Among the many congenital abnormalities found in the dog and cat, cleft lip, cleft palate or the concomitant presence of both of these malformations are among the most common; however, no precise data on their incidence in these species is available. In the dog, the reported frequency varies from 1/1000 to around 27%; in the cat, no official publication on the subject is available. Although congenital cleft palate may occur as an occasional finding in the dog population, certain breeds seem to be particularly susceptible to this condition.
DEFINITION AND AETIOLOGY
In mammals, the palate is a structure that separates the oral cavity from the nasal cavity; during milk feeding, it allows neonates to simultaneously suckle and breathe. During embryonic development the palate is derived from the fusion, on the medial plane, of different osseous and non-osseous structures, which then form the hard and the soft palate, respectively. Abnormalities in the fusion process occurring during organogenesis may result in an anomalous communication between the oral and the nasal cavity. Fusion of the palatine structure occurs between 25 and 28 days of gestation; the secondary palate is considered completely closed at around 32 days in the cat and 33 days in the dog.
The abnormal communication between the oral and nasal cavity, with involvement of the soft palate, hard palate, incisive bone and/or upper lip, takes the name of congenital oronasal fistula. Based on the structures involved, it can be defined as cheiloschisis or cleft lip (upper lip and incisive bone) or cleft palate (hard palate and/or soft palate); these abnormalities can also be present simultaneously. While the presence of a cleft lip alone is a rare finding, more frequent is the concomitant presence of cleft lip and cleft palate (Fig. 1); however, the most common form is cleft palate alone, implying the communication between the digestive and the respiratory tract (Figs. 2, 3).
In the dog, the condition is particularly common in certain breeds (especially in brachycephalic dog breeds) and several studies have also shown the hereditary nature of the disease. Inheritance with incomplete penetrance has been demonstrated in the Shih-Tzu, and is very likely also in the Bulldog, Pointer and Swiss Shepherd. In the Pyrenean Mountain Dog the inheritance of cleft palate, which is not genetically distinct from cleft lip (in combination or not with cleft palate), is linked to a monogenic autosomal recessive trait. Cleft palate is particularly common also in other breeds, however its inheritance has not been investigated. Breeds in which it has been reported include: the Bulldog (risk >30%), Pekingese, Pug, Boston Terrier, Shih-Tzu, Beagle, Cocker Spaniel, Dachshund, German Shepherd, Australian Shepherd, Shetland Sheepdog, Pyrenean Mountain Dog, Labrador Retriever and Schnauzer. In the cat, it is frequently reported in the Siamese, but cases have also been reported in the Maine Coon. Although inheritance has long been substantiated, the precise mechanism of transmission is not clear; the hypothesis favours the presence of a multifactorial, recessive, polygenic or dominant trait, with partial penetrance.
Although some Authors have assumed a greater presence of cleft palate in female dogs, its frequency in relation to gender has not been examined in depth. A study of 37 litters in Pyrenean Mountain Dogs found a male:female ratio of 1:0.96.
Besides the accepted hereditary nature, other factors that may play a role in this condition are maternal nutritional deficiencies or vitamin excess, exposure of gravid females to chemical agents or toxic substances, drug therapies and viral infections contracted during pregnancy. The main maternal conditions that may be associated with the birth of puppies with cleft palate include: diabetes, hypovitaminosis B₁₂, hypo- and hypervitaminosis A, folic acid deficiency, poisoning, increase of endogenous steroids during the first weeks of gestation or taking of steroids, exposure to chemical agents.
CLINICAL SIGNS AND DIAGNOSIS
Depending on the severity of the cleft palate, the abnormality may be the cause, in the more severe cases, of sudden death following the first milk feed, or of aspiration pneumonia due to bronchial inhalation of colostrum or milk, or of food intake disorders of varying intensity in those cases in which the cleft allows an albeit partial separation of the aerodigestive tract. In these latter cases the symptoms include unproductive milk sucking, dysphagia, leakage of milk from the nostrils, coughing and sneezing during or after suckling, rhinitis, recurrent respiratory infections and growth retardation.
The diagnosis of cleft palate must be made immediately after birth, as in addition to the risk of sudden death after the first milk feed also the eventual bronchoaspiration of milk and the consequent aspiration pneumonia are frequently fatal (Fig. 4). Early diagnosis is particularly important for the management of the affected neonate and diagnosis should be made immediately after parturition and before the first milk feed by means of a scrupulous examination of the oral cavity (deeper portions included) and of the conformation of the nose.
PROGNOSIS AND TREATMENT
In less severe cases the prognosis may be favourable, especially if orogastric tube feeding is possible while waiting for the surgical correction of the malformation; in other cases, the prognosis is poor. It should also be recalled that in about 8% of affected puppies and kittens the malformation may be accompanied by the presence of developmental abnormalities of other organs or systems, which often jeopardize the survival of neonates with cleft palate. Congenital aberrations associated with cleft palate include various limb abnormalities, especially of the rear limbs, dysgenesis of thigh muscles and even seizures.
The treatment of cleft palate is surgical, tobe carried out at 6-8 or, better, 12 weeks of age; goal of the palatoplasty is the reconstruction of the floor of the nasal cavity with an approach appropriate to the age of the patient and to the size of the defect. As is the case of human medicine, also inpuppies multiple surgeries may be required before achieving the full resolution of the malformation. In preparation for surgical correction, in most cases oro-gastric probe feeding is indicated (Fig. 5) until the time of surgery and for 7-10 days after surgery, in order to avoid food contamination of the respiratory tract that may result in aspiration pneumonia that is often fatal. In the literature, several methods have been reported for the temporary reduction of the palate while waiting for the surgical correction; details of such techniques are provided in specific texts of veterinary surgery. Recently, Martìnez-Sanz and colleagues (2011) proposed the use of baby bottles with teats modeled on casts of the individual cleft abnormality and modified in order to reflect changes in the age of the puppy; this allows the intake of food, avoiding the risk of milk bronchoinhalation, until weaning and the reaching of an age compatible with surgical correction.
PREVENTION
Given the multifactorial nature of the disease, prevention is carried out on several fronts. In view of a recognized hereditary component, prevention should be based on the exclusion from the reproductive career of genetic carriers, especially when the abnormality occurs repeatedly in the same breeding pair or in the same breeding animal. In sporadic cases, or in breeds highly predisposed to the malformation, all other potential risk factors should be eliminated, through a proper dietary management of gravid animals and by avoiding drug treatments associated with a higher risk of occurrence of cleft palate. In the bitch, it has been reported that the administration of folic acid at a dose of 5 mg/day, from mating until three weeks after whelping, has reduced the incidence of cleft palate by up to 76%. A study performed in Boston terrier breed dogs has shown that supplementation with folic acid decreased the occurrence of cleft palate from 17.6% to 4.2%, a reduction rate of 76%. Although, at present, no precise information is available on the dosage, as well as on the timing of the preventive administration of folic acid to gravid animals, as well as on the actual effectiveness evaluated in large case series of dogs, the results available to date support the use of folic acid in an attempt to limit cases of cleft palate in puppies.
Suggested reading
- Veronesi MC, Castagnetti C, Taverne MAM. Neonatologia veterinaria. EdiSES. Napoli, 2013
- Hyttel P, Sinowats F, Vejlsted M. Essentials of domestic animal embryology. Saunders, Edimburgh, 2010.
- Martínez-Sanz E. et al. A new technique for feeding dogs with a congenital cleft palate for surgical research. Laboratory animals, 2011;45:70-80.
- Kemp C, Thiele H, Dankof A, Schmidt G, Lauster C, Fernahl G, Lauster R. Cleft lip and/or palate with monogenic autosomal recessive transmission in Pyrenees shepherd dogs. Cleft Palate Craniofac J, 2009;46: 81-88.
- Elwood JM, Colquhoun TA. Observations on the prevention of cleft palate in dogs by folic acid and potential relevance to humans. New Zealand Veterinary Journal, 1997;45:6, 254-256.