Diseases of domesticated birds

Front matter

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Chapter I

The structure of birds differs in many respects from that of mammals and deserves a special description. The aim of the authors is to brino; to the attention of the veterinarian the more important differences which are observed in the structure of domesticated birds as compared with that of domesticated mammals. The subject will be considered under the following; sub-divisions. 1. Skeleton, 2. Musculature, 3. Circulatory system, 4. ISTervous system, 5. Alimentary system, 6. Respiratory system, 7. Urinary system, 8. Generative system, and 0, The skin and its appendages.

SKELETON

Skull. The bones of the skull become united shortly after hatching and lose their individual identity except in the case of the ascending processes of the premaxillary and nasal bones which are not rigidly joined to the frontal bone but through their cartilaginous attachment permit the elevation of the superior mandible. The inferior processes of the premaxillary bone, the supermaxillaries and the palatine bones which form the roof of the palate do not meet in the median line, with the result that the palate presents an elongated opening or cleft.

Vertebral column. The cervical vertebrae vary in number in the different species. Statements of anatomists differ concerning the number, because of difficulties experienced in defining cervical and thoracic vertebra. The atlas or first cervical vertebra is ring-like in form and articulates with the occipital bone of the skull by means of a deep concavity into which the condyle of the occipital bone is received. This articular arrangement and that of the other cervical vertebras gives the head and neck great mobility. The articular surface is concave from side to side and convex in a dorso-ventral direction on the anterior extremity of each vertebra, presenting a saddle shaped appearance. The posterior extremity is the reverse, that is, concave dorso-ventrally and convex from side to side.

DISEASES OF DOMESTICATED BIRDS Nasal 45S13I

Incisive

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-Carpus Ulna

Pygostyle

Metatarsus

Fig. 1. The skeleton of the fowl. (Bradley)

The thoracic vertebrae are nearly al"wajs fused together by the consolidation of their spinous and transverse processes. The first may be free and the last may be fused -with the lumbar vertebrae.

The lumbar and sacral regions of the vertebral column show no special line of demarcation. The fourteen vertebrae are consolidated into one bony mass which carries ridges on its ventral surface representing the transverse processes of the original independent vertebrae.

The coccygeal vertebrae are seven in number. The last is the largest, is flattened on both sides and curves in a dorsal direction

ANATOMY OF BIRDS d

at the end. It is known as the pygostyle. The coccygeal vertebrse are movable upon each other.

Ribs. These bones articulate dorsally with the thoracic vertebrse, and ventrally with the sternum by means of the inferior ribs, except in the case of the first two which do not reach the sternum. The last rib is often united to the one adjoining and does not connect with the sternum. Some of the ribs have flat uncinate processes which extend from the posterior border and lie over the external face of the following rib near its middle.

The sternum is highly developed in birds and forms the floor of the thoracic cavity and to some extent, of the abdominal cavity. It is concave on its dorsal or internal face and convex on its ventral or external face. In fowls and pigeons a deep ridge extends along the median line of the ventral face. This is known as the brisket or keel. It serves to increase the area of attachment for the powerful breast muscles. The sternum of the duck and goose does not present as large a keel as that of the fowl and pigeon, but owing to the greater breadth of the sternum and more solid construction the area for muscular attachment is as great. In the fowl two long slender lateral processes are formed on each side as a result of deep notches which extend anteriorly into the body of the sternum. The lateral external process is shorter than the lateral internal process and covers the last two ribs with a broadened terminal bony plate. The lateral borders of the body of the sternum support articular facets for the reception of the inferior ribs. The anterior border presents an eminence, the episternal process to which the furculum (wishbone) is attached by a ligament. The articular surfaces for the coracoids are located on each side of the episternal process on the anterior border.

Tlie internal surface of the sternum exhibits several openings through which air is passed to the interior of the bony structure.

Bones of the wing. These comprise the scapula, coracoid, and clavicle in the shoulder region ; the humerus in the arm ; the radius and ulna in the forearm ; two carpal bones, the radio-carpal bone and ulno-carpal bone; one carpo-metacarpal bone, and three digits the second of which has two phalanges.

The scapula is long, narrow, thin and curved like a sabre. It extends caudad over the ribs to near the pelvis. Anteriorly it is united with the coracoid with which it forms an articular cavity for the reception of the head of the humerus. The coracoid also articulates with the sternum by its ventral extremity. It is rod shaped and extends in a posterior direction obliquely ventrad from scapular to sternum. The coracoid at its ventral extremity presents an opening for the passage of air to the internal air space. The clavicle is attached to the coracoid at its superior end. It extends ventrad and caudad and curves in to the median line at the point of the sternum where the two clavicles unite in a flattened plate and become attached to the episternal process by a ligament. The united clavicles form a V or U shaped bone termed the fork or furculum. This bone represents an elastic spring and serves to prevent the wings from approaching each other during contraction of the depressor muscles.

The humerus is long in palmipeds and the gallinse, and short in the pigeon. It is stout, slightly curved and presents a pneumatic foramen near its articular head.

The ulna is much larger than the radius and is separated from it except at the extremities, where the two are united by ligamentous bands. The olecranon process of the ulna is only slightly developed.

The two carpal bones represent fusions in embryonic life, of the four bones of the proximal row. The distal carpal row of three bones fuse with the metacarpal bones.

Bones of the leg. These are the pelvic or hip bone; the femur or thigh bone; the patella, tibio-tarsus and fibula in the lower leg region ; a tarso-metatarsal bone, and four digits.

The pelvic bone is made up of three bones as in mammals, the ilium, ischium and pubis. It differs from the mammalian bone in that the pelvic girdle is not complete on the ventral floor, the two pubic bones failing to meet in the center to form the pubic symphysis. This arrangement facilitates the passing of the egg through the cavity. The ilium is the largest segment and extends along the vertebral column in the lumbar and sacral regions. It is consolidated with the last two thoracic vertebrae and the lumbar and sacral vertebrse, this extensive fusion giving the pelvis a rigidity which compensates for the lack of a pubic union. The ischium partly forms the side of the pelvic cavity. The pubis is mainly attached to the ischium along the lower border and bends inward to form the incomplete floor of the pelvic cavity. The ilium, ischium and pubis are united at the acetabulum or articular cavity for the reception of the head of the femur.

The femur articulates at its distal extremity with the patella, tibia and fibula. The latter bone is united to the tibia, but does not extend to its distal articulation. The tibia is comparatively long.

ANATOMY OF BIKDS 5

It has two articular surfaces on its distal extremity which articulate with the tarso-metatarsal bone. The tarsus is absent in birds. In males the tarso-metatarsus exhibits a slightly curved conical projection near the distal third for the support of the spur.

Four digits articulate with the distal extremity of the tarso-metatarsus. Three are directed radially cephalad. The internal digit has three phalanges; the middle, four and the external, five. The fourth digit is directed caudad and has two phalanges succeeding a rudimentary first metatarsal bone attached to the metatarsus by fibro-cartilaginous tissue. The distal bone of each digit is covered by a horny claw.

MUSCULAR SYSTEM

In general the muscles of birds correspond to those of mammals, with such modifications as are most suited to the mechanism of avian structure. The tendency, especially in turkeys and fowls, is toward extensive ossification of the muscle tendons. This is particularly noticeable in the tendons of the legs but may also be observed in the wing and neck in some cases. The fowl and turkey also present a marked contrast in the appearance of the muscles of the breast and wings as compared with those of the legs. The breast and wing muscles are white, due to the relatively small amount of sarcoplasm in the muscle fibers. The red muscles are rich' in sarcoplasm. White muscles are more powerful but have less endurance than red ones. Free flying birds have red pectoral or breast muscles.

The pectoral muscles are two in number, the superficial or great and the deep or small pectoral. The former depresses the wing and the latter elevates it. These muscles are very massive. The great pectoral muscle is attached to the clavicle, to the sternal crest near its border, to the posterior lateral process of the sternum and to the last ribs. It is inserted into the lateral tuberosity near the head of the humerus. It is this muscle that propels the bird in flight.

The small pectoral muscle originates from the portion of the ventral face of the sternum not occupied by the great pectoral and also from the clavicle and membrane between the latter and the sternum. Its tendon is inserted into the humerus opposite that of the great pectoral muscle after passing through the foramen trios^ seum which acts as a pulley. This foramen is formed by the union of the scapula, coracoid and furculum.

The diaphragm does not exhibit the muscular development of that of mammals. It is principally membranous with fine muscular bundles attached to the ribs. Two thin, delicate membranes compose the diaphragm and divide it into two planes, a pulmonary and a thoracic-abdominal plane. The former is spread over the inferior face of the lungs and is attached to the ribs on its border. It assists in respiration. The thoracic-abdominal plane has its origin on the dorsal spine in common with the pulmonary plane. It is convex anteriorly and extends to the sternum, dividing the body cavity into a thoracic and an abdominal cavity. It also assists in respiration and is particularly concerned with the abdominal air sacs.

The pectineus muscle assists in the mechanical flexion of the toes in the act of perching on the roost. It originates on a tuberosity of the hip bone in front of the acetabulum and is continued by a long thin tendon to a short distance distad from the head of the tibia where it joins the flexor perforatus of the three anterior digits.

CIRCULATORY SYSTEM

The heart of birds is cone shaped, short and wide in the ostrich, elongated and possessing a more acute apex in the common fowl. It is placed in the anterior extremity of the thoracic cavity. Three veins, two anterior venae cavse and one posterior vena cava, terminate in the sinus of the right auricle. A peculiarity of the heart of birds is the absence of a tricuspid valve at the right auriculo-ventricular opening. Instead, a strong muscular fold which becomes closely applied to the ventricular septum during systole prevents regurgitation of blood into the auricular cavity. Two pulmonary veins empty into the left auricle. The left auriculo-ventricular opening is provided with a bi-cuspid or mitral valve. The pulmonary artery and aorta each has a semilunar valve.

Arteries. The aorta gives off two innominate arteries, right and left brachio-cephalic, on leaving the heart and then passes over the right bronchus to become the descending or dorsal aorta. It continues along the spine, giving off numerous branches, to the coccygeal region where it separates into three terminal arteries.

The two carotids leave the innominate arteries and curve toward the ventral median line of the neck where they ascend in close proximity to each other to near the head. At the angle of the jaw each carotid divides into the external and internal carotid arteries. The arteries, especially those of the head and viscera, are distinguished by their frequent anastomoses. This is also true of the veins of birds.

Veins. The blood is returned to the heart by three trunks, the two anterior vense cavse and the posterior vena cava. The right jugular exceeds the left in size. The two communicate with each other by means of a cross branch at the base of the cranium.

Lymphatics. The lymphatics of birds do not form two strata, a superficial and a deep seated, as in mammals. The latter only is observed. Lymphatic glands are few. The most conspicuous are located at the base of the neck and in the anterior thoracic cavity. They are replaced by plexuses of IjTiiphatic vessels surrounding the principal blood vessels. From the aortic plexus arise tw^o thoracic duets which pass cephalad on the ventral surface of the lungs and terminate respectively in the jugular vein of the same side.

NOEMAL AVIAN BLOOD

In birds as in mammals the blood is composed of a straw colored fluid or plasma in which float several types of blood corpuscles. One important difference between avian and mammalian blood, excepting the camel, is the presence of nuclei in the red corpuscles of the former. The formed elements or corpuscles are divided into two main divisions, the red cells or erythrocytes and the white cells or leucocytes. These elements vary greatly in number in different birds, and even in the same bird at different ages. Each cubic millimeter of an adult fowl's blood contains approximately 3,250,000 red cells and 26,000 white cells, giving a percentage relation of 125 to 1. In certain pathologic conditions this relation is markedly changed, the red cells rapidly decreasing and the white cells increasing in numbers.

Red blood corpuscles or erythrocytes are straw colored, nucleated, oval, flattened discs, about 12 microns in length and 7.3 microns in width. The nuclei take a deep blue stain with methylene blue, or Giemsa. The surrounding protoplasm takes a light yellow with methylene blue and a pink color with Giemsa's stain.

White blood corpuscles or leucocytes are nucleated, colorless cells, rounded or irregular in form. They exhibit ameboid movement in the blood stream, some being more actively motile than others. The variations in their size, character of the nuclei, presence of granules and character of the inclosed granules dift'erentiate these cells into five varieties. These varieties with their percentage ratio are as follows :

Small mononuclear leucocytes (lyraphocytes) 40

Large mononuclear leucocytes 18

Polymorphonuclear leucocytes 35

Eosinophiles 4

Mast cells 3

Lymphocytes. In these blood cells the nucleus is rounded or oval and almost completely fills the cell. It stains a deep blue with Giemsa. The narrow band of cell body stains a lighter blue and is not readily differentiated from the nucleus by ordinary staining. The lymphocytes are from 5 to 7 microns in diameter.

Large mononuclears have a round or oval nucleus surrounded by a well defined border of cell protoplasm. The nucleus takes a deep blue stain, the cell body a pale blue. The cell diameter is 10 to 15 microns.

Polymorphonuclears have the appearance of having several nuclei held together by threads or nuclear bands. They contain considerable protoplasm inclosing rod shaped or rounded granules. The nucleus stains blue, the protoplasm, a lighter color and the granules violet or brownish red with Giemsa's stain. Diameter, 10 to 15 microns.

Eosinophiles have an irregular nucleus. The cell protoplasm is filled with rounded granules which stain a bright red with Giemsa's stain. The nucleus takes a blue stain and the cell body a pale blue. Diameter, 12 microns.

Mast cells have a lobulated nucleus which stains a deep blue. The cell protoplasm takes a pale stain. The granules are small and rounded and stain a dull violet with Giemsa and a deep blue with methylene blue. Diameter, 8 to 10 microns.

Other blood cells of less importance which may be observed are as follows :

Blood platelets are small colorless discs with granular centers. They are 3 to 4 microns in diameter and are usually found in small heaps of 6 to 8 cells.

Shadow cells contain a rounded or broad oval nucleus which takes a deep blue stain. The cell body is colorless and not well defined or irregular in outline. These apparently represent red blood corpuscles undergoing degeneration. The stroma of the corpuscle loses its pigment, becomes colorless and gradually disappears leaving the nucleus partially or wholly separated. They are especially numerous in pathologic blood.

Microblasts and macroblasts are found in the blood of voung fowls. These represent red corpuscles which are smaller and larger respectively than the average red corpuscle.

Myelogenous leucocytes appear frequently in young fowls. They are like mast cells except that their protoplasm is vacuolated.

NERVOUS SYSTEM

The nervous system of birds, with few exceptions, corresponds with that of mammals. However, there are several modifications which are of considerable interest. The cerebral hemispheres of the brain are well developed but have a smooth surface in contrast to the convoluted surface observed in the cerebrum of mammals. The cerebellum is conspicuous by the smallness of its lateral lobes. The optic lobes are placed in a lateral inferior position at the sides of the cerebellum. The large size of the optic chiasma and nerves indicates the paramount importance of the visual apparatus. The diameter of an optic nerve is equal to that of the spinal cord in its dorsal region. The olfactory lobes are relatively small. The hippocampi are absent in the cerebrum of birds. An important feature of the nervous system of birds is the absence of nervous tracts leading to the spinal cord from the cerebrum. The cerebrum does however exert an influence over the rest of the nervous system through its nervous tracts connecting it with the other divisions of the brain. The anatomical evidence of the absence of nervous tracts between the cerebral hemispheres and the spinal cord is supported bv the absence of any marked defects of movement succeeding the removal of the cerebrum. The fowl so treated, on recovery from the operation, is not sensitive to light or sound. It fails to pick up grains and must be fed. Movement is not interfered with as the bird constantly walks about aimlessly. Its avoidance of obstacles shows that it is giiided by some obscure means. Ability to perch and to maintain its balance is not lost. The weight of the brain of a medium sized fowl is ten grams.

The spinal cord of birds extends into the coccygeal vertebrae. It is cylindrical throughout its length except in the sacral and cervicodorsal regions where two expansions are noted. The dorsal columns of the cord diverge from each other in the sacrum to form the cavity kno^ni as the sinus rhomboidalis which represents a ventricular dilatation of the spinal canal. The brachial plexus is formed by the last cervical and first two dorsal spinal nerves in ducks and geese and by the last three cervical and first thoracic spinal nerves in fowls, turkeys and pigeons. It furnishes branches to the pectoral region and wing. The pelvic region and legs are supplied by the lumbosacral plexus which is formed by two lumbar and four sacral spinal nerves. The spinal nerves vary in number according to the number of vertebrse present in each species. They arise from the spinal cord by two roots. The anterior or ventral root is motory, the posterior or dorsal, sensory in function. The ganglia on the latter are proportionately large.

ALIMENTARY SYSTEM

The alimentary system of birds differs to a considerable degree from that of other animals. There is no provision for mastication of food in the mouth owing to the absence of teeth. The food is taken up by the beak and is immediately passed by the tongue into the pharynx. From there it enters the esophagus and is carried to the crop where it is stored, partially softened, and slowly passed on to the proventriculus or glandular stomach. The gall bladder is absent in the pigeon and ostrich and occasionally in the guinea fowl.

Mouth. The mouth is triangular in shape in such birds as the chicken, turkey, pigeon and canary. In the duck, goose and ostrich the mouth is comparatively long, with parallel borders and rounded anterior extremity. The roof of the mouth or hard palate is divided in the median line from near its anterior extremity to the pharynx, thus allowing free communication with the nasal passages. The soft palate observed in mammals is absent. The pharynx is relatively voluminous and permits the passage of large grains, or food masses. On its floor is the entrance to the larynx. The esophagus lacks the well developed muscular wall of mammals but relatively has a much greater diameter.

Crop. Gallinaceous birds possess a crop or ingluvies which represents a dilatation of the esophagus near its entrance to the thoracic cavity. Its wall, like that of the esophagus, consists of an outer membrane, a longitudinal muscular layer, a circular muscular layer, and an inner mucous membrane. Passage of its contents to the first stomach is aided by a wide circular muscle in the subcutaneous tissue surrounding the crop. Palmipeds, such as ducks and geese, are not provided with a distinct crop. Instead, the cervical portion of the esophagTis may become greatly distended in such a manner as to form a lone; fusiform reservoir.

Fig. 2. Diagrammatic representation of the principal internal organs of the fowl. 1, tongue; 2, pharynx; 3, upper portion of esophagus; 4, crop; 5, lower portion of esophagus ; G, proventriculus; 7, gizzard; 8, origin of duodenum ; 9, first branch of duodenum ; 10, second branch of duodenum; 11, origin of floating portion of small in- 29.. testine; 12, small intestine; 12', terminal portion of small intc'^tine; 13, free ends of ceca; 14, origin of ceca; 15, rectum; 16, cloaca; 17. vent; IS. mesentery; 19, left lobe of liver; 20, right lobe of liver; 21, gall bladder; 22, spleen; 23, pancreas; 24, lung; (Heart not shown but located approximately here) ; 25, ovary; 2(), o\iduct; 27, kidney; 28, ureter; 29, up])oi larynx; 30, trachea; 31, lower larynx or syrinx ; 32, bronchus; 33, cleft palate; 34, common ori- ¥• . fice of eustachian tubes. (Redrawn from Chauveau, with sliglit additions)

■/3.

In pigeons the crop is divided into two lateral pouches. In both male and female, marked changes take place in the mucous mem brane shortly before the young are hatched. The membrane becomes thickened, epithelial cells are rapidly proliferated, undergo fatty degeneration and lead to the formation of a milky fluid which accumulates in the depressions between the ridges of the mucosa. This fluid is used to feed the young during the first days of life.

A certain amount of fluid is secreted by the alveolar glands of the esophagus which together with the water consumed serves to soften grains to some extent and also to produce a slight fermentation of the crop contents. The crop has no secretory glands other than mucous glands. It is connected with the proventriculus or first stomach by a continuation of the esophagus which passes into the thoracic cavity and along the ventral face of the left lung.

Proventriculus. The proventriculus is small and fusiform in shape. Its walls are thick and contain numerous secretory glands which pour out gastric juice. The food is not held in the proventriculus to be digested but after becoming saturated with the gastric secretion is forced into the gizzard where it is triturated by the powerful muscles of this organ with the aid of pebbles picked up by the bird.

Gizzard. The gizzard or ventriculus bulbosus is a dense, muscular organ, flattened on two surfaces, with rounded border. Internally it is lined by a thick, tough, corrugated membrane which incloses a cavity of considerable volume, in which may be found food in various stages of disintegration and numerous pebbles, or bits of stone. Secretion of gastric juice also takes place in the gizzard according to Jobert. However, this organ acts principally in a mechanical way to grind the food and serves as a substitute for teeth. It is more highly developed in grain eating birds than in those subsisting principally on fish or animal food. In strictly carnivorous birds such as eagles, or hawks, the dense muscular wall is absent, or is limited to a portion of the organ, the remainder consisting of a membranous cul-de-sac. When reduced to a semi-fluid mass the food is released into the duodenum or first portion of the intestine, which joins the gizzard at a point near the entrance of the proventriculus.

Intestines. On leaving the gizzard the duodenum extends posteriorly, bends on itself and returns to near its origin. Between its two parallel branches rests the pancreas which gives off its secretion into the lumen of the duodenum near its termination.

The pancreatic juice acts on the starchy material while the secretion of the proventriculus acts on the proteins in the food. Succeeding the duodenum are, according to some writers, the other two divisions of the small intestine, the jejunum and ileum. These form several convolutions and are continued by the rectum to the cloaca.

At the point of juncture of the small intestine and rectum, in certain species of birds, are found two elongated diverticula leading from the intestine. These are the ceca or blind pouches. In grown fowls and turkeys they are from 4 to 7 inches in length and may be distended to a diameter of ^ to % of an inch. Especial importance is attached to them because of the fact that they are the seat of marked lesions in coccidiosis of chickens, and of turkeys, and in infectious entero-hepatitis of turkeys. In some species of wild birds, the ceca may reach a length of 10 inches while in others they are absent or merely rudimentary. Their function is apparently the retention of food material which has not been absorbed in passage through the small intestine.

The cloaca serves as a common cavity for the entrance of the intestine, ureters, oviduct in the female, and vasa deferentise in the male. It is divided into three parts. The rectum enters the first part, the ureters and genital canals open on the lateral faces of the second and the bursa of Fabricus, a blind sac or glandular cavity, opens on the dorsal wall of the third or outer division. The bursa of Fabricus may disappear in adults. The one oviduct in the female opens on the left side of the second division. The material from the intestine and ureters is held in the cloaca to form the characteristic droppings and is then passed out through the anus or vent.

Mucosa of the alimentary canal. The alimentary canal is lined internally by a mucous membrane which is thick, and composed of many layers of cells in the mouth, pharynx, esophagiis and crop. The mucosa is thin, and composed of one layer of columnar epithelial cells in the proventriculus, gizzard and intestine. In the gizzard the membrane is covered by a homy surface layer. In the submucous tissue of the mouth and pharynx are found several pairs of glands. These, however, are not considered as true salivary glands but produce a mucous secretion. The esophagus exhibits numerous alveolar secretory glands in the submucous tissue. The glandular stomach is conspicuous for the layer of tubular secretory glands which are set perpendicularly to the mucous membrane and which pour their secretion of gastric juice into the interior of the stomach. Over the mucous membrane of the gizzard is a tough horn-like covering formed by the hardening of the products secreted by the underlying simple glands.

The mucous membrane of the intestine presents innumerable cylindrical elevations known as villi. It is through these that the digested food is assimilated and carried by means of the chylevessels or lacteals to the portal vein and thence to the liver. !N^umerous goblet cells for the secretion of mucin are present in the villi.

Liver. This organ is dark brown in color and composed of a right and left lobe, the former being the larger. The right lobe has a gall bladder on its ventral surface, while the bile from the left lobe is poured directly into the duodenum through a separate bile duct, the hepatic or choledic duct, which empties a short distance behind the two pancreatic ducts. The cystic duct opens caudad of the hepatic duct and drains the gall bladder.

Pancreas. This organ is long, narrow and lobulated. In color it is pale red. It is highly developed in birds and occupies the space between the two branches of the duodenum. Two or sometimes three ducts carry its secretion into the ascending arm of the duodenum near its extremity and just anterior to the hepatic duct.

RESPIRATORY SYSTEM

The organs of respiration in birds differ markedly from those of mammals. They resemble more nearly the reptilian type of formation.

Air passages. The nostrils are represented by two narrow openings at the base of the upper mandible of the beak. The nasal chambers are short and narrow and are separated by a septum which is partly bony and partly cartilaginous. The turbinated bones of mammals are represented by three cartilaginous structures. The nasal cavities open into the mouth by a common, elongated slit in the median line of the hard palate. Cavities known as the suborbital or infraorbital sinuses occupy a position on either side of the head. They commiinicate with the nasal cavity by narrow passages which extend from a comparatively low level in the sinus, upward into the nasal cavity. The arrangement prevents natural drainage of the sinuses.