Disorders of the neuromuscular system of ratite species are fairly commonly encountered. These may manifest themselves as primary neurologic disorders (ataxia, locomotor problems, blindness, seizures, encephalitis), primary musculo-skeletal disorders (angular limb deformities, myositis, slipped tendons), secondary neuromuscular disease signs, or mysterious and vague combinations of these groups. This paper will outline and describe those diseases that are presently known to involve these systems, their clinical signs, diagnosis and treatments.

General Information

Ratite birds are a loose group of birds that share the common characteristics of being large, flightless and ground dwelling birds. These birds have a sternum that lacks a keel and is flat. All ratite birds originate from the southern hemisphere, all can swim, and males all have a protrusible phallus. Ratite birds include the ostrich, emu, rhea cassowary and kiwi.

Pertinent Anatomy

Integument

Anatomy of the ingegumentary system of these birds is included in this discussion, as the integument can most definitely influence the musculoskeletal system in its function. The skin of these birds is relatively thick along the legs and body, but comparatively thin along the neck. Ostrich, emu and rheas have sternal callosities, the cassowary does not. The plantar metatarsal pad at the proximal end of the metatarsal bone is covered with a callosity in the ostrich only. The ostrich also has a callosity distal to the point of the pubic bone, which is not present in the rhea, emu or cassowary. All ratites have digital cushions similar to that of the horse, although the ostrich digital cushion is contiguous along the plantar aspect of the weight bearing digit, and the other ratites have cushions only underneath the joints. Ratite skin has no sweat glands.

The large ostrich toenail is typically blunted, whereas the emu, rhea and cassowary have pointed nails. The medial digit (P2) of the cassowary has a large spike shaped nail that can be used for fighting. The tip of the alula has become cornified to form a hook in the ostrich and rhea, wheras the distal phalanx of the emu and cassowary has become cornified to form a hook. The head of the cassowary is covered with a bony, horn covered casque which grows continuously throughout life. This casque is absent at hatching.

The ostrich thigh and flank is devoid of feathers, and the rhea is similar in appearance in the thigh, but the flank is fully feathered. Emu and cassowary feathers have a double rachis, and rhea and ostrich feathers are single-shafted. All feathers are limited to pterylae in ratite species, as is seen in other birds. Apteria are present along the lateral body wall of the ostrich and the rhea, but these areas are fully feathered in the emu and cassowary. Ostrich, emu and rhea feathers lack barbiceli, making their feathers appear more hair-like and less water resistant than other birds. The primary remiges of the cassowary lack barbs, and almost appear thorn-like.

Musculoskeletal system

All ratites have a raft-like sternum, with no keel bone. The thoracic girdle of the ostrich consists of a fused scapula, coracoid and clavicle attached to the cranial sternum. Ostrich and rheas have large wings; emus and cassowaries have rudimentary wings. In the kiwi and cassowary, the alular digit has only one phalanx, possibly the primordial third, unlike most other avian species which has two phalanges. The pelvic girdle consists of ilia that form an inverted osseous shield over the top of the fused synsacral vertebrae. In the ostrich, the ischial and pubic bones project caudally to fuse and then turn ventrally and cranially to form a pubic symphysis. In the other ratite species, the ischial and pubic bones are separate and there is no pubic symphysis. The patella is absent in ratites. The ostrich may have a small bone in the tendon of insertion of the muscle on the cnemial crest of the tibiotarsus. In the ostrich and emu, one of the tarsal bones remains unfused to the contiguous bones and its location gives the radiographic appearance of a patella. The only pneumatized long bone in the ostrich and emu is the femur.

The rhea, emu and cassowary have three toes (digits 2,3 and 4). The ostrich has only two toes (digits 3 and 4). The third digit of the ostrich is the large toe. There are four phalanges in each ratite digit, as opposed to most other birds which have only three. The metatarsal-phalangeal joint is suspended so that the standing weight of these birds is born entirely by the digits.

The ventral abdominal midline consists of the aponeuroses of the abdominal muscle. There is no muscle for 19 cm on either side of the side of the linea alba in the rhea and emu, extending 13 cm caudally from the sternum. Muscle fibers are found only dorsally, and the ventral abdomen is supported by a tunic. A surgical incision made along the midline penetrates the skin, a minimal amount of subcutaneous fat, fibrous abdominal tunic, retroperitoneal fat and parietal peritoneum.

Organs of Special Sense

Ratites have excellent vision. The ostrich has the largest vertebrate eye (about 50 mm) relative to body size. Hearing is also acute. The external ear orifice is located caudal to the eye. Kiwis locate food by a particularly acute sense of olfaction. Their nostrils are located at the rostral end of their elongated beaks. Cataracts have been reported in the ostrich, and surgical removal is possible.

Nervous system

The olfactory bulbs reach their largest relative size in the kiwi brain. Ratites are not noted for their intelligence. Although the ostrich can lie in sternal recumbency for days, lateral recumbency for one hour may result in peroneal nerve paralysis, and this should be a significant concern with anesthetic procedures and positioning.

Nutrition

Numerous pelletized diets are currently available for ratite species. Most of these products are quite variable in price, content and quality, and very few fomulated diets are actually supported by scientific trials and clinical evaluation methods. Range raised ostriches in Africa are fed on alfalfa pastures and supplemented with maize. General targets of 16-20% protein, 10% fat, 10% fiber are believed to be good starting points for most captive ratite species. Diets of 18% protein produced the best weight gains in one study of ostrich chicks that compared only the effects of varying the dietary levels of protein.

In adult bird nutrition, the adequacy of the breeder diet is believed to be reflected in the eggs produced. Generally speaking, hens deficient in carbohydrates, proteins and fats produce fewer and smaller eggs. Vitamin and mineral deficient breeder diets can result in similar nutrient deficient eggs.

The feeding of higher protein diets to young birds is expected to induced accelerated rates of growth and potentially predispose to some leg deformities. Hypovitaminosis A was described in rhea chicks with clinical epiphora, oral abscesses and decreased growth rates. A goose stepping gait was believed to have been corrected with supplemental vitamin B6. Thiamine deficiencies are thought to produce "star gazing" in ostriches. Riboflavin is possibly incriminated in the curled toe deformities of ostriches. Pantothenic acid and biotin are associated with curling of the feathers and hyperkeratosis of the skin around the mouth, beak, feet and neck. Hypovitaminosis E was suspected in a group of ostrich chicks fed a diet of crushed corn. Clinical signs were characterized by paresis, poor weight gains, high AST and CPK levels.

Metabolizable energy values (ME) for 3,6,10 and 17 week old and 30 month old ostriches was determined, and fat and neutral detergent fiber (NDF) digestibilities were also determined. The determined levels of ME were: 3 weeks, 1731; 6 weeks, 2337; 10 weeks, 2684; 17 weeks, 2739, and 30 months, 2801 kcal/kg. Fat digestibility was 44.1% at 3 weeks and 91.1% by 17 weeks of age. NDF digestibility was 6.5% at 3 weeks, 51% at 10 weeks and 61.6% at 30 months. Also, vitamin and mineral levels were determined in the eggs of ostriches and emus and compared to poultry values. Deficiencies or excesses of vitamins and/or minerals in the laying hen, and thus in the egg can lead to infertility, poor hatchability and early chick health problems.

The emu was found to have digested 35-45% of the neutral deterget fiber (NDF) in their diet when fed a high fiber diet (26-36%) and that the energy from the digestion of NDF contributed up to 50% of the maintenance requirements. When compared to similar data of the ostrich above, the emu is clearly less efficient at NDF digestion than the emu.

NetPets® Main Page

contact information Healthspa

The Bird Center