Toxic Parts:
seeds, wilting leaves
phenolic compounds, pyrogallol
Flower Color:
  • flower color
ornamental, meadows, agricultural

Time of Greatest Risk


Geographical Distribution

Pistachio distribution - United States


Pistacia spp

Persian Turpentine Tree, Mt Atalas Mastic Tree
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Pistachio trees (Pistacia spp) are evergreen or deciduous resin-bearing shrubs and trees that belong to the Anacardiaceae plant family, which contains over 70 genera and 600 species. Of them, the most important to horses is P. atlantica, P. terebinthus, P. vera, P. khinjuk, and P. chinensis. P. vera is the only species of the genus used for commercial purposes.

Pistachio Tree Toxic Components

Pistacia spp. contain tannic acid, gallic acid, and a metabolite of gallic acid, pyrogallol, which are oxidizing toxins. If eaten by horses, it causes hemolytic anemia and methemoglobinemia. The effect is similar to that seen by horses that eat wilting red maple leaves and high doses of onions or garlic. Horses have a unique susceptibility to oxidative erythrocyte damage, more so than other animals.

Summary of Documented Equine Poisoning Cases from Pistachio Trees

No. horses SeasonLocationHistoryClinical SignsOutcome of survivorsRef
5 died and 1 one brought to the equine hospitalOctoberCaliforniaThe herd of 29 horses had recently moved to the property (40 acres which included an orchard of Pistacia spp (containing P. atlantica, P.terebinthus, P. chinesis) 6 months prior. The horses were given plenty of water and supplemental hay, however the owner saw the horses eating from the trees that had been cut down.Varying degrees of colic, ataxia, abnormally colored urine, pale and icteric mucous membranes, lethargy and loss of appetite. 3 of the mares had elevated rectal temperatures ranging from 102 to 102.5°F. The surviving mare was treated with intravenous fluids, ampicillin, flunixin meglumine, and minocycline. She was also given activated charcoal (1 mg/kg) in her feed over a 12-hour period in an attempt to adsorb potential toxins from the gastrointestinal tract. Intravenous fluid therapy was continued for 2 days and oral activated charcoal (0.1 mg/kg q 6 hrs) for 3 days. On the third day, the mare showed great improvement and was discharged from the equine hospital.R Bozorgmanesh et al., 2015
1 horse died and the other brought to the equine hospitalOctoberArizonaThe horses' pasture had sufficient grass coverage and housed a single Pistacia atlantica tree. The owner saw the horses eating wilting leaves that had fallen from the tree. The horse that died had signs of hemolytic anemia and acute renal failure. The surviving horse had signs of dullness and red-brown discoloration of urine.The horse was treated with IV fluids for 7 days, activated charcoal (1 mg/kg q 12h for 2 days, then 30 mL paste PO, q 6 hours) and enrofloxacin. After two weeks of hospitalization the horse recovered and was discharged from the hospital.R Bozorgmanesh et al., 2015

What Pistachio Trees Look Like

P. atlantica is a deciduous tree that grows up to 7 m (23 ft) in height, with spreading branches, dense crown, and trunk diameter up to 2m (6 ft). It has pinnate leaves, with 7 to 9 lance-shaped leaflets. Oblong, fleshy pink fruit develop that ripen to blue from July to October. The flowers are unisexual, small, discreet green pea-fruit like.