Obesity and orthopedic disease: a relationship to remember

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Max walked slowly into the exam room and lay down immediately on the floor. Rising to the exam room scale was a struggle for him. His limbs shook and lameness in both hind limbs was obvious. The dog's body weight had reached 109 lb (49.5 kg), and his owners were desperate for their 6-year-old Labrador retriever to return to the active and pain-free dog of his youth.

His tail continued to wag and he often wanted to be with them, but Max experienced exercise intolerance and could no longer go on family hikes like he used to. His left stifle had been stabilized 2 years previously following a cranial cruciate ligament tear, and a partial tear was now suspected in his right stifle. The orthopedic surgeon also appreciated crepitus in Max's elbows. When the surgeon stressed weight management as an essential part Max's orthopedic care, the dog was referred to my nutrition service.

The impact of overweight and obesity

Overweight and obesity can significantly impact the quality and length of life as well as the development of chronic diseases in both dogs and cats. The health consequences of excess body weight are seen in dogs whose body weight is just 10% to 20% over their ideal.

In a well-known lifetime study, Labrador retrievers fed 25% less (feed-restricted) than age-matched pairs (control-fed) had a median life span of 13 years, while dogs fed 25% more had a median life span of 11.2 years.1 Importantly, dogs fed more were overweight, not obese, with a mean body condition score (BCS) of 6.7 ± 0.19 compared with 4.6 ± 0.19 in the feed-restricted dogs. A more recent retrospective assessment of BCS and life span in 50,787 dogs representing 12 popular breeds found an increase in the relative risk of dying for overweight dogs compared with dogs that had an ideal body condition across all breeds.2

In particular, the development of orthopedic disease in dogs is associated with excess body weight. Overweight dogs in the lifetime study developed radiographic evidence of osteoarthritis (OA) earlier than their feed-restricted counterparts.3 The median age at which OA was radiographically evident in the control-fed group was 6 years compared with 12 years in the feed-restricted group.4

The mechanism by which excess body fat contributes to the development of OA may be multifactorial through the production of inflammatory mediators, changes in the gut microbiota and biomechanical forces on the joints. In addition to its relationship with OA, obesity in dogs quadruples the risk of cranial cruciate ligament rupture.5 The results of one study suggest that this relationship may be due to increased loading of the limbs and tension on the ligaments within the stifles. Compared with cats at optimal body weight, overweight cats were nearly three times more likely to present to a veterinarian with lameness not associated with a bite wound.6 Further, obese cats were nearly five times more likely to develop lameness requiring in veterinary care.6

Max's weight loss journey

Calculating ideal body weight using body fat percentage7

Ideal Body Weight = Current Body Weight X [100 – Current Body Fat % / 100 – Lean Body Fat %*]

Max: 74.9 lb = 109 lb X [100 – 45% / 100 – 20%]

*Assuming ideal body fat percentage = 20%

Max's nutritional assessment revealed a BCS of 9/9 with mild wasting of his thigh muscles. His body fat was estimated to be 45%, and his ideal body weight was calculated to be approximately 75 lb (34.1 kg) using body fat percentage. (See Calculating ideal body weight using body fat percentage at right.)7 When using a 9-point BCS scale, the relationship between BCS and body fat percentage is significant. Every 1-point increase in BCS is equivalent to a 5% increase in body fat percentage. A dog with a BCS of 5/9 has approximately 20% to 24% body fat, whereas a dog with a BCS of 9/9 has 40% body fat or more. Max's diet history revealed that he was consuming about 1,400 kcal/day. About 1,125 kcal/day were from a calorie-dense, all-life-stage, kibble-based dog food (450 kcal/cup fed at 2.5 cups per day) with the rest of his calories coming from treats and table foods (275 kcal/day).   

I recommended a weight management program that included the initial visit plus six monthly follow-up appointments. Max's caloric requirements for weight loss were calculated using his ideal body weight. (See Calculating caloric requirements for weight loss below.) His maintenance energy requirement for weight loss was about 40% less than his current intake. Max was started on a therapeutic weight loss diet, which allowed him to consume more food with fewer calories than his previous diet. Calories from treats and table foods were limited to no more than 10% of his total caloric intake (90 kcal/day). 

Calculating caloric requirements for weight loss

Resting Energy Requirement (RER) = 70 X (Body Weight0.75 [kg])

Max: 988 kcal = 70 X (34.1 kg0.75)

Maintenance Energy Requirement (MER) = RER x Life Stage Factor*

Max: 988 kcal = 988 kcal X 1

*A life stage factor of 1 is recommended in dogs; in cats, 0.8 is recommended.

In addition to his weight management program, Max was referred for physical rehabilitation. Exercise can build and preserve muscle mass and increase energy expenditure. In one recent study, dogs undergoing a physical training program (three times per week) along with a weight loss diet were able to preserve lean body mass and lose a similar amount of weight compared with sedentary dogs that lost lean body mass through diet only.8   

At Max's first monthly recheck, his body weight was 103.5 lb (47 kg), for a loss of 5.5 lb (5% body weight). His rate of weight loss over 4 weeks was 1.3% per week-well within the ideal range of 1% to 2% per week. At his second recheck (8 weeks), his body weight was 99 lb (45 kg), for a total weight loss of 10 lb (4.5 kg) or 9.2% of his body weight. His owners noted that Max's mobility was starting to improve and he even jumped on the couch-something the dog hadn't been able to do for more than a year.

Mobility is often a factor for owners when assessing their pet's quality of life. Modest weight loss of just 6.1% body weight significantly decreases lameness in dogs.9 Max achieved his ideal body weight after 9 months of hard work and dedication from his owners and veterinary team. During this time, his caloric intake was adjusted to maintain his rate of weight loss.

Results of one study showed that following a weight loss program, 48% of dogs regained more than 5% of their body weight.10 Dogs switched to a standard maintenance diet were more likely to regain body weight compared with dogs fed a purpose-formulated weight management diet. Max's owners committed to intermittent weigh-ins and keeping him on a weight management diet to ensure that he maintained his ideal body weight. Max was able to rejoin his regular family hikes. 

Conclusion

As seen with Max, the consequences of excess body weight go beyond the health of the pet, potentially also impacting the human-animal bond. Additionally, the cost of overweight and obesity is relevant. According to the 2017 State of Pet Health Report by Banfield Pet Hospital, owners of overweight dogs spent 17% more on healthcare and 25% more on medications than owners of dogs at ideal body weight.11 Owners of overweight and obese cats also spent more money-36% more on diagnostic procedures compared with owners of cats at ideal body weight.11 The cost of cruciate surgery was a financial burden for Max's owners, and they were grateful to avoid a second procedure.

As veterinary professionals, we should make every effort to prevent this epidemic of overweight and obesity early in our patients so we can improve their health and well-being and strengthen the human-animal bond.  

Dr. Martha Cline practices at Red Bank Veterinary Hospitals in New Jersey.

References

1. Kealy RD, Lawler DF, Ballam JM, et al. Effects of diet restriction on life span and age-related changes in dogs. J Am Vet Med Assoc 2002;220:1315-1320.

2. Salt C, Morris PJ, Wilson D, et al. Association between life span and body condition in neutered client-owned dogs. J Vet Intern Med 2019;33:89-99.

3. Kealy RD, Lawler DF, Ballam JM, et al. Five-year longitudinal study on limited food consumption and development of osteoarthritis in coxofemoral joints of dogs. J Am Vet Med Assoc 1997;210:222-225.

4. Smith GK, Paster ER, Powers MY, et al. Lifelong diet restriction and radiographic evidence of osteoarthritis of the hip joint in dogs. J Am Vet Med Assoc 2006;229:690-693.

5. Adams P, Bolus R, Middleton S, et al. Influence of signalment on developing cranial cruciate rupture in dogs in the UK. J Small Anim Pract 2011;52:347-352.

6. Scarlett JM, Donoghue S. Associations between body condition and disease in cats. J Am Vet Med Assoc 1998;212:1725-1731.

7. Brooks D, Churchill J, Fein K, et al. 2014 AAHA weight management guidelines for dogs and cats. J Am Anim Hosp Assoc 2014;50:1-11.

8. Vitger AD, Stallknecht BM, Nielsen DH, et al. Integration of a physical training program in a weight loss plan for overweight pet dogs. J Am Vet Med Assoc 2016;248:174-182.

9. Marshall WG, Hazewinkel HAW, Mullen D, et al. The effect of weight loss on lameness in obese dogs with osteoarthritis. Vet Res Commun 2010;34:241-253.

10. German AJ, Holden SL, Morris PJ, et al. Long-term follow-up after weight management in obese dogs: The role of diet in preventing regain. Vet J 2012;192:65-70.

11. 2017 State of Pet Health Report. 2017. Banfield Pet Hospital website: https://www.banfield.com/Banfield/media/PDF/Downloads/soph/2017-SOPH-Infographic.pdf