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OBESITY in companion animals is a well-recognised welfare concern (Ellis 1990, German 2006). Rabbit obesity has been anecdotally associated with several health disorders of rabbits such as myiasis, pododermatitis, pregnancy toxaemia, gastrointestinal stasis and ileus (Harcourt-Brown 2002). There is little peer-reviewed literature describing pet rabbit obesity or identifying potential risk factors for the condition. This study aimed to use a first-opinion clinical database to describe the prevalence of obesity in rabbits and identify demographic risk factors associated with obesity.
The data were collected from a national database consisting of 41 primary companion animal practices from a large veterinary group in Great Britain. Data consisted of body condition score (BCS), sex/neutered status, age, location and country (England, Scotland or Wales) of practice, and date of birth of rabbits presenting at 11 equally spaced time points throughout 2008 and 2010.
The rabbits' BCS was rated at each veterinary consultation using a five point scale (1 = Very underweight, 2 = Underweight, 3 = Ideal, 4 = Overweight, 5 = Obese) by the attending veterinarian. Overweight/obese animals were defined as animals with a BCS of 4 or 5 while non-overweight animals were classed as all animals with a BCS of 3 or under. As there are no published guidelines giving age ranges for different life stages, the authors defined age categories, derived from date of birth and consultation dates, as less than eight months – juveniles, eight months to 2.5 years – adults, 2.5 to five years – older adults, and five years and over – geriatric, based on clinical experience.
Associations between age, breed, sex, neutered status and being overweight/obese were evaluated using either Fisher's exact or chi-squared tests as appropriate. Odds ratios (OR) and 95 per cent confidence intervals (CI) were also calculated. Statistical significance was defined as P<0.05. Differences in age between neutered and entire categories were assessed using the Mann-Whitney U test. All analyses were carried out in R version 2.10 (R Development Core Team 2009).
As exploring the data through multivariable significance testing was not appropriate due to data sparsity, correspondence analysis was used to examine the relationship between variable categories as described by Sourial and others (2010). This analysis used the FactoMineR package (Husson and others 2010).
Forty-one practices submitted records on 157 rabbit BCSs. In terms of BCS, nearly three-quarters of the rabbits were ideal (BCS 3) (76.4 per cent, n=120). 7.6 per cent (n=12) were overweight (BCS 4) and none was obese (BCS 5). Five rabbits were classed as very underweight (BCS 1, 3.2%) and 20 rabbits were underweight (BCS 2, 12.7%).
One hundred and fifty-two (96.8 per cent) rabbits had records for both age and BCS. Twenty-seven per cent (n=41) were eight months or younger, 41 per cent (n=62) were between eight months and 2.5 years, 21 per cent (n=32) were between 2.5 years and five years and 11.1 per cent (n=17) were five years or older. The median age of the rabbits was 1.5 years (range = 0 to 10.2). Entire males made up 52.4 per cent (n=79) of rabbits, 5.0 per cent (n=8) were male neutered, 37 per cent (n=56) female entire and 5.3 per cent (n=8) female neutered. Overall, 10.6 per cent (n=16) of rabbits were neutered and there was no significant difference in the prevalence of neutering between males and females (males = 9.2 per cent, females =12.5 per cent, P = 0.53). There was no significant difference in the age of neutered and entire rabbits (Entire median 0.5 years [interquartile range = 3], Neutered median 1 years [interquartile range = 2], P = 0.26).
Potential risk factors stratified by overweight status are summarised in Table 1.
The percentage overweight differed between age categories although this difference was not statistically significant (<eight months 2.4 per cent [n=1], eight months to 2.5 years 6.8 per cent [n=4], 2.5 years to five years 15.6 per cent [n=5], and five years and above 5.9 per cent [n=1], P=0.198).
Six per cent (n=5) of male rabbits were overweight whereas 11.1 to (n=7) of female rabbits were overweight. There was no statistically significant association between sex and being overweight (OR=0.5 [0.12 to 1.95), P=0.249] but this lack of significance may be an artefact of the low power of the study. However, neutered rabbits were 5.4 times more likely to be overweight than entire rabbits (OR=5.44 [1.05 to 24.3), P=0.006]. It was not possible to explore interactions between neutering, sex and being overweight because of the small numbers of subjects involved.
There was variation in the proportion of rabbits that were overweight between countries, although the differences were not statistically significant, again due to low power in this study (England 5.7 per cent Wales 7.7 per cent Scotland 20 per cent, P=0.145)
The multiple correspondence analysis was run on the 141 records with no missing values using all risk factors. The correspondence plot is shown in Fig 1. Rabbits that were female, neutered or in Scotland were more likely to be overweight than rabbits in the other categories.
Relative to the most recent reported prevalences of cat and dog obesity in Great Britain (feline = 39 per cent [Courcier and others 2010a]; canine = 59.3 per cent [Courcier and others 2010b]), the prevalence of overweight/obesity in rabbits was low. The descriptive statistics and correspondence analysis did suggest that rabbits that were female and/or had been neutered were more likely to be overweight. Interestingly, these are similar risk factors as those identified in cats and dogs (see review by German ). Data were not available on husbandry factors,which is disappointing as, if rabbits are similar to other species, these are likely to be influential in the development of obesity. This warrants further investigation in other studies given the disease/welfare burden obesity is likely to present to the pet rabbit population. Although very unlikely. it is also possible that the same rabbit could have been included twice if it presented at another time point, although the time points were months apart.
Body condition scoring in rabbits is not well described and has not been validated in small animal practice. Further studies are needed to describe and validate a rabbit body condition scoring system in the first-opinion setting, as previous published studies have been limited to commercial production (Cardinali and others 2008) or the scoring size has been aimed at owners and not fully validated, that is, PFMA Size-O-Meter (www.pfma.org.uk/pet-size-o-meter). Consulting veterinarians may be less accustomed to body condition scoring rabbits than other species because of the lower proportion of consultations that involve rabbits. Nevertheless, dichotomising these data into overweight and not overweight categories should have greatly reduced the potential for misclassification bias in the study.
This preliminary study demonstrates that the prevalence of being overweight in rabbits does not appear to be as great as for other companion animals. Interestingly, from the limited data available here, it appears as though the risk factors associated with overweight are likely to be similar as for other species, providing evidence to support a common aetiology. A larger study, among vets trained in body condition scoring specifically for rabbits, allowing investigation of risk factors including husbandry is justifiable, as this information is vital for successful obesity management and prevention.
The authors thank the PDSA for providing the data used in this study.
Provenance not commissioned; externally peer reviewed
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