Chocolate-coloured Labrador retrievers have, on average, 10% shorter lives than black or yellow Labradors, according to a study we co-published today in Canine Genetics and Epidemiology. Ear infections and skin diseases are also more common in chocolate Labradors than non-chocolate Labradors.
Research in humans has suggested a link between inflammation and shorter life expectancy and lower quality of life. It’s possible that, by a similar process, repetitive inflammatory skin and ear infections in chocolate dogs create an immunological burden that effectively shortens their lives.
Breeding for colour, not health
Colour might not seem linked to health at first glace, but some connections between coat colour and disease in dogs are well established. The Piebald or “S” gene variants can increase the amount of white in a dog’s coat and lighten its eyes to blue, but also cause high rates of deafness in one or both ears.
In another example, the Merle or “M” gene variant gives dogs a pale speckled coat and often blue eyes, but has been also linked with high rates of blindness and deafness. Rarer examples include cyclic neutropaenia (“Grey Collie Syndrome”) and colour dilution alopecia.
Even when the coat colour genes themselves are not themselves bad for dogs’ health, problems can still arise when an unusual colour becomes popular. The genes for some colours may be quite rare in the population or else hidden inside a parent of a different colour, meaning breeders may be tempted to overuse dogs they know for sure either show or hide the rare gene.
This is the case for our chocolate Labradors: chocolate is a recessive trait, which means both parents must carry it. Breeding chocolate puppies from this shallower gene pool carries with it additional risks of ill health and disease.
And it’s not only physical health with has surprising links to coat colour – behaviour has been linked to coat colour too. For example, there appears to be an association between coat colour and aggression in self-coloured (golden and black as distinct from roan) cocker spaniels.
While it is not clear whether coat colour affects the widely prized personality of the Labrador, chocolate Labradors have different retinas to their yellow and black counterparts and retinal differences in various other breeds are thought to account for some behavioural differences in other breeds (for example in the chasing behaviour of so-called sighthounds, such as whippets, greyhounds and Afghan hounds).
The power of preference
Surprisingly, even if it turns out that the colour of Labradors doesn’t affect how they behave around us, there is some evidence that it may affect how we humans behave towards them. One study found people who look at photos of yellow and black dogs rate the yellow dogs significantly higher in agreeableness, conscientiousness and emotional stability.
Similarly, a study found pedestrians perceived pale-coloured dogs as being friendlier than dark-coloured dogs. Indeed, black dogs have been maligned by no less a figure than Winston Churchill, who referred to his own depression as a black dog. It is even possible that breeders may have selected the tan eyebrows of breeds such as Rottweilers and Kelpies because the contrast on their expressive eyebrows make their faces easier to read.
But whatever our first impressions of a dog in a photograph, a dog on the street, or the new puppy we’ve just brought home, any dog owner can tell you that our relationships with our canine companions matter far more than appearances.
With every generation in a breeding program, one can make only a certain number of strides. Since breeders have to take into account the many detailed traits specified in breed standards, there’s limited opportunity to also breed for traits that boost welfare and adaptability to urban environments.
Breeders could focus more on selecting for good temperament and health, but only if less attention were paid to superficial traits. After all, a dog can never be the “wrong” colour.