Do dogs eat grass because they feel ill?


Living with dogs, you will have observed them eating grass. If you do a quick poll amongst your friends as to why they think their dogs eat grass, the common answer is because the dog is feeling nauseous or not feeling well. Some might even say that there is something lacking in the diet. Neither of these is accurate.

Dogs eats grass because its an ancestral habit and it can also be hypothesized that dogs eat grass as a form of worm control, however this would have to be studied.

Evaluation of scats and stomach contents of wild canids indicate that they regularly ingest plant material, especially grass. Such studies report the appearance of plant matter in about 11% of samples of Latvian wolves (Andersone and Ozolins, 2004) and approximately 74% of samples collected in the summer from grey wolves reintroduced to Yellowstone National Park (Wyoming, USA) (Stahler et al., 2006). In studies where specific plant types were identified, grass was found in 2–3% of the samples of timber wolves (Mech, 1966), 10% of samples in Latvian wolves (Andersone, 1998) and 14% of samples from Greek wolves (Papageorgiou et al., 1994). Some blades of grass undoubtedly appear in scats as a result of adherence to carcasses being eaten, or from ingestion of the intestinal contents of herbivorous prey. However, intentional consumption of grass by wolves has also been documented (Murie, 1944; Stahler et al., 2006). After observing blades of grass wrapped around intestinal worms in wolf scats, Murie (1944) suggested that grass might have a scouring effect in removing worms.

Karen Lynn Chicko Sueda, Benjamin Leslie Hart, Kelly Davis Cliff ( Applied Animal Behaviour Science 111 (2008) 120 -132 ) targeted owners of plant-eating dogs, using an internet survey. They collected information regarding the frequency and type of plants eaten frequency with which dogs appeared ill before eating plants and frequency with which vomiting was seen afterwards. Out of 1571 pet owners surveyed. Sixty-Eight percent of dogs were reported to eat plants on a daily or weekly basis with the remainder eating plants once a month or less.

Grass was the most frequently eaten plant by 79% of dogs. Only 9% were reported to frequently appear ill before eating plants and only 22% were reported to frequently vomit afterwards. While no relationship was found between sex, gonadal status, breed group or diet type with regard to frequency or type of plants eaten, a younger age was significantly associated with: (1) an increase in frequency of plant eating; (2) an increase in consuming non-grass plants; (3) a decrease in regularly showing signs of illness before eating plants and (4) a decrease in regularly vomiting after consuming plants

Another perspective on this issue comes from observations of parasite loads in young canids compared with older canids. Coyotes less than 1 year of age (Franson et al., 1978) and young dogs, especially those without close medical oversight (Fontanarrosa et al., 2006; RamirezBarrios et al., 2004; Kirkpatrick, 1988), have a higher prevalence of intestinal parasites than adults. If the predisposition towards plant eating in domestic dogs stems from an innate behaviour in ancestral canids for periodic expulsion of intestinal parasites, one would expect younger canids, including dogs, to engage in the behaviour more frequently than older dogs. This perspective is supported by the finding of an inverse relationship between age and frequency of plant eating. The data also reveal that younger dogs are less likely to appear ill before, or vomit after, eating plants, a finding consistent with the concept of ongoing control of parasites. The finding that some dogs do not eat plants at all could be explained on the basis of relaxation of selection for plant-eating behaviour, reflecting dog-owner use of prophylactic treatment for intestinal parasites.

Plant eating, especially grass eating, commonly occurs among all breed groups of domestic dogs and appears to be a normal behaviour unassociated with illness, vomiting or dietary deficiency.