Timothy Hay Mites

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Timothy is an excellent hay choice for horses, but you may have noticed increasing amounts of brown, curled leaf. Timothy producers, especially in the Mid-Atlantic region, are having problems with mite infestation. Yield may be reduced from 30% to 70% (driving hay prices up), and hay with this infestation is of poorer nutritional quality. The mite and/or its droppings may also be potential respiratory allergen.

The culprit is the cereal rust mite, Abacarus hysterix. It originated in Europe and has been in this country for 50 years. However, for unclear reasons, this mite has been causing much greater damage in the past few years. One theory is it might have mutated to a form that is particularly suited for timothy. The mite is tiny, less than 1 mm long, and hides in the leaf vein grooves. It can be seen with a 20X magnifying lens.

First-cutting hays are the worst affected. The first cutting removes many reproductively active mites. This combined with higher heat later in the season results in less severe problems with second cutting hay. Crop management experts are also recommending a third cutting late in the season, even if yield and quality doesn’t warrant it, again to remove mites from the field. However, these measures are not 100% effective, and the only insecticide that works for the hay farmers is Sevin, a carbamate pesticide with poisoning symptoms the same as organophosphates. Producers must wait a minimum of 30 days after application before the fields can be harvested or grazed. Only one application per year is permitted, which is done in early spring so residues would be highest in first-cutting hay.

Researchers were suggesting hay growers consider using improved strains of reed canarygrass in place of timothy to avoid the problems with this mite, but a study just published in the Journal of Animal Science has put a damper on that idea. The hay was tested by feeding it to 12 mature thoroughbreds. Analysis showed both hays came up short for copper and zinc, very common deficiencies.

The calcium-to-phosphorus ratio of the timothy hay was good, but the reed canary hay was short on calcium. Crude protein in the reed canary hay was higher (17.1% versus 14.4%), but its digestibility was lower. Overall digestibility was also lower by more about 10% and the horses found the timothy to be much more palatable, consuming significantly less reed canary hay.