THE ETHICS OF BREEDING FOR DEFORMITY: EXTREME BRACHYCEPHALY
Owners of Persians and Exotic Shorthairs are advised by cat care books that these breeds may have problems grooming, have dribbling eyes and overcrowded teeth. Roger Tabor noted, in "The Rise of the Cat", that exhibitors had to continually wipe the dribbling eyes of Persian cats. Cats are instinctively fastidious animals and the inability to groom properly and the constant tears must frustrate them. Owners have noticed that these cats tend to eat by flinging food upwards to catch it in the mouth. There is even biscuit food aimed at Persians where the pieces are designed to be scooped up with the tongue (anyone doubting this problem should try to eat cat-style, after all Persian/Exotic faces are becoming almost as flat as ours). In the most extreme case, that of the Peke-Faced Persian, the high palate meant many kittens were unable to suckle effectively and had to be hand-reared. Modern extreme-typing (ultra-typing) has led to Persians approaching the level of deformity and handicap founded in the Peke-Faced Persian.
Reports on the problems associated with short muzzles have often been dismissed by fanciers as rants from people who don't appreciate the aesthetics of the modern breeds. Health problems have been downplayed by breeders and registries as alarmist or overstated, but there is a growing body of veterinary evidence showing the problems associated with the facial anatomy of modern Persians/Exotics. This article looks at veterinary research into the effects of the flattened face as well as legislative measures that might come into play if cat fanciers continue to value extreme conformation over feline health and if registries do not rein in these excesses.
The following terms are used in this article and in quoted material.
Brachycephaly - having a disproportionately short head (flat faced)
Brachygnathia - having a disproportionately short jaw
Nasolacrimal - relating to the nose and tear-producing apparatus
Exposure keratitis - drying and inflammation of the eye surface because the eyelids cannot cover it fully.
Corneal sequestra - dark patches of dead tissue on the cornea
Stenotic nares - constriction of the nostrils
Stridulous breathing - noisy breathing associated with partial obstruction of the larynx or windpipe (snoring)
Sleep apnoea - unable to draw breath when asleep
Syringomyelia - a spinal abnormality; flow of cerebrospinal fluid is obstructed
THE PERSIAN'S PROGRESS
The Persian is one of the oldest cat fancy breeds, dating back to the late 19th century. It resulted from crossing imported Angoras with British longhairs and selecting for cats with long, dense coats, cobby build and short muzzles. Over the years this was taken to greater extremes, partly because breed standards didn't tell breeders where to stop. In 1958, breeder and author PM Soderberg wrote in "Pedigree Cats, Their Varieties, breeding and Exhibition" "Perhaps in recent times there has been a tendency to over-accentuate this type of short face, with the result that a few of the cats seen at shows have faces which present a peke-like appearance. This is a type of face which is definitely recognized in the United States, and helps to form a special group within the show classification for the [Persian] breed. There are certainly disadvantages when the face has become too short, for this exaggeration of type is inclined to produce a deformity of the tear ducts, and running eyes may be the result. A cat with running eyes will never look at its best because in time the fur on each side of the nose becomes stained, and thus detracts from the general appearance." Soderberg mentioned the extreme typing in another section: "The nose should be short, but perhaps a plea may be made here that the nose is better if it is not too short and at the same time uptilted. A nose of this type creates an impression of grotesqueness which is not really attractive, and there is always a danger of running eyes"
The Persian standard called for a "high nose leather", leading to cats with the shortest and highest noses being judged the "typiest". As a result of open-ended standards, some Persians had the nose flat against the face and almost between the eyes. European standards have been amended so that the top of the nose leather must not be above the lower rim of the eye, but cats are still seen where the nose is above that level. The muzzle became grossly distorted and in extreme typed cats, it barely protrudes, there is an indentation above the nose and the mouth does not fully close. Unable to breathe through compressed nostrils, the cats may breathe through the mouth (something cats are normally reluctant to do). The distorted facial bones means the tear ducts are distorted or missing. while the eyes have become more protruberant due to shallow sockets.
The natural feline muzzle evolved to suit the feline diet and lifestyle. Cats slice their food using their side teeth (carnassials) and also use the front teeth in grooming. Unable to get a purchase on their food with their teeth, flat-faced cats tend to "throw" food upwards into the air in order to manoeuvre it into their mouths. Some owners of extreme-typed Persians and Exotics puree their cat's food so the cat can lap it up. Breeding for extreme facial type makes the cat wholly dependent on humans and compromises its lifestyle.
The American Red/Red Tabby Persian was taken to extremes with the 'Peke-faced' Persian, a mutation which was established as a breed despite reservations about its health and which died out in the 1990s. The CFA (a US registry) standard (1991) stated: "Nose should be very short and depressed, or indented between the eyes. There should be a decidedly wrinkled muzzle." This squashed and wrinkled muzzle was accompanied by a high palate, causing suckling problems in the kittens and high kitten mortality (as high as 50%), breathing difficulties and faulty teeth. The kittens often needed to be delivered by caesarian due to their large heads. Adult Peke-faceds tended to have breathing difficulties and even good specimens had constantly weeping eyes due to compressed tear ducts. Roger Tabor referred to it as "breeding gone too far, yet it often wins top American honours". The Peke-Faced mutation died out, but Persians and Exotics are emulating it both in looks, and in health issues.
According the the CFA Peke-face red Persians are not seen in exhibition today and few CFA judges can remember handling one. Only one (a male) was registered with the CFA in 1993 and a total of only 98 had been registered since 1958. In November 2003. the CFA's Persian Breed Council discussed eliminating the Peke-Face red and red tabby Persian. Only one such cat was registered as a Peke-face in 2002 and there were only 3 Peke-face Persians registered in 2000 and 2001. It was not even certain that those cats were genuine Peke-faced Persians or were extreme-type Persians erroneously registered as Peke-faces. No CFA breeder was known to be working with Peke-face Persians. It is unlikely that any geneuine Peke-face Persians survive in 2010.
Peke-face Persians (solid red and red tabby) generally conformed to the red Persian standard. However, they had slightly higher ears and a very different head due to the skull structure differing greatly from the standard Persian. The bone structure created a very round head with a very strong chin. Eyes were large, round and very wide-set. The nose was depressed and indented between the eyes. The muzzle was wrinkled and there was a horizontal break located between the usual nose break and the top dome of the head. This second break created half-moon boning above the eyes and an additional horizontal indentation in the center of the forehead. The Standard for the Peke-Face called for a brow ridge, dimple, and a double dome. The term peke-face is often incorrectly used to describe extreme-typed Persians, some of which are certainly flat-faced, but do not have the forehead indentation or brow ridge of the true Peke-face Persian. Peke-face reds appeared in litters of normal reds, but mating two Peke-face Persians together was not guarantee of getting Peke-face kittens in the resultant litter.
However, the Peke-face may have left its legacy in the increasingly brachycephalic modern Persians in the USA. During the mid 1970s and early 1980s, American Persians changed dramatically. The pre-1980s look had heavy brows, flat-topped heads rather than domed heads. During this period, the "sweet, open-expression" was lost as fanciers pursued an extreme head type (ultra-type). These Persians were dubbed "pigs" or described as having a "piggy expression." The nose became narrow and ultra-high; the breaks above the eyes were moving towards the forehead; the eyes were tiny and the jaws often misaligned to produce a frowning mouth. It is suggested that Peke-Face red Persians were bred to other solid colour Persians to produce this piggy look. The teardrop-shaped eye of modern ultras is attribited to the legacy of Peke-face cats. The new look was deemed an exciting development and open-ended standards favoured this look on the showbench. During the 1990s, both open-face and Persian pigs were advertised, but the trend later moved back towards the healthier open-face cats. Besides which, the piggy Persians were just plain ugly.
The extreme-typing seems to have been American-led, with British and European breeders following suit (since cats are traded between these countries). According to the December 11 (1994) edition of the British "Sunday Express", "Judges at the 1994 National Cat Show at Olympia were so concerned by the increase in breeding extremely freakish cats that they voted to ban the Over-Typed Persian from competing. Other previously banned mutant breeds include [...] the Peke-faced Persian, whose face is so flat that its eyes and sinuses are deformed [...] one breeder at the 1994 show claimed that 90 per cent of Persians, whether they're ultras or not, have blocked tear ducts." While this halted the progress of the nose further up the face, the health of the Persian/Exotic was already compromised by its conformation.
In Germany, it is already prohibited to breed from brachycephalic cats in which the tip of the nose is higher than the level of the lower eyelid, and which show other anomalies of the facial bones. Elsewhere, it is left to cat fancies to govern themselves and as yet none seem willing to recognise just how unhealthy modern Persian/Exotic conformation is. Some breeders are fiercely protective of their right to breed flat-faced, runny-eyed, snuffling monstrosities. There may also be fears that Persians/Exotics could not be traded between Europe and the USA. On both sides of the Atlantic, a few breeders produce traditional-type Persians/Exotics, although these cannot compete on the showbench as standards favour the flatter-faced extreme-type cats.
The highly modified shape of the head has resulted in health issues and there are published veterinary papers relating to problems caused by the Persian/Exotic facial anatomy. Similar problems have already been seen in dog breeds such as the Bulldog and and Pekingese which could have served as warnings to the cat fancy, but the aim seemed to be to emulate these breeds (e.g. in Peke-Faced Persians) including their associated health issues!
"Brachycephalic Syndrome" is a term sometimes used by vets to describe the set of health problems found in Persians and Exotic Shorthairs. According to Australian feline vet Richard Malik "severely brachycephalic cats [...] have a nasolacrimal system that doesn't work properly, so tears stream down the front of their face causing staining and secondary dermatitis. It doesn't help that they often have excessive folds of skin that rub against the cornea. Their orbit is shallow, leading to a tendency to exposure keratitis and growth of corneal sequestra. The tear film just can't stretch that far! Their teeth erupt at such bizarre angles that they cannot masticate properly; the resulting propensity for food to accumulate between the teeth leads to accelerated plaque formation and periodontal disease. Stenotic nares and a soft palate too long for the length of the head cause upper airway obstruction, stridulous breathing and possible obstructive sleep apnoea. Their brain is crammed into the wrong-sized cranial vault, so conceivably we may soon be seeing syringomyelia, just like in Cavalier King Charles spaniels."
For a layman to get an idea of what Malik is talking about, here's a list of some of the problems caused by brachycephaly. These are all taken from veterinary reports:
Vets treating Persians/Exotics have also noted other problems resulting from the facial combination or to a coat that is unmanageable without human help.
Add up all of those and you can see that the more extreme Persians/Exotics have a lot of health problems bred into them as a result of the quest for ever higher noses, flatter faces and dense fur. Many of the problems would be eliminated by returning to a moderate skull conformation. The extreme facial conformation turns the independent feline into a highly dependent, handicapped creature - far more handicapped, in fact, than the much-maligned Munchkin.
VETERINARY REPORT INTO EXTREME TYPING OF PERSIANS/EXOTICS
A report by Claudia Schlueter and colleagues from the veterinary universities of Leipzig and Vienna appeared in the Feline Advisory Bureau's Journal of Feline Medicine and Surgery in November 2009. It looked at the problems caused by breeding for extremely short faces e.g. in Persian and Exotic Shorthair breeds and compared their facial anatomy with that of cats with normal muzzles. The investigations included examination of live patients (sometimes under anaesthetic) and post mortem studies of cats that had to be put to sleep.
The studies looked at the nose and tearduct system in 31 brachycephalic cats and 15 mesocephalic (normal length muzzle) cats. X-rays, MRI scans and post-mortem dissection showed the degree of distortion of the skull. The shorter the cat's face, the more the facial bones and upper canine teeth were displaced causing the tear duct to follow an abnormal path and be unable to drain properly (its normal course being obstructed by the upper canines). In some cases, the upper canines were almost horizontal. By comparing these to normal skulss, it demonstrates how the selection for brachycephaly has been detrimental to health and function.
The 4 categories of brachycephaly that were identified by Schueter et al:
Category I, mild: nearly vertically positioned upper canine teeth without a dorsally rotated jaw, an inconspicuous stop, and clearly developed facial and neurocranial (brain-case) bones.
Category II, moderate: characterised by an incipient dorsorotation (lifting) of the upper canine teeth and jaw to a dorsal direction, a distinct stop, reduced nasal bones and a rounded or even apple-shaped brain-case.
Category III, profound: pronounced rotation of the jaw and the upper canine teeth was obvious. Additionally, these cats showed a distinct stop with reduced nasal and neurocranial bones. Because of the dorsally rotated upper jaw, the tip of the nose was at a higher level than the lower eyelid.
Category IV, severe: a more extreme form of the characteristics described for category III. These handicapped cats showed nearly horizontally positioned upper canine teeth and a high-grade dorsorotation of the jaw. An overly pronounced stop, underdeveloped facial bones and a rounded neurocranium were visible.
The diagrams (drawn from x-rays and scans) show the abnormal positions of the upper and lower canines as the muzzle becomes shorter. As the upper canines become higher, they obstruct the tear ducts that drain into the nose. Although the face is wider than a cat with normal muzzle, the eye sockets are shallower and the braincase is smaller. In Peke-face Persians, the change in head shape caused birthing difficulties; this is the future modern Persians/Exotics are facing if current trends continue.
This study did not go down well with the cat fancy in the UK. The report contained images of deformed tear-ducts (that do not drain), shallow eye-sockets (that cause eyes to protrude) and deformed jaws (where teeth are at unnatural angles), all of which affect the cats' health, yet Persian/Exotic fanciers and breeders refused to accept it as anything other than a rant against the breeds.
PERSIAN BRACHYCEPHALY GENES IDENTIFIED
The current interpretation of the Persian breed standard requires an extremely brachycephalic face. Little is known about the underlying genetics of this trait. DNA from 800 cats from different breeds including Persian, non-Persian breeds (Abyssinian, Cornish Rex, Bengal, La Perm, Norwegian Forest, Maine Coon, Manx, Oriental, and Siamese), and Persian-derived breeds (British Shorthair, Scottish Fold, Selkirk Rex) was analysed by the researchers.
(i) the DNA samples from Persians was analysed to look for regions that were highly homozygous i.e. were both DNA strands had the same versions of the genes (alleles).
(ii) A number of those homozygous regions were compared to the same regions of DNA in non-Persian breeds.
(iii) The Persian homozygous regions that were most different from the same regions in non-Persian breeds were further investigated in the Persian-derived breeds.
Four regions with high homozygosity were detected. Three of those regions appear unique to the Persian breed. Those regions are also highly homozygous in the Persian-derived breeds, but not so much as in the Persian breed. Two genes, CHL1 and CNTN6, which are known to determine face shape modification in humans, reside in one of the identified regions are potential candidates for the brachycephalic face in Persians. Those homozygous regions also contain several neuronal genes that might be involved in Persian cat behaviour and might provide new insights into cat domestication.
NEUROLOGICAL IMPACT OF BRACHYCEPHALY IN EXTREME-TYPED PERSIANS
The Persian cat is one of the oldest cat breeds and its conformation remained unchanged until cat fanciers desired a cobby conformation and round skull. Modern breed standards vary, but generally require an extremely round, wide head with a “high nose-leather”. The forehead, nose, and chin are supposed to be in vertical alignment when viewed from the side (i.e. flat face with large forehead), and the nose break) should be centred between the eyes. This is often called the peke-face or ultra-type conformation. Some German breeders preserved the traditional type of Persians (“doll-face”) where the nose is small, but still protrudes and is more proportional to the head. These breeders noticed abnormalities when outcrossing to extreme-typed cats in order to “improve” the German breeding lines.
The researchers determined the degree of brachycephaly using CT and MRI scan data. Cranial measurements were examined for a possible correlation with relative ventricular volume, and cranial capacity. Persians with high and low grades of brachycephaly were investigated for the presence of skull dysmorphologies (abnormalities). Skulls of dead peke-face Persian kittens were also examined. High grades of brachycephaly were associated with malformations of the calvarial (skull-cap) and facial bones as well as dental malformations. These dysmorphologies can affect health and welfare, so the selection for extreme brachycephaly in cats should be reconsidered.
German cat breeders, who outcrossed their traditional-type Persians to more brachycephalic Persians to establish modern show lines in Germany, observed the frequent occurrence of internal hydrocephalus leading to high losses of kittens in the new lines. Veterinarians and breeding associations dismissed the higher prevalence of hydrocephalus in Persians as a random error in foetal development, or as a separate genetic defect unrelated to brachycephaly. However, internal hydrocephalus linked to brachycephaly is found in humans, dogs, and experimental rodents. There is link between the brachycephalic skull conformation and enlarged ventricular volumes in these species. Hydrocephalus is, therefore, not an incidental observation.
Neurological assessment found that all the doll-faced Persians were clinically sound. However, in the peke-faced (extreme) Persians:
14 (66%) were obtunded (dulled alertness) and unresponsive to external stimuli.
8 (38%) lacked the menace responses with preserved pupillary light reflexes indicating a visual impairment.
6 (28%) did not react to sound (only one of the deaf cats was white and its eyes were copper).
3 (14%) showed delayed hopping and wheelbarrowing reactions (hopping is where the forelimbs are supported, wheelbarrowing is where the hindlimbs are supported – the normal reaction is to immediately hop or walk the unsupported limbs).
7 (33%) lacked postural reactions.
12 (57%) had mild ataxia (tremor, incoordination).
5 kittens (23%) from 3 different litters had severe ataxia in all four limbs and were unable to stand most of the time. They had dulled alertness, mild head tremors and degrees of nystagmus (flickering eye movements) and strabismus (crossed eyes) and an abnormal breathing pattern. The owners reported these kittens had long periods of aimless screaming. Due to their severe clinical signs these kittens were euthanised.
Compared to both domestic shorthairs and doll-faced Persians, peke-Face Persians had grossly reduced cranial length and increased width and height. The eye orbits were shallow, wide-set and tended to diverge, and the bone between the eyes was indented. The frontal sinus was small or absent in all peke-face cats. The nasal bone was found to be notably short, or even absent. The lower jaw protruded and tilted upwards. The ventral nasal passages were obstructed. A 6 year old male peke-faced Persian showed profound aberrations compared to the other cats.
With reduction in the skull length there was a push back of the conchal bones (one of the turbinate bones inside the nose) toward the cranial cavity. The frontal sinuses were more and reduced. The frontal lobes are compressed. There was severe dilatation of the lateral ventricles, reduction, and destruction of the cerebral parenchyma (the functional cells of the brain i.e. neurons and glial cells), as well as severe cerebellar herniation into the vertebral canal. The euthanized peke-face kittens had internal hydrocephalus and severe cerebellar herniation
All doll-faced Persians showed normal ventricular dimensions. Ventricular enlargement and cerebellar herniation were clearly associated with the peke-face morphology. The study showed that an increasing emphasis on a brachycephalic phenotype has a correlating negative impact on general skull- and brain morphology in Persian cats. Although breeders might assume that brachycephalic conformation is an accentuated characteristic of a spectrum of normal head shapes, brachycephaly is a not a normal facial characteristic. There two candidate genes for brachycephaly in Persian cats: CNTN6 and CHL1. The skull conformation of the peke-face Persian can be considered a feline form of coronal craniosynostosis (a condition in which one or more of the fibrous sutures in the skull of a very young infant prematurely fuses by turning into bone, thereby changing the growth pattern of the skull). It has already been demonstrated that the premature closure of cranial growth centres has a major impact on the morphology of the face and brain-case in brachycephalic dogs.
Apart from the euthanized kittens, neurologic signs were often mild or absent in the affected cats. The degree of intraventricular pressure probably determines the speed and severity of white matter injury and thereby functional brain deficits. Signs of cognitive impairment are difficult to diagnose in cats, but breeders and owners often describe their cats as “dummies”, sometimes running into objects or falling from the windowsill. They are often uninterested in playing and have reduced social interactions with other cats and with the owner. These behaviours might be due to neurological deficits.
Appearance-oriented breeding in Persian cats emphasizing the brachycephalic head shape can lead to severe skull and brain abnormalities. Breeders and cat fanciers must accept that desirable phenotypic traits in these cats would be considered a severe developmental abnormality
CONFORMATION VS CRUELTY - TIME TO REWRITE BREED STANDARDS
Malik, writing in Journal of Feline Medicine and Surgery (2009), suggested enlisting the help of organisations such as the RSPCA to press cruelty charges on the breeders of cats with extreme brachycephaly as they are handicapped and prone to illness and discomfort. In Germany, this is already in place. Extreme brachycephalic cats where the tip of the nose is higher than the level of the lower eyelid, and/or which show other anomalies of the facial bones detrimental to health may not be bred.
The "European Convention for the Protection of Pet Animals" was issued by the Council of Europe and potentially bans genetically defective and ultra-typed breeds. It covers 41 member States including the UK, but not all member states have signed up to it. Being legislation, it would override breed standards, however it contains a number of errors (see Legislation against Extreme Typing, Breeding for Deformity and Genetic Defects). The section on facial defects covers brachycephaly and brachygnathia (short muzzle) and also to any cats with misaligned jaws, brachygnathia inferior (under-bite) and brachygnathia superior (over-bite). The legislation recommends breeding associations determine an index defining over-typing (Schlueter et al have effectively now done this) and banning the breeding of over-typed cats not meeting. This means a breeding ban on extremely short-nosed cats where the upper edge of the muzzle is higher than the edge of the lower eye lid. Health screening is required for brachycephalic individuals: examination for breathing problems, tear duct problems, shortened upper jaw, dental problems and a ban on breeding individuals with any of these problems. A further recommendation is modification of the breed standard to avoid an overly pronounced stop, too high nose, too short muzzle etc and preference being given to cats with longer facial bone structure.
American cat breeders are concerned that an equivalent "Convention for the Protection of Pets" could happen in their own country. Some humane societies, veterinary associations and animal rights groups would like to see comparable legislation on certain breeding practices (currently most are aimed at ear-cropping and tail-docking in dogs). The US government's Animal Welfare Act regulates conditions in breeding facilities, research facilities and shows, but breeding ethics remain the province of breeders and breed societies and are jealously guarded from interference. Some breeders do breed traditional style Persians/Exotics, but breed standards discriminate against the more moderate types.
In Victoria, Australia, The Animals Legislation (Animal Care) Bill was released by the Minister for Agriculture, the Hon Jo Helper MLA, on 11 Oct 2007. This included amendments to the Prevention of Cruelty to Animals Act (POCTA) 1986 that would effectively outlaw a number of cat breeds, but does not mention brachycephaly or brachygnathia.
The UK has not yet signed up to the European legislation so any changes are voluntary and often driven by public pressure. Of late, the UK's Kennel Club has had to rewrite some of its standards due to the health problems caused by extreme breeding and following investigation/condemnation by the BBC and RSPCA (both pulled out of Crufts, the major UK dog show in protest at the damage done by extreme breeding). The Cat Fancy needs to follow suit before it too comes under the spotlight. In Europe, there is already legislation, although not all of the contents are sound.
The GCCF produced a extensive draft rewrite to the Breeding Policy, but did not tackle brachycephaly. The GCCF will require each Breed Advisory Committee to have in place a breeding policy by January 1st 2011, to be reviewed by the Genetics Committee to ensure they are comprehensive and consistent with the GCCF's General Breeding Policy. However the GCCF seems to have opted for the easy route of discriminating against new mutations while failing at the difficult task of curtailing extreme-typing in existing breeds that already have health problems.
At present, surgery may be required to correct the dental and eye problems and improve the quality of life for individual cats. There is a danger that if the obstructing canines are removed, the abnormally routed nasolacrimal duct will be damaged. Some pregnancies may require caesarian deliveries and kittens are at increased risk of umbilical hernia as extremely brachycephalic mothers cannot cleanly sever the umbilical cord.
Not all of the issues are surgically correctable. The extreme change of head conformation means the Persian/Exotic cat's brain is now crowded into the wrong-sized skull. In brachycephalic dogs, this has already been shown to result in syringomyelia resulting in chronic pain, seizures and increasingly abnormal behaviour due to pressure on the brain.
The public are in the position of buying cats that may need extensive and expensive veterinary care to address an array of health issues that go hand-in-hand with the Persian/Exotic conformation. Some of the issues may even necessitate euthanasia. Only by reverting to more moderate conformation can these health issues be avoided.
When surgery is required to alleviate the health problems caused by extreme breeding, it is obvious that breeders have already taken conformation changes too far. When the cats have problems eating due to their face shape, the breed is clearly in serious trouble. Once females have problems giving birth normally and kittens have problems suckling, the breed is dangerously close to being non-viable.
The dog fancy in the UK has already been subjected to scrutiny by the media, by welfare organisations and even by the government over health issues caused by dog breed standards and extreme typing. if the cat fancy wishes to avoid similar scrutiny, it needs to recognise and address the issue rather than dismissing it as the views of outsiders. If adverse publicity means the public are no longer willing to buy extreme brachycephalic cats then breeders will be unable to sell or home their kittens and may be forced to stop breeding. Legislation may even force the issue and take the matter out of breeders' hands if they are unwilling to undo the damage caused by extreme brachycephaly and brachygnathia.
REFERENCES AND FURTHER READING
LEGISLATION AGAINST EXTREME TYPING, DEFORMITY AND GENETIC DEFECTs
Bertolini, F., Gandolfi, B., Kim, E.S. et al. “Evidence of selection signatures that shape the Persian cat breed” Mamm Genome (2016) 27: 144.
Breit S, Künzel W, Oppel M. The course of the nasolacrimal duct in brachycephalic cats. Anat Histol Embryol 2003; 32: 224-27.
Hobson HP. Brachycephalic syndrome. Semin Vet Med Surg (Small Anim) 1995; 10: 109-14.
Künzel W, Breit S, Oppel M. Morphometric investigations of breed-specific features in feline skulls and considerations on their functional implications. Anat Histol Embryol 2003; 32: 218-23.
Malik, R. Brachycephalia - a bastardisation of what makes cats special (editorial); Journal of Feline Medicine and Surgery (2009) 11, 889-890
Noeller C. CT-anatomy of the brachycephalic and normal feline nasolacrimal drainage system [abstract]. Vet Radiol Ultrasound 2008; 49: 207.
Schlueter C, Budras KD, Ludewig E, et al.. Brachycephalic feline noses CT and anatomical study of the relationship between head conformation and the nasolacrimal drainage system; Journal of Feline Medicine and Surgery (2009) 11, 891-900
Schmidt MJ, Kampschulte M, Enderlein S, et al. “The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus." Journal of Veterinary Internal Medicine. 2017;31(5):1487-1501