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* Nutrition and Notifiable Diseases, Ecole Nationale Vétérinaire d'Alfort, Maisons–Alfort, France
3 To whom correspondence should be addressed. E-mail: lcolliard{at}vet-alfort.fr.
KEY WORDS: • obesity • risk factors • dogs • survey • body condition
Obesity is defined as "a condition of positive energy balance and excessive adipose tissue formation with adverse effects on morbidity and mortality" (1). A working definition of obesity has been suggested for dogs as an excess of 15% over the ideal bodyweight (2).
The prevalence of obesity in dogs, as in humans, is on the increase in all developed countries. Previous studies, mainly in Great Britain and United States, showed that from 18 to 44% of dogs were overweight or obese (3–10). However, hypotheses about canine obesity are based on very limited surveys.
These studies suggested risk factors for obesity include: female gender, neutering, age (3,4,6,10), and breeds [Labrador Retriever, Cairn Terrier, Cocker Spaniel, Daschund, Shetland Sheep dog, Basset Hound, Cavalier King Charles Spaniel and Beagle (6,7)] as well as dietary factors, including the type of diet, especially home prepared (3), although this remains controversial. Edney and Smith (6) reported no clear relation between food types and obesity, but 78.3% of dogs had some form of home-prepared food (fresh food or scraps). Other factors were strongly related to changes in lifestyle, such as the socio-economic and dietary conditions of dog owners.
In France, there is only one previous study: a survey prepared for Hill's Pet Nutrition at the beginning of 2003 (Hill's Pet Nutrition Survey, Ipsos France, unpublished data). This survey, in which 180 dog owners were interviewed by phone, revealed that 20% of the dogs were considered overweight or obese. However, Mason in 1970 (3) showed that one-third of owners underestimated their dog's body condition (BC)4 when compared with a professional assessment.
Our study had 3 objectives: 1) to assess the prevalence of overweight dogs in the population presented over a 3-mo period for vaccination at the National Veterinary School of Alfort (ENVA), 2) to explore the risk factors associated with overweight and obesity, and 3) to evaluate the owner's perception of their dog's BC. The dogs in the study were considered to be a healthy population.
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MATERIALS AND METHODS |
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 TOP MATERIALS AND METHODS RESULTSDISCUSSIONLITERATURE CITED |
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The owners of 681 dogs were asked by a veterinarian to supply details regarding their social status, age, and lifestyle. Then, the dog's BC was evaluated twice by each owner: first, from a verbal description by selecting 1 of 5 descriptors: very thin, thin, optimal, little too fat, and obese; and second, by choosing 1 of 5 drawings of dogs with increasing BCS arranged in a circle. A circular arrangement was intended to avoid the immediate perception of extremes and no titles accompanied the drawings. The owners were then asked to estimate the body wt of their dogs. Finally, they provided information on the dogs themselves (age, gender, sexual status, and type of diet). BCS by a veterinarian, and the dog's measured wt (Soehne scale) completed the questionnaire.
The questionnaires were entered in a database (Microsoft Access). Statistical analyses were performed with STATA 8.0 software (StataCorpLP). The level of agreement between owner and veterinarian BCS was measured by 
-coefficient (0 
1 with: 0.61 1: high agreement; 0.41 0.60: means agreement; 0 0.40: low agreement). For body weights (estimated and real), the level of agreement was measured by correlation coefficient.
To examine associations between overweight and some presumed risk factors, crude odds ratios (OR) and 95% CI were calculated. Then, a stratified analysis by Mantel-Haenszel test [adjusted odds ratio (aOR)] was applied to variables suspected to be confounding factors in univariate analysis: neutering, dog's age and owner's age.
Lastly, a multivariate logistic regression analysis [multivariate odds ratio (mOR)] was used for variables significantly associated with overweight in previous analyses (gender, sexual status, dog's age, and owner's age) and for variables strongly suspected to be risk factors, such as breed, housing, food type, and distribution of extra food.
OR estimates were considered significantly different from 1 if the 95% CI did not include 1.0 (12). A covariate was considered to be a confounder and included in the multivariate regression model if its exclusion altered the OR for overweight by >10%.
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RESULTS |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Age distribution
Among the population of dogs (n = 616), the mean age was 5.7 y old (2 mo to 20 y). A total of 22.7% of the dogs were 1 y of age (16.6% were <1 y and 6.5% were between 1 and 2 y old), and 22.8% of dogs were 
10 y old (17.5% were >10 y).
Breed and type
Overall, 67% of the dogs were identified as purebred, one-third of which were pedigree dogs. Yorkshire Terrier (14%), Poodle (12%), Retriever (9%), Bichon (8%), Rottweiler (6%) and German Shepherd dog (4%) were the 6 most represented breeds of the purebred dogs; together they accounted for 53% of all purebred dogs and 34.5% of all dogs. Of the purebred dogs, 46% were identified as toys (group IX) and of all dogs, 94% were considered pets and 6% as utility or working dogs.
Sexual status of the studied population of dogs
Of the total dog population surveyed, 52.6% were males, made up of 45.5% entire and 7.1% neutered. Similarly, the 47.4% females were made up of 31.5% entire and 15.7% neutered. Thus a higher percentage of females, 49.7%, compared with 15.7% of males, were neutered.
Owners and lifestyle
The population of dog owners surveyed was composed of 76.6% active and 18.7% retired individuals. This distribution is biased compared with the national French population, which is made up of 55.3% active and 24.5% retired people. Unemployed people accounted for 6.4% of the active studied population compared with 8.8% in the French active population (data not shown).
Of the 616 dogs, 62.3% lived in apartments, 37.7% in houses, and 0.2% in the street; 42.7% had access to gardens, 28.2% to balconies, and 29.1% had no outdoor access except on a lead.
Diet type and distribution
Owners mainly used commercial dry or canned food to feed their dogs (85.9%), one-third of them (37.5%) used only commercial food. Nevertheless, nearly half (48.4%) had some prepared food in their regular diet and 14.1% were fed only a home-prepared diet. A total of 89% of all dogs received snacks, treats, or table scraps (data not shown).
Of the 616 dogs, 45.6% were fed 1 meal/d, 30.8% 2 meals/d, and 11.9% 3 meals/d, whereas 6.7% were self-fed with a limited amount of food, and the last 5% were fed ad libitum.
Overweight rating
Through visual assessment by a veterinarian, 38.8% (95% CI: 34.9–42.7%) of all dogs exceeded normal BC (BCS of 4 and 5): 33.8% (95% CI: 30–37.6%) were overweight (BCS of 4) and 5% (95% CI: 3.2–6.8%) were obese (BCS of 5). Optimal BC accounted for 56.5% of dogs (95% CI: 52.5–60.5%), underweight for 4.7% (95% CI: 3–6.4%), and none were thin.
The agreement between the owner's and the veterinarian's visual assessment of the dog's BC was poor ( = 0.33; P < 0.001), mainly due to the owner's underestimation of the BC of his dog. The underestimation of the BC of overweight or obese dogs by their owner compared with the veterinarian was high, but even higher by verbal description than by a visual scale (Table 1). Nevertheless, the correlation between measured and estimated wt was high (owner: r = 0.97; veterinarian: r = 0.99).
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The multiple logistic regression confirmed a significant positive OR for the dog's age [from mOR 2.74; 95% CI: 1.28–5.89, for 2–3 y old to 12.33; 95% CI: 4.92–30.90, for >12 y old], for the gender and sexual status, with a higher risk for intact female [mOR 1.57; 95% CI: 1.09–2.27] and neutered males [mOR 2.81; CI 1.29–6.11] and for the Retriever breed [mOR 4.65; 95% CI: 2.20–9.8]. Likewise, retired persons were more likely to own an overweight dog than others [mOR 2.98; 95% CI: 1.24–7.18]. Living in a house [mOR 1.42; 95% CI: 0.98–2.07] did not represent a risk of overweight in the multiple logistic regression analysis.
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DISCUSSION |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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In our study, significant risk factors for overweight are gender, neutering, the dog's age, and the retriever breed, which is in agreement with previous studies. Females (1.57-fold the male) and neutered (2.23-fold the entire) animals, as well as retriever breed (4.65-fold) were the highest risk factors. The risk of overweight also increases dramatically with age (from 2.74-fold at 2–3 y, to 12.33-fold for >12 y old). This should encourage veterinarians to follow this specific population and give special nutritional advice to their owners.
The age of the owner was not a risk factor, but as retired persons owned the oldest dogs, age of the dogs was confounded with age of the owner.
Our study showed that owners underestimate their dog's BC when overweight compared with a veterinarian's assessment. In contrast, owners appear to estimate correctly the weight of their dogs even when they never weighed them (data not shown). This finding has been reported by Mason in 1970 (3). From a practical point of view, a visual scale comparison produced better results than a verbal description for estimating an overweight dog by the owner. This finding suggests that practitioners may achieve greater recognition of overweight dogs if they use a visual scale. Veterinarians could also be encouraged to weigh their patients and communicate this information to the owner, especially if the dog is young (and of normal BC), to provide a baseline for future reference.
In this study, approximately one-third of the dogs received home-prepared food, or a mixture of home-prepared and commercial food. This proportion is much greater than reported by either Edney and Smith (6) in 1986 (15.9% of the dogs) or by Mason (3) in 1970 (who reported 30% of dogs had only home-prepared diets and 48% a mixture of canned and home made diets). These studies were conducted >35 y ago, and the difference between them and the current study may be a reflection of the public's attitude toward feeding commercial diets. The feeding of extra food as a treat was a widespread practice and increased with the dog's age, independent of the owner's age.
This study confirms that the major risk factors for overweight are female gender, neutered, the dog's age, and the retriever breed. Veterinarians should give special attention to this high risk population and provide advice regarding appropriate diet and exercise. The high prevalence of overweight and the reluctance of dog owners to recognize it makes prevention an important challenge to the small animal veterinarian.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Author disclosure: This study is part of the residency program of the corresponding author, supported by Hill's Pet Nutrition Europe.
4 Abbreviations used: BC, body condition; BCS, body condition score; OR, odds ratio; aOR, adjusted odds ratio; mOR, multivariate odds ratio.
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LITERATURE CITED |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Crane SW. Occurrence and management of obesity in companion animals. J Small Anim Pract. 1991;32:275–82.
2. Lewis SD. Obesity. In: Lewis LD, Morris M, Hand MS, editors. Small animal clinical nutrition III. Topeka, KS: Mark Morris Associates; 1987. pp. 639–43.
3. Mason E. Obesity in pet dogs. Vet Rec. 1970;86:612–6.[Medline]
4. Anderson RS. Obesity in the dog and cat. Vet Annu. 1973;1441:182–6.
5. Steininger E. Die adipositas und ihre diabetische behandlung [Obesity and diabetes management]. Wein Tierarztl Monat. 1981;68:122–30.
6. Edney AT, Smith PM. Study of obesity in dogs visiting veterinary practices in the United Kingdom. Vet Rec. 1986;118:391–6.[Abstract]
7. Kronfeld DS, Donoghue S, Glickman LT. Body condition and energy intakes of dogs in a referral teaching hospital. J Nutr. 1991;121:S157–8.
8. Sonnenschein EG, Glickman LT, Goldschmidt MH, McKee LJ. Body conformation, diet, and risk of breast cancer in pet dogs: a case-control study. Am J Epidemiol. 1991;133:694–703.
9. Lund EM, Armstrong J, Kirk C. Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. J Am Vet Med Assoc. 1999;214:1336–41.[Medline]
10. Robertson ID. The association of exercise, diet and other factors owner-perceived obesity in privately owned dogs from metropolitan Perth, WA. Prev Vet Med. 2003;58:75–83.[Medline]
11. Laflamme D. Development and validation of a body condition score system for dogs. Canine Practice. 1997;22 (Jul-Aug):10–15.
12. Fletcher RH, Fletcher SW, Wagner EH. Chance. In: Fletcher RH, Fletcher SW, Wagner EH, editors. Clinical epidemiology: the essential. 3rd edition. Baltimore, MD: Williams and Wilkins; 1996. pp. 186–207.
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