Wednesday, April 23, 2014

Why Color is Good on a Jack Russell Terrier


Jack Russell Terriers are defined as being more than 51% white.

How much more than 51% white is a matter of preference and genetics.

Color distribution on the coat of Jack Russell terriers is not random.

In fact, the creep of whiteness and the addition of color tends to follow clear patterns. As the good people at doggenetics in the U.K. explain:

Whichever white pattern a dog has, its white will always follow the same rules of spread. White starts on the farthest "edges" of the dog - the tail tip, the tip of the muzzle, the paws and the tip of the breastbone. This is known as the "trim" pattern. From there it spreads to cover the muzzle and forehead, the front of the chest, the lower legs and more of the tail tip, creating irish spotting. Next it spreads round from the front to the back of the neck, and creeps up the legs and tail. On a piebald dog, only the head, back and tail base may still be colored. The back coloring is the next to go, followed by the tail base, then the face markings. The ears will always remain colored unless the dog has a very high amount of white. The ears are generally the last part of the dog to turn white.

This is exactly what happens with most Jack Russell Terriers.
One way to think of it is that the dog retains color best in the most important areas of its body - around its internal organs (body and tail base patches) and its brain (ears and face patches) - and loses color easiest from the parts farthest from these areas. In technical terms, pigment "migrates" to different parts of the body during the development of the embryo, and the S gene determines how far the pigment migrates.

Folks that want to read a more detailed explanation of the alphabet soup of alleles implicated in coat color and spotting patterns can read this very good article from Holly Steel.

For the rest of us, the bottom line is that pure white Jack Russells come with a caution.

The extreme white pattern consists of a completely or predominantly white dog with just small amounts of colour on its head and sometimes base of tail.... Extreme white can occasionally cause problems when it removes large amounts of pigment from the face and ears. The most common problem is deafness (due to lack of pigment in certain parts of the inner ear, which prevents it from functioning properly)....

And, of course, deafness is a problem in extreme white Jack Russell Terriers, which is why I am always troubled when I see entire kennels full of pure white dogs.


KryswynUSA said...

That's why BAER testing is so important AND why if a BAER normal dog sires a deaf or uni pup, it should be bred with caution or removed from the gene pool. Same thing with a dam. The only deaf puppies I ever bred were from a #10 and a number 8. Of the resulting 6 pups, the all white pup was a uni and a #7 pup was bilaterally deaf. I spayed both the dam and the deaf pup and neutered the sire and the uni pup.

J.Deans said...

I had been finding, a few years back, that the dogs with nice full colour were few and far between and the predominantly white dogs were more prevalent.
My preference is #1 - #5 on the chart you posted, and it was extremely difficult to find #1's.
I see a lot of #5's and #6's today but not much above that. I don't know if it's a "show" thing, as a lot of the terriers that I see from breed stock here are usually found in the show ring of the JRT clubs and not the working grounds.
I'd be really interested to know why many have turned away from the more "full" coloured dogs.

Jennifer said...

Is there any functional reason to want > 50% white on a terrier?

PBurns said...

Yes and no.

I favor "no" but with an explanation.

Broadly said, it's simply part of a breed description. In the field the animal in the ground does not care a bit. After all, in complete darkness there is no color at all!

That said, some will tell you different, and I have my opinions and preferences.

One argument is that you can easily tell a white dog bolting from the earth, and so you are less likely to shoot a white dog than a red fox or a raccoon or a groundhog or a badger.

Makes sense in theory, but if the man with a gun is simply shooting at any bit of colored fur, then please take the damn gun away from him! I have had pure white dogs come out the ground red with clay and have posted pictures of the same.

And what about border terriers and patterdales and fells -- all working dogs ranging from tan to red to brown to black?> All work, and there is no white (or very little white) on them. So nice, theory, but reality knocks...

Now, I have to say I DO find border terriers hard to locate in a hedge -- they are the color as dirt and bark, and it's hard enough to keep your eye on a dog that can dive underground without the thing going commando on you above ground!

That said, a very white Jack Russell in snow can also be hard to find (though I seem to have less trouble there because we rarely get snow on the ground, and when we do I can track in snow pretty well).

The bottom line is that a good dog, like a good horse, is never the wrong color.


Alaa Sobhy said...

A complete black head and a body that has black spots. Is this a good feature or no ?

SuperLeigh1983 said...

I've just had 2 pups that are between 4-5 on the chart. Brothers, one being black and white with touches of brown and the other brown and white with touches of black. Is this a good combination regarding pigment/quality of health and bread?