If you have ever watched your dog enthusiastically chomp on a mouthful of lawn and wondered, “Why do dogs eat grass?”, you are in good company. This is one of the most common questions pet owners ask veterinarians. The behavior, formally known as herbivory, sits in a curious space between a harmless ancestral habit and a potential warning sign of an underlying medical problem.
Understanding why your dog eats grass, and knowing when grass eating crosses from normal behavior into a medical emergency, can help you protect your pet from serious complications like intestinal obstruction and surgery.
Why Do Dogs Eat Grass? The Evolutionary and Behavioral Explanation
For years, the dominant theory was that dogs eat grass specifically to make themselves vomit when they feel unwell. Modern veterinary research tells a more nuanced story. Large-scale surveys indicate that fewer than 10% of dogs appear ill before grazing, and fewer than 25% actually vomit afterward (Sueda et al., 2008).
Instead, grass eating is now widely classified as a normal ancestral behavior. Wild canids routinely ingest plant material, possibly as a natural method of purging intestinal parasites. The fibrous blades of grass may physically wrap around nematodes (worms) in the digestive tract, helping push them out mechanically (Bjone et al., 2007). In today’s well-cared-for pets, that instinct persists even though monthly deworming preventatives have largely replaced the biological “need” for parasite control. Interestingly, while some assume grass eating increases during illness, some studies have actually shown a reduction in grazing behaviors in response to mild gastrointestinal disturbances (McKenzie et al., 2009).
Do Dogs Eat Grass Because of Fiber or Nutrient Cravings?
Another explanation for why dogs eat grass is simple dietary variety. Although modern commercial dog foods are formulated to be nutritionally complete, some dogs may still seek out grass to satisfy a craving for fiber or particular phytonutrients. Studies have shown that dogs fed a low-fiber diet may increase their grass consumption, suggesting grazing can be a functional attempt to regulate gastrointestinal motility (Bjone et al., 2007).
