Vitamin B1 (thiamin)
Fast fact: Anecdotal evidence suggests that feeding brewers yeast, which contains B1, calms nervous horses and stimulates appetite.

How your horse uses it: To metabolize carbohydrates and, therefore, extract energy from his diet. B1 also is critical to nervous system function.

Where it's found: Vitamin B1 is produced by gastrointestinal bacteria, but not in a sufficient quantity to meet a horse's needs. Fresh and dried green leaves and cereal grains contain high levels of B1, but several factors affect content: After a year in storage, hay contains only 5 percent of its original B1. Heat processing of grains decreases its level and stripping the husks removes all of it.

Dietary requirements: The minimum recommended amount of B1 is 3 mg/kg of dry diet matter daily--enough to be supplied by average-quality legume or grass hay and cereal grains.

If he doesn't get enough: Horses low in B1 develop ataxia, lethargy, loss of appetite, a dull coat and nervousness. Since gastrointestinal bacteria produce some B1, deficiencies are unlikely and, if they do occur, the signs are subtle. Intestinal disease and parasite damage can interfere with B1 synthesis. Poisonous plants, such as bracken fern, horsetail and yellow star thistle, interfere with B1 absorption.

If he gets too much: B1 toxicosis is nearly always the result of an overdose of an injectable supplement, usually administered to enhance performance. Signs include restlessness, labored breathing and convulsions.
Horses injected with high, but nontoxic, doses of B1 may be temporarily excitable.

Excerpted from an article by Christine Barakat in EQUUS Magazine, Issue 263 (September 1999), copyright 1999 by PRIMEDIA Enthusiast Publications, Inc. All rights reserved.

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