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Feature Article: December 2018

Toxic Plants: what you need to know to keep your horse safe

On the whole, horses generally avoid eating poisonous plants, especially when more palatable choices are available, and especially if they have lots of good-quality hay and good-quality pasture available to them. Most poisonous plants have defense mechanisms; syrup or sap that’s very bitter, or spines and thorns that make them uncomfortable to chew or swallow — so horses will generally avoid them.

Even so, there are some harmful plants that are attractive to horses at certain times of the year. Wilted Red Maple leaves, for example, are among the plants most toxic to horses. However, they can be hard for horses to resist because the leaves’ high sugar content entices them. Horses can be exposed to red maple leaves in the autumn when drying leaves blow into pastures. Ingesting 680 g is toxic in a horse and 1.4 kg is lethal. Red maple has an oxidant that destroys hemoglobin (red blood cells). Horses will present with weakness, jaundice and anemia, and their urine may turn dark brown as the body filters out the dead cells.

Other plants outside-of-pastures can also be toxic to horses; such as ornamental plants used in landscaping, including rhododendron, azalea and yew. The latter ornamental plant is an evergreen, so it (and other evergreens) remain toxic year-round because they never lose their leaves. Between 300 g and 450 g of yew leaves are sufficient to kill a 453 kg horse. Often these plants are introduced into a horse’s environment via a well-meaning neighbour. For example, a neighbour might clip rhododendron, azalea, or Japanese yew plants and put the clippings in the pasture, thinking they are helping to feed the horses. The best thing an owner can do to prevent this from happening is to talk with neighbours and ask them not to feed the horses anything, including lawn and garden clippings.

Some weeds and wildflowers are also toxic to horses. One such plant is the weed Senecio, also known as groundsel. Senecio‘s toxic effects can take a month or more to appear in horses, but clinical signs of Senecio-related poisoning are generally easy to identify. Senecio gradually destroys the liver, causing the owner to see weight loss, jaundiced eyes, and in white skinned areas -- photosensitization that looks like severe sunburn. At this stage, there is no effective treatment or way to reverse the liver damage.

Detection and Prevention

Horse owners need to be extremely watchful to changes in their horses’ appearance and behaviour in order to detect possible plant poisoning. So it's important to know your horse well — what is normal for your horse. If you suspect your horse has ingested something toxic, call your veterinarian right away.

The first thing you shiould do as a horse owner, is walk your pastures to see what kind of plants are growing there to identify the ones that are toxic to your horses. Anytime you find a plant you can’t identify or are not familiar with, take a digital photo of the plant and try to identify it through someone who is knowledgeable (or identify it online). You can also minimise the risk of toxic plants growing in your pastures if you create buffer zones between neighbours’ properties and your own. These zones will separate your horses from toxic plants residing next door and allow you to control plant growth without violating property lines.

If you use herbicides to keep toxic plants from invading pastures, you need to be sure that the herbicidal preparations are manufactured to be effective on the plants you specifically want to destroy. It is also advisable to read labels carefully and be strict about following manufacturers’ application directions -- especially for restricting grazing on treated pastures. Use organic weed killers if possible and always wear gloves when removing poisonous plants from your property by hand -- immediately disposing of any toxic plants in a location where horses cannot access them.

Another point, is to ensure that your horse's bedding is not toxic. For example, a bedding made of shavings derived from black walnut wood is dangerous and can cause laminitis in horses simply from standing in it. In fact, bedding that is only 20% black walnut shavings is toxic to horses and can cause laminitis -- so it is wise to know what your bedding is made of and where it comes from.

Likewise, be watchful of toxic plants that could have been incorporated into bales when the hay was harvested and examine the hay before you feed it to your horse. Ideally, purchase certified weed-free hay to reduce the risk of toxic weeds which can often invade hay meadows. It is also wise to inspect the bottoms of hay feeders or buckets for plant seeds and clean out the feed bunk regularly, as some horses are ‘bottom feeders’ -- i.e., they eat the seeds that fall to the bottom of the feed bucket (which might be toxic). You can minimise the risk of toxins in hay and bedding by purchasing your horses products from familiar, reputable local suppliers. Likewise, any supplements you add to your horses' diets should be purchased from reputable manufacturers and it is advisable to follow feeding directions carefully. Doses in herbal supplements are very small, so they are not likely to be harmful if you follow the instructions.

A final note ...

Unfortunately, despite horse owners’ best efforts, horses can still ingest poisonous plants. If this happens, try to identify the plant your horse ingested and contact your veterinarian right away. Besides calling a veterinarian immediately, there’s not much a horse owner/carer can do except remove the horse from the suspected source — be it the hay or the pasture. A quality diet helps minimise plant-poisoning risks. Even though some horses might sample the potentially poisonous plants they find in their pastures, most will not ingest these ill-tasting plants in quantity as long as lush grass and quality hay are available.

Reference:

Keep your horse safe from toxic plants (2018, May 14). The Horse. Retrieved from https://thehorse.com/120513/keep-your-horse-safe-from-toxic-plants/