Bob Judd, DVM, DABVP (Equine Medicine), DABVP (Canine and Feline Practice)
The first thing to consider when feeding any fruits or vegetables to your horses is whether the item is toxic. Just because a human can eat it does not mean a horse can.
An article by Dr. Clair Thunes, Ph.D., published in The Horse, says it is generally suitable to feed horses pumpkin, but you still need to be careful when feeding any fruits or vegetables to horses.
You do need to consider the nutrient profile of the food, and this is especially important for horses that have equine metabolic syndrome, or EMS.
For example, pumpkin has a low glycemic index, which means it does not cause a rapid increase in blood glucose, so it should be safe for horses with EMS, assuming a small amount is fed.
However, pumpkin is high in potassium, so it would not be right for horses with Hyperkalemic Periodic Paralysis (known as HYPP, an inherited disease of the muscles). You can see that pumpkin, as well as other fruits and vegetables, are not always good for all horses.
Dr. Thunes suggests cooking the pumpkin and making horse treats by adding oats, wheat bran, cinnamon, and molasses. However, these treats should not be given to overweight horses or those with metabolic diseases.
Dr. Thunes also suggests placing a pumpkin in your horse’s stall for them to play with after first removing the stem to prevent choking.
A major concern with feeding any abnormal food, meaning foods they would not usually have access to or eat, to horses is that it could lead to gastrointestinal problems, causing colic.
It may not be worth taking the chance to feed your horse any of these fruits and vegetables. Always check with your veterinarian before feeding any fruits, vegetables, or other abnormal foods to your horse.
You can find checklists of poisonous items on the Cornell University website and on the site of the Association for the Society for Prevention of Cruelty to Animals (ASPCA).