Evaluation of dietary energy intake and physical activity in dogs undergoing a controlled weight-loss program

Joseph J. Wakshlag Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Angela M. Struble Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Barbour S. Warren Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Mary Maley Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Matthew R. Panasevich Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Kevin J. Cummings Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

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Grace M. Long Nestlé Purina Research and Development, 1 Checkerboard Square, St Louis, MO 63102.

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Dorothy E Laflamme Nestlé Purina Research and Development, 1 Checkerboard Square, St Louis, MO 63102.

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Abstract

Objective—To quantify physical activity and dietary energy intake in dogs enrolled in a controlled weight-loss program and assess relationships between energy intake and physical activity, sex, age, body weight, and body condition score (BCS).

Design—Prospective clinical study.

Animals—35 client-owned obese dogs (BCS > 7/9).

Procedures—Dogs were fed a therapeutic diet with energy intake restrictions to maintain weight loss of approximately 2%/wk. Collar-mounted pedometers were used to record the number of steps taken daily as a measure of activity. Body weight and BCS were assessed at the beginning of the weight-loss program and every 2 weeks thereafter throughout the study. Relationships between energy intake and sex, age, activity, BCS, and body weight at the end of the study were assessed via multivariable linear regression. Variables were compared among dogs stratified post hoc into inactive and active groups on the basis of mean number of steps taken (< or > 7,250 steps/d, respectively).

Results—Mean ± SD daily energy intake per unit of metabolic body weight (kg0.75) of active dogs was significantly greater than that of inactive dogs (53.6 ± 15.2 kcal/kg0.75 vs 42.2 ± 9.7 kcal/kg0.75, respectively) while maintaining weight-loss goals. In regression analysis, only the number of steps per day was significantly associated with energy intake.

Conclusions and Clinical Relevance—Increased physical activity was associated with higher energy intake while maintaining weight-loss goals. Each 1,000-step interval was associated with a 1 kcal/kg0.75 increase in energy intake.

Abstract

Objective—To quantify physical activity and dietary energy intake in dogs enrolled in a controlled weight-loss program and assess relationships between energy intake and physical activity, sex, age, body weight, and body condition score (BCS).

Design—Prospective clinical study.

Animals—35 client-owned obese dogs (BCS > 7/9).

Procedures—Dogs were fed a therapeutic diet with energy intake restrictions to maintain weight loss of approximately 2%/wk. Collar-mounted pedometers were used to record the number of steps taken daily as a measure of activity. Body weight and BCS were assessed at the beginning of the weight-loss program and every 2 weeks thereafter throughout the study. Relationships between energy intake and sex, age, activity, BCS, and body weight at the end of the study were assessed via multivariable linear regression. Variables were compared among dogs stratified post hoc into inactive and active groups on the basis of mean number of steps taken (< or > 7,250 steps/d, respectively).

Results—Mean ± SD daily energy intake per unit of metabolic body weight (kg0.75) of active dogs was significantly greater than that of inactive dogs (53.6 ± 15.2 kcal/kg0.75 vs 42.2 ± 9.7 kcal/kg0.75, respectively) while maintaining weight-loss goals. In regression analysis, only the number of steps per day was significantly associated with energy intake.

Conclusions and Clinical Relevance—Increased physical activity was associated with higher energy intake while maintaining weight-loss goals. Each 1,000-step interval was associated with a 1 kcal/kg0.75 increase in energy intake.

Obesity in dogs has become a common problem in veterinary medicine, with estimates that approximately 35% to 40% of adult dogs are overweight to obese.1–3 Although the health implications of obesity in dogs may not be as established as in human medicine, the limited evidence suggests that conditions such as osteoarthritis and other orthopedic problems, metabolic syndrome, renal disease, and cancer may be increased in overweight dogs.4–7 It has also been shown that weight loss is beneficial in alleviating clinical signs of osteoarthritis in dogs, with as little as 11% weight loss needed for clinical benefits to become evident.4

Multiple studies8–10 have proven the efficacy of weight loss protocols, and various mechanisms to improve compliance have been examined. Few strategies have proven to be as effective for successful weight management as strict dietary restriction and owner accountability with consistent veterinary supervision.9,10 Typically, weight-reduction protocols require reduced dietary energy intake as well as increased physical activity.2,3 Advocates of increasing physical activity suggest that it not only may increase the number of kilocalories expended, but also may improve metabolism by maintaining lean mass, which has the capacity to expend more kilocalories than does fat mass.2,3 However, anecdotally, some skeptics believe that a typical dog cannot get enough exercise on a daily basis to influence weight loss. To date, there has been no direct evidence reported that physical activity can directly impact weight loss or kilocalorie expenditure in this species. Epidemiological data and short abstracts have alluded to the idea that increased activity might influence weight loss or BCS in companion animals11,a,b; however, prospective studies of this kind are difficult to perform because of the requirements for exercise regimens, staffing to ensure that exercise occurs daily, or owner compliance with a strict activity and feeding protocol. Human studies12,13 have shown that walking programs can have short-term effectiveness in increasing activity and potentially weight loss, yet long-term compliance with such programs is questionable.

In veterinary medicine, patient activity can be evaluated in many ways. Examples include client questionnaires or the use of activity-monitoring devices such as accelerometers and pedometers.14–20 The most accurate quantitative measure of steps can be acquired through accelerometer use; however, the cost of accelerometers makes a clinical field study in dogs prohibitive, particularly because dogs have a propensity for destroying such devices during water-related activities or with destructive mastication. Pedometers are a more cost-effective approach to evaluate activity. Results of a recent study14 examining the use of these devices in dogs revealed that an increased number of steps was correlated with decreased BCS and that pedometers can provide a reasonably accurate assessment of activity in this species. Numerous human studies21,22 have shown more effective weight loss and improved body mass index scores with increased walking activity when pedometers are used as a tool to monitor this variable.

The study reported here was designed to use pedometer-based measurements in a manner similar to that previously described14 for monitoring activity in dogs, with post hoc stratification of dogs into active or inactive groups on the basis of mean number of steps taken during a successful weight-loss program. The purpose of the study was to quantify physical activity and dietary energy intake in dogs enrolled in a controlled weight-loss program and assess relationships between energy intake and physical activity, sex, age, body weight, and BCS while achieving weight-loss goals.

Materials and Methods

Animals—Client-owned dogs were prospectively enrolled in the study at the Cornell University College of Veterinary Medicine from June 10, 2007, to March 12, 2009. Signalment, weight, and BCS23 (on a scale of 1 to 9) were recorded; a BCS ≥ 7 was required for inclusion in the weight-loss portion of the study. Initial examination for inclusion in the weight-loss study included collection of a blood sample from a cephalic vein for evaluation of Hct and serum biochemical analysis including free thyroxine concentration to rule out hypothyroidism or other diseases associated with altered metabolic function. Dogs receiving metabolism-altering medications such as thyroid hormone replacements, insulin, or glucocorticoids were excluded. A signed client consent form was obtained for each dog before initiation of the study. The protocol was approved by the Cornell University Institutional Animal Care and Use Committee.

Validation of pedometer accuracy—Prior to the use of pedometers in the weight-loss study, 20 student-owned or faculty-owned dogs of various sizes (weight range, 4 to 50 kg [8.8 to 110 lb]; BCS, 5 to 7) were included in a preliminary experiment to confirm that collection of data by use of collar-mounted pedometers as described in a previously published validation study14 with minor modifications would yield similar results. The equipment used consisted of a pedometerc suspended from a 3/8-inch-diameter elastic bungee cord by use of a threaded eye screw attached to the top of each pedometer unit. The eye screw was attached to the bungee-cord collar with a small zip-locking cable tie. This configuration allowed the pedometer to hang in a near-vertical position and to move freely. An adjustable collar loop was formed with the bungee cord by apposing the ends with a larger cable tie. This created an apparatus that could be easily positioned for accuracy as well as easily applied and removed.

Validation of the accuracy of forelimb step counts measured via pedometers focused on the walking and trotting gaits because these were gaits most commonly observed by the authors when walking with these dogs. For this evaluation, the dogs were videotaped while walking, trotting, or both on leash over a 25-m (approx 82-foot) distance. This procedure was repeated 6 times for each dog, and tapes were reviewed to count the number of foot strikes for both forelimbs. All evaluations were performed by 1 investigator (MRP) who was unaware of the pedometer-recorded counts when evaluating the videotapes. Accuracy of readings was determined by direct comparison of the actual forelimb paw strikes on the ground versus the pedometer reading for each 25-m trial.

Weight-loss program—After validation of pedometer accuracy, the study of physical activity and weight loss was performed between June 10, 2007, and March 12, 2009. On the basis of results from the pedometer validation experiments, only dogs that weighed > 12 kg (26.4 lb) and measured ≥ 35.6 cm (approx 14 inches) from the ground to the highest point of the withers (ie, the most dorsal extent of thoracic vertebrae between the scapulae) were included in this part of the study.

Dietary energy consumption at the time of study enrollment was calculated in kilocalories on the basis of known cups or cans of dog food per day plus any treats or table foods being fed. Caloric density was determined on the basis of the manufacturer's label information for commercial dog foods and treats given, and that of table foods was assessed on the basis of the USDA Nutrient Database.d Diets for all dogs were gradually switched to a therapeutic weight-loss diete (dry or canned formulation) over a 4-day period, and dogs were allowed up to 15% of the daily energy intake at their present MER from commercial treats without activity modification during a 2-week washout period. All dogs were fitted with a collar-mounted pedometer, and their owners were asked to record each dog's dietary intake on a daily basis and to record pedometer measurements of the number of steps taken each day at a specific time (eg, upon waking in the morning or at bedtime) for the next 2 weeks. Clients were given multiple pedometers and were shown how to replace the collar-mounted pedometers if mechanical failure occurred. The age, sex, BCS (based on the validated 9-point scale23), and weight of enrolled dogs were recorded at baseline (ie, the end of the 2-week washout period).

At the end of the 2-week washout period, the daily MER for each dog was calculated on the basis of total dietary energy intake in kilocalories and any weight gain or weight loss during the washout period when the new diet was being fed. To assess a kilocalorie value for lost body mass, each gram of fat or lean mass lost during the washout period was assumed to equate to approximately 7.5 kcal/g on the basis of information that weight loss comprises approximately 80% fat and 20% lean mass loss, with a potential for even more lean mass loss at the beginning of a weight-loss program caused by a need to upregulate fat metabolism.24 Thus, the formula used was as follows: daily energy deficit = (weight loss in grams ×7.5 kcal/g)/14 d. This initial calculation of daily deficit was added to known energy intake, and the resulting value was accepted as the MER. The MER values were entered into a clinically proven, safe, and effective weight management systemf that tracks weight loss in dogs and provides a predicted value for daily energy intake expected to result in 2% weight loss/wk.12 Calculations for the predicted value are based on an algorithm that uses the initial MER calculation and weight of the dog to compute the energy deficit in kilocalories needed to equal a 2% loss of body weight per week on the assumption that, throughout the entire weight-loss period, the dog will primarily lose fat mass, which has an energy value of 7.92 kcal/g.12 The amount of therapeutic weight-loss food and allowable treats was adjusted on the basis of this information to initiate weight loss.

Body weight, BCS, and daily pedometer readings were recorded for each dog every 2 weeks until a BCS of 5 or 6 was achieved. One calibrated scale was used to determine weights throughout the study, and BCS was assessed by 1 trained veterinary technician (AMS). Pedometer reports were accepted for use in the study if a dog's activity was logged on at least 8 of the 14 days and at least 5 consecutive days within the 2-week period. At each visit, owners were encouraged to walk their dog 3.22 km (2 miles) daily in addition to continuing its normal activities. If a dog's weight loss was ≤ 1% of body weight/wk for the preceding 2-week period, its dietary energy intake allowance was decreased by 15%. A plan was in place to increase the kilocalorie intake allowance by 15% if weight loss of ≥ 2.5% of body weight/wk was detected. The weight-loss program was continued for each dog until a BCS of 5 or 6 was achieved and the owner and technician were satisfied with the dog's condition.

At the end of the study, the dogs were assigned to 1 of 2 groups (inactive or active) on the basis of mean number of pedometer-recorded steps per day. Dogs were ranked according to this variable, and because the number of dogs in the study was uneven, the dog with the median value (7,267 steps/d) was included in the active group. The mean number of steps per day for this dog was approximately 50 steps less than that of the dog ranked immediately above it and approximately 200 steps more than that of the dog ranked immediately below it. This resulted in dichotomization of the population into dogs that had < 7,250 steps/d recorded (inactive group) and those that had > 7,250 steps/d recorded (active group). To assess the change in activity of dogs during the weight-loss program, the mean number of steps per day recorded during the washout period (before extended walks were encouraged) was compared with that recorded during the first and last months of the weight-loss program for all dogs.

In dogs that reached ideal body weight, we were able to calculate an assumed daily MER at the end of the study based on the National Research Council's MEROPD according to the following formula25: 95 kcal × (body weight in kg0.75). We then compared the mean reduction in energy intake (kilocalories) for the inactive and active groups with the MEROPD to determine the percentage of the MEROPD needed to achieve 2% weight loss/wk in a typical obese medium-sized to large dog.

Statistical analysis—Accuracy of pedometer readings was determined via direct comparison of the actual number steps counted on each videotape with the number recorded by the pedometer. The difference was then evaluated statistically for the 6 recorded trials for each dog by use of paired Wilcoxon rank sum tests. To evaluate accuracy for dogs of various sizes, a Wilcoxon rank sum test was used to compare median values for pedometer readings with the median number of actual steps taken for dogs grouped according to size (small [n = 5], medium-sized [8], or large [7]). For the weight-loss program, the mean daily energy intake (calculated per unit of metabolic body weight as kcal/kg0.75) and mean number of daily pedometer-recorded steps were determined for the entire weight-loss period. All calculations for dietary energy intake were performed on the basis of body weight after weight reduction to provide a more accurate assumption of this variable. Visual assessment of the data and results of Shapiro-Wilk testing indicated that data were approximately normally distributed for all variables; therefore, paired Student t tests were used to examine age, mean number of steps recorded per day, body weight and BCS at baseline and at the end of the weight-loss program, percentage of body weight lost during the program, mean time (weeks) to achieve ideal BCS, and mean daily energy intake of active and inactive group dogs.

Nonparametric variables included sex and reproductive status, which were compared between the 2 groups via χ2 analysis. A multivariable linear regression model was used to determine whether daily energy intake (kcal/kg0.75) was significantly associated with number of steps recorded per day, body weight at the end of the weight-loss program, age, or sex. A backward step-wise approach was used to identify a final model. Metabolic body weight (ie, body weight in kg0.75) calculations used in the regression analysis (Pearson method) were based on weight of dogs at the end of the weight-loss program as a more precise measurement of this variable.

A Kruskal-Wallis test was used to compare the daily number of steps recorded during washout with those during the first and last months of participation in the weight-loss program for the entire population of dogs enrolled. Additionally, the relationship between BCS at baseline and daily number of steps recorded during the washout period in this cohort of obese dogs was examined by use of linear regression analysis. Values of P < 0.05 were considered significant for all tests. All statistical analyses were performed by use of commercially available softwareg,h programs.

Results

Validation of pedometer use—The 20 dogs used in this part of the study ranged in weight from 4 to 50 kg, and the mean number of steps taken by each dog during the six 25-m trials ranged from 29 to 116. Examination of the percentage difference between actual number of steps taken (counted on videotaped recordings of each trial) and those recorded via pedometers revealed that for 6 dogs, pedometers recorded a considerably smaller number than the actual count of steps taken. Interestingly, 5 of these 6 dogs weighed < 10 kg (22 lb) and were considered small-breed dogs (2 Jack Russell Terriers, 1 Cocker Spaniel, 1 Dachshund, and 1 Tibetan Spaniel). As a result of this finding, dogs were further grouped and assessed according to size as small (< 10 kg; n = 5), medium-sized (10 to 25 kg [22 to 55 lb]; 8), or large (> 25 kg; 7). Mean ± SEM percentage difference between actual and pedometer-counted steps was −6.2 ± 7.1% for dogs of all sizes, −21.0 ± 6.7% for small-sized dogs, −0.7 ± 4.8% for medium-sized dogs, and 6.1 ± 3.4% for large dogs. Only 2 of the 15 medium-sized and large dogs had a significant difference between the number of actual and pedometer-recorded steps, whereas differences between these values were significant for all 5 small dogs. When assessed according to group, the difference between the number of actual and pedometer-recorded steps was significant (P < 0.01) only for small dogs. Therefore, for purposes of the present study, only dogs that weighed > 12 kg (these were of Beagle stature or larger and all measured ≥ 35.6 cm at the withers) were included in the weight-loss part of the study.

Weight-loss program—Sixty-one dogs were evaluated for inclusion in this part of the study. Two were excluded because of low (ie, < 9 pmol/L) serum concentrations of free thyroxine; during the study, 21 dogs were removed because of poor compliance with the weight-loss program or unacceptable pedometer recordings, 2 were euthanized because of neoplasia, and 1 died unexpectedly (cause of death was not determined). Thirty-five dogs completed the weight-loss program. All were considered healthy throughout the entire study period. Only 2 dogs were administered medications (one received cephalexin for chronic Staphylococcus spp infection, and the other received NSAIDs intermittently for signs of orthopedic pain). The study population comprised the following dog breeds: Labrador Retriever (n = 8); mixed (7); Beagle (4); Golden Retriever, Bernese Mountain Dog, and Rottweiler (3 each); Samoyed (2); and Australian Shepherd Dog, Boxer, Bull Mastiff, Cocker Spaniel, and Siberian Husky (1 each). Median age was 6 years (range, 1.5 to 11 years). Nineteen (54%) patients were males, of which all but 1 were neutered; all 16 females were spayed. All dogs achieved ideal BCS (5 or 6) during the weight-loss program, and no dog had > 2.5% weight loss during any 2-week period.

Most of the examined variables were not significantly different between the active and inactive groups, including median age and mean values for time (weeks) to achieve ideal BCS, percentage of body weight lost, body weight in kilograms, and BCSs at baseline and at the end of the weight-loss program (Table 1). Similarly, the χ2 analysis of sex and reproductive status revealed no significant differences between groups. Mean number of steps per day and mean energy intake (kcal/kg0.75) were significantly different between the 2 groups.

Table 1—

Comparison of variables of 35 obese dogs (BCS at baseline, > 7 [scale, 1 to 9]) enrolled in a weight-loss program and stratified post hoc according to the mean number of steps taken per day into inactive (< 7,250 steps/d) and active (> 7,250 steps/d) groups.

 Group 
VariableInactiveActiveP value
Sex  0.87
 No. of males1010
 No. of females78
Reproductive status  0.89
 No. neutered1717
 No. sexually intact01
BCS   
 Baseline7.8 ± 0.78.1 ± 0.90.44
 End of weight-loss program5.2 ± 0.45.2 ± 0.60.88
Bodyweight(kg)   
 Baseline44.0 ± 19.137.3 ± 14.90.25
 End of weight-loss program33.6 ± 14.128.4 ± 10.80.22
Age (y)5.76.80.18
Weight loss (%)*23.6 ± 7.324.1 ± 7.50.86
Time to ideal BCS(wk)28 ± 10.126 ± 9.60.35
No. of pedometer-recorded steps/d*4,619 ± 1,2439,721 ± 3,105< 0.01
Daily energy intake (kcal/kg0.75)*†42.2 ± 9.753.6 ± 15.20.02

Median values are reported for age; sex and reproductive status are reported as number of dogs. All other values are reported as mean ± SD. Baseline values were collected at the end of a 2-week washout period during which dogs were transitioned from their typical diets to a therapeutic weight-loss diete and were allowed < 15% of their daily energy intake from commercial treats; no activity modification was suggested prior to the weight-loss program.

Calculated on the basis of mean values for each dog for the entire weight-loss period.

Energy value of food consumed was calculated per unit of metabolic body weight as kcal/kg0.75.

— = Not applicable.

Results of multiple linear regression analysis revealed that the daily number of steps recorded was significantly associated with mean energy intake (Figure 1). Results of this analysis suggested that an increase of 1,000 steps was correlated with an increase in energy intake of 1 kcal/kg0.75 (R = 0.36; P = 0.03), whereas no associations with energy intake were evident for body weight at the end of the weight-loss program, sex, or age. Associations with reproductive status could not be evaluated because of the homogeneity of the study population.

Figure 1—
Figure 1—

Scatterplot of daily energy intake (kcal/kg0.75) versus the number of pedometer-recorded steps per day (mean values for each dog throughout the entire weight-loss period) of 35 dogs enrolled in a weight-loss program. Dogs in the study weighed > 12 kg (26.4 lb). The solid line represents the Pearson correlation (R = 0.36; P = 0.03).

Citation: Journal of the American Veterinary Medical Association 240, 4; 10.2460/javma.240.4.413

Mean number of steps per day for all dogs during the washout period (6,940 ± 3,938) was compared with that recorded during the first (6,916 ± 3,617) and last (7,021 ± 3483) months of participation in the weight-loss program. These values were not significantly (P = 0.86) different. Linear regression analysis revealed no significant (P = 0.84) association between BCS and mean number of steps per day during the weight-loss program in this population of dogs.

Further assessment of the energy intake restriction needed to achieve approximately 2% weight loss/wk revealed that dogs in the active group needed to receive approximately 55% of the calculated MEROPD, whereas inactive group dogs needed to receive approximately 45% of the MEROPD to achieve weight-loss goals.

Discussion

Pedometers have been used to measure activity patterns in many species.14,18–20 Pedometer use as a measure of activity has been validated in dogs,14 and our evaluation of pedometer accuracy further validates their use in this capacity. Unfortunately, our results were similar to those of the previous study14 in that when dogs were grouped according to size, pedometer accuracy was flawed in small dogs and underrepresented the number of actual steps taken. The number of pedometer-recorded steps was not significantly different from actual step counts in medium-sized and large dogs during our evaluation study; therefore, for practical purposes, we excluded dogs < 12 kg from the weight-loss part of our study. Pedometers were attached to a bungee-cord collar in the present study, rather than a lightweight chain as described in the previous study,14 and this may have contributed to pedometer accuracy in medium-sized and large, but not small, dogs.

Results of studies21,22 examining human weight loss have revealed that pedometers can be used to assess the influence of walking on weight loss. Although somewhat inferior to accelerometer-generated data, which can measure intensity as well as quantity of activity, pedometers have practical utility because of the limited expense involved in use of such units.16,21 In a previous study,14 pedometers were used to examine walking activity and a negative correlation was found between the number of steps recorded and BCS between 5 and 7 on the 1 to 9 scale. Results of the present study, in which dogs of higher BCS (7 to 9) were examined, did not confirm this finding. The reasons for this are unclear but may be related to differences in the populations of dogs in the 2 studies in regard to multiple variables, including BCS and activity patterns. These diverse results could also have been influenced by owner demographics and geographic location. These differences warrant further investigation into the relationships between owners and dogs and the epidemiology of obesity. Importantly, pedometers appear to be a reliable and inexpensive way to successfully monitor activity in medium-sized to large dogs and can be used to gauge physical activity.

Factors such as inherent metabolic rate and dietary energy consumption play a much larger role than does exercise during weight loss; however, the results of human studies26,27 suggest that the role of physical activity and an active healthy lifestyle are important in maintaining a healthy weight. Increasing exercise during a weight-loss regimen can augment weight loss in humans; however, results of these studies28–30 suggest that moderate physical activity for approximately 60 to 90 min/d is necessary to achieve this effect. Although increasing physical activity is recommended as part of a successful canine weight-loss protocol, there has been little evidence in the veterinary literature that it can be increased enough to augment weight loss. This is a difficult problem to address without assigning dogs exercise regimens of sufficient intensity on a routine basis in a clinical setting, and the practicality of distinct exercise regimens is often affected by poor compliance, making a clinical field study very difficult to complete. Despite this, results of a previous study31 indicated that walking the equivalent of approximately 5 km (3.1 miles)/d would be needed to achieve a 7% to 15% increase in energy (kilocalorie) expenditure.

Enforcing a specific amount of walking activity in our study would have been difficult and would have required an unusually large sample population to compensate for poor compliance; therefore, we encouraged all owners to enhance their dogs' walking activity by taking their dogs on a 2-mile walk each day. Our goal was to implement a weight-loss program that was similar for all dogs enrolled but to dichotomize the population into active and inactive groups on the basis of the mean number of steps recorded via pedometers daily during the study. Unfortunately, our attempt to enhance physical activity in this population of dogs was unsuccessful. The number of steps per day for dogs remained fairly constant among the washout period (before clients were encouraged to increase exercise by walking), the first month of participation in the weight-loss program, and the last month of participation, although clients were regularly encouraged to walk dogs 2 miles daily (in addition to their regular activities) during the latter 2 periods. This was not surprising, considering that results of a previous study9 examining owner education and awareness about canine obesity during a similar weight-loss program showed no significant difference in weight loss between dogs whose owners attended regular educational meetings on this subject and those whose owners did not attend such meetings. It must also be recognized that some dogs enrolled in the present study were already considerably active and owners may not have been able to increase their daily activity beyond what was already being done; however, dogs in the inactive group also had no appreciable increase in physical activity. Better compliance has been reported in human walking activity studies12,13; therefore, further investigation of the methods by which clients can be encouraged to enforce walking activities in dogs is warranted.

Voluntary activity is often diminished according to the amount of energy intake restriction in humans, and daily activities (not planned exercise) can account for a difference of approximately 700 kcal/d in energy expenditure.32,33 In the study reported here, no differences were detected in the amount of activity (assessed via pedometer recordings of steps taken) of dogs during participation in the weight-reduction program. The similar values for number of steps taken prior to and during the weight-loss program suggest that during energy intake restriction, activity does not decrease in dogs. Exactly why this happens is hard to define; however, it can be assumed that in general, most dogs' daily activity patterns are relatively constant and are greatly influenced by external factors that have yet to be determined.

The most important finding of the present study was that mean daily energy intake (calculated per unit of metabolic body weight as kcal/kg0.75) of dogs in the active group was significantly higher than that of dogs in the inactive group while achieving weight-loss goals during nearly identical weight-loss programs. The mean daily energy intake was approximately 27% higher for active dogs than for inactive dogs, suggesting that physical activity may influence allowable dietary energy intake during a successful weight-loss program. Other variables have been associated with weight loss including body size, sex, and age.9,12 These variables were not significantly different between active and inactive group dogs in the present study, and results of multivariable regression analysis suggested that age, sex, and body weight did not affect dietary energy intake. The only variable that was significantly associated with energy intake was the number of steps taken. Results of multivariable analysis suggest that for every pedometer-recorded step taken, there is an expenditure of approximately 0.001 kcal/kg0.75. Therefore, on a daily basis, for every 1,000 steps taken, energy intake can be increased by approximately 1 kcal/kg0.75.

Our study was limited to dogs that weighed > 12 kg (all were of Beagle stature or larger), and enrollment of smaller dogs was precluded because of detectable inaccuracies in pedometer-generated data. Small-breed dogs have a slightly higher MER during participation in a weight-loss program and may lose weight more quickly than do large-breed dogs.10 The restricted inclusion criteria regarding the size of dogs enrolled in the present study might have decreased our ability to find body weight at the end of the study as a variable that affected the allowable energy intake.

According to a recent National Research Council publication,25 the daily MEROPD is approximately 95 kcal × (body weight in kg0.75) for dogs of ideal body condition. In the study reported here, mean daily energy intake during weight loss was approximately 45% of the calculated MEROPD in dogs of the inactive group and approximately 55% of this value in active group dogs. These values were slightly lower than the allowable energy intake typically suggested by clinicians (60% to 70% of MER or MEROPD).8 This difference may be attributable to the exclusion of dogs OPD< 12 kg or to our study population being uniquely obesity prone because many owners of dogs in the study complained about previous weight-loss failures for their dogs. This suggests that the National Research Council's recommendation is an adequate starting point for most obesity-prone dogs, but energy intake of some dogs in our study population was closer to the RER (70 kcal × [body weight kg0.75]). These findings underscore the variability in dietary energy restriction needed for successful weight loss, and restrictions for some dogs (in particular, large dogs) may need to be based on RER for ideal body weight rather than on MEROPD calculations.

Although results of the present study indicated that activity (assessed as the number of steps taken daily) was correlated with energy intake during weight loss, questions regarding physical activity remain. Our results did not reveal whether physical activity could enhance weight loss during a weight-loss program. This type of study would be a tremendous undertaking requiring owner commitment to the multiple-week exercise regimen or a controlled exercise regimen monitored by a clinical staff. Even in a controlled clinical study, influencing owner-controlled activity could be difficult. A study of this nature could be performed in an academic or industry setting with obese dogs in a laboratory environment, but the information gained may still have limited clinical utility. Furthermore, results of the present study did not provide any conclusive evidence as to whether the increased energy expenditure of dogs that had greater physical activity was enhanced by this exercise or whether enhanced physical activity enhanced lean body mass during the weight-loss program, thereby increasing metabolically active tissue. Our data suggest these investigations in a controlled laboratory or clinical environment examining exercise and body composition during a weight-loss program are likely to provide clinically useful information.

ABBREVIATIONS

BCS

Body condition score

MER

Maintenance energy requirement

MEROPD

Maintenance energy requirement for obese-prone dogs

RER

Resting energy requirement

a.

Tippany JR, Funk J, Buffington CAT. Effects of environmental enrichments on weight loss in cats (abstr). J Anim Phys Anim Nutr (Berl) 2005;89:427.

b.

Chauvet A, Laclair J, Holden SL, et al. Exercise and active client motivation improve rate of weight loss in obese dogs (abstr). J Vet Intern Med 2009;24:714.

c.

Accusplit AE120 with a Yamax digiwalker engine, Accusplit Inc, Livermore, Calif.

d.

USDA Nutrient Database [database online]. Washington, DC: USDA Agricultural Research Service, 2006. Available at: www.nal.usda.gov/fnic/foodcomp/search/. Accessed May 20, 2006.

e.

Purina Veterinary Diets OM Overweight Management canned and dry formulas, Nestlé Purina, St Louis, Mo.

f.

Nestlé Purina Weight Management Software, Nestlé Purina, St Louis, Mo.

g.

Kaleidagraph software, version 4.0, Synergy Software, Reading, Pa.

h.

SAS software, version 9.0, SAS Institute Inc, Cary, NC.

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