Avian medicine is an important interest of the veterinary profession.
It comprises two significantly different branches, one concerned with disease control in commercial flocks of the half-dozen species of domestic poultry and the other with the treatment of the much larger variety of cage, aviary, and zoo birds; frequently, some of the latter group are treated as individual patients.
In addition, rehabilitation of wild birds, most notably oiled seabirds and injured raptors, is rapidly increasing. This chapter seeks to supply practitioners working in poultry medicine with a basic knowledge of anatomy sufficient for the understanding of the special features of poultry physiology and pathology, including that required for the conduct of postmortem examinations. This chapter is based on the chicken, and most of the data and illustrations refer to that species. Some details relevant to the examination and treatment of companion and exotic birds are included.The evolution of birds from reptiles is indicated by reptilian features such as scales on their beaks, legs, and feet; a single occipital condyle; a single middle ear bone (columella); and a complex construction of the jaws. Birds have nucleated erythrocytes and a renal portal system that excretes uric acid. They range in size from the ostrich, weighing more than 100 kg, to tiny species such as the wren. They owe their extreme evolutionary success to the acquisition of the power of flight, which has enabled them to disperse ubiquitously and adapt to more niches than any other class of vertebrate. However, the imposition of rigid anatomic requirements for flight has limited the variation in morphology among all species. The high metabolic demands of flight have resulted in anatomic or physiologic modifications or both in nearly every body system. These modifications increase energy output and stability while decreasing body weight and wind resistance. They range from the grossly visible, as in the loss of heavy teeth and masticatory musculature, to the microscopic, as in the airways of the lung and the arrangement of conduction fibers in the heart. Together, these specializations render birds at once singularly uniform and strikingly diverse.