition to many pasture mixtures, the Alsike clover (Trifolium hybridum) is known to cause photosensitivity and liver damage to horses.
Signs associated with clover toxicity are usually slow acting, taking weeks to months to show up. Symptoms of photosensitization can occur anywhere on the body but are most common in areas of low pigment or in places where the hair is sparse:
Liver disease is less common than photosensitization, and the symptoms more severe:
Several types of clover are commonly found in pastures and fields. Alsike clovers have white flowers and leaves with finely serrated edges. It can also be differentiated from the other varieties by the lack of a white V on the leaves. Some of the most common other than Alsike clover include:
Red Clover - This variety has red or purplish flowers and hairy stems; red clover takes the longest to dry and is the most likely to develop mold in periods of high humidity and he mold that grows on clover plants is responsible for a disorder known as “slobbers” causing the horse to drool in excessive amounts
White Clover - Also known as Dutch clover, this is a low growing variety with white flowers; the mold responsible for slobbers also grows on this variety of clover
The toxin in Trifolium hybridum is still a mystery. The amounts that are required to damage the liver or induce toxicity is unknown, but the number of cases seems to be increased when this type of clover is comprising 20% or more of the diet. Incidents of this disorder are sparse in winter months and eating the flower seems to increase the chances of developing symptoms.
A visit with your equine veterinarian will typically begin with a comprehensive history of the horse. This usually includes getting as much information as possible about the horse’s diet, medications, and environmental factors. Standard blood tests, including a biochemistry profile and complete blood count, will be evaluated to see if a systemic infection is present and to check the levels of liver and kidney enzymes in the blood. Phototoxicity is generally more prominent on areas with low pigment or on the areas most exposed to the sun.
A sample of the affected skin will be taken to examine by cutaneous cytology. This microscopic examination will help reveal if mites, fungal infections, or allergies are the cause of the rash. If that does not locate the underlying cause, a biopsy of the tissue will be required for further evaluation. If any dysfunction with the liver is revealed then ultrasound technology may be used to get a better view of the abdomen, and confirm if any swelling is present.
Treatment for this disorder, beyond removing the clover from the horse’s diet, is mainly supportive and symptomatic and will, therefore, depend on which symptoms are being displayed. If the horse is demonstrating signs that they are in serious distress, IV fluids will generally be offered to prevent dehydration and ensure that any imbalances in the system are addressed. If the patient is exhibiting signs of photosensitization, they should be kept out of the sun until the liver enzyme results have returned to their normal levels.
Antibiotic, antifungal, and anti-inflammatory medications may be prescribed for the animal as needed, either orally, topically, or by injection. Generally, once the symptoms of liver disease become obvious, the bile ducts and surrounding tissue are irreversibly scarred, and the disease has progressed past the possibility of significant improvement. A change to a low-protein diet is sometimes recommended to reduce the amount of intestinal ammonia in the system in order to prevent any further damage to the liver.
The best treatment for this type of disorder is prevention. Luckily, alsike clover can usually be easily differentiated from the other clovers in the field as it grows much taller than its cousins. If you locate alsike clover in your area, it is usually easiest to plow and replant the entire field. Other possible options include increasing the amount of grass forage to reduce the amount of clover in the field or reducing the overall concentration of clover plants in the pasture by using a broadleaf herbicide.
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