Grass clippings and yard waste trimmings can be toxic.

By Laura Kenny, Extension Educator, Equine

As horse owners, we spend a lot of time and effort making sure our horses are healthy and well cared for. However, a simple mistake by a family member or neighbour could be disastrous.

In urban and suburban areas where your neighbours may not be familiar with horses, it is important to make sure they know not to throw anything over your fence into your horse paddocks. The same goes for any family members or gardeners who care for the yard. Grass clippings and trimmings from common landscape plants can cause major problems for your horses.

Yew shrub. Photo: Canstock/AmeliaM

Grass Clippings

Many people think that dumping fresh lawn clippings over the fence will be a tasty treat for horses, but unfortunately, this can lead to a number of health problems.

• Any dietary changes should be made gradually to avoid digestive upset such as colic. Large quantities of grass clippings would count as a different feed source, especially if horses consume them rapidly or are on a dry lot. Therefore, feeding grass clippings can lead to increased risk of colic.
• The small particle size and high carbohydrate content of lawn grass clippings make them highly digestible. When horses gorge themselves on feeds like this, it can cause rapid fermentation in the hindgut, leading to acidosis and possibly laminitis (similar to a horse getting into the feed bin).
• A large pile of grass clippings is very easy for a horse to eat quickly. This presents a risk of choke, or feed getting stuck in the horse’s esophagus, which requires veterinary assistance to resolve.
• Piles of wet grass clippings may mold and ferment in warm weather, increasing risk of colic.
• If you have a horse with a metabolic disorder such as insulin resistance or equine metabolic syndrome, the lawn clippings may be far too high in non-structural carbohydrates (sugars, starch, fructan) and could trigger an episode of laminitis.
• Lawns may be treated with chemicals that are not approved for use with grazing animals. Pasture managers must pay careful attention to product selection and grazing intervals when using these chemicals, but your well-meaning neighbour may not consider this. Lawn/turf herbicides have not been tested for safety with grazing animals.

Clippings from regular pasture mowing are less of a concern as long as they are evenly spread out and dry quickly. More frequent mowing creates less cut grass residue, which dries faster.

Related: How to Protect Your Horse from Hazards on the Farm

Yard Trimmings

The green leaves and stems of freshly pruned shrubs may also seem like a nice treat for horses. However, many ornamental plants are toxic to horses.

• Yew - The greatest risk comes from a very common evergreen shrub called yew. This plant is highly toxic to both animals and humans. As little as a half a pound of yew can be fatal to a horse. There is no known antidote to yew poisoning.
• Rhododendrons and Azaleas - Two related common ornamentals that are toxic to horses are rhododendrons and azaleas. These are less toxic than yews, but two pounds has caused poisoning. All parts of the plant are toxic, especially the leaves.
• Other common ornamentals that are toxic to horses include box shrubs, monkshood, milkweed, jimsonweed, day lilies, wisteria, oleander, foxglove, hydrangea, lupine, daffodils, and many more. Several trees are also toxic to horses.

Rhododendron shrub. Photo: Canstock/A40757

It is very important to communicate with family members, yard care professionals, and neighbours about the dangers of throwing grass clippings and yard trimming into your pastures. While there may be some plants that won’t hurt your horses, it is safer to have a strict “no dumping” rule when it comes to yard waste. It may be useful to post signs in some cases.

Related: How to Reduce your Ecological Hoofprint - 21 Steps

Related: Pasture Perils - Plants Toxic to Horses

The Penn State Extension Equine Team is a group of equine educators providing research-based information on equine health, nutrition, and pasture/environmental management. Serving the state of Pennsylvania, the team offers educational material to horse owners through publications, workshops, online courses, webinars, and consults. 

For more information about the team and current educational offerings, visit the Penn State Extension Equine Team website. Be sure to follow the team on Facebook.

Photo: iStock/Capecodphoto