Many states are fortunate to be beautified and shaded by an abundance of oak trees.  Springtime brings on new leaves, buds and blooms in response to warmer temperatures and rains.  Fall brings acorns that cover the ground in grazing areas. Leaves, buds and acorns may all cause problems with livestock and, although the exact cause of the toxicity is not known, the long-held theory is that tannic acid, present in all parts of the tree, is the culprit.  Many experiments have been conducted where tannins were fed and injected into a variety of species.  The results of these studies, however, have often failed to produce the exact syndrome seen in livestock consuming oak.  Regardless of the exact cause, we do know that the buds, small leaves, flowers and stems are all toxic and are palatable to livestock; as the leaves age, they become less palatable and therefore pose less risk.   For this reason, poisoning most commonly in the spring, although acorns can cause toxicity in the fall or winter, particularly after summer draught. It is also interesting to note that oak can be toxic to humans.  Native Americans produced a meal from acorns, but they removed the outer hull and leached the meal repeatedly prior to consumption in order to remove the toxins.

All livestock species are potentially at risk, with cattle and sheep most commonly affected.  Goats, because they are a browsing species like deer, are designed to be a bit more resistant to some toxic plants as compared to grazing species like cattle and sheep, but they are still susceptible and, because of their climbing behavior, often have better access to plant parts.  Additionally, horses and chickens may be affected, while swine appear to be resistant. Calves that are nursing seem to be more susceptible but oak toxicity can occur at any age.

As a historical note, in April 1935, 502 cattle and 426 sheep died in Sutton County, Texas after a drought caused no other forage to be available.  This pattern of oak toxicity continues to this day. Where forage is otherwise limited, cattle will search and be attracted to consume toxic plants of all types. Unfortunately, death can be sudden from oak toxicity, with sheep and cattle sometimes dying within 24 hours of onset of illness or they may live up to 10 days. The tannins or other toxic components of oak cause direct damage to the lining of the stomach and intestines and the kidneys.  The symptoms may include constipation or diarrhea, and stool produced may be bloody or black and sticky like tar.  Livestock will lose their appetite, have a rough hair coat and dry muzzle, and they may act colicky.  If you are able to observe urination, the urine may be reddish or brown, but this is typically short-lived and may go unnoticed.

Treatment of oak toxicity can be successful if initiated early, with the principles of therapy being fluid therapy to support kidney function and measures to stimulate and maintain appetite.  Cattle that will continue to eat often make a complete recovery.  In one study of affected steers, those affected by oak bud toxicity actually showed improved weight gains and feed efficiency in the feedlot, showing that they could catch up and compensate. I always encourage livestock producers to have unexplained deaths on their operation investigated through necropsy of freshly dead animals.  Oak toxicity has very specific signs that can be seen in the carcass and help you, along with your veterinarian, identify the cause of death and develop a plan to limit toxicity in the remainder of the herd.

As with all diseases, we like to focus on prevention over treatment. So, what can you do short of total oak tree removal from your property to limit their potential toxicity this spring and fall?

  1. If available, put livestock in pastures without oak during the riskiest times of year (spring, fall).
  2. Always have adequate feed a forage available. Cattle who are satisfied are less likely to eat oak and, if they do, the toxic oak will be diluted in their system by the appropriate feeds.
  3. Make sure fresh water is always available. This helps with overall kidney health and can help wash the toxic tannins out of their system to limit damage.
  4. Toxicity has occurred from livestock drinking water from sources where oak leaves had been soaking. Be sure to clean leaves out of water tanks regularly.
  5. Remove any downed branches from the pasture when first noticed.
  6. Don’t forget that oak can be toxic to humans – monitor children around trees and don’t allow them to chew on leaves or acorns.

Your veterinarian is always a great source of information on potential risks and opportunities to improve the environment for animal health on your operation. Don’t hesitate the next time he or she is out to ask them to help you identify these risks and opportunities.

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