Do Not Feed Moldy Hay to Horses!

That sounds like pretty good advice, and in fact is the title of a University of Minnesota Extension publication written by a host of specialists from Wisconsin, Minnesota, Pennsylvania, Michigan, Idaho, and North Carolina.  Most of the time, it is pretty easy to tell if hay is moldy but if it is not obvious, then perhaps a forage test is in order to confirm the hay is free of mold and the accompanying spores and dust.   More on that later.

It doesn’t take much moisture for mold to grow in hay.  Moisture levels above levels above 14 – 15 % with no preservative added can result in moldy hay.  The mold process causes heat, which in turn reduces TDN and binds up protein molecules, making them non-digestible.  However, that isn’t the main problem with moldy hay.  Molds produce toxins – a whole host of them, including Aflatoxin (AFL), Deoxynivalenol (DON or vomitoxin), T-2 Toxin (T₂), Zearalenone (F₂), and Fumonisin (FB₁).  They are all bad news , but some can be tolerated in very small amounts.  However, FB₁ should not be present in hay.  Tolerance levels for the other four are:

AFL -      50 parts per billion (ppb)

T₂ -          50 ppb

DON -   400 ppb

F₂ -        100 ppb

As you can see, these are pretty low levels of concentration.  AFL is considered carcinogenic, DON causes reduced feed intake and is implicated in colic cases, T₂ causes digestive tract irritation and has been implicated in colic, F₂ reduces fertility and reproductive performance, and FB₁ is implicated in impaired immune function, liver and kidney damage, and a condition known as moldy corn poisoning, hence the recommendation for zero FB₁.   More details and definitions on these toxins can be found in the publication Horse Feeding Management; Feed Sampling and Analysis.

While most of these toxins are more closely related to wet grains, they can occur in moldy forages.  However, the biggest problem with moldy hay is that it is usually very dusty and full of mold spores.  Horses are particularly sensitive to mold spores and often develop respiratory problems similar to asthma when fed moldy, dusty hay.  This condition is known as Recurrent Airway Obstruction (RAO).    Affected horses don’t have elevated temperature and have a good appetite, but when exercising, breathing quickly becomes labored, and can even be labored while at rest. 

A list of tips on reducing the affects of moldy, dusty hay on horses is found in the University of Minnesota publication and is repeated here:

·      Do not feed dusty and moldy hay and grains.

·      Use dust-free bedding

·      Don’t use old moldy hay as bedding. (I added this one to the list!)

·      Place feed at a lower level so particles are not inhaled through the nostrils

·      Keep horses out of the stable when sweeping and cleaning to reduce exposure to dust

·      Feed hay outside

·      Soak dusty hay from 5 to 30 minutes before feeding and let the horse eat it wet

·      Store hay away from the horse as much as possible and keep hay dry to reduce the chance of mold growth

·      Make sure stalls and stables are well ventilated.

Horse owners should insist on seeing a forage analysis before buying horse hay.  That is an expensive commodity, and we want to make sure that we are getting a product that is worth what is being paid.  If a forage test isn’t available, it is a good idea to send a sample for analysis on each load of hay purchased. 

When submitting a sample for analysis, remember that the test for mycotoxins is free of charge if the nutritive value is not tested.  However, for $10, the information on protein, digestibility, and micronutrients in the hay is well worth the money.  Add in the “freebies” like mycotoxin testing and nitrate testing, well, that makes a good value a great value.

For more information on testing forages for molds and mycotoxins, contact your local Cooperative Extension Agent.