Chapter 172 Avian Digestive System Disorders
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.
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.
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.
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.
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.
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.
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.
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.