Many people are aware that certain holiday plants, such as Mistletoe and Holly, are poisonous to pets, but what about the most common holiday "plant," the Christmas tree? We worry about pets tipping the tree over or tearing open the presents, but what about those pets who chose to eat the tree?
Christmas can be a scary time for pets, especially cats who can't resist the tree and other holiday plants, many of which are poisonous. Toxicity of holiday plants varies from mild to extreme. The level of poisoning (illness) is also related to the amount of the plant ingested.
Christmas trees are considered to be mildly toxic. The fir tree oils can be irritating to the mouth and stomach, causing excessive drooling or vomiting. The tree needles are not easily digested either; possibly causing GI irritation, vomiting, gastrointestinal obstruction or puncture.
Even though the question refers to "live" trees, artificial trees, such as the one in the photo, are also dangerous when eaten. The principal things to worry about are toxin release from the artificial material and intestinal obstruction (not digestible).
As noted earlier, the amount of trouble depends on how much is consumed. Many times, pets don't consume mass quantities of tree material.
I would recommend confining your pets away from the tree when you are not home. This will allow you to be able to "supervise" any tree or plant-eating activity. Other plants, such as Mistletoe and Holly are also poisonous.
What to Look For
If your pet has chewed on the Christmas tree or other plants, monitor for any changes in behavior (excessive licking, salivating), appetite, activity, water consumption, vomiting, and diarrhea.
Additional Tree Safety Concerns
While we are on the subject of Christmas trees, also consider the tree water. Preservatives, pesticides, fertilizers and other agents, such as aspirin, are commonly used in the tree water to keep the tree fresh. These may have harmful or deadly consequences for cats and dogs (and children) who drink the water! A covered tree water dish is the safest.
Holiday plants that are used as decoration and those given as gifts may pose threats to your pets, ranging from mild to severe toxicity potential. Learn more about toxic holiday plants.
Christmas lights on the tree and elsewhere in the home also pose a hazard to curious pets. Chewing on cords and lights will cause electric shocks and burns in the mouth. Check cords regularly for signs of chewing and general wear and tear.
If you notice that your pet is reluctant to eat, drooling or showing signs of a painful mouth (i.e. not wanting to play with regular toys), be sure to rule out electrical burns in addition to dental and other diseases.
Ornaments also pose a risk. Ingestion of ornaments can cause gastrointestinal blockage or rupture. Depending on what materials were used to make the ornament, toxicity may result if ingested.
Be careful and have a safe and happy holiday season!