New Zealand Tree Crops Association

Trees and Livestock

We plant trees. As a group we are always extolling their benefits to humans, the landscape and in the creation of micro climates. Trees are windbreaks and beauty, sheltering from cold winter winds or hot summer sun. Their fruit and nuts provide food and their wood warmth from building or in the fire. Trees also help stabilise slipping hillsides, bring up nutrients from deep below the surface, and absorb water that might otherwise cause erosion. They are homes to birds and insects. They can also shade and protect waterways so aquatic creatures can thrive.

Trees planted for shelter are appreciated by animals in the pastures. On hot days livestock can be seen resting in the shade. On cold days they cluster in the lee of hedges and shelter belts. From time to time, whether we want them to or not, they will browse on those trees. Some trees make excellent fodder crops. Others are not, but different animals may be affected differently by plants.

Tree tutu (Coharia arborea) and ngaio (Myoporum lactum) caused major stock losses to early British settlers when their cattle, sheep and horses ate them. Just recently in the news we have heard of honey being contaminated by tutu and poisoning a number of people. Pinatoro or Strathmore weed (Pimelea prostrata), a ground-hugging, open-country shrub, is poisonous to horses and cattle but seems to have little effect on sheep.

Some trees are only a problem if large quantities are eaten. Horses can be partial to acorns. Leaves and acorns of oak contain tannins that are toxic in large enough doses. Black and red oak are more toxic than while oak. The needles of pine trees contain a variety of compounds such as resins, mycotoxins and lignols that can cause toxic reactions in livestock if ingested. Horse chestnuts (young leaves, flowers and nuts) are known to contain toxic compounds that have caused poisoning in livestock.

Some problem trees

Avocado (Persea Americana) All parts of the avocado tree - the leaves, bark, skin and stone - are poisonous to horses and most other animals but the leaves contain the highest levels of toxins, even when fallen and withered. Anecdotal evidence suggests that it is dangerous to even graze horses on pasture where avocado trees are growing or have grown.

Black locust / false acacia / locus tree / robinia / yellow locust (Robinia pseudoacacia)
Seeds, leaves, bark and twigs of black locust contain several toxic proteins that can poison all livestock types. The honey locust (Gleditsia triacanthos) appears to be a safe tree. It is important to distinguish between the two locust tree species.

English Yew (Taxus Baccata)
All species of yew and all parts of the tree, particularly mature leaves in winter, are toxic to all livestock, although they will not intentionally eat the unpalatable leaves or seeds.

Kalmia (Kalmia spp)
Kalmias are a large shrub or small tree and are primarily a threat to browsing animals like sheep, goats and, less commonly, cattle and horses

Laburnum (Laburnum anagyroides)
Laburnum is toxic to children and all livestock, but especially to horses.

Macrocarpa (Cupressus macrocarpa)
Pregnant cows are likely to abort if they eat macrocarpa leaves late in pregnancy.
Isocupressic acid (ICA) has been identified as the abortifacient agent contained in Macrocarpa It is also present in Ponderosa pine (Pinus ponderosa Laws) and Leyland cypress (Cupressocyparis leylandii). Although Pine (Pinus radiata) has negligible concentrations of ICA an association between cattle abortion and ingestion of pine needles has also been suggested

Prunus spp. - peach, plum, cherry, almond, apricot and nectarine
There are more than two hundred species of ornamental, fruit and shade trees in the prunus family, all of which are highly toxic to horses. Prunus species trees kill by cyanide poisoning. While trees containing cyanogenic glycosides are usually unpalatable to horses, wet leaves or leaves mat are damaged or stressed by drought, frost, seasonal wilting or storms may be more attractive and the ingestion of only small quantities of leaves can be enough to cause poisoning

Red maple (Acer rubrum)
Known and loved for its striking autumn foliage, the deciduous red maple is grown as a street tree, garden ornamental or a summer shade tree. Red maple is a potent killer of horses and ponies. Ingestion of wilted red maple leaves causes hemolytic anemia, which can be deadly.

Rhododendrons and azaleas need to be avoided as well. These plants contain toxins that can be deadly within 1-2 days.

Some other poisonous plants
These plants are poisonous to horses and some will be poisonous to other animals as well.
Arum lilies (Zantedeschia aethoiopica, Buttercup (Ranunculus acris). Blue lupin (Lupinus sp, St Johns wort (Hypericum perforatum, Foxglove (Digitalis purpurea, Hemlock (Atropina belladonna, Ragwort (Senecio jacobae)