In the dog, obesity and overweight are arbitrarily defined as a body weight 20% and 10% greater than ideal, respectively (Burkholder and Toll 2000
). Previous studies examining weight loss in osteoarthritic dogs have included subjects that ranged from 11–29% overweight (Burkholder and Hulse 2000
; Impellizeri et al. 2000
). The current study included only obese dogs, estimated to be 20% greater than ideal body weight. It was expected that weight loss would have its most significant effect on lameness in obese dogs with OA. Furthermore, in humans, it is the obese (body mass index greater than 30) population with OA that tends to be the focus of research examining the beneficial effect of weight loss (Christensen et al. 2007
; Hooper et al. 2007
; Christensen et al. 2005
). A limitation of the study reported here is the small number of obese dogs recruited - only fourteen completed sufficient visits for data analysis. Stimulating and maintaining client interest in canine weight loss programs can be challenging (Burkholder and Toll 2000
) and this hindered recruitment of cases. Inclusion of multiple centres in any future studies of a similar nature should be considered to maximize sample size.
In two of the previous weight loss studies the dogs enrolled were limited to those with hip dysplasia and secondary OA (Burkholder and Hulse 2000
; Impellizeri et al. 2000
). By contrast, the most recent study (Mlacnik et al. 2006
) included dogs with OA of the hip, elbow, shoulder and stifle. The dogs of the study reported here had between one and four affected hip and / or elbow joints. In all cases but one (with an obvious UAP) the (suspected) underlying developmental abnormality causing elbow OA could not be definitively diagnosed. The fact that a positive response to weight loss was seen in this somewhat heterogeneous experimental population suggests that our results are relevant to the wider population of dogs with hip and / or elbow OA (Thrusfield 1995
It has been stated that to maintain owner’s interest and compliance to complete a canine weight loss program within a reasonable time frame a minimum of 0.5% body weight should be lost per week (Burkholder and Toll 2000
). Conversely, a rate of weight loss greater than 2% per week is considered unhealthy, since this may result in loss of lean tissue (Burkholder and Toll 2000
). In this study a target of 0.5–1% per week was set and achieved, with 0.55% body weight lost on average. At the end of the 16-week weight loss period the average body weight reduction was 8.85%. This is comparable to 9.3% body weight loss reported by Mlacnik and co-workers (2006
) for dogs with OA at the conclusion of a six month caloric restriction program combined with moderate physiotherapy. In that study, a separate group of dogs underwent intense physiotherapy and lost 13.6% of their body weight over six months which was attributed to increased owner compliance and physical activity. In the studies by Impellizeri et al. (2000
) and Burkholder and Hulse (2000
) body weight reductions of 11–18% and 3.9–12 kg were achieved. In the former study the weight loss period was 10–19 weeks; in the latter the time period is not given and all dogs reached their ideal body weight. Pelvic circumference is an objective measure that changes significantly with body weight and is proportional to the amount of body fat in both cats and dogs (Burkholder and Toll 2000
). In the study reported here a statistically significant decrease in pelvic circumference was seen with decreasing body weight.
A significant decrease in NRS lameness score at trot and walk were seen beginning at visits 5 and 7, following a mean body weight decrease of 6.10 and 8.85%, respectively. It has been shown, using an ovine model, that the NRS method of lameness assessment is relatively insensitive (Welsh et al. 1993
), and therefore to increase sensitivity, we combined the NRS lameness scores and defined “improvement” as a decrease in lameness score by one grade for either walk or trot. By this method 56% of dogs had improved by visit 4 (4.81% body weight reduction), and 82% had improved by the end of the study. A statistically significant decrease in VAS lameness score was seen starting at visit 2, two weeks after starting the weight loss program, with on average 1.62% body weight lost. Examination of the NRS and VAS results together, suggests that a statistically significant improvement in lameness was seen beginning at visit 5 (6.10 % body weight reduction). This is comparable to the results of Impellizeri et al. (2000
) where significant improvement in NRS and VAS lameness scores were seen after a mean body weight decrease of 2.4 kg (6.2%) in overweight and obese dogs with hip OA. In the study that compared moderate and intense physiotherapy in combination with weight loss, a significant decrease in NRS lameness score was seen in both groups of dogs following body weight reduction of approximately 5% (Mlacnik et al. 2006
In the dogs with bilateral elbow OA and forelimb lameness, significant asymmetry between contralateral limbs was demonstrated for PFz, PFy and IFz at the start of the study. In the worst affected limb there was a significant increase in PFz and IFz with weight loss, and an increase in PFy that tended towards significance. By visit 7 (8.85% body weight reduction) the mean difference in PFz, PFy and IFz between forelimbs was in line with previously reported forelimb ground reaction force values for normal dogs (Rumph et al. 1994
). This suggests that after body weight reduction of 8.85% the ground reaction forces measured in the worst affected limb had increased such that the degree of symmetry between forelimbs had returned within normal limits. The significant decrease in hindlimb PFy in dogs with forelimb lameness is interesting. It is recognized that the forelimb is primarily responsible for braking, and the hindlimb for propulsion (Budsberg et al. 1987
). It is possible that in dogs with forelimb OA and lameness, a relatively greater proportion of braking is performed by the hindlimbs. The decrease in hindlimb and increase in forelimb PFy seen with weight loss may reflect a shift in the distribution of braking force back to the forelimbs. Because of equipment limitations, it was not possible to measure subject acceleration during kinetic gait analysis in this study. According to previous work, this could only have influenced the results for forelimb PFy as acceleration has no effect on forelimb PFz or IFz, or on hindlimb PFy (Budsberg et al. 1999
In this study, the improvement in NRS and VAS lameness scores was not reflected in the force-plate results in the dogs with hindlimb lameness—there was no change in PFz, IFz or PFy with weight loss. There is a degree of similarity between these results and some of those reported by Mlacnik et al. (2006
). In that study, subjective improvement in lameness was first demonstrated among the dogs enrolled in the protocol of weight loss combined with moderate physiotherapy after 60 days and this improvement was maintained throughout the remainder of the study period at days 120 and 180. However, subjective improvement was only confirmed by the force-plate results at day 120, and then only by the symmetry index for PFz, not for IFz. By contrast, the dogs that were enrolled in the protocol of weight loss and underwent intensive physiotherapy showed a consistent improvement in PFz and IFz symmetry indices starting from day 60, though it is unclear whether the intensity of physiotherapy or faster rate of weight loss was the important factor underlying this difference. The majority of the dogs in our study with hindlimb lameness had bilateral hip OA, and it was often difficult to determine subjectively which leg was worst affected. It is therefore unsurprising that the ground reaction forces were not significantly different between contralateral limbs. In addition to a lack of asymmetry, there was no change in absolute ground reaction force values produced by either hindlimb following weight loss in our study. This differs from the results of Burkholder and Hulse (2000
) who report average increases in PFz of up to 0.98 N/kg in dogs with hip OA following weight loss to ideal body weight. Fourier analysis of force-time curves obtained from dogs with hindlimb lameness in this study could prove interesting. This method can reveal subtle differences between curves that are not necessarily apparent by conventional analyses (Katic et al. 2009
). The more demonstrable benefit of weight loss in obese dogs with forelimb versus hindlimb lameness in the current study may be related to the fact that around 60% of canine body weight is borne by the forelimbs (Budsberg et al. 1987
). Because of this asymmetrical weight distribution, for a given decrease in bodyweight a more significant decrease in pain may be experienced by dogs with forelimb OA.
This is the first study to assess both subjectively and objectively, the effect of weight loss alone on lameness in obese dogs with hip and / or elbow OA. The results indicate that body weight reduction will cause a decrease in clinical signs of lameness, and a significant effect was seen from a weight loss of 6.10% onwards. Kinetic gait analysis supported the results for dogs with elbow OA and forelimb lameness from a body weight reduction of 8.85% onwards. These results confirm that weight loss should be presented as an important treatment modality to owners of obese dogs with hip and / or elbow OA and that noticeable improvement may be seen after modest weight loss in the region of 6.10–8.85% body weight.