Safety Concerns for Certain Forages

Horses have unique digestive tracts which can lead to sensitivities to certain forages. Unless there is nothing else to eat, most animals will avoid harmful plants because they are generally unpalatable. It is important to give horses access to a variety of high energy, protein-rich hay and pasture. This is especially important for high performing horses. Horses not being worked should be fed lower quality feed to avoid problems with weight and blood sugar. There are some forage situations that should be continually looked for regardless of your horse’s activity level.

Nitrates

High nitrate concentrations in forages is seen in young and rapidly growing plants, plants that have been fertilized with too much nitrogen, and in stressed plants (during and after a drought). Nitrates in the plant are converted to nitrites in the hindgut (cecum) which can be absorbed into the bloodstream and convert hemoglobin into methemoglobin preventing the release of oxygen. Ruminants (cows, sheep, and goats) are more susceptible to nitrate poisoning than horses because of the ruminant digestive system. Certain weeds can be nitrate accumulators meaning they uptake more nitrogen than they can convert to protein leaving excess nitrates in the plant tissue. Lambsquarter, redroot pigweed, curlydock, and johnsongrass are all weeds that are nitrate accumulators. Symptoms include difficulty breathing, bluish mucus membranes, and weakness.

Sorghums

Sorghums species include sudangrass, sorghum-sudangrass, and johnsongrass. Sorghums contain cyanogenic glycosides with concentrations varying among species and should not be fed to horses. If fed, horses can get cystitis (a urinary tract disease), mares can abort, and foals can be born with contracted tendons.

Endophyte-Infected Fescue

In endophyte-infected fescue, the endophyte lives in the plant and has a positive influence on the plant’s growth by helping defend the plant from pests among other things. The endophyte produces ergopeptide alkaloids which are toxic to horses when eaten as fresh forage and as hay. The alkaloids cause vasoconstriction of blood vessels. Symptoms from eating endophyte-infected fescue include abortion, decreased conception rates, prolonged gestation, weak foals, stillborns, thickened placenta, and decreased milk production. Another symptom can be fescue foot which is when there is the loss of feet, ears, and/or tails due to the vasoconstriction. If you are grazing fescue pasture and feeding fescue hay make sure it is endophyte-free.

Alfalfa Hay and Blister Beetles

There are six species of blister beetles associated with alfalfa and hay. They are black, grey, or grey with yellow stripes. The striped blister beetle is most associated with hay poisoning. The adult beetles feed on the leaves of various plants including alfalfa and soybeans and are attracted to flowering plants. They contain the toxin cantharidin which causes irritation that can blister the skin and internal body surfaces. In horses, this can cause colic, diarrhea, and blood in the stool and urine. The beetles are more likely to appear later in the summer (starting in July) so the first cutting of alfalfa is less likely to contain the beetles than later cuttings. Alfalfa should be harvested before it flowers to decrease the chance of a blister beetle infestation. It is important to make sure you are getting hay from the first cutting and that the hay was harvested prior to flowering. Inspect any alfalfa hay for beetles before feeding.

Molds

Horses are especially susceptible to mold and fungal toxins. These usually come from hay that was baled at a higher moisture or hay that is allowed to sit out in the elements. This can be an issue with the first cutting because it is cut when rain is frequent and optimal drying conditions are not common. If you have hay that was baled at a higher moisture do not stack those bales. It is best to get the bales under a shelter and keep them spread apart to encourage air flow which can help dry them out a little more. Hay should be stored and fed in structures that prevent the bales from getting wet. It is best to only feed the amount of hay that will be consumed in one day.

Poisonous Weeds

Poisonous weeds can sneak up in pastures so it is important to know how to identify them. Some weeds of concern in North Carolina are cocklebur, johnsongrass, pigweed, lambsqaurter, and bittersneeze weed. Again, most animals will only eat poisonous weeds if there is nothing else to eat. Good pasture management can help prevent these weeds with the correct stocking rate, utilizing pasture rotation and rotating before the horses are allowed to overgraze the pasture. Soil fertility is also important when trying to eliminate weeds. Taking soil samples of your pastures will tell you what the current soil fertility is and what to add to have correct fertility for the grass you are growing.

Please contact your local Extension agent if you have any questions about the topics listed in this article.