National and regional specialties bring together dogs of all ages from one breed. Fanciers and breeders attend, keen to study the latest crop of puppies, evaluate youngsters from previous years to see how they’re maturing, size up potential studs, and in general, “check in” with their respective breeds.

It’s ideal when fanciers can return home from a National feeling good about the direction of their breed, but there are some years when something worrisome is spotted, and then it’s all the more reason to follow up at future specialties to see if, for example, toplines that appeared to be weak one year have been “course corrected” by breeders in subsequent litters. If the problem was rectified, was it as the expense of some other part of the dog? Or did breeders find the “sweet spot” of balance in their breeding programs? Were it only as easy as assembling a Mr. Potato Head.

The underjaw. Admittedly, an underjaw is not something that worries the average pet owner, but we mention it not only because it illustrates the kind of thing a heritage breeder does think about, but because some breed fanciers who, when asked about problem spots in their breed, often mention weak underjaws.

For clarity, when we say “underjaw,” we’re referring to the shape and degree of curve in the lower jaw. It is one of the last things to finish growing in a dog, and while it may not seem to be that important, it’s actually really important. Phenotypically speaking, it’s one part of a breed that can make or break expression. A Bulldog without its lower jaw projecting considerably in front of its upper jaw and turning up lacks type. And while – mercifully –  we don’t bait bulls anymore, a Bulldog without such a lower jaw would not have been successful at doing its job back in the day.

A weak lower jaw can impact the number and position of incisors, hugely important in a breed like the Doberman Pinscher which, per its standard, calls for 42 correctly placed teeth, and identifies as a disqualification four or more missing teeth.

A weak lower jaw can impact the gripping power of breeds like the Bulldog, but also breeds that need a strong, well developed underjaw for overall soundness, and to do their jobs well: To name a few: The Komondor (from the AKC standard: “Underjaw is well-developed and broad), Shetland Sheepdog (“The deep, well-developed underjaw”), the Kuvasz (“underjaw well developed“), Australian Cattle Dog (“…the underjaw strong, deep and well developed”), the Lagotto Romagnolo (the wide robust underjaw defines the shape of the muzzle so that the lips form an upside- down semi-circle), the American Staffordshire Terrier (“jaws well defined. Underjaw to be strong and have biting power), and the Irish Water Spaniel (The muzzle is long, deep and somewhat square in appearance with a strong underjaw).

There are any number of terms that identify a weak lower jaw: A shallow underjaw lacks depth, a shark jaw is slang for a shallow or inadequate underjaw, and a slack jaw refers to a weak underjaw that lacks biting power.

The underjaw. It’s more important than some might think.

Image: American Staffordshire Terrier by Mark Ashkenazi is available for purchase as a print here