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Alsike Clover and Horses

Based on an Indiana case I became aware just recently, this may be the year for expression of alsike clover in pastures and resulting concerns of horses grazing this forage.  Until a few years ago, I had not even heard of the concern.  My memory suggests that there were reports of horses several years ago in the northeastern USA having photosensitization problems when grazing pastures with an abundance of alsike clover.  Horses are documented to be the animal most effected with use of alsike clover.

Alsike clover is commonly included as a part of a prepackaged pasture seed mix.  This forage is well adapted to cool climates and poorly drained clay soils.  In my opinion, as compared to alfalfa, red clover, ladino clover, and birdsfoot trefoil, alsike clover is an inferior forage to be used by Indiana farmers unless they have the soil type where preferred forages cannot survive.

An excellent reference I have in my library, and one I would suggest for yours, is Natural Toxicants in Feeds, Forages, and Poisonous Plants Second Edition by Peter R. Cheeke.  It is published by Interstate Publishers, Inc. phone:800-843-4774.  This reference indicates that there are two syndromes associated with use of alsike clover by horses, secondary photosensitization and alsike clover poisoning. Secondary photosensitization produces skin lesions.   Alsike clover poisoning can occur after exposure of several weeks or greater than a year.  It appears that the amount of time to note symptoms is dependent upon the amount of the clover being consumed as pasture or hay.  Symptoms include jaundice, neurological disturbances, anorexia and loss of body condition.

It is perplexing to me, and I am sure to many, that the causative agent within alsike clover that causes photosensitization has not been identified.  Likewise, evidence is not real strong to incriminate alsike clover as the causative agent of alsike clover poisoning. Evidence from alsike clover poisoning cases in Canada suggest that an endophytic (within plant) bacteria of the genus Capnocytophaga may have an important part in the expression of the disease.

Based on these experiences, I would advise horse producers in Indiana not to include alsike clover as a part of their pasture seeding or renovation practices.

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Keith Johnson
Professor of Agronomy and Forage Crops Specialist
1150 Lilly Hall of Life Sciences
West Lafayette, IN 47907-1150
phone: 765-494-4800
fax: 765-496-2926




For more forage information contact Dr. Keith Johnson: johnsonk@purdue.edu

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