Page 495 - Small Animal Clinical Nutrition 5th Edition

Obesity 511

VetBooks.ir mendations may also lead to excessive caloric intake. This older become thinner and tend to be in less than optimal body
condition (Armstrong and Lund, 1996; Scarlett et al, 1994;
results not because manufacturers make inappropriate or self-
serving recommendations, but rather because manufacturers Kronfeld et al, 1991).
base recommendations on ranges and average caloric require- However, an alternate hypothesis suggests that overweight
ments for a given body weight. Recommendations often list a dogs and cats die sooner and do not reach ages attained by thin-
minimum and maximum amount of food to feed within a given ner animals because excess weight is detrimental to overall
range of body weights (e.g., two to four cups for a 5.9- to 11.4- health (Armstrong and Lund, 1996). Caloric consumption has
kg dog). The maximum amount can be one and one-half to been inversely related to lifespan of dogs (Kealy et al, 2002),
four times the minimum amount listed for a given range of rodents (Masoro, 1984, 1988, 1992) and rhesus monkeys (Lane
body weights. Excess caloric intake can occur if pet owners et al, 1997). Cats may be similarly affected.
interpret that a smaller dog should be fed the larger amount.
Furthermore, excess caloric intake can occur because pet own- Gender and Neuter Status
ers overestimate the activity of their pet. Many pets today are Small differences in body composition and energy intake
relatively inactive due to the lifestyle of their owners. (See between intact male and intact female cats have been reported
Activity below.) Also, cat and dog owners underestimate the (NRC, 1986; Jewell et al, 1996). The differences in energy
body condition of their pets (Singh et al, 2002; Allan et al, intake appear to be due to gender-related differences in lean
2000), increasing the likelihood that pets will be overfed. body mass (Jewell et al, 1996; Klausen et al, 1997).
No controlled studies have been done in dogs to measure dif-
Activity ferences between energy requirements of intact males com-
Many pets, particularly cats, live indoors, which is often associ- pared to intact females. As in other mammals (e.g., cats) intact
ated with reduced physical activity. Physical activity is the most females probably require less caloric intake than intact males.
variable component of energy expenditure. Adequate exercise This assumption is probably due to gender-related differences
can contribute markedly to daily energy expenditure. in lean body mass. The lean body mass of an animal accounts
Furthermore, the risk of obesity decreases with each hour of for nearly all of its RER (Blaxter, 1989).
weekly exercise in dogs (Robertson, 2003). Thus, it is not sur- One study showed that female dogs had an average of 16%
prising that animals with decreased activity or restricted oppor- more body fat than male dogs (Meyer and Stadtfeld, 1980).
tunities for exercise are at greater risk for becoming overweight These findings suggest that intact female dogs need fewer calo-
(Scarlett et al, 1994). Unfortunately, most owners consider their ries than intact male dogs. Surveys found a much higher preva-
dogs to be moderately or very active (Slater et al, 1995). lence of overweight and obese female than male dogs (Edney
Caloric intake can also become excessive if changes occur in and Smith, 1986; Mason, 1970).
a pet’s lifestyle or daily routine that markedly reduce activity Neutering increases the risk of obesity in dogs and cats
without reducing calories. Such changes include moving to (Jeusette et al, 2006; Lund et al, 2005; McGreevy et al, 2005;
smaller dwellings, musculoskeletal injuries and diseases that Kanchuk et al, 2003; Scott et al, 2002; Martin et al, 2001;
require persistent long-term use of central nervous system Harper et al, 2001; Robertson, 1999; Fettman et al, 1997; Root
depressants or corticosteroids. et al,1996).Neutered cats are more likely to be overweight than
are intact cats of either gender (Scarlett et al, 1994; Root and
Age Johnston, 1995; Flynn et al, 1996). Neutered female dogs are
Caloric requirements decrease as some animals age. Re- about twice as likely to be overweight than are intact female
quirements for a given weight are less for maintenance of adults dogs (Edney and Smith, 1986). A similar trend occurs in cas-
than for growing individuals of similar weight. Age has been trated male dogs (Edney and Smith, 1986). Neutering predis-
correlated with the prevalence of excess body weight in dogs poses dogs and cats to weight gain and eventual obesity for sev-
and cats (Armstrong and Lund, 1996; Mason, 1970; Scarlett et eral reasons. Neutered cats had resting metabolic rates 20 to
al, 1994; Sloth, 1992; Kronfeld et al, 1991). Dogs and cats have 25% below those of intact cats of similar age, as measured by
the highest prevalence of obesity from five to 11 years of age indirect calorimetry (Root et al, 1996). In practical terms, this
(Lund et al, 2005, 2006). After about 12 years of age, the preva- finding indicates that neutered cats require only 75 to 80% of
lence tends to decrease markedly in most cross-sectional stud- the food needed by intact cats to maintain optimal body
ies (Armstrong and Lund, 1996; Scarlett et al, 1994; Sloth, weight. These studies confirm the previously suspected
1992; Kronfeld et al, 1991).These observations have bearing on decrease in metabolic rate caused by loss of estrogens and
two theories concerning obesity and aging. First, one theory androgens from neutering. This reduction in resting metabolic
suggests that aging causes a decrease in energy requirement as rate appears to be in addition to any decrease in physical activ-
a result of concomitant loss of lean body tissue and that obesi- ity that might occur from decreased roaming and sexual behav-
ty will result if energy intake fails to decrease. Except for one ior (Hart and Barrett, 1973; Hopkins et al, 1976).
study (Mason, 1970), the data from other cross-sectional stud- Furthermore, estrogens suppress appetite in several animal
ies appear not to support this theory on initial examination species (Czaja and Goy, 1975). Neutered female beagles and
(Armstrong and Lund, 1996; Scarlett et al, 1994; Sloth, 1992; cats will eat more food and gain more weight than sham-oper-
Kronfeld et al, 1991). Instead, dogs and cats 12 years of age or ated females fed an identical food (Flynn et al, 1996; Houpt et