ArticlePDF Available
Central
2008 Practical advice from the presentations PEER-REVIEWED
D
ogs and cats are frequently observed eating grass
and other plants of no apparent nutritional value.
Unfortunately, little on this topic appears in the vet-
erinary literature. Although the prevalence of plant eating in
domestic dogs and cats has not been documented, wild canids
and felids in nature are known to eat grass and plants—plant
material has been found in 2% to 74% of scats and stomach
content samples of wolves and cougars.1-6
Clients commonly ask questions about plant eating in their
pets: Do animals eat grass to induce vomiting because they’re
sick? Do they eat plants because they have a dietary deciency?
In a recent study by Dr. Karen Sueda, Dr. Kelly Cliff, and myself,
three surveys of pet owners were conducted to nd answers to
these and other questions about plant eating in dogs.7
FINDING THE ANSWERS
Our surveys were designed to test the hypothesis that most
plant eating in dogs is associated with illness or a dietary
deciency and that ingestion of plant material is usually
followed within a few minutes by vomiting.
First, we surveyed veterinary students who had pet dogs
(n=25) about the frequency of grass eating in their own dogs
and whether the students observed signs of sickness before
grass consumption or vomiting afterward. All of the students
reported that their dogs ate grass. None reported observing
signs of illness before their dogs ate grass, and only 8% said
that their dogs regularly vomit afterward.
Next, we surveyed a group of dog owners (n=47) who had
brought their dogs to our teaching hospital for outpatient care.
We asked these owners for their observations on their pets
Why do dogs and cats eat grass?
A) They are sick and need to vomit.
B) They have a dietary deficiency.
C) Studies point to a third option that may may well be the correct answer
to this often-asked client question.
Benjamin L. Hart, DVM, PhD, DACVB
Benjamin L. Hart, DVM, PhD, DACVB
Department of Anatomy, Physiology
and Cell Biology
School of Veterinary Medicine
University of California
Davis, CA 95616
Coauthor of Canine and Feline Behavior Therapy,
2nd edition, Blackwell Press 2006.
Getty Images
648 De c emb er 2008 VETERINARY MEDICINE
consumption of plants and the animals’
behavior before and afterward. Of this
group, 79% had observed their dogs eating
plants (grass was the plant most frequently
consumed). Thirty-three owners answered
questions about their dogs’ behavior before
and after eating plants. Of these owners’
dogs, signs of illness were infrequent (four
dogs), and vomiting afterward was only
occasional (six dogs).7
Faced with the prospect of a null hy-
pothesis—that plant eating is not particu-
larly related to illness or vomiting—we
conducted a large Web-based survey
targeting owners of plant-eating dogs.
More than 3,000 owners responded to
our survey. We asked these owners
questions about their dogs’ plant-eating
habits and diet, and we gathered data on
the dogs’ sex, gonadal status, breed, and
age. After applying inclusion criteria (e.g.
excluding responses from owners who
spent less than six hours a day with their
dogs, and excluding dogs that appeared
to only chew but not ingest plants), we
narrowed the usable surveys to 1,571. Our
ndings included the following:
• Sixty-eight percent of the respondents
said their dogs ingest plants on a daily
or weekly basis.
• Eight percent of the respondents re-
ported that their dogs frequently show
signs of illness before plant eating.
• Twenty-two percent reported that their
dogs regularly vomit afterward.
• Of the plant-eating dog population,
younger dogs ate plants more fre-
quently than did older dogs and were
less likely to appear ill beforehand or
to vomit afterward.
Our study revealed that a few dogs
do appear to be ill before eating plants
and that vomiting does sometimes fol-
low plant eating. While we attempted
to exclude dogs with known medical
problems, it is possible that subclinical
gastric or intestinal distress occasionally
evokes grass eating, which may facilitate
vomiting. In fact, we found from our
large study that if dogs showed signs of
illness before eating plants, they were
more likely to vomit afterward than
were dogs that did not show signs of
illness beforehand.
In all the surveys, we asked specic
questions about the dog’s diet. There was
no indication that dogs fed primarily table
scraps or raw food were more prone to
grass eating than those on a commercial,
nutritionally balanced diet. Nor was there
any indication that dogs receiving less
ber in their diets tended to eat plants
more than those getting more ber.
So contrary to the common perception
that grass eating is associated with observ-
able signs of illness and vomiting, we found
that grass eating is a common behavior in
normal dogs unrelated to illness and that
dogs do not regularly vomit afterward.
Vomiting seems to be incidental to, rather
than caused by, plant eating.
WHAT ABOUT CATS?
In an ongoing study with my colleagues
Drs. Sueda, Melissa Bain, and Gretel de
la Riva, preliminary ndings suggest that
plant eating is less common in cats than
in dogs. As in dogs, cats typically do not
appear to be ill before eating plants nor
do they regularly vomit afterward. Our
preliminary data suggest that cats eat
more nongrass plants than do dogs.
AN ETHOLOGIC EXPLANATION:
HERBAL PROPHYLAXIS
Our current hypothesis is that plant eat-
ing is a common behavior that usually
occurs in normal dogs and cats. It is
generally unassociated with illness or a
dietary deciency but reects an innate
predisposition inherited from wild canid
and felid ancestors. More studies are
needed, but plant eating likely serves
a biological purpose. One explanation
is that plant eating played a role in the
ongoing purging of intestinal parasites
(nematodes) in wild canid and felid an-
cestors (that were always exposed to
intestinal parasites). As observed in wild
chimpanzees, which eat whole leaves
from a variety of plants, the plant mate-
rial passes through the intestinal tract,
increasing intestinal motility and wrap-
ping around worms and thereby purging
the tract of intestinal nematodes.
8,9
In our
study, younger animals were observed
to eat plants more frequently than did
older animals.7 Perhaps young animals
eat plants more often because they are less
immune to intestinal parasites and are
actively growing, thus nutritional stress
could be more costly than in adults.
Whether intestinal parasites in wild an-
cestors of domestic cats were less prevalent
than in wild ancestors of domestic dogs
is an open question. Certainly cats are
more fastidious about making their feces,
a major source of intestinal infestations,
less available for incidental ingestion.
CONCLUSION
When owners ask about their pets’ ten-
dency to consume plants, let them know
that their pets are fairly typical—most
dogs and cats consume some plant mate-
rial. In addition, plant consumption is not
usually associated with gastrointestinal
illness but instead may be a trait inher-
ited from their wild ancestors. Advise
owners to keep their grass-eating dogs
and cats away from chemically treated
lawns and toxic plants.
REFERENCES
1. Andersone Z, Ozolins J. Food habits of wolves Canis lupus in
Latvia. Acta Theriologic 2004; 49:357-367.
2. Andersone Z. Summer nutrition of wolf (Canis lupus) in the
Slitere Nature Reserve, Latvia. Proc Latvian Acad Sci 1998; 52:79-80.
3. Papageorgiou N, Vlachos C, Sfougaris A, et al. Status and diet
of wolves in Greece. Acta Theriologica 1994;39:411–416.
4. Mech LD. Results—the Timber wolf and its ecology. Fauna of
the National Park of the United States: The Wolves of Isle Royale.
National Park Service. 3 September 2004. http://www.cr.nps.
gov/history/online_books/fauna7/fauna5g.htm.
5. Stahler DR, Smith DW, Guernsey DS. Foraging and feeding
ecology of the grey wolf (Canis lupus): lessons from Yellowstone
National Park, Wyoming, USA. J Nutr 2006;136:39:1923S–1926S.
6. Robinette WL, Gashwiler JS, Morris OW. Food habits of the
cougar in Utah and Nevada. J Wildl Manage 1959;23:261-273.
7. Sueda KLC, Hart BL, Cliff KD. Characterisation of plant eating
in dogs. Appl Anim Behav Sci 2008;111:120-132.
8. Huffman MA, Canton J. Self-induced increase of gut motility
and the control of parasitic infections in wild chimpanzees. Int J
Primatol 2001;22:329–346.
9. Huffman MA, Page JE, Sukhdeo MVK, et al. Leaf-swallowing
by chimpanzees: a behavioural adaptation for the control of
strongyle nematode infections. Int J Primatol 1996;17:475-503.
Gender-specific behaviors
in dogs and cats
To hear Dr. Hart talk about
some surprising differences
between these species, go to
dvm360.com and click
on “Medicine.”
VETERINARY MEDICINE D e cem ber 2 0 0 8 649
... First is the self-medication hypothesis (Hart, 2008). Many animals are known to use plants to counter parasites or diseases (Hart & Hart, 2018;Huffman, 2003;Huffman & Canon, 2000). ...
... However, fruit was detected more frequently in domesticated cats than in feral cats living on a Croatian island (Lanszki et al., 2016), suggesting that the detection of fruit content might be associated with proximity to human activity [e.g., food provisioning or scavenging garbage (Yamane et al., 1994)]. Additionally, there were several studies showing the presence of nonfruit-bearing plants, which may have other benefits, such as parasite control (Hart, 2008;Hart & Hart, 2018;Sueda et al., 2008). ...
Article
Full-text available
Plant‐eating behavior is one of the greatest mysteries in obligate carnivores. Despite unsuitable morphological and physiological traits for plant consumption, the presence of plants in scat or stomach contents has been reported in various carnivorous species. However, researchers’ interpretations of this subject are varied, and knowledge about it is scarce, without any multispecies studies. This study assessed the extent of variation in the frequency of plant occurrence in scat and stomach contents, as well as its relationship with various factors in 24 felid species using data from 213 published articles. Since the frequency of plant occurrence has not always been reported, we created two‐part models and estimated parameters in a Bayesian framework. We found a significant negative relationship between the frequency of plant occurrence and body mass. This may be because plant‐eating behavior reduces the energy loss caused by parasites and increases the efficiency of energy intake, which has a greater importance in smaller animals that have relatively high metabolic rates. This exploratory study highlights the importance of considering plant consumption in dietary studies on carnivorous species to understand the adaptive significance of this behavior and the relationship between obligate carnivores and plants. Plant‐eating behavior is one of the greatest mysteries in obligate carnivores. This study assessed the extent of variation in the frequency of plant occurrence in scat and stomach contents, as well as its relationship with various factors in 24 extant felid species using data from 213 published articles. We found a significant negative relationship between the frequency of plant occurrence and body mass.
... In contrast, fructo-oligosaccharide supplementation to induce mild GI disturbance in dogs did not lead to using grass as an emetic [21]. Other authors concluded that grass-eating should be regarded as a normal behaviour of dogs [22][23][24]. Excessive surface or object licking was found to be a behavioural change associated with gastrointestinal abnormalities [25]. Currently it is unknown to which extent such non-specific signs are associated with early or advanced gastric mucosal pathology in dogs. ...
... Eating grass failed to show significant association with vomiting. Plant-eating has been hypothesized to serve various purposes such as inducing vomiting or controlling gastrointestinal parasite burden [20,23]. About 70% of all dogs eat plants on a daily or weekly basis, with grass being the most commonly consumed. ...
Article
Full-text available
Background Gastric carcinoma (GC) is uncommon in dogs, except in predisposed breeds such as Belgian Shepherd dogs (BSD) of the Tervuren and Groenendael varieties. When GC is diagnosed in dogs it is often late in the disease, resulting in a poorer prognosis. The aim of this prospective clinical study was to investigate possible associations of gastric mucosal pathologies with clinical signs, laboratory test results and GC in BSD. An online survey gathered epidemiological data to generate potential risk factors for vomiting as the predominant gastric clinical sign, and supported patient recruitment for endoscopy. Canine Chronic Enteropathy Clinical Activity Index (CCECAI) score and signs of gastroesophageal reflux (GER) were used to allocate BSD older than five years to either Group A, with signs of gastric disease, or Group B, without signs. Findings in the clinical history, laboratory tests and gastric histopathology of endoscopic biopsies were statistically analysed in search of associations. Results The online survey included 232 responses. Logistic regression analysis recognized an association of vomiting with gagging, poor appetite and change in attitude. Recruitment for endoscopy included 16 BSD in Group A (mean age 9.1 ± 1.8 years, mean CCECAI = 3.1 ± 2.2 and signs of GER); and 11 in Group B (mean age 9.8 ± 1.4 years, CCECAI = 0, no signs of GER). Seven (25.9%) of the 27 BSD (Group A 4/16, Group B 3/11) had leukopenia. Serum C-reactive protein tended to be increased with more advanced GC (P = 0.063). Frequency of GC, mucosal atrophy, mucous metaplasia, or glandular dysplasia did not differ between groups. GC was frequently diagnosed (6/27), even without clinical signs (2/11). The odds ratio for vomiting (OR = 9.9; P = 0.016) was increased only when glandular dysplasia was present. GC was associated with mucous metaplasia (P = 0.024) and glandular dysplasia (P = 0.006), but not with mucosal atrophy (P = 1). Conclusions GC can develop as an occult disease, associated with metaplasia and dysplasia of the gastric mucosa. Suggestive clinical signs, notably vomiting, should warrant timely endoscopy in BSD. Extensive endoscopic screening of asymptomatic dogs remains, however, unrealistic. Therefore, biomarkers of mucosal pathology preceding clinical illness are needed to support an indication for endoscopy and enable early diagnosis of GC.
... Grass eating may be an innate behavior in some species of the Carnivora (Bjone et al. 2009), as even well-cared for domestic cats (Felis catus) and dogs (Canis familiaris) that might be free of intestinal parasites often regularly consume grass (Hart 2008;Hart & Hart 2018;Hart et al. 2019). A long-held belief is that grasses are consumed by cats or dogs to alleviate nausea or induce vomiting (Huidekoper 1895;Cameron 1927;Powell 1957: 210;Beaver 1981;Bush 1995;Cannon 2013). ...
... Fenn (1790) wrote that dogs eat grass to vomit, but for cats Fenn stated only that they eat grass as medicine. Recent studies show that when domestic cats or dogs consume grasses or other vegetation, they usually do not vomit nor appear to the owners to be nauseous (Sueda et al. 2007;Hart 2008;Bjone et al. 2009;McKenzie et al. 2010;Hart et al. 2019). Dudley (1892: 87) also noticed that dogs frequently ate grass without vomiting, but rather suggested that grass ingestion prevented vomiting. ...
Article
Full-text available
Within the Carnivora order, the consumption of fibrous plant tissues (FPT), such as leaves and stems, is only known to serve the nutritional needs of eight species in the Ailuridae and Ursidae. Apart from the Ailuridae and Ursidae, the extent of FPT ingestion in the Carnivora is poorly understood. A literature search was conducted to compile studies containing evidence of FPT consumption in the Carnivora, primarily based on analyses of scats or gastrointestinal tracts. Among 352 studies, there was evidence of FPT consumption in any amount in 124 species, or 41%, of the Carnivora. Grass consumption was documented in 95 species, while ingestion of sedges, marine plants, bryophytes, conifers, and dicots was much less frequent. A few species showed evidence of consuming fungi or soil. Nine studies observed co-occurrences of intestinal parasites with grasses or sedges in the scats of the Carnivora, suggesting these abrasive or hairy plant tissues help to expel intestinal parasites. The relevance of consuming marine plants, bryophytes, conifers, dicots, fungi, or soil has also been underappreciated. Deliberate ingestion of FPT may be more widespread and important than previously realized in the Carnivora.
... Main prey items were identified as those species contributing >40% per volume in scats (following Avenant & Nel 1997). Grass always contributed less than 2% to the volume, of a very small number of scats, and was therefore not included in further analysis here; these ingestions could happen accidentally (together with other prey, following Hawthorne 1972) or for health purposes (see Bjone et al. 2007;Hart 2008;Atkinson et al. 2002;Yoshimura et al. 2021). Mammalian food items were identified by hair and teeth samples. ...
... However, the food source hypothesis may not always apply to felids, as they frequently consume grass or leaves [7,13,14], which should be less nutritional than fruits. Second is the selfmedication hypothesis: Hart [15] suggests that dogs use plant materials for self-medication to expel parasites or treat inflammation; this was particularly common in young individuals, which are less immune to intestinal parasites. However, this self-medication effect has not been verified in dogs or cats. ...
Article
Full-text available
Although most felids have an exclusive carnivore diet, the presence of plant matter in scat has been reported among various species. This indicates that there may be an adaptive significance to the conservation of plant-eating behavior in felid evolution. Some studies have hypothesized that felids consume plants for self-medication or as a source of nutrition. In addition, it is thought that plant intake helps them to excrete hairballs, however, no scientific work has confirmed these effects. Thus, the objective of this study is to investigate the relationship between plant intake and hair evacuation in felid species. We selected snow leopards (Panthera uncia) as the study species because they have longer and denser hair than other felids. The behavior of 11 captive snow leopards was observed and scat samples from eight of them and two other captive individuals were analyzed. Snow leopards evacuate hair possibly by vomiting and excreting in scats. The frequency of plant-eating and vomiting and the amount of hair and plant in scat were evaluated. We found that the frequency of vomiting was much lower than the frequency of plant-eating. In addition, there was no significant relationship between the amount of plant matter contained in scats and the amount of hair in scats. Contrary to the common assumption, our results indicate that plant intake has little effect on hair evacuation in felid species.
... In veterinary clinical practice, the traditional explanation for plant-eating in dogs and cats is that there is a dietary deficiency or that plant-eating is a way of inducing vomiting. In two broad-ranging Web-based surveys of thousands of dog and cat owners, it was found that the great majority of dogs and cats appeared normal before and after eating plants and did not vomit [72,73] (figure 4). An important finding was that animals under 1 year of age ate plants much more frequently than older ones, the explanation being that the young are more vulnerable to the cost of intestinal parasites, and hence have an evolved tendency to eat plants more frequently. ...
Article
Full-text available
Mammals live and thrive in environments presenting ongoing threats from parasites in the form of biting flies, ticks and intestinal worms and from pathogens as wound contaminants and agents of infectious disease. Several strategies have evolved that enable animals to deal with parasites and pathogens, including eliminating away from the sleeping–resting areas, use of an array of grooming techniques, use of saliva in licking, and consuming medicinal plant-based compounds. These strategies all are species-specific and reflect the particular environment that the animal inhabits. This article is part of the Theo Murphy meeting issue ‘Evolution of pathogen and parasite avoidance behaviours’.
Article
Full-text available
Diet and grass eating in dogs Do dogs eat grass because they have a dietary deficiency? Based on three arguments, the answer to that commonly asked question (1) is no. For one, a deficiency of any nutrient is highly unlikely in grass-eating dogs fed on commercial, complete diets. Secondly, if a nutrient deficiency would inspire grass eating, the low bodily status of the nutrient in question somehow connects with grass as replenisher and directs its selection and consumption. So far, these capabilities have not been shown in dogs. Thirdly, dogs fed a fiber-deficient diet did not engage in eating fresh grass more frequently than did their counterparts fed the same diet, but with alfalfa meal as fiber source. In a questionnaire-based study, 71 (11%) out of 626 owners stated that their dogs never ate grass or other green plants (2). A web-based survey showed that 1068 (68%) out of 1571 plant-eating dogs ingested plants on a daily or weekly basis (3, Note 1). In 79% of those 1571 dogs, grass was the most frequently eaten plant. Plant-eating frequency (˂ 1 or ≥ 1/week) was unassociated with diet type: the frequencies were similar in dogs fed either commercial kibbled and/or canned food (n =1245) or home-cooked or raw food (n =326). As mentioned, fiber deficiency may not increase grass eating. Contrarily, an experimental diet did affect grass eating: excessive intake of a non-digestible carbohydrate had a diminishing effect. For the 1571 plant-eating dogs, 8% of their owners frequently noticed signs of illness before plant eating, while 23% frequently saw their pets vomit afterward (3). These outcomes indicate that overt illness is a minor correlate of grass eating and that vomiting is not a fixed consequence (Note 2). Another question that dog owners may put to veterinarians (1)-Do dogs eat grass to induce vomiting because they are sick?-cannot be answered, but grass eating mostly is not followed by vomiting (Note 3). Plant eating likely serves a biological purpose, but so far the interpretation is subject of speculation (1). Canine grass eaters may ingest 0 to 30 blades of grass per day, or 0 to 2 g of grass (= 0.32 g of dehydrated grass, Note 4). Multiple, commercial dry dog foods contain alfalfa meal derived from the green, leguminous alfalfa plant. The meal consists of dried, chopped, short-stem and leaf-rich alfalfa. A 20-kg dog may consume 12 g dried alfalfa (about 60 g fresh stems with leaves) per day when fed on a dry food containing 4% alfalfa meal (Note 5). That level of alfalfa inclusion is safe and contributes significantly to the amount of crude fiber in the diet. Diverging health benefits are attributed to alfalfa in dog food (Note 6), but the assertions remain unproven.
Book
How well can you answer pet owners' questions about proper diet and feeding? Canine and Feline Nutrition, 3rd Edition describes the role of nutrition and its effects upon health and wellness and the dietary management of various disorders of dogs and cats. By using the book's cutting-edge research and clinical nutrition information, you'll be able to make recommendations of appropriate pet food and proper feeding guidelines. Pet nutrition experts Linda P. Case, MS, Leighann Daristotle, DVM, PhD, Michael G. Hayek, PhD, and Melody Foess Raasch, DVM, provide complete, head-to-tail coverage and a broad scope of knowledge, so you can help dog and cat owners make sound nutrition and feeding choices to promote their pets' health to prolong their lives. Tables and boxes provide quick reference to the most important clinical information. Key points summarize essential information at a glance. A useful Nutritional Myths and Feeding Practices chapter dispels and corrects common food myths.New clinical information covers a wide range of emerging nutrition topics including the role of the omega-3 and omega-6 fatty acid families in pet health and disease management. Coverage of pet food safety and pet food ingredients includes both commercially and home-prepared foods and provides answers to pet owners' questions on these topics. Completely updated content reflects the latest findings in clinical nutrition research. Information regarding functional ingredients and dietary supplementation provides a scientifically based rationale for recommending or advising against dietary supplements. Guidelines for understanding pet food formulations and health claims differentiate between "market-speak" and actual clinical benefits for patients, with practice advice for evaluating and selecting appropriate foods.
Article
Understanding the diets of carnivores is essential for resolving food web interactions and the population dynamics of both prey and predators and for designing effective strategies for species and ecosystem conservation. As effective predators, wild felids play important roles in various ecosystems, but relatively little is known about the dietary habits of many species, primarily owing to their elusive behavior. We used a DNA-based method to analyze the vertebrates and plants constituting the diet of leopard cats (Prionailurus bengalensis) in the temperate forests of the mountains of southwest China, a global biodiversity hotspot. DNA extracted from leopard cat scats was amplified with primers targeting either the vertebrate mitochondrial 12S rRNA gene (N = 25 scats) or the psbCL region of the chloroplast genome of vascular plants (N = 42 scats). The polymerase chain reaction products were sequenced and prey taxa were assigned based on sequence similarity. We identified a total of 16 taxa of vertebrate prey, with pikas (in 76% of the scats) and rodents (40%) predominating. Plant material belonging to 12 taxa was found in 76% of the samples, and the genus Solanum and subfamily Rosoideae were the most frequently detected plant taxa. The frequency of occurrence of identified plant taxa differed between the spring–summer and fall–winter months. Thus, the leopard cats in our study area have a diversified diet and are highly flexible in adapting their foraging behavior to the locally available prey. Our data suggest that preserving their natural prey base dominated by pikas and rodents may be vital for the subsistence of local populations. The high species resolution and detection sensitivity of the DNA-based method we used in this study make it a powerful and efficient tool for fine-scale analysis of complex diets.
Article
The most commonly kept domestic animal in the developed world, the cat has been a part of human life for thousands of years. Cats have been both worshipped and persecuted over this long period - either loved or hated for their enigmatic self-reliance and the subject of numerous myths and fables. Highlighting startling discoveries made over the last ten years, this new edition features contributions from experts in a wide range of fields, providing authoritative accounts of the behaviour of cats and how they interact with people. Thoroughly revised and updated to include information on the basic features of cat development and social life, the history of their relations with humans, health and welfare problems, and the breeding of cats for sale and for show. It is intended for all those, whether specialist or general reader, who love or are simply intrigued by these fascinating animals.
Conference Paper
Full-text available
The foraging and feeding ecology of gray wolves is an essential component to understanding the role that top carnivores play in shaping the structure and function of terrestrial ecosystems. In Yellowstone National Park (YNP), predation studies on a highly visible, reintroduced population of wolves are increasing our understanding of this aspect of wolf ecology. Wolves in YNP feed primarily on elk, despite the presence of other ungulate species. Patterns of prey selection and kill rates in winter have varied seasonally each year from 1995 to 2004 and changed in recent years as the wolf population has become established. Wolves select elk based on their vulnerability as a result of age, sex, and season and therefore kill primarily calves, old cows, and bulls that have been weakened by winter, Summer scat analysis reveals an increased variety in diet compared with observed winter diets, including other ungulate species, rodents, and vegetation. Wolves in YNP hunt in packs and, upon a successful kill, share in the evisceration and consumption of highly nutritious organs first, followed by major muscle tissue, and eventually bone and hide. Wolves are adapted to a feast-or-famine foraging pattern, and YNP packs typically kill and consume an elk every 2-3 d. However, wolves in YNP have gone without fresh meat for several weeks by scavenging off old carcasses that consist mostly of bone and hide. As patterns of wolf density, prey density, weather, and vulnerability of prey change, in comparision with the conditions of the study period described here, we predict that there will also be significant changes in wolf predation patterns and feeding behavior.
Article
Full-text available
1994. Status and diet o f wolves in Greece. Acta theriol. 39: 411—416. The stomach contents of 32 wolves Canis lupus Linnaeus, 1758 collected through­ out Greece during autumn and winter 1991 and 1992 were examined for prey remains. O f these 28 stomachs contained measurable quantities of food. Of the 19 species that were found in the w olf diet 12 species were mammals. The main food items were goats, sheep, pigs and cows. Large wild herbivores did not play a significant role in the w olf diet. The observed consumption of grasses and fruits are important when they are available. The maximum food content in the examined stomachs was 1860 g.
Article
Full-text available
Diet of wolvesCanis lupus Linnaeus, 1758 in Latvia was studied from 1997 to 2001 based on 302 scats and 107 stomachs. Wild ungulates (cervids and wild boarSus scrofa) and beaverCastor fiber were the dominant prey. Cervids were found in 50% of samples (62% biomass), wild boar in 25% (21% biomass), beavers in 14% (12% biomass). Wolves selected for wild boar, especially in winter when its ratio in the diet increased to 34% from 20% in summer. It was a more common prey species in the east of the country. The ratio of beavers, small rodents and plant food was higher in summer, which resulted in a broader food niche in summer than in winter (B = 2.53 versus 1.81, respectively). The role of domestic animals in the wolf diet was minimal except for winter when they were consumed as carrion (13%). More than 1/3of all stomachs investigated were empty. The average weight of stomach contents was 972.8 g. The importance of the beaver as an alternative prey is discussed. We conclude that wolves in Latvia prey mainly on wild animals and conflicts with livestock owners are only occasional and/or local.
Article
Full-text available
Grass or plant eating is a widely recognized behaviour amongst domestic dogs. We first estimated the prevalence of plant eating by administering a written survey to owners of healthy dogs visiting the outpatient service of a veterinary medical teaching hospital for routine health maintenance procedures. Of 47 owners systematically surveyed whose dogs had daily exposure to plants, 79% reported that their dog had eaten grass or other plants. Using an internet survey targeting owners of plant-eating dogs, we then acquired 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. Of 3340 surveys returned, 1571 met enrollment criteria. Overall, 68% 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. The findings support the perspective that plant eating is a normal behaviour of domestic dogs.
Article
Full-text available
Swallowing whole leaves by chimpanzees and other African apes has been hypothesized to have an antiparasitic or medicinal function, but detailed studies demonstrating this were lacking. We correlate for the first time quantifiable measures of the health of chimpanzees with observations of leaf-swallowing in Mahale Mountains National Park, Tanzania. We obtained a total of 27 cases involving the use ofAspilia mossambicensis (63%),Lippia plicata (7%),Hibiscus sp. (15%),Trema orientalis (4%), andAneilema aequinoctiale (11%), 15 cases by direct observation of 12 individuals of the Mahale M group. At the time of use, we noted behavioral symptoms of illness in the 8 closely observed cases, and detected single or multiple parasitic infections (Strongyloides fulleborni, Trichuris trichiura, Oesophagostomum stephanostomum) in 10 of the 12 individuals. There is a significant relationship between the presence of whole leaves (range, 1–51) and worms of adultO. stephanostomum (range, 2–21) in the dung. HPLC analysis of leaf samples collected after use showed that thiarubrine A, a compound proposed to act as a potent nematocide in swallowingAspilia spp., was not present in leaves ofA. mossambicensis or the three other species analyzed. Alternative nematocidal or egg-laying inhibition activity was not evident. Worms ofO. stephanostomum were recovered live and motile from chimpanzee dung, trapped within the folded leaves and attached to leaf surfaces by trichomes, though some were moving freely within the fecal matter, suggesting that the physical properties of leaves may contribute to the expulsion of parasites. We review previous hypotheses concerning leaf-swallowing and propose an alternative hypothesis based on physical action.
Article
Full-text available
When physiological adaptation is insufficient, hosts have developed behavioral responses to avoid or limit contact with parasites. One such behavior, leaf-swallowing, occurs widely among the African great apes. This behavior involves the slow and deliberate swallowing without chewing of whole bristly leaves. Folded one at a time between tongue and palate, the leaves pass through the gastro-intestinal (GI) tract visibly unchanged. Independent studies in two populations of chimpanzees (Pan troglodytes schweinfurthii) showed significant correlations between the swallowing of whole leaves and the expulsion of the nodule worm Oesophagostomum stephanostomum and a species of tapeworm (Bertiella studeri). We integrate behavioral, parasitological and physiological observations pertaining to leaf-swallowing to elucidate the behavioral mechanism responsible for the expulsion and control of nodule worm infections by the ape host. Physical irritation produced by bristly leaves swallowed on an empty stomach, increases motility and secretion resulting in diarrhea which rapidly moves leaves through the GI tract. In the proximal hindgut, the site of third-stage larvae (L3) cyst formation and adult worm attachment, motility, secretion and the scouring effect of rough leaves is enhanced by haustral contractions and peristalsis-antiperistalsis. Frequently, at the peak of reinfection, a proportion of nonencysted L3 is also predictably vulnerable. These factors should result in the disruption of the life cycle of Oesophagostomum spp. Repeated flushing during peak periods of reinfection is probably responsible for long-run reduction of worm burdens at certain times of the year. Accordingly, leaf-swallowing can be viewed as a deliberate adaptive behavioral strategy with physiological consequences for the host. The expulsion of worms based on the activation of basic physiological responses in the host is a novel hitherto undescribed form of parasitic control.
Article
Full-text available
The foraging and feeding ecology of gray wolves is an essential component to understanding the role that top carnivores play in shaping the structure and function of terrestrial ecosystems. In Yellowstone National Park (YNP), predation studies on a highly visible, reintroduced population of wolves are increasing our understanding of this aspect of wolf ecology. Wolves in YNP feed primarily on elk, despite the presence of other ungulate species. Patterns of prey selection and kill rates in winter have varied seasonally each year from 1995 to 2004 and changed in recent years as the wolf population has become established. Wolves select elk based on their vulnerability as a result of age, sex, and season and therefore kill primarily calves, old cows, and bulls that have been weakened by winter. Summer scat analysis reveals an increased variety in diet compared with observed winter diets, including other ungulate species, rodents, and vegetation. Wolves in YNP hunt in packs and, upon a successful kill, share in the evisceration and consumption of highly nutritious organs first, followed by major muscle tissue, and eventually bone and hide. Wolves are adapted to a feast-or-famine foraging pattern, and YNP packs typically kill and consume an elk every 2-3 d. However, wolves in YNP have gone without fresh meat for several weeks by scavenging off old carcasses that consist mostly of bone and hide. As patterns of wolf density, prey density, weather, and vulnerability of prey change, in comparison with the conditions of the study period described here, we predict that there will also be significant changes in wolf predation patterns and feeding behavior.
Fauna of the National Park of the United States: the Wolves of Isle royale. National Park Service
  • Ld Mech
Mech LD. results—the timber wolf and its ecology. Fauna of the National Park of the United States: the Wolves of Isle royale. National Park Service. 3 September 2004. http://www.cr.nps. gov/history/online_books/fauna7/fauna5g.htm.
Summer nutrition of wolf (Canis lupus) in the Slitere Nature reserve
  • Z Andersone
Andersone Z. Summer nutrition of wolf (Canis lupus) in the Slitere Nature reserve, Latvia. Proc Latvian Acad Sci 1998; 52:79-80.