John Kirk, John Adaska and Pat Blanchard

Veterinary Medicine Extension, University of California Davis (Kirk) and California Animal Health and Food Safety Laboratory (Adaska, Blanchard), Veterinary Medical Teaching and Research Center, Tulare, CA.

One of the most common ornamental plants seen across California is oleander. This evergreen shrub is commonly used as a highway median divider or hedge around yards or orchards. The flowers often catch our eyes as they occur in beautiful white, red and pink colors. However, these plants are a definite potential danger to all animals and humans. All parts of the plant either fresh or dried contain several toxins that affect the heart. There is no specific treatment once a toxic dose of the plant has been eaten. Symptomatic treatments are often attempted but are usually unsuccessful.

Most oleander poisonings occur when plant clippings are thrown over the fence into livestock pastures. Often the oleander clippings or trimming are thrown in the pasture by well-meaning neighbor who think they are doing the cattle a favor. Occasionally, oleander becomes baled with hay or chopped into silage for cattle feed. Intake of leaves at 0.005% of body weight can be lethal to cattle. This equates to about 0.08 lbs plant or about 10-20 leaves for a 1500 lb cow. Human cases have happened when oleander twigs were used for meat skewers. A single leaf has been reported to be fatal to a small human.

Animals exposed to oleander are often found suddenly dead. When noted while still alive, signs of oleander poisoning are severe diarrhea with abdominal pain along with sweating, trembling and weakness. If examined, the poisoned animal may have an irregular heart rate. The poisoned animal becomes progressively paralyzed. Eventually they enter a coma and die. The signs become apparent within a few hours after eating the plant and death is rapid.

A presumptive diagnosis can be made for oleander poisoning by finding leaves or clippings in the area when the animals became sick or died. In some cases, oleander leaves may be identified in the ingesta or rumen contents of the cattle; however, the leaves are often chewed up beyond recognition. The California Animal Health and Food Safety Laboratory has developed laboratory tests that can detect oleandrin, one of the toxic elements in oleander, in the rumen or cecal contents as well as feces and milk. This test is very helpful when the actual leaves cannot be found.

These recent case histories serve to illustrate factors involved with oleander poisoning in cattle. On one dairy, oleander clippings were the source of the deaths of two dairy heifers and several others became ill but recovered. Five heifers from 400 died from oleander poisoning in a pasture next to a housing development that was ringed with oleander. In another case, 24 of 200 cows died within 1 to 3 days after consuming hay that contained oleander. In this case, the oleander toxin was found in the milk during necropsy of the dead cows. As a result of this finding, milk was discarded from the affected pen of cows. In another case, a gardener dumped a load of oleander clipping into a dry lot containing 120 heifers. By the next afternoon, 5 had died, 2 were severely ill and 30 more had diarrhea.

In summary, oleanders are beautiful plants but very toxic to cattle and humans. Often cattle are found suddenly dead while at other times they are ill showing diarrhea, sweating, trembling or weakness. The toxin does appear in the milk. Treatment is routinely not successfully. The source is usually oleander clippings or trimming that should be removed immediately to prevent further consumption by the cattle. The California Animal Health and Food Safety Laboratory has the capabilities to make a diagnosis of oleander poisoning by testing intestinal contents, feces or milk.