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Wednesday, March 25, 2015

What Defines Dog Size?

Here's a question from a reader.....
Why does the canine world categorise dog breed size using its weight?
Why don't they use height instead?

Pet food company sell food meant for large, medium, small, toy breed by categorizing them through weight. What about the dogs on the cusp? For example, a female Belgian Shepherd could be 25kg, the male Belgian Shepherd would be well over 30kg. Does that mean a certain breed needs different sized pet food for differrent gender?

I understand pet food are formulated taking into account of kcal, minerals ratio for a certain size, however, a tall dog can often be thin, think greyhounds etc. Does that turn them into a medium breed?

What do you think of the categorisation? How did it came to be in the first place? Who placed the call to set the figures as such initally? I think this should be very interesting.

I'll start with the last questions.  I honestly don't know how categorizing dogs into "small", "medium" and "large" came to be, and I don't think it can be traced to a single person or moment in time.  This has kind of developed and become accepted without there being hard and fast rules.  Some of the breed clubs do have rules as to what weight a dog of a given breed should be, but that doesn't translate across all breeds.
In general we consider dogs to be "toy" if they are under 10lbs, small if they are under around 20-25lbs, medium from around 30 to 50lbs, and large if they are over 50lbs.  However these are not hard, set rules, and there can be variation around the borders of the categories.  It also depends on what that dog's normal weight should be.  If a dog who should weigh 8lbs actually weighs 13, we'd still consider it a toy breed because of the normal weight range.
Height is irrelevant in determining general size for food, as the calories and nutrient requirements are based off average basal metabolic rate, which is closely tied to weight. Two 60 pound dogs (assuming both are of the same body condition, i.e. neither is over- or underweight) would burn a similar amount of calories even if one was short and stocky and the other was tall and lean.  The height of a dog is determined by bones and the genetics of their development rather than the soft tissue structures.  A basset hound is short because of their leg structure, but they are rather stout dogs.  If their genetics caused them to have longer legs, they would still be of the same body size.

We also don't "split hairs" (no pun intended) when it comes to gender.  In the reader's example of a 25kg female and 30kg male, those 5kg really don't make a big difference.  The average of the breed determines whether it is small, medium, and large, not the individuals within the breed.  Also, the actual amount fed is determined by the individual dog's weight.  Labrador retrievers are considered a large breed, but I've seen normal weight vary from 60lbs to 90+lbs.  We obviously wouldn't feed individuals on either end of the range the same amount of food.  The smaller lab would need far fewer calories than the larger one.

Really, we don't need to over-think this.  Sometimes the only difference in the foods is the size of the kibble and not the nutrient content.  If you have questions about which food to feed your own dog, ask your vet.