Mustard is Not My Friend


Every good horse person knows that alsike clover in a pasture can cause photosensitization in horses. But did you also know that mustard growing in your pasture can be just as bad? Photosensitization is the presence of a photoactivating substance in the skin, exposure to UV light and lack of skin pigment enabling more light to penetrate the skin.

The mustard plant family is made up of a large group of herbaceous plants, most of which are annuals, winter annuals, or biennials. Flowers, with four sepals, four petals, and six stamens (two short and four long) are yellow or white, and arranged in racemes. Fruits are borne in two-chambered, flat-round, or beaked tubular capsules.

Since mustard is one of our farm’s important crops, it’s easy for plants to pop up here and there in our horse fields. The seeds are sometimes carried by the wind or possibly, birds. And when it does, we are ready with a herbicide and action plan (of course, this can only happen if we are able to take the horses off the field first).

Many mustards are harmless when young and are grazed without incident. However, seeds and vegetative parts (fresh and dry) may contain the toxic principle glucosinolate (isothiocyanate). And if horses eat too much mustard, signs of poisoning can include acute/chronic anorexia, severe gastroenteritis, salivation, diarrhea, paralysis, hemoglobinuria and photosensitization.


In our herd, we have only ever had a problem with sunburns which we cure with zinc applied directly to the affected skin and by removing the horses from direct sunlight. In this case, our horses are typically not happy to be placed inside a  barn during the day but the alternative is not an option. Sunburned muzzles or white socks can be pretty painful for horses.


Usually within a couple of days, the sunburn starts to fade away if proper care with zinc cream and shade is given to a photosensitive horse. And from one year to the next, it\’s easier to control mustard plants because you have a vague idea where they\’ll pop up again. As the old saying goes, \”Take care of your pastures and they will take care of you.\”

And by that I\’m sure it means, \”ensure those beautiful yellow mustard flowers are not present where your horses roam.\”


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