Chihuahuas: shocking new research finds they are full of holes (no really)

You're looking at a CT scan of a Chihuahua featured in a new study from researchers at the Universities of Helsinki and Surrey. The red circles mark where there are holes in the skull exposing the brain underneath and it raises big and urgent questions about the breeding of the world's smallest dog. 

A linked paper from the same authors (currently in pre-print) reports that more than 90% of the Chihuahuas they examined have these holes - known as persistent fontanelles - along what are known as the suture lines of the skull. It's a result of the skull not fusing properly.

The holes are likely linked to the miniaturisation of a breed that can weigh as little as 1.5kg and sometimes less; also to the shape of the skull, which has become shorter and more domed over the years, particularly in show-bred dogs.

The consequence is a high disposition to head trauma. One vet recalls a Chi that died when a tennis ball dropped on its head. Devastating for the kid that threw it.

Until recently, an open fontanelle in the middle of the head (called a molera by breeders) was actually a mark of purity in the breed - a neurological jewel in the crown. Breeders denied there was a problem with them.

Today, the breed-standard demand for a molera has been dropped by all forward-thinking kennel clubs - ie not the American or Canadian KCs, both of which still mention a molera as being permitted in their luddite breed standards. 

In fact, it's very clear from this statement by the Chihuahua Club of America that a molera should not be considered a handicap:.  

"Historically, the Chihuahua developed in Mexico and the United States has displayed a “soft spot” on the top of the head. In the Chihuahua this spot, or fontanel, is known as a MOLERA; and is the same as that found in human babies. In the past, this molera was accepted as a mark of purity in the breed, and it is still mentioned in most Chihuahua breed standards the world over. It is important to note that while many Chihuahua puppies are born without the molera, there are probably just as many born with one and its presence is nothing to become alarmed over. As shown in the illustration below, the molera in a Chihuahua will occur on the top of the head and may vary in shape and size when present." 

Further, it goes on to maintain: "... the presence of a molera does not mean the Chihuahua has a medical problem."

This is what the researchers set out to find out, prompted in no small part by the knowledge that syringomyelia (fluid-filled cavities in the spinal cord) and other brain abnormalities are found in the breed. Hydrocephalus is also common - although it is true that it does not affect every Chi with a persistent fontanelle and breeders fiercely deny that it is linked. 

The UK Kennel Club standard no longer includes any mention of a molera and the FCI standard lists an open fontanelle as a disqualifying fault. Progress.

Indeed, many Chi breeders have recognised that a hole in the head is as undesirable as, well, a hole in the head. In a recent discussion, one UK breeder told me: "The majority of adult Chihuahuas in the UK show ring have no molera at all."

The British Chihuahua Club says: "These days few Chis have permanent molera which persist into adulthood."

But these new papers show that this is not true. The researchers found that even if a central molera is absent, some Chi skulls are littered with these holes, something I imagine is going to come as a shock to most Chi breeders and owners.  

Significantly, the scientists found that persistent fontanelles (PFs) are more numerous and larger in smaller Chihuahuas and they also found an association between PFs and syringomyelia, overcrowding at the junction where the brain meets the neck (known as the craniocervical junction - CCJ) and ventriculomegaly (enlargement of the brain's ventricles). 

The authors write: "Although their concurrent occurrence does not prove causality, our findings suggest that PFs are associated with the occurrence of these structural abnormalities... Because SM and CCJ overcrowding may cause neuropathic pain and motor deficits, our findings challenge the current conception that PFs are a clinically irrelevant finding not associated with other structural abnormalities."

The suggestion is that the dogs may suffer less if we allowed them to be a little bigger - and in the interests of health, we probably need to moderate their heads, too. We know now that excessive miniaturisation is problematic. We know that brachycephaly and domed skulls are a problem, too (the latter now well documented in Cavaliers as being strongly associated with the endemic syringomyelia in the breed).

Many of today's Chihuahuas have domed heads, short, narrow muzzles which leave limited room for teeth/tongues, and foreheads that fall off a cliff into an abrupt, 90 degree stop. Breeders have selected for a short cranium which overcrowds the brain, pushing the structures upwards into the desired "apple-shaped" head.

The UK Kennel Club standard asks for "an apple-dome skull", sets an upper weight limit of 2.7kg (6lb) and suggests a minimum weight of 4lb (1.8kg).

The AKC disqualifies dogs over 6lb (2.72 kg), with no minimum.

The FCI standard disqualifies dogs weighing less than 1kg (2lb 3oz) or more than 3kg (6lb 10oz).

Interestingly, today's show-bred Chi looks very different from the Chihuahuas of old.

This champ dog from 1949 is admittedly rather weedy-looking but note how the forehead flows into his muzzle from both the top and side. Added bonus: his eyes are well-set into his head.

This European modern Chihuahua (over 40 Bests in Show) is an improvement structurally from the neck down but just look at this head - almost a ball, with a sharp stop and a much shorter, stuck-on muzzle that's beginning to look like an afterthought. Not all of today's show dogs have muzzles this short but it is a trend and there really is no historical rationale for it.

Link

Almost unbelievably, the AKC illustrated standard (NB this is a link to a direct download on dogwellnet.com - the only place I could find it online) features these heads as examples of a correct head. I mean.... the bottom right 😱

Pet-bred Chihuahuas  split into two camps - tiny"teacup" Chihuahuas bred by breeders with zero regard for health and bigger/heavier dogs (often up to 10lbs) which tend to  have less extreme heads and longer muzzles. When breeders are not actively selecting for small size, nature tries to normalise. 

The dogs with more moderate heads/longer muzzles are often referred to as "deer-head" Chihuahuas. It's a term show breeders loathe. ("There's no such thing - it's not a Chihuahua if it doesn't have an apple-shaped head"). These dogs would never win today, but they were the predominant type in the early show-ring.

'There is little doubt the Chihuahua has improved since the breed was first recognized by the AKC in 1904," write two American doyennes of the breed here. 'Chihuahuas shown prior to 1940 were generally of the "deer" or "fawn" type, a bit leggy and longer bodied, and - too frequently, roach backed. Also, well into the 1930's the breed was still showing the results of mixed breeding. The year 1940 brought a marked change for the better, with more breeders recognizing the true Chihuahua type. The strength of the Chihuahua rests entirely in the hands of the dedicated breeders who strive, with each breeding, to produce dogs meeting the breed standard. We think this is a pretty good testimony of the Chihuahua today!'

Nevertheless, "deer-head" Chis are the ones still found in much of Mexico  - and they tend to be more popular with pet owners not involved in the pursuit of rosettes. It is also impossible to find anything like the dogs above in the photographic archive.

The closest I can find is this 1903 dog featured in the book "British Dogs" by WD Drury.

I posted this graphic on CRUFFA a few weeks ago to illustrate the difference.  NB: I'm reliably informed the Crufts winner posted top left does not have an obvious fontanelle - certainly not one that can be felt by a judge. The skulls beneath are from a dog with the same type of head that did have a molera. 

The Chi breeders on CRUFFA objected to me calling the dog on the right a "deer-head", saying the dog still has an apple-shaped head. They did however recognise the dog as a Chihuahua (not always the case when I post more moderate dogs) and although a dog like this would not win in the show-ring today, it gave me some hope that show-breeders could be persuaded to to start selecting for a more moderate head like this one. Aesthetically it is so much more attractive.

The KC's Breed Watch scheme does ask judges to monitor the following in Chis:


Incorrect dentition
Wry jaw
Retained puppy teeth
Misplaced teeth
Protruding tongue as a result of incorrect teeth
Missing teeth
Incorrect bites
Excessively short muzzles

But here's the bitch that won BOB at Crufts in 2019.

This bitch's head makes me wince. There's a significant indent between her eyes (which of course helps give her the desired apple-shaped head) and the muzzle shoots off at less than a 90 degree angle. The tear-staining also suggests a problem with tear-drainage, often seen in Chihuahuas and other brachy breeds and linked to the skull confirmation/shallow eye sockets. Dogs' eyes shouldn't weep.

"Frontal bossing" is a medical term used to describe a prominent forehead and it is often seen in Chihuahuas. In humans - and dogs - it is associated with a number of genetic abnormalities (see here). It is also associated with Hydrocephalus, one consequence of the enlarged brain ventricles documented in Chis in this new study.

But back to the problem of those holes in the skull.

In their upcoming paper, the authors conclude:

"[Persistent fontanelles] are almost ubiquitous in the examined group of Chihuahuas. They are located at dorsal, lateral, and caudal surfaces of the cranium, and hence are not all recognized reliably by palpation in adult dogs. Though the pathogenesis of the PFs described here is unknown, bone-deficient lesions may occur due to congenital defects in cranial bone ossification, delayed closure of cranial sutures, or bone resorption, as is observable in children with craniosynostosis (premature cranial suture closure). Because the imaging findings described in the Chihuahuas of this study are similar to findings among children with craniosynostosis/premature cranial base synchondrosis closure, this growth disorder may be a predisposing factor for the PFs described here."

Research comparing apple v deer-heads in terms of predisposition to persistent fontanelles or neurological issues has not been done.  We also have no way of knowing how numerous PFs have been in the breed historically - clearly at least one has been a mark of the breed for a long time.  

This skeleton, dating from 1910, shows a Chihuahua skull with several holes in it. 

There were no really tiny "teacup" dogs in this study cohort - the smallest dog in the study was 1.4kg (and the largest 4.3kg), and it would be good to look at those too (there's certainly a rationale for thinking that their skulls could be even worse). 

It should also be said that persistent fontanelles have been documented in other toy breeds such as Yorkshire terriers (although there are no studies elucidating how common they are). This suggests that they are likely a consequence of miniaturisation. 

The authors conclude: "Further studies are necessary to evaluate the pathogenesis and clinical relevance of these lesions."

You bet your bippy and as a matter of urgency - hopefully funded and supported by kennel clubs and breeders. If breed standards, or the interpretation of them, are found to be the cause, major changes in the breed must follow.  

References

Persistent Fontanelles in Chihuahuas. Part II: Association with craniocercival junction abnoramilies, syringomyelia and ventricular volume

Persistent fontanelles in Chihuahuas and inter- and intra-rater reliability of fontanelle area measurement in computed tomography images

Molera Statement - The Chihuahua Club of America

Syringomyelia and Craniocervica Junction Abnormalities in Chihuahuas

The extraordinary story of how the Boston Terrier lost its nose

This photograph stopped me in my tracks this week. It shows Image Catcher of Ziost, who won the bitch CC at Crufts 2020 earlier this year. Her win is not a one-off. She has since been made up to a Champion.

As she's slightly turning away in the top pic, here are a couple more showing that her face really is very flat.

The reason it stopped me in my tracks is because the Boston used to have a muzzle and neither were their actual noses pushed back into the face like this.  Here's a champ from 1910.

These winners are from around that time, too.

So how did a breed that once had a muzzle end up without one?

There are three main reasons. First is the pernicious effect of the show-ring which too often leads to exaggeration over time. Second is the cult-like lure of brachcycephaly that has transformed several breeds (and threatens several others). The third, slightly more surprising one, is that the breeders have full-on fucked-up in their reading of the breed standard.

Here's how it happened...

The Boston Terrier was first recognised in the US in the 1890s.

Below is a contemporaneous report and illustraiton of the 1898 Boston Breeders Club Dog Show (in Boston itself, I believe),where muzzles, albeit of various lengths, are very much in evidence.

In the 1910 breed standard it states this: 

"MUZZLE - Short, square, wide and deep, without wrinkles.... the jaw broad and square, with short, regular teeth"

Ten years later, there was a revision that included a max muzzle length (my bolding).

"MUZZLE - short, square, wide and deep, and in proportion to skull;' free from wrinkles; shorter in length than in width and depth, not exceeding in length approximately one-third of length of skull; width and depth carried out well to end; the muzzle from stop to end of nose on a line parallel to the top of the skull"

Also of interest in the 1920 standard are the head faults listed - too short a skull and a jaw that turned up (as in the Bulldog).

"HEAD FAULTS - Skull "domed" or inclined; furrowed by a medial line; skull too long for breadth, or vice versa; stop too shallow; brown and skull to slanting... Muzzle wedge shaped or lacking depth; down faced; too much cut below the eyes; pinched nostrils; protruding teeth; weak lower jaw; showing "turn-up"

In 1919, the National Geographic Book of Dogs described the Boston's muzzle like this:

"The face is intelligent, rather square, the nose, while short, is not pushed in, and the jaws are even, broad and fairly deep. He is in every sense a good practical dog."

And that, indeed, is what the accompanying illustration shows (here with a French Bulldog).

In 1926, breed historian E J Rousuck offered this clarification re muzzle proportions:

"Conforming to outline to nearly every other part of the Boston's head, the muzzle must be square. It should be as perfect a square as possible, its width and depth and length being about equal; the "about" meaning that the slight deviation will probably take place in its length because, inasmuch as blockiness is a true requisite, the aim has ever been toward a short nose.  The muzzle should come out squarely from the stop, its length not exceeding one third of the entire head, that is, the distance from tip of nose back horizontally as far as the set-on of the ears, should measure three times the length of the muzzle." 

Today's AKC standard now says this: 

"The muzzle is short, square, wide and deep and in proportion to the skull. It is free from wrinkles, shorter in length than in width or depth; not exceeding in length approximately one-third of the length of the skull."

And it also now allows an underbite, never a part of the original standard.

"The jaw is broad and square with short regular teeth. The bite is even or sufficiently undershot to square the muzzle"

We now even have some Boston breeders talking about layback - essentially a nose that recedes into the head like this, aided and abetted by the removal of an upturned jaw as a fault being removed from the standard. 

Unfortunately, the max-third demand is now interpreted by show-breeders as something to avoid at all costs and because too-short-a-muzzle has been removed as a head fault, there is nothing to prevent fanciers breeding the face off the dog. 

On my Facebook group CRUFFA yesterday, a US Boston breeder interpreted the proportions of the Crufts winner at the top as being correct with this illustration.

Leaving aside the fact that "muzzle" cannot possibly mean just the mandible (lower jaw), it is a plain wrong interpretation of the breed standard. 

A dog's skull is not just from occiput to stop - it is the whole head, as E J Rousuck made clear in 1926, writing:  "The muzzle should come out squarely from the stop, its length not exceeding one third of the entire head, that is, the distance from tip of nose back horizontally as far as the set-on of the ears, should measure three times the length of the muzzle."  

To suggest otherwise would be considered a nonsense by any anatomist. But sadly, we've seen this error also appear in other breeds where it has also been used to justify increasingly brachycephaly - "brachy creep" as we've dubbed it on CRUFFA.

Now it is true that there has been some variation in muzzle length over the years, and it is possible to find past Champions with a very short muzzle, only recently has it led to dogs as extreme as this dog, a show champion in the US.

And dogs like these in the UK show-ring.

I recently spotted this breeder meme, produced in response to recent legislation in the Netherlands that prohibits the breeding of extremely brachycephalic dogs.

The irony is that if they had stuck to muzzles the length of the dog on the right, the breed would not now be one of the 12 extreme brachycephalics whose breeding has been restricted in the Netherlands. 

In fact, Bostons like this (and yep, they do still exist) are fine to be bred in the Netherlands because they meet the demand for a muzzle that is a third the length of the whole head. It's perfectly within-standard, too, but show breeders would dismiss this dog as "pet-bred"... the wrong colour... and far too "snouty"

The latest trend is for show breeders to claim themselves "preservation breeders", apparently oblivious to the fact that the dogs they are breeding today often look nothing like the original dogs.  They will tell you the dogs are unchanged in 150 years, asking us to not believe our lying eyes. 

  

So does it matter? After all, we know that the Boston is a better breather than its fleshier cousins the Frenchie, Bulldog and Pug.  

But this is not just about breathing (although some Bostons do struggle). Dogs' muzzles are where you find their cooling system. Crush them and the dogs overheat. Brachy mouths are also almost always a mess with rotated/crowded/mismatched teeth - an under-recognised cause of trauma and pain. A lack of a muzzle also makes eyes very vulnerable - as admitted by the Boston Terrier Club of the USA. 

"Because their eyes protrude and their muzzles are short, there is an increased chance over other dogs that they will scratch their eyes by accident. When walking with your Boston never allow them to come into contact with thorny plants."

So yes, it does matter. All dogs need a muzzle - as a physical buffer, as air-con and for a comfortable mouth.

POINTS OF ACTION:

• introduce a minimum muzzle length into the breed standards of breeds vulnerable to brachy creep
• KCs and breed clubs to educate and encourage honest debate about phenotypic changes in the breed, with an emphasis on what is and isn't an improvement from a welfare point of view
• more emphasis on the perils of shortening muzzles in judges' training
• add "brachy creep" to the KC's Breedwatch for the Boston (and other breeds where it is evident - eg Dogue de Bordeaux, Boxers, Newfies and sadly many others).

And a point of action for me personally: to give the Brachycephalic Working Group a kick up the bum. Set up in 2016 by the Kennel Club after a veterinary petition calling for brachy reform was signed by over 40,000 veterinary professional), progress has been glacial - particularly re changes to breed standards that were reported to be imminent more than a year ago.