Wilted Leaves, Acorns, and Horses

There are not many sights that are more pleasing to the eye than a horse pasture in the fall.  Horses, green grass, a nice fence, and fall colors showing on the trees just makes a great Kodak moment.  Horse owners do need to be aware and take some precautions to protect their horses from potential harmful effects that those beautiful fall leaves can cause.

There are three types of trees in particular that horse owners need to pay attention to in the fall.  Those are oaks, red maples, and wild cherry. While most of the time these trees and horses can coexist with no problems, horse owners should not become complacent just because there has never been a problem. 

Let’s talk about how these trees can cause problems in horses.  First, we’ll discuss the red maple.  In the fall, red maples are one of the more brilliant trees when the leaves are changing color prior to dropping.  The problem with red maples and horses is caused by wilted leaves that horses ingest, primarily in the fall. Wilted leaves can also be ingested at any time of the year, mainly after a storm or high wind event that blows leaves off the tree, breaks a limb, or blows a tree down.  However, the main season of horses ingesting wilted red maple leaves is in the fall during normal fall leaf season.  

According to Doctors Martinson, Hovda, Murphy, and Weicherding of the University of Minnesota Horse Extension team, dried leaves can remain toxic for four weeks, and ingesting 1.5 to 3 pounds of leaves per 1000 pounds of body weight can cause problems with the horse’s red blood cells. The exact cause of red blood cell damage from wilted red maple leaves has not yet been identified, but several chemicals are being looked at as possible causal agents. 

Affected horses become depressed, lethargic, and anorexic.  Urine will become dark red or brown the first day after ingestion.  Breathing will become labored and heart rate will increase, depending on how much was ingested.  Severe cases can result in death.  

Treatment recommendations from the veterinarians include administering activated charcoal followed by mineral oil soon after ingestion.  More severe cases may require fluids and whole blood transfusions. Vitamin C, anti-inflammatory drugs, and corticosteroids have also been used in some cases.

While there is some risk associated with Red Maples, don’t go and cut every one of these trees down.  They also provide some good benefits, such as shade, wildlife habitat, and beauty. The risk can be managed by protecting young trees, by removing low branches to a height where the horses can’t reach them, and by fencing out areas where a lot of wilted maple leaves are found in the fall.

There are several species of oaks in North Carolina.  Oak trees are usually considered to be a problem in the fall when the acorn crop is falling to the ground.  Tannins and gallotannins are the toxic agents in green acorns and in oak buds and young leaves, so there are actually two seasons when oaks can be a potential hazard – spring and fall.  Horses don’t usually eat a lot of acorns or buds, but cases have been documented where horses have eaten enough acorns to require treatment.  Again, removing all the oak trees from the pasture is not recommended, but some prudent actions can be taken, including pruning branches so the leaves and acorns are out of reach, fencing around young or small oak trees, and fencing horses out of areas where acorns are plentiful in the fall.   

Acorns or oak buds/young leaves can become a problem if horses ingest large amounts over two days to a week.  Horses can develop anorexia, colic, constipation, diarrhea, edema of the neck and abdomen, and will urinate frequently.  Treatment for kidney and GI tract damage from acorns includes fluid and electrolyte therapy over several weeks.  Liver damage rarely ever occurs in horses. More information on oaks and horses is available from the University of Minnesota Horse Extension team. 

Another tree to be very careful about with horses and other livestock is the wild cherry, or black cherry.  Usually problems occur with this tree after a storm when a limb or leaves are blown off the tree, or when a tree is uprooted by a storm.  Ingesting wilted wild cherry leaves can cause death within a few hours, so more care should be taken with wild cherry trees.  The causal agents are cyanogenic glycocides contained in the leaves. 

Immediate treatment is necessary.  According to the Merck Veterinary Manual, nitrites are usually administered, followed by a slow IV injection of sodium thiosulfate. Vitamin B12a and sulfanegen have also been used as a cyanide antidote.

Extra care with pruning and fencing should be taken around this tree species to prevent ingestion of the leaves.  This is one species that horse owners may want to remove from pastures if there is a chance of branches breaking off or the tree blowing over.  However, pruning branches to keep the leaves out of reach and good fencing will certainly reduce the risk.  

Again, these risks are very manageable, and most horses likely will never develop a problem from being around these tree species.  Horses much prefer to eat good hay and grain over wilted leaves.  Using some common sense and not exposing horses to the wilted leaves or acorns when they are plentiful can usually be accomplished without resorting to draconian measures such as cutting down trees.  A little pruning and use of some temporary fencing will provide an extra bit of risk reduction to better allow these beautiful trees and our horses to peacefully coexist.