PREVALENCE AND CAUSES
Obesity is one of the most important medical problems in dogs. Studies from throughout the world have estimated the prevalence
of overweight or obese dogs to range between 22% and 40%.13-17 Cross-sectional data suggest one in three dogs seen by U.S. veterinarians is overweight.18
Breed predisposition
Recent data in various animal species provide new insight into the genetic basis of obesity.19-21 A significant breed predisposition to obesity has been shown in certain breeds including Cairn terriers, West Highland white
terriers, Scottish terriers, Shetland sheepdogs, basset hounds, Cavalier King Charles spaniels, dachshunds, beagles, cocker
spaniels, and Labrador retrievers.12,15,22-24 Conversely, certain breeds, particularly sight hounds, appear to be resistant to the development of obesity.24
Age
As an adult animal ages, lean body mass declines, resulting in a decrease in total daily energy needs.25 The loss of lean body mass is exacerbated if aging is accompanied by a decrease in voluntary activity. The total daily energy
needs of an average-sized 7-year-old dog may decrease by as much as 20% when compared with its needs as a young adult. If
food intake does not decrease proportionately with the decreasing energy needs, weight gain results.26 The end result is an increasing prevalence of obesity in older dogs. In short, a reduced metabolic rate associated with
aging predisposes dogs to being overweight or obese.27
Neutering
Neutering results in the net loss of circulating sex hormones, slowing an animal's metabolism and predisposing the neutered
animal to becoming overweight or obese.14,15,28 Changes in sex hormones after neutering directly affect the satiety center in the brain through changes in leptin and ghrelin
concentrations and possibly indirectly affect it by altering cell metabolism and hormonal regulators of food.24,29-31
Gonadectomy in dogs also results in modified feeding patterns. Compared with before surgery, four female ovariectomized beagles
fed ad libitum for three months after surgery ate significantly more food and gained more weight.28
The study suggested that energy intake should be reduced by 30% after ovariectomy to maintain optimal body weight for a period
of six months.28 These results confirmed those of a previous experiment that also used four young adult female beagles and showed that energy
requirements are 20% lower after ovariectomy.31
Medications
Certain medications may also contribute to obesity in dogs. Phenobarbital, a common anticonvulsant, causes polyphagia at high
serum concentrations. The increase in food consumption may contribute to a worsening body condition, resulting in an overweight
or obese dog. Glucocorticoids stimulate gluconeogenesis and abdominal lipogenesis, which may contribute to fat deposition
and weight gain.
Adipokines
Excessive white adipose tissue impacts canine health through two main mechanisms. First, excessive fat deposition may have
physical effects on the body, including excessive weight bearing, which worsens orthopedic diseases; constriction of upper
airways, which exacerbates respiratory disorders; an inability to groom, which leads to dermatologic issues; and an insulating
effect, which causes reduced heat dissipation. Second, the normal endocrine function of white adipose tissue may be disturbed,
a now-recognized significant pathogenetic mechanism for the development and exacerbation of many of the obesity-associated
metabolic disorders in both humans and domestic animal species.32
Table 1: Common Adipokines in Dogs*
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White adipose tissue is an active endocrine organ, secreting protein modulators called adipokines (Table 1).33-37 Adipokines have proven endocrine, autocrine, and paracrine roles, regulating energy balance, immune function, angiogenesis,
glucose and lipid metabolism, and hemostasis in people, dogs, and cats.34,38-40
Proinflammatory adipokines secreted by white adipose tissue increase as tissue mass rises. Thus, obesity may be viewed as
a state of chronic inflammation. Increases in inflammatory adipokines have been causally linked to the development of metabolic
syndrome and other obesity-related disorders in people.37,40 Increased inflammatory adipokine gene expression has also been documented in canine white adipose tissue.20
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