Avian Digestive System Disorders

Chapter 172 Avian Digestive System Disorders

Barbara L. Oglesbee

DISORDERS OF THE BEAK

General Principles

Normal Structure and Function

• The beak includes the bones of the upper and lower jaws and their keratinized sheaths or rhamphotheca. This horny covering functionally replaces the lips and teeth of mammals.
• The shape of the beak varies, depending on how the species feed and live.
• In psittacines, the upper beak is massive and curved, and the lower beak is small and horseshoe shaped (this is why psittacines are called hookbills).
• The beak is adapted to cracking large nuts and seeds, as well as tearing and shredding wood from trees to provide nest sites.
• Histologically, the horny beak resembles skin and consists of dermis and modified epidermis. The stratum corneum of the epidermis is very thick.
• The horny tissue of the beak is continuously replaced during normal wear and tear.

Normal Beak Growth

• Many bird owners erroneously believe that the upper beak grows only from the cere and continues to the tip (or edges), where it is then worn off (and that the process is similar in the lower beak). On the contrary, beak tissue grows continuously outward (toward the surface) over much of the beak.
• As the keratinized epithelium reaches the surface, it is worn off or may move distally a short distance before it is shed.
• Beak tissue truly moves rostrally only toward the edges and tip.

Beak Overgrowth

Many pathologic conditions can change the normal outward appearance of the beak, adversely affecting its primary functions of food gathering, prehension, preening, and protection. Regardless of the etiology, overgrowth may take various forms, the most common of which are listed here.

• The tip of the upper beak, lower beak, or both may be overgrown.
• Elongation of the upper beak, usually accompanied by subcorneal petechia and increased malleability, is commonly seen in budgerigars with underlying metabolic disease (most commonly hepatic disease).
• Malocclusion of the beak causing the upper beak to angle off to one side, while the lower beak angles in the opposite direction, is referred to as scissors beak. The tips and outer edges usually are overgrown owing to a lack of occlusal wear.
• The upper beak is shortened and does not extend out over the tip of the lower beak (prognathism).
• An area of the beak may appear bulged or thickened because of buildup of covering horn. This commonly is seen in birds lacking access to rough surfaces but may also been seen in birds with systemic disease or malnutrition.

Beak Trimming

• Severe malocclusions, such as scissors beak, require surgical correction. See “Supplemental Reading” at the end of this chapter.
• When the underlying condition has been identified and treated, corrective beak trimming may be necessary.
• Mild overgrowth or a buildup of covering horn may be trimmed if it is interfering with the function of the beak. Depending on the size of the bird, use human fingernail trimmers, cuticle nippers, Roscoe nail trimmers, or an electric hobby tool (Dremel) with a coarse sanding bit.
• Anesthesia usually is not required; however, be aware that some birds stress easily during this procedure, especially when a hobby tool is used, and deaths have been reported.

Key Point

Knowledge of the normal anatomy and conformation of the beak for each individual species is necessary for proper trimming. Inaccurate trimming, and especially overtrimming, can cause malocclusion, pain and potentially severe hemorrhage.

Nutritional Disorders

An all-seed diet is deficient in many nutrients, especially vitamin A, essential in maintaining the health and integrity of epithelial tissues. Hypovitaminosis A may cause hyperkeratosis of epithelial surfaces.

Clinical Signs

Signs include beak thickening and overgrowth. The surface of the beak is hard and thickened, and it appears flaky and chipped instead of smooth.

Diagnosis

Base the diagnosis on clinical signs and a history of a seed-based diet.

Treatment

Key Point

Place pet birds on a commercial pelleted diet whenever possible.

• Supplement a commercial diet with fruits, vegetables, legumes, wholegrain cereals or rice, and small amounts of lean-cooked meats or eggs.
• If the bird will not convert to a commercial diet, then use a commercial avian vitamin supplement.
• Perform beak trims as necessary.

Bacterial and Mycotic Infection

Superficial or deep bacterial and mycotic infections occasionally are seen. These usually are secondary to trauma, chronic rhinitis, or other systemic diseases. Gram-negative enteric organisms (e.g., Pseudomonas, Escherichia coli, and Klebsiella species) are the most common bacteria isolated. Aspergillus fumigatus is the mycotic agent most commonly identified. In budgerigars, Knemidokoptes mite infestation is the most common infectious cause of beak deformity.

Clinical Signs

• The surface of the beak appears brittle and crumbly instead of smooth and hard. This may involve the entire beak or may be localized. Lesions may occur externally or within the oral cavity.
• The bird is reluctant to eat, crack seeds, or play with toys. The beak may seem painful.
• Areas of localized necrosis may be found on the beak surface or on the underside of the upper beak.

Diagnosis

• Examine stained specimens from affected areas for inflammatory cells, bacteria, or fungi.
• Obtain bacterial and fungal cultures of lesions.

Treatment

Key Point

Bacterial and mycotic infections of the beak usually are secondary to trauma, systemic disease, or nutritional deficiencies. Whenever possible, identify and treat the primary disease.

• Debride localized necrotic areas with the bird under anesthesia.
• Base antibiotic therapy on culture and sensitivity testing. Pending culture results, begin antibiotic therapy with a broad-spectrum antibiotic such as trimethoprim-sulfa or enrofloxacin (Baytril, Haver/Diamond) (see Chapter 169 for dosages). Long-term systemic therapy usually is required in addition to local debridement.
• For localized Aspergillus infection, see Chapter 169 for diagnosis and treatment. Treatment for months may be required.
• The prognosis is guarded if the fungal disease is systemic.

Trauma

Beak damage from trauma can occur in all species and often is the result of aggressive behavior among individual birds housed together, flying into walls or windows, struggling after beak entrapment, or improper beak trimming. A split lower beak may result from a fall, injury from another bird, biting with excessive force, or beak trimming.

Clinical Signs

• An inability to eat and manipulate food or toys may be the only presenting signs. Thoroughly inspect the beak to identify trauma because some injuries are not obvious.
• The beak may seem painful.
• Look for hemorrhage, cracks, punctures, avulsions, or complete amputation.

Treatment

Treatment varies with the type of injury. If the bird is reluctant to eat, forced alimentation may be necessary until the beak has healed sufficiently.

Cracked Upper Beak Tip

• Remove the tip with nail clippers or grind it with a hobby tool.
• Apply ammonium sulfate or ferric subsulfate powder to control hemorrhage.

Split Lower Beak

• If the crack extends the entire length of the beak, dividing it into two movable segments, nothing can be done to permanently fuse the pieces back together. However, most birds eventually adapt to this condition.
• Wire and dental acrylics can only temporarily repair the crack.
• Birds can eat a normal diet with this condition; cracking seed or pellets is usually not a problem.
• Occasional trimming of the lower beak segments may be necessary because of inadequate occlusion with the upper beak.

Puncture Injury Penetrating the Horny Layer

• Initially treat as an open wound and debride damaged and necrotic areas with the bird under general anesthesia.
• Administer topical and systemic antifungal or antibiotic agents, based on culture and sensitivity testing.
• Defects in the horny layer may be filled or patched with acrylic compounds once a healthy granulation bed has been established.

Beak Avulsions

• If avulsion of the distal one-third occurs, treat as follows:
• Treat initially as an open wound (as described previously).
• Cover the open end with acrylics as a temporary patch if necessary (see “Supplemental Reading”).
• Regeneration of the beak is possible, but the beak may never appear totally normal.
• Damage to the proximal one-third of the beak usually is not reversible.
• If the injured birds can be kept alive with forced alimentation, the damaged beak may scar over and the bird may adapt to a soft-food diet.
• Avulsion of the entire upper or lower beak is not reversible. Affected birds usually die of starvation or secondary infection, or they require euthanasia.
• Successful use of beak prosthetic devices has been reported but is rare.

Prevention

• Do not leave birds uncaged unless they are closely supervised.
• Keep apart birds that exhibit obvious aggressive tendencies toward each other. This is a common problem in breeding pairs of cockatoos. Sexually active males may attack females that are not sexually receptive, and beaks commonly are bitten. Preventive measures include the following:
• Large flight cages
• Clipping wings of the male but not the female bird
• Nest boxes with two separate entrances

Neoplasia

Neoplasia of the beak is encountered infrequently, usually in older birds. Fibrosarcoma, fibroma, and squamous cell carcinoma are the most common types.

Clinical Signs

• Fibrosarcoma usually appears as a well-demarcated, fleshy protrusion from the horny layer.
• Squamous cell carcinoma appears as a focal area of hemorrhage or ulceration.
• Common signs include weight loss and inability to eat.

Diagnosis

Base the diagnosis on histologic examination of excised tissues.

Treatment

• Surgical excision or debulking of beak tumors is rarely successful.
• Cryosurgery or radiation therapy may be beneficial, but the prognosis is generally guarded.

Environmental Factors

• To maintain a normal appearance of the beak, chewing on hard objects and rasping of the outer horny layer of the beak is necessary.
• Lack of access to materials necessary for normal beak wear can result in beak overgrowth or a flaky, chipped surface.
• Provide ample amounts of wood for the bird to chew on. This may be in the form of perches, nest boxes, or wood toys.
• Other items suitable for chewing include rawhide, concrete perches, lava stones, mineral blocks, and leather.

Growth and Developmental Abnormalities

• These conditions usually are seen in preweaned or recently weaned birds. The exact causes are unknown.
• The most common presentations are as follows:
• Scissors beak, a lateral deviation of the upper beak seen most often in macaws
• Prognathism, which affects the architecture of the upper beak and is seen most often in cockatoos
• Treatment by construction and application of a simple, durable prosthesis allows the redirection of beak growth (see “Supplemental Reading”).

DISORDERS OF THE ORAL CAVITY

Normal Structure and Function

• Because birds lack a soft palate, which separates the nasal and oral parts of the pharynx in mammals, the oral cavity and pharynx of birds form a single cavity called the oropharynx.
• The roof of the mouth, or hard palate, is located immediately behind the upper beak.
• Rostrally, the palate resembles a hard, fleshy cushion against which the tongue can manipulate objects.
• Caudally, the palate is divided into two folds containing numerous caudally directed papillae, which are referred to as the choana. The choana communicate directly with the nasal passageway.
• The floor of the oropharynx is occupied by the tongue and the glottis.
• The psittacine tongue is thick, blunt, and dexterous.
• The glottis lies on the midline directly behind the tongue.
• Papillae are distributed over the laryngeal prominence and posterior floor of the pharynx. Birds do not have an epiglottis.
• The surface of the oropharynx is lined by stratified squamous epithelium that is keratinized in regions subject to abrasion, such as the papillae.
• Salivary glands are not visible grossly and are distributed over the palatine folds, base of the tongue, laryngeal prominence, and pharynx. These glands primarily produce mucus and thus often are referred to as mucous glands.
• Psittacine birds do not produce the large amount of watery saliva seen in mammals. Therefore, the oral mucosa is normally only slightly moist, and the tongue is dry.

Key Point

Diseases of the oral cavity are common in pet birds. Routinely inspect the mouth during examination.

Hypovitaminosis A

Hypovitaminosis A, which is generally the result of an unsupplemented, all-seed diet, causes squamous metaplasia of the oral epithelium and subsequent hyperkeratosis of the mucous glands. Keratin-filled cystic structures may be found on the palatine folds, base of the tongue, laryngeal prominence, and pharynx. These lesions may coalesce and become secondarily infected to form large abscesses.

Lesions are more likely to be seen in large psittacine birds (e.g., Amazon and African grey parrots, macaws, and cockatoos) than in small species (e.g., budgerigars and cockatiels).

Clinical Signs

• Signs include white or yellow cysts and abscesses in the oral mucosa.
• If the lesions become secondarily infected, anorexia, general malaise, and weight loss may be present.
• Accompanying signs include blepharitis, conjunctivitis, uveitis, rhinitis, sinusitis, and dyspnea.

Diagnosis

• The diagnosis usually is based on the history and physical examination.
• Obtain biopsy specimens to confirm the diagnosis.

Treatment

• Change the diet as previously described under “Nutritional Disorders.”
• Under isoflurane anesthesia, lance and curette oral abscesses; perform a Gram stain and bacterial and fungal culture on the abscess contents.
• Administer systemic antibiotic or antifungal agents, as indicated by culture.
• Provide supportive therapy, such as forced alimentation and fluid therapy, as needed.

Prevention

• Provide a diet adequate in vitamin A or add vitamin supplementation, as described under “Nutritional Disorders.”
• Dark green and yellow vegetables are good sources of vitamin A.

Psittacine Pox

See Chapter 169 in this section for discussion of this disorder.

Oral Candidiasis

Candida albicans is a secondary invader that affects the mouth, esophagus, and crop. Factors predisposing to oral candidiasis include poor sanitation, malnutrition, coexisting disease, and prolonged antibiotic therapy. Cockatiels and macaws are affected most commonly.

Clinical Signs

Clinical signs vary with the severity of the disease and include the following:

• Anorexia, general malaise, and weight loss
• Vomiting, regurgitation, and mucus evident on the feathers of the head
• Wet feathers surrounding the mouth, halitosis, and oral hemorrhage
• Poor feeding response in hand-fed baby birds

Diagnosis

• Examine the oral mucosa for lesions that typically appear as a thickening of the oral mucosa associated with a mucoid exudate.
• Lesions may progress to focal or widespread mucosal necrosis, forming diphtheritic membranes or white caseated plugs.
• Perform a Gram or Diff-Quik stain on exudate from oral lesions; look for budding yeasts.
• Perform a fungal culture of oral lesions.

Treatment

Key Point

Candidiasis is usually a secondary invader. Correct predisposing factors in conjunction with specific antifungal treatment.

• In mild cases, birds may respond to nystatin (Mycostatin, Bristol-Myers Squibb), 1 ml/300 g q8h, PO.
• More often, systemic therapy with one of the azole antifungal agents is necessary. Administer ketoconazole (Nizoral, Janssen), 20 to 30 mg/kg q12h, PO, or fluconazole (Diflucan, Roerig), 20 mg/kg q48h, PO.
• Continue treatment until all lesions are healed (usually 1 month or longer).

Prevention

• Provide a clean environment, including food and water. Do not leave moist foods in the cage longer than 2 hours.
• Thoroughly disinfect utensils when feeding baby birds. Soak utensils in chlorhexidine solution (Nolvasan, Fort Dodge), 2 oz per gallon of water.
• Do not save powdered baby foods once they are reconstituted beyond one feeding or overgrowth of yeast and bacterial occurs.
• If long-term antibiotic therapy is indicated (e.g., to treat chlamydiosis), give antifungal agents such as nystatin and ketoconazole prophylactically.

Bacterial Infections

Bacterial infections of the mouth are unusual and are usually caused by similar conditions that encourage the growth of C. albicans. Common pathogens include E. coli and Salmonella, Proteus, Pseudomonas, Enterobacter, and Citrobacter species.

Clinical Signs

Lesions are variable but can appear similar to those of candidiasis (e.g., mucoid exudate or abscess formation).

Diagnosis and Treatment

Perform a Gram stain and bacterial culture on any exudate found in the mouth.

• Large numbers of enteric bacteria present in clinically ill psittacines with accompanying oral lesions are significant.
• Administer systemic antibiotic therapy, based on susceptibility testing.

Prevention

• Treat underlying systemic disease.
• Provide a clean environment and offer fresh food, as described previously under “Oral Candidiasis.”

Oral Papillomas

See the discussion of oral papillomas in Chapter 169 in this section.

Trichomoniasis

Trichomonas gallinae is a flagellated protozoan parasite. Trichomoniasis usually occurs in aviaries with many birds housed together and rarely is seen in individual pet birds. Infection may extend into the esophagus, crop, lungs, and oral cavity. The budgerigar is the most commonly affected pet bird. Outbreaks have been reported in neonatal Amazon parrots, conures, and cockatiels.

Clinical Signs

• White, sticky plaques may coalesce to form yellow, caseated masses on the choana, tongue, or pharyngeal mucosa.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Avian Digestive System Disorders

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