The musculoskeletal system consists of bones, cartilage, muscles, ligaments, and tendons. Primary functions of the musculoskeletal system include support of the body, provision of motion, and protection of vital organs. The skeletal system serves as the main storage system for calcium and phosphorus and contains critical components of the hematopoietic system. Many other body systems, including the nervous, vascular, and integumentary systems, are interrelated, and disorders of any one of these systems may also affect the musculoskeletal system and complicate diagnosis.
Congenital and inherited anomalies can result in the birth of diseased or deformed neonates. Congenital disorders can be due to viral infections of the fetus or to ingestion of toxic plants by the dam at certain stages of gestation. The musculoskeletal system can also be affected by certain congenital neurologic disorders.
The principal causes of osteodystrophies are deficiencies or imbalances of dietary calcium, phosphorus, and vitamin D, as well as dysregulation of parathyroid hormone (PTH) activity. Their interrelationships are complex and not easily defined.
Sarcocystosis is an intracellular protozoan infection that is generally asymptomatic but can cause mild gastrointestinal signs, including diarrhea, in cattle, sheep, pigs, horses, dogs, cats, and people. Typical control strategies are to prevent ingestion of prey or raw tissues and to reduce contamination of grass and water with feces of intermediate hosts.
Bursitis is an inflammatory reaction within a bursa. The causes can range from overuse, mild trauma, or severe trauma to sepsis. Bursitis in its various forms is more common and a more important cause of dysfunction in horses than in other species. It can be classified as true bursitis or acquired bursitis. True bursitis is inflammation in a normal bursa that is naturally present. Some examples are trochanteric bursitis, supraspinous bursitis ( fistulous withers), and bicipital bursitis. Acquired bursitis is development of a subcutaneous bursa where one was not previously present and inflammation of that bursa. Examples of acquired bursitis include capped elbow over the olecranon, and capped hock over the tuber calcaneus (when a natural bursa was not present). Accumulation of fluid in acquired bursitis is termed hygroma.
The lesions that cause lameness in dairy cows result in intense pain and are a major animal welfare issue. Lameness also causes stress, which debilitates and reduces productivity. The financial impact of lameness includes losses from decreased production, cost of treatment, prolonged calving interval, and possibly nursing labor. Loss of milk of 1.7–3 L/day for up to 1 mo before and 1 mo after treatment (because of pain) plus milk discarded because of antibiotic therapy must also be considered. Lame cows are more reluctant to use automatic milking systems and show visible signs of stress when forced to do so.
Abnormal gait in goats is a nonspecific sign common to many diseases and conditions. A thorough history is important for diagnosis and should include incidence and duration in the individual or herd, nutrition, feed changes, method of rearing, and recent introductions to the herd. (Also All.see chapter Preventative Health Care and Husbandry of Goats.)
Lameness is defined as an abnormal stance or gait caused by either a structural or a functional disorder of the locomotor system. The horse is either unwilling or unable to stand or move normally. Lameness is the most common cause of loss of use in horses. It can be caused by trauma, congenital or acquired disorders, infection, metabolic disorders, or nervous and circulatory system disease.
Lameness has been an issue in swine production for many years and continues to be a problem worldwide. Although lameness can be caused by congenital or developmental abnormalities, most lameness in production animals is caused by pain associated with infections, trauma-related injuries, or underlying metabolic diseases. As such, it has become an area of focus for swine farm audits of animal well-being. It is also an economic issue, because an increasing prevalence or incidence of lameness in a herd is likely to affect viability, growth, or reproduction of pigs. Pig flow may be affected if farrowing targets are not met because of high rates of breeding stock removal or if growth of grower/finisher pigs is slowed by high lameness incidence. As with diseases of other body systems, lameness problems in a swine herd require a comprehensive approach if a diagnosis (or diagnoses) is to be reached so that preventive or curative measures can be instituted.
Lameness in sheep is often due to injuries. Limb fractures are common in young lambs, which are frequently injured inadvertently by adults. Usually, limb splints and casts may be used for stabilization of injuries, with fractures healing within 3–6 weeks. However, leaving the limb immobilized and unobserved for too long may also lead to iatrogenic lameness. The general principles of treatment and prevention of musculoskeletal injuries are the same as in other species.
Muscle disorders in horses are associated with a variety of clinical signs ranging from muscle stiffness and pain to muscle atrophy, weakness, exercise intolerance, and muscle fasciculations. The most common clinical signs are muscle pain, stiffness, and reluctance to move due to rhabdomyolysis. Rhabdomyolysis (ie, disruption of striated skeletal muscle) can broadly be grouped into causes associated with exercise (exertional rhabdomyolysis) and causes unrelated to exercise.
Bovine secondary recumbency is defined as the inability of cattle to rise and stand for a period of at least 12–24 hours, resulting from the delayed or unsuccessful treatment of a different primary cause of recumbency. "Downer cow syndrome" is a colloquial term that more broadly refers to the inability of cattle to rise and stand for a period of at least 12–24 hours for undetermined reason. Treatment is guided by the cause; supportive care is of major importance to improving the prognosis. Animal welfare considerations are paramount in guiding the overall management of affected cows.
Clinical signs of musculoskeletal disorders include weakness, lameness, limb swelling, and joint dysfunction. Motor or sensory neurologic impairment may develop secondary to neuromuscular lesions. Abnormalities of the musculoskeletal system may also affect other organs of the endocrine, urinary, digestive, hemolymphatic, and cardiopulmonary systems.
Many arthropathies are developmental, including aseptic necrosis of the femoral head, patellar luxation, osteochondrosis, elbow dysplasia, and hip dysplasia. Other arthropathies are degenerative, infectious or septic, immune-mediated, neoplastic, or traumatic.