An article from LiveScience has me thinking. Well, it has me speculating, but please hear me out.
It turns out that the production of pheomelanin, the melanin that produces the red, gold, and yellow color in golden retrievers, may actually make them susceptible to oxidative damage to their cells, which might make them more susceptible to cancer.
Spanish researchers examined a large sample of wild boars, and they found that wild boars with reddish colored coats, which are produced through that same melanin as golden retrievers, have more cell damage from oxidative stress than those with grayer coats.
Pheomelanin production requires a chemical called glutathione (GSH). GSH is also an important anti-oxidant.
The researchers found that the more pheomelanin a boar had in its hair, the more likely it was to have lower GSH levels in its muscle cells.
Now, this is an interesting finding about wild boars, but it instantly got me thinking about golden retrievers.
Virtually all golden retrievers I’ve known are entirely gray-muzzled by the time they are 6 or 7 years old.
I’m so accustomed to seeing how golden retrievers age that I often think dogs of other breeds are younger than they actually are.
Maybe the reason why golden retrievers turn gray so early is related to this discovery in Spanish wild boars.
Maybe the early graying is an attempt to free up some of the dog’s GSH for fighting free radicals. Once the dog’s muzzle turns gray, those hairs are no longer using up GSH for the production of the color and can be used for that purpose.
Or maybe that coloration uses so much of the GSH that the dog simply can’t produce enough of it to keep the muzzle red, yellow, or gold once it hits a certain age.
Or maybe this breed is just generally prone to oxidation damage and the coat color just makes it a bit worse, and the dogs eventually have to convert all that GSH to anti-oxidant duties instead of pheomelanin production.
I’d really like to see a study on pheomelanin and GSH in golden retrievers.
This discovery in wild boars could explain why golden retrievers get gray-muzzled at such early ages.
It’s something that has intrigued me for quite some time, and maybe this is the answer.
It also means that golden retrievers may need a diet richer in anti-oxidants than other breeds. They may need it to make up for the GSH deficiency that is caused by their coat color.
I knew there was a reason this sounded familiar:
http://scienceblogs.com/pharyngula/2012/06/24/the-curse-of-the-gingers/
Yeah. I saw that when it first came out, too.
We find in Papillons that early graying is inherited, and is very evident in some lines. Some dogs begin to go gray at as early as a year old,
I find it interesting that golden’s sister breed, where the yellow color also comes from phenomelanin, seems to grey later . . . I’ve never noticed a six year old yellow Labbie go grey. But maybe that’s due to the relative rarity of really dark yellows and popularity of cream yellows . . . a creme doesn’t go grey . . . they go white . . . so the change is less conspicuous. Eg,,. http://www.blackboykennels.com.au/crakka.html scroll the the bottom of the page. is Crakka, at 10+ years, grey. I prefer blacks and chocolates, who grey around the muzzle, but I’ve never seen one get that raccoon mask look that some goldies get.
Is it possible that the feature found in wild boars was bred into goldies and bred out of Labbies in the half century or so when those breeds parted ways? Or does it have something to do with Labbies retaining three colors, two with eumelanin, while goldies kicked the eumelanin individuals into a separate breed.
Concerning the curse of the gingers, seems highly likely that yellow evolved in dogs for hunting in dry vegetation. What color are dingos?
Dingos are red to yellow. FWIW New Guinea Singing Dogs get gray in the face, too.
That may be that Labradors are less likely to have oxidation damage than golden retrievers are, and it would lend support toward the third hypothesis in the post.
While we say that Goldens go “gray”, the hairs are actually white. Because they are interspersed with colored hairs, the visual effect is often not “pure” white, although very elderly Goldens may well have completely white faces. And often white hairs occurring throughout the body coat and even on the paws. There is a great deal of variation between individual dogs, both in age of onset and in extent of change. The “graying” is less obvious on pale-colored Goldens, as it is on the light yellow Labradors as well, largely simply because of lack of contrast.
Irish Setters also grey fairly young, but I think on average live longer and are less cancer-riddled than Goldens (though someone can correct me if that’s not true… just the impression I’ve received so far). They also are much darker red and must be producing more pheomelanin. Wonder how that works? Probably your last hypothesis is most likely, that Goldens are more cancer-prone in the first place, and the color just makes it worse, while Irish are less so (wonder why? They also have a very restricted gene pool and come from similar roots… or maybe they are as bad, but it’s not made public… hmm) so the color makes little difference.
Very interesting idea overall though. And thanks to Jess for think about pheomelanin in humans- I have a redheaded sister and father, they might get a kick out of it.
We actually don’t have a good handle in terms of good studies on cancer rates in goldens. The GRCA health survey has several methodological problems, and it’s not current. The Swedish Dog Insurance study, which included much more representative sample, found that they were no more likely to die of cancer than a mixed breed dog.
Irish setters are considered prone to cancer, but finding good studies on all of this is difficult.
Anecdotally, goldens are prone to certain cancers, but they aren’t as prone as flat-coated retrievers are, which have a much shorter average lifespan.
The best studies show that goldens have about a 12-13 year average lifespan, while flat-coats are more in the 8-9 average lifespan. Flat-coats rarely come in yellow (it’s not a standard color), so there has to be another factor or factors going on. (Probably the closed registry system’s various problems).