Dr. Bom Harris, DVM, Old Dominion Veterinary Services, VA
(Previously published online with Old Dominion Veterinary Services: March 17, 2021)
Some 
of the most beautiful and luscious plants can have deadly consequences for our livestock. These are the plant toxicities seen most commonly in livestock in our area:
Acorns
Cattle are most susceptible to acorn toxicity, although sheep can be affected. Tannins in the acorns and oak leaves are the main toxic agent and are present in higher quantities in green acorns. Toxicity is most commonly observed in recently weaned calves. The tannins consumed in acorns can cause kidney failure. Typical signs of this include abdominal pain, excessive thirst, frequent urination and down animals off-feed.
Cherry
Wild cherry and other members of Prunus spp. can cause toxicity and death in a matter of minutes. Cherry trees typically grow in damp soil, often in thickets, hillsides, slopes and along streams. The berries are non-toxic, but the leaves, especially immature or stressed plants, contain a compound that makes cyanide when ingested. Toxicity occurs when a large amount of leaves is consumed over a short period of time. The toxin makes cells unable to use oxygen causing rapid death in a matter of minutes. All species, but especially ruminants (cattle, sheep and goats), are susceptible.
Perilla Mint
Perilla mint can grow anywhere but prefers semi-shaded environments, often seen around farm structures, edges of the woods and fence rows. It is most toxic when it blooms in the late summer and early fall. Cattle are the primarily affected species, but any grazing animal can be affected. The ketones in the plant cause rapid damage to the lungs, resulting in acute respiratory distress syndrome and rapid death.
Rhododendron and Azalea
Rhododendron, azalea and mountain laurel toxicity can affect all animals. In fact, although non-toxic to bees, the toxin can be passed into the honey made from rhododendron or azalea nectar causing “mad honey,” or hallucinations, when consumed by humans. In animals, signs following consumption of even a small amount of the plant include salivation, vomiting, diarrhea, colic and bloat. This is the most common toxicity that we see in goats in our area.
Pine needles
Pine needles can cause toxicity to cattle, sheep and goats when consumed in large quantities over a period of several days. Toxicity typically occurs when cattle co-mingle under pine trees during inclement weather. The toxin in the needles causes decreased blood flow to the placenta, fetal stress, followed by premature delivery or abortion. Although abortion has not been definitively observed in small ruminants following consumption of popular species of Christmas trees, as a precautionary measure it is recommended not to feed large amounts of pine of any source to pregnant sheep and goats.
For the majority of plant toxicities, there is no antidote or specific treatment; therefore, prevention is key! Animals often do not favor these toxic plants, but rather consume when there is a shortage of quality feed. Plant toxicities typically occur during droughts or during the late summer and early fall when there is a short supply of other grasses and forages. Supplementing feed during these times can reduce the risk of exposure to toxic plants. Do not allow animals to free-range around the house where ornamental plants may be growing, and be mindful of your animal’s access to yard trimmings. If you suspect that your animals have consumed a toxic plant, remove them from the source and contact your veterinarian.