Trees in Horse Pastures

Trees are a beautiful source of shade in horse pastures providing a lovely picturesque landscape. Most of the time trees pose no risks to horses in pastures. However trees can cause problems in pastures including toxicity to horses injury to trees and broken fences from fallen branches.
Toxic Trees
There are numerous trees that can be toxic to horses. They each have different levels of toxicity and some specific parts of the plant can be more toxic than others i e. leaves acorns depending on the species.

Red maple Acer rubrum. The wilted leaves of this tree are highly toxic though the toxin is unknown. Even after they fall off the tree in autumn the dried leaves can retain toxicity for up to a month. The worstcase scenario would be a branch falling into a pasture and horses eating the wilting leaves. This can result in rapid death. It is thought that hybrids of red maple including sugar and silver maple may also be toxic.
Chokecherry Prunus virginia. These trees and other cherries like wild black cherry Prunus serotina contain cyanide compounds in the seeds leaves bark and shoots. Toxicity is highest in both new growth and wilted leaves and branches i e. if a branch falls during a storm. Apricot and peach trees are in the same genus Prunus and are thought to contain the same toxins in the leaves and seeds.
Horse chestnutBuckeye Aesculus hippocastanumAesculus glabra. These pretty trees with their distinctive fruits and seeds contain toxins in the leaves sprouts seeds and seed husks. Horses may eat them because they typically leaf out earlier than other plants in the spring. Note that the horse chestnut is a different plant than the American chestnut Castanea dentata and other chestnuts.
Black locust Robinia pseudoacacia. The bark and seeds of this showy tree contain lectins that

can cause gastrointestinal problems. Paired thorns at the base of each twig aid in identification of this tree. Note that honey locust Gleditsia triacanthos is a different plant than black locust.
Oaks Quercus spp.. It is not uncommon to see a large old oak in or next to a horse pasture. Unfortunately the leaves bark and acorns containing high levels of tannins can be toxic to horses when consumed in quantity. Young leaves and flower buds and unripe green acorns are the most toxic. Many horses will leave them alone and never have a problem but others may gorge themselves on green acorns and get sick.
Black walnut Juglans nigra. This tree is also common in horse pastures and its primary danger is not from being consumed. Shavings from black walnut wood can cause laminitis when horses stand on them. As little as 20 black walnut shavings in a bedding mix can be enough to cause laminitis. If you remove a black walnut tree from a pasture be aware of the danger from the sawdust that remains on the ground. It has also been suggested that pollen and leaves from black walnut can be toxic to horses causing mild respiratory signs. The walnuts that fall on the ground may become moldy which can cause health problems as well.
Other toxic trees
Kentucky coffee tree Gymnocladus dioicus
Chinaberry tree Melia azadarach
Crab apple tree Malus sylvestris
Cherrylaurel Prunus laurocerasus
Golden chain tree Laburnum spp.
Tung nut tree Aleurites fordii
Mesquite Prosopsis spp.
American persimmon Diospyros virginiana
This is not an exhaustive list. Many ornamental trees and plants can be toxic. When researching trees to plant make sure to look up whether they are toxic to horses. Use the sources cited at the end of this article or contact your local Extension office.
There are many clinical signs of toxicity in horses. These signs can