Ministry of Agriculture

Alsike Clover Toxicity in Horses

Alsike Clover Toxicity in Horses

Hay or pasture containing a large percentage of alsike clover is generally not recommended for horses. Why is this? What are the symptoms of alsike poisoning? Why is it that some horses seem to be able to eat alsike with no ill effects? The confusing aspect of the disease is that none of these questions have straightforward answers. Firstly, the compound that causes the toxicity is not known for sure. Secondly, the symptoms vary and thirdly, susceptibility seems to depend on the area where the alsike is grown and the individual horse.

The most common symptom of alsike clover poisoning is photosensitization or a reaction to light. The real problem, however, which is not so readily observed, is liver damage.

The photosensitization is not caused directly by the alsike, but rather is a secondary problem. Dr. A. A. Seawright has summarized the literature concerning photosensitization. Alsike clovers may contain some compound, possibly an alkaloid, which causes liver dysfunction. If this cirrhosis of the liver is allowed to continue, death may result.

Another possible cause for the phosensitivity and liver cirrhosis is a fungus growing on the Alsike Clover leaves. This fungus (sooty blotch) is outlined in the paper written by Dr. W. Majak, B. M. Brooke and Dr. R. T. Olgivie (see pages 77-81).

The plant material that the horse eats contains chlorophyll. Bacteria in the intestinal tract change the chlorophyll into another substance, phylloerythrin. This is all quite normal. In an animal with a healthy liver, the phylloerythrin is removed from the blood by the liver, and excreted in the bile. However, in an animal where the liver has been damaged, it cannot pick up the phylloerythrin. It then is carried by the blood and deposited in the skin cells. When light of a certain wavelength is absorbed by the skin it reacts with the compound, damaging the cell and causing inflammation and redness. This occurs only on areas unprotected by thick skin, hair covering or pigmentation, such as in black skin. Therefore, liver damage may be present without any signs of photosensitization. Some horses may die within 24 hours of alsike consumption.

Symptoms of Photosensitization

  • Lining of eyelids, or conjunctiva, become red and swollen
  • Inflammation and lesions of the muzzle, mouth, tongue, eyes, eyelids, and ears, with discharge from the lesions
  • Jaundice
  • Nervousness
  • Digestive disorders; "off feed"
  • Brownish urine
  • Clay-colored feces

These are all possible symptoms; animals may show all of these or none.


If you notice symptoms that you suspect indicate alsike clover toxicity, remove horses from the pasture and change their feed. Contact your veterinarian to obtain a correct diagnosis. There is no specific remedy, but treatment may combat secondary infections. Some relief may be obtained by keeping the horse in a dark or shaded area.

If your only available pasture has alsike clover in it, you may wish to remove it or reduce alsike clover content in the forage.

Control of Alsike Clover in Horse Pastures

If you have a grass-legume pasture for horses where alsike clover is a problem, the clover can be removed by spraying with the herbicide Banvel/Banvell II (dicamba). Apply at 600 ml/ha (240 ml/acre) in at least 110 L/ha of water. The application should be made when the clover is actively growing but before it gets too large.

Spraying can also be done in the fall after grazing or haying while the clover is still green. Fall spraying is not quite as effective as in May or early June.

While no grazing restriction is indicated on the label for horses, there is one if beef or dairy cattle are grazing the same pasture. Do not slaughter meat animals fed with treated forage or grazed on treated areas within 30 days after application.

Lontrel 360 (clopyralid) provides excellent control of clover when applied to actively growing plants either in the spring or fall. Use 420 ml/ha (170 ml/acre) applied in 100 to 200 L/ha of water. Forages treated with Lontrel may be grazed immediately following treatment. Recropping restrictions preclude the seeding of any legume crops the year following application.

If the decision is made to remove the clover from a horse pasture or hay field, then it should be fertilized with nitrogen to compensate for the clover removal. This is necessary to maintain yield, forage quality and competition against weeds. High rates of nitrogen fertilizer (67 to 100 Kg/ha actual N) will also help to suppress clover growth and promote good grass growth.

A quick method for identifying different clovers

Identification of the different clovers used for forage can be difficult at times because they all display similar features. The quickest method of identifying the different clovers is by comparing where the flower appears on the plant.


White Clover

White clover drawing White clover photo
Drawing courtesy of Agriculture & Agri-Food Canada, Research Branch. Reproduced from "111 Range and Forage Plants of the Canadian Prairies" Reproduced with the permission of the Minister of Public Works and Government Services Canada, 2000. Photo courtesy of Agriculture & Agri-Food Canada, Research Branch. Publication "Licensed Varieties of Cultivated Grasses and Legumes" Reproduced with the permission of the Minister of Public Works and Government Services Canada, 2000. Found in "Alberta Forage Manual"

Low growing white and tall growing ladino clover have a white flower that terminates a single stalk coming from the above-ground stem (stolon). The leaflets are also found on separate stalks from the stolon.

Alsike Clover

Alsike clover drawing Alsike clover photo
Alsike clover drawing Photo courtesy of BC Agriculture

Alsike clover flowers are usually pink and white in color but can be darker depending on growing conditions. The flower stem originates from the same point off the main stalk as separate leaflet stems.

Red Clover

Red clover drawing Red clover photo Red clover photo
Drawing courtesy of Royal British Columbia Museum "The Pea Family" Photos courtesy of BC Agriculture

Red clover leaves are usually hairy and may contain an inverted "V" watermark. The flowers are usually dark purple and are borne at the terminal end of the stems which also bear leaflet clusters.

For More Information

Ken Awmack
BC Agriculture - Regional Agrologist
William Lake, B.C.
250 - 398-4500

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