With the continuing drought many horse owners are forced to continue to find hay supplies out of state. Before you take a delivery of hay, be cautious of several things that may be in the hay and which may adversely affect your horse.
With alfalfa and clover hay one must be concerned about blister beetles. Blister beetles, any of six species of the genus Epicauta, can inhabit alfalfa and clover fields from the central through the southern United States. They exude a highly caustic substance called cantharidin, which can cause inflammation and blistering of the skin within hours of contact. If ingested, the cantharidin is absorbed and rapidly excreted in the urine, causing inflammation of both the digestive and urinary tracts. Horses seem to be particularly susceptible to blister beetles and can suffer severe poisoning from even a few beetles, alive or dead, lurking in a bale of hay. Decreased feed intake, frequent drinking and urination, colic, and depression are signs of blister beetle poisoning. At its worst, blister beetle poisoning can cause horses to suffer severe pain, shock, and death within a few hours.
Another problem with legumes (alfalfa and clover) is called "slobbers", excessive salivation caused by the fungus Rhiozoctonia leguminicola. This fungus produces a toxoid alkaloid slaframine, which can infect these forages. The treatment for this is to simply remove the forage from the horse and a rapid recovery results.
Costal Bermuda grass and Bermuda grass hay is common in the southern tier states. In certain fields where the grass is harvested, an unknown toxin can cause "grass staggers". This involves the nervous system of the horse causing tremors, ataxia, stiff gaits and stumbling. Most all horses recover and deaths are rare.
Another hay that can cause problems is tall fescue. The trouble with this hay mainly lies with pregnant mares. If mares eat fescue 60-90 days prior to foaling, a number of problems can occur, including prolonged gestation, difficult birth (dystocia), thickened placenta, decreased colostrum production, and lower milk production. Mares often show false heats and have difficulty re-breeding. Worst of all, foals are often stillborn or born weak. Those, which do survive, are often somewhat unhealthy and need supplemental colostrum. A fungus called an endophyte living within the cell walls of the plant causes all these problems.
Yet another possible hay problem is a horse coming in contact with botulism. Botulism can occur in all hays but requires high moisture (greater than 15% moisture) and decaying plant or animal material baled within the hay to grow. Clostridium botulinum bacteria produce toxins that cause a flaccid paralysis. The first signs are usually a reluctance to eat and difficulty swallowing or with more severe toxicity, sudden death. For those that survive, there is a generalized weakness, depression, muscle tremors, and a reluctance to move. Depending on the dose, a horse may die suddenly or within a few days of seeing clinical signs. Those that live usually are better within 2-3 weeks.
There are many dangerous things, which can be in the hay that you intend to feed to your horse. Getting to know where the hay you feed comes from and/or the supplier you are using can help you to avoid an assortment of problems.