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BMI or Condition Score?

A New Year, a new diet? At the start of every year filled with resolve or just tired of over indulgence following the festive season many of us declare ‘This is the year I’m losing the spare tyre!’ Unfortunately so many of us succumb to temptation and slip back into bad habits and by February that tyre that started to deflate is soon back at full pressure.

We fail with our diets because we control what we put into our mouths. Pets don’t have opposable thumbs, they cannot use scissors to open foil bags or tin openers to access food – they need us to do that. So pets can only fail on diets if we let them or they scavenge.

Dogs and cats pursuit of pleasure is unbridled and over-indulgence leads to dangerous excess or even deficiency if the diet is not balanced. Pets have no concept of future so have no concept of consequences – they don’t know when to stop eating or the dangers of obesity. Some dogs would, given the opportunity, literally eat themselves to death! Owners have a responsibility to moderate their pet’s food intake and maintain them at an optimal weight. People who have ignored warnings to reduce the weight of a morbidly obese pet have been prosecuted under animal welfare laws.

How do we tell if our pets are over weight? It’s easy for humans we have Body Mass Index (BMI) which is a ratio of a person’s mass in kilograms divided by their height in meters squared. A BMI of 18.5 to 25kg/m² is optimal for humans, less than 18.5kg/m² is considered to be underweight and over 25kg/m² is overweight but people with BMI’s of over 30kg/m² are considered to be obese!

Pets and dogs in particular, have diverse body shapes and sizes so a BMI simply would not work. An 80kg Great Dane could have an ideal weight but a 15kg Westie could be obese! This is overcome by having optimal weights for individual breeds but how does that work for cross breeds? Many vets will make an assessment of an animal’s condition by just feeling its body, you want to be able to feel ribs but not see them. Some pets I saw were so obese that the only way you’d see their ribs was with x-rays.

Body condition scores have been used in veterinary medicine for years to assess the condition of livestock. This practice has been adopted by small animal vets and applied to dogs and cats. The pet food manufacturer Purina have created body condition chart for dogs with pictures to help you determine what your dog’s body condition is. The scores are from 1 to 9:  4 and 5 are ideal, 1 to 3 are too thin, and 6 to 9 are too heavy. Purina have also created a body condition score chart for cats, this again runs from 1 to 9 but for cats only a score of 5 is considered ideal. Other body condition score protocols for both dogs and cats run from 1 to 5, 3 being ideal (The Ohio State University, College of Veterinary Medicine). The pet food manufacturer Royal Canin have developed a body condition assessment protocol for dogs and cats in conjunction with the Faculty of Veterinary Science at the University of Liverpool & Leahurst called S.H.A.P.E.™ (Size Health And Physical Evaluation) using a flow diagram with conditions scores from A to G. D being ideal, A extremely thin and severely overweight G.

The problem with body condition scoring systems is that there is no standard system for livestock, dogs, or cats. The creators of each system undoubtedly think that theirs is better than anyone else’s. Ultimately it doesn’t matter what system you or your vet use they just have to be consistent and stick to that system. If one vet used a system that ran from 1 to 5 and scored your cat’s body condition as ideal and gave them a score of 3 then another vet using a system that ran from 1 to 9 might think that 3 indicated that your cat was too thin. Care must be taken to not only quote the score but also the protocol used.

Unfortunately too many dogs and cats in Britain are obese, that’s 5 on the Ohio State system, 9 on the Purina system or G on the Royal Canin system! Vets estimate that as much as 36% of dogs are obese and 29% of cats. Vets also suggest that like their human counterparts obese pets suffer with under confidence as well as associated health risks!

For years I have felt that pet food manufacturers feeding guides always tended to encourage owners to feed their pets too much. Well now that situation appears to be changing and many manufacturers are moderating their portion sizes. Owners have a responsibility to not only follow feeding guides but also to treat their pet as an individual. Just like some poor unfortunate people, some pets are far more prone to weight gain than others. Even if you are following the feeding guide religiously, if your pet is becoming overweight owners have a moral duty to address this by reducing portion sizes. If owners are in any doubt they should always consult their own vet because some diseases can cause weight gain such as underactive thyroid disease in dogs.

If owners give training treats to dogs an equal quantity of food should be subtracted from the daily meals to balance this out. The same is true of scraps; if scraps are given occasionally then the daily food ration requires readjustment too. Owners often underestimate the calorific value of scraps and treats -- for a dog a slice of toast is equivalent to a cheese burger and for a cat a saucer of milk is equivalent to four cheese burgers!


David Chamberlain BVetMed., MRCVS.
Veterinary Consultant to PetSafe®