A congenital abnormality is an abnormality present at birth. While some diseases are immediately apparent after parturition, others may not be clinically apparent until the animal goes through a period of growth or may even not become obvious until maturity. Those diseases affecting the musculoskeletal system are referred to as developmental orthopedic diseases and are likely multifactorial—a combination of inherited and genetic factors, as well as postpartum factors such as nutrition.
Flexural Limb Deformities in Large Animals
Flexural limb deformities are probably the most prevalent abnormality of foals and calves. The majority occur in the sagittal plane and primarily affect the soft tissues (tendons, ligaments), resulting in joint hyperflexion or hyperextension.
Persistent hyperflexion is often referred to as "contracted tendons." However, the pathology is rarely of the tendons themselves; rather, the tendon unit is too functionally short for the correct joint orientation.
Flexural limb deformities have a complex pathogenesis, with possible congenital contributing factors including the following:
in utero exposure to teratogenic or infectious agents
in utero malpositioning
goiter
neuromuscular disorders
genetics
Severe joint hyperflexion can occur with uterine malpositioning, which may cause dystocia in the mare.
Severe joint hyperflexion can also result in rupture of the common digital extensor tendon. (See ruptured tendon image.)
Courtesy of Dr. Reid Hanson.
Joint hyperextension is common and usually mild, a result of flaccidity of the flexor muscles. The problem usually corrects as the neonate grows in strength and size; however, if there is abnormal weight-bearing, skin can become traumatized.
Light bandaging and farriery (glue-on shoes with palmar/plantar extensions) are indicated in more severe cases. Prolonged periods of heavy bandaging or the use of splints and casts are contraindicated because they can worsen the situation. Complications of bandaging can range from sores and abrasions to neurovascular compromise and subsequent tissue necrosis.
Joint hyperflexion can be an indication of abnormal osseous changes within a joint. In particular, carpal/tarsal hyperflexion in a neonate can indicate incomplete ossification of the small cuboidal bones (see cuboidal bone hypoplasia radiograph). Radiographic examination is therefore indicated in these cases.
Courtesy of Dr. Robert Cole.
Treatment and prognosis depend on the severity of the joint contracture; neonates born with contracted carpi that cannot be manually straightened have a poor prognosis.
Mild cases can be treated with controlled exercise, analgesics, and oxytetracycline (44–70 mg/kg, IV slowly, diluted in 250–500 mL of saline [0.9% NaCl] solution, every 24 hours for 2–3 days). Oxytetracycline exhibits a dose- and age-dependent inhibition of collagen contraction and matrix-metalloproteinase 1 mRNA expression, preventing myofibroblasts from shortening collagen fibrils. Efficacy decreases as foals mature. At this dose, a risk for induced renal failure exists; therefore, biochemical monitoring and hydration maintenance is critical.
Moderate to severe cases of joint hyperflexion should be managed by splinting or casting, frequent manual extension of joints, and possible surgical intervention. Toe extensions are not indicated in severe cases because pressure on the toe can lead to dorsal hoof wall separation.
Angular Limb Deformities in Large Animals
Angular limb deformity is relatively common in young animals, particularly fast-growing breeds.
A conformational deviation of one or more limbs in the frontal plane results in valgus (lateral deviation) or varus (medial deviation), from uneven growth at the epiphysis or diaphysis of long bones, abnormal development of the small cuboidal bones of the carpus or tarsus, or laxity of the supporting ligamentous structures.
Pearls & Pitfalls
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Angular limb deformities occur regularly in horses, cattle, sheep, goats, llamas, alpacas, and deer (see carpal valgus photograph).
Courtesy of Dr. Reid Hanson.
Incomplete cuboidal bone ossification is most commonly reported in horses and occurs in premature animals or those with abnormal uterine position, placentitis, placental insufficiency, severe maternal malnutrition, heavy parasitic infection, chemical insults, thyroid insufficiency, or a systemically ill dam (colic, shock).
Foals with incompletely ossified bones may develop permanent conformational defects due to compression and crushing of bones; however, treatment is usually attempted because even foals without radiographic evidence of ossification can have good outcomes. Treatment consists of rest with or without splinting or casting of the limb.
Similarly, angular limb deformity due to congenital ligamentous laxity commonly occurs in young animals, usually in several joints or regions, and results in rotational as well as frontal limb deformities. It may be due to prematurity, hormonal imbalances or intrauterine malpositioning. If the limb can be manually straightened on palpation, the angular limb deformity is due to ligamentous laxity; if it cannot be straightened, the deformity is due to an osseous abnormality. Radiographs should be obtained for treatment planning.
Uneven physeal growth is generally considered a developmental orthopedic condition (ie, acquired, not congenital); however, a genetic predisposition likely exists. Physeal lesions are occasionally present at birth but usually occur secondary to trauma or as a manifestation of osteochondrosis as the animal grows. Horses, cattle, sheep, and goats, especially those fed a high-energy ration, can be affected. In sheep, this is often referred to as "bent leg" or "bowie."
Angular limb deformity resulting from uneven physeal growth can be diagnosed with a conformation examination and radiographic evaluation. Treatment consists of rest or surgical manipulation of physeal growth, either by accelerating growth or retarding it. Surgical procedures to manipulate physeal growth include the following:
Hemicircumferential periosteal transection and elevation is the only growth acceleration procedure and may work by reducing static compression of the physis, allowing cell growth acceleration, or by influencing the pace of chondrocyte proliferation via a signaling loop involving parathyroid hormone–related peptide (PTHrP) and other factors.
Transphyseal bridging, which retards growth of the physis, is more common and involves static compression of the physis by a surgical implant (transphyseal screw, screw and wire, or bone plate). The implant must be removed when limb deviation is corrected. The prognosis for athletic soundness depends on the degree of deformation but is generally good.
Uneven diaphyseal growth is less common but usually results in more serious deformation. Surgical correction is by corrective osteotomy. The prognosis is usually guarded to fair.
Skeletal Dysplasias in Large Animals
Skeletal dysplasias, disorders consequential to abnormal development of the skeleton, primarily result from genetic abnormalities. The complex processes involved in bone formation and remodeling are controlled by multiple genes, and mutation or deficiency in any one of these genes can result in disease.
In addition to genetic abnormalities, dysplasias can result from exposure to toxins or infectious agents in utero or from mineral deficiency in the dam.
Generalized Skeletal Dysplasias
Most generalized skeletal dysplasias are lethal or semilethal and are associated with short stature, bones of abnormal shape or length, and increased bone fragility. (See the table Generalized Skeletal Dysplasias Affecting Large Animals.
Further details on species-specific disorders are provided in species-specific chapters; conditions affecting multiple species are detailed in the text.)
Generalized Skeletal Dysplasias Affecting Large Animals
Dysplasia | Nature of the Disorder | Large Animal Species Affected |
|---|---|---|
Chondrodysplasia | A genetic defect compromises the ability to undergo endochondral ossification; thus the ability to form cartilage and bone from cartilage is lost. | Horses, cattle, sheep, pigs |
Osteogenesis imperfecta | A defect in type 1 collagen formation in bone results in osteopenia and excessive bone fragility, with multiple intrauterine fractures, skeletal deformity, fetal death, fragile teeth, joint laxity, and blue sclera. | Cattle, sheep |
Osteopetrosis | A primarily genetic inherited disorder causes a defect in osteoclastic bone resorption, resulting in accumulation of primary spongiosa within the medullary cavities and overall systemic increase in skeletal mass. | Cattle, horses, deer |
Disproportionate dwarfism | An inherited, genetic disorder results from disrupted signaling pathways or structural disruptions. Physical characteristics are breed-specific. | Cattle, horses, sheep, goats |
Chondrodysplasia
Chondrodysplasia is disordered cartilage development. The underlying defect affects cartilage formation, resulting in defects of all bones formed by endochondral ossification.
Chondrodysplasia is considered somewhat different from osteochondrosis. Osteochondrosis is a common and important disease of all large animal species. In this disorder, a disturbance in endochondral ossification occurs, resulting in the cartilage separating from the underlying epiphyseal bone. Osteochondrosis is considered a developmental disease and is discussed elsewhere; see Osteochondrosis in Horses.
Osteogenesis Imperfecta
Osteogenesis imperfecta is a generalized, inherited bone defect in cattle and sheep, characterized by extreme fragility of bones and joint laxity attributable to any of a large number of possible mutations of type I collagen.
Although bones are essentially normal in shape, they are very brittle and break with little effort. The long bones are slender and have thin cortices. Calluses and recent fractures may be present—eg, within the ribs, indicating multiple intrauterine fractures. The sclera may be bluish. Inheritance is most likely polygenic.
Osteopetrosis
Osteopetrosis is a rare metabolic bone disease characterized by a systemic increase in skeletal mass. It appears to be inherited as a simple autosomal recessive trait in Angus, Simmental, Dutch Holstein-Friesian, and Hereford cattle. It also occurs in horses and deer.
Osteopetrosis is characterized by the following:
premature stillbirth 10 days to 1 month before term
brachygnathia inferior
impacted molar teeth
easily fractured long bones
Bone marrow cavities are absent and replaced by primary spongiosa in osteopetrosis. The fetal-like abnormal intramedullary bone consists of chondro-osseous tissue. Foramina of the skull and long bones are hypoplastic or aplastic. The cranium is thickened and compresses the brain. Extensive mineralization is present in vessel walls and neurons in the brain.
Diagnosis is confirmed by a longitudinal bisection of long bones, revealing the diaphyses filled with a plug of bone instead of marrow.
Dwarfism
Dwarfism is an impairment of bone growth, usually inherited. It can be categorized as proportionate (overall size decrease without changes in body proportions) or disproportionate (decrease in the size of one or several body parts such that body proportions are altered).
Dwarfism due to chondrodysplasia is somewhat common and usually disproportionate. In contrast, dwarfism due to congenital growth hormone deficiency is rare and usually proportionate.
Localized Skeletal Dysplasias
Some skeletal dysplasias are localized to a particular region of the appendicular or axial skeleton, and morbidity is dependent on the location and extent of disease (see the table Localized Skeletal Dysplasias Affecting Large Animals).
Localized Skeletal Dysplasias Affecting Large Animals
Dysplasia Name | Region Affected | Nature of the Disorder | Species Affected |
|---|---|---|---|
Syndactyly | Digit | Partial or complete fusion of functional digits | Cattle, sheep, pigs |
Polydactyly | Digit | Increase in the number of digits | Cattle, sheep, pigs, horses |
Hemimelia | Limb | Partial or complete absence of one or more bones in a limb | Cattle, goats, sheep |
Brachygnathia inferior | Mandible | Shortening of the mandible | Horses, cattle, sheep, pigs |
Brachygnathia superior | Maxilla | Shortening of the maxilla | Horses, cattle, sheep, pigs |
Spina bifida | Spine | Defective closure of the dorsal vertebral laminae in a segment of the vertebral column (usually lumbosacral) | Cattle, sheep, pigs, horses |
Perosomus elumbis | Spine | Agenesis of the lumbar, sacral, or coccygeal spinal cord and vertebrae | Cattle, sheep, pigs |
Block vertebrae | Spine | Complete or partial fusion of adjacent vertebrae | Cattle, sheep, pigs, horses |
Butterfly vertebrae | Spine | Presence of a dorsoventral sagittal cleft in a vertebral body | Cattle, sheep, pigs, horses |
Hemivertebrae | Spine | Inappropriate fusion of somites with resulting lack of formation of one half of a vertebral body | Cattle, sheep, pigs, horses |
Complex vertebral malformation | Spine | Shortening of the cervical and thoracic vertebral column due to multiple hemivertebrae or misshapen vertebrae | Cattle |
Cervical vertebral stenotic myelopathy | Spine | Compression or stretching of the spinal cord due to narrowing of the vertebral column | Horses |
Brachyspina (“short spine lethal”) | Spine | Shortening of the entire spinal column | Cattle |
Atlanto-occipital fusion | Spine | Failure of the atlas to separate from the occipital bone | Cattle, sheep, pigs, horses |
Kyphosis | Spine | Dorsal arching of the spine | Cattle, sheep, pigs, horses |
Lordosis | Spine | Ventral arching of the spine | Cattle, sheep, pigs, horses |
Scoliosis | Spine | Lateral arching of the spine | Cattle, sheep, pigs, horses |
Torticollis | Spine | Twisting of the spinal column | Cattle, sheep, pigs, horses |
Syndactyly
Syndactyly, or mule foot, is partial or complete fusion of the digits of one or more feet. Syndactyly may be subclassified according to the type and extent of fusion, such as affecting only the skin and soft tissues (simple syndactyly) or the bony structures as well (complex syndactyly).
Reported in numerous cattle, sheep, and pig breeds, it is most prevalent in Holstein cattle and is inherited as a simple autosomal recessive condition.
The forefeet are affected most often, but one or all four feet may be affected. Animals with syndactyly walk slowly, usually have a high-stepping gait, and may be more prone to hyperthermia.
Polydactyly
Polydactyly is a genetic defect of cattle, sheep, pigs, and occasionally horses.
In its most common form, the second digit is developed, but the medial dewclaw is missing. The toes may be fused to give rise to polysyndactyly. Polydactyly rarely affects just one limb or all four limbs. The condition is more commonly seen in multiple, but not all, limbs.
Polydactyly in cattle appears to be polygenic, with a dominant gene at one locus and a homozygous recessive at another. (See radiograph of polydactyly in a calf.)
Courtesy of Dr. Robert Cole.
Perosomus Elumbis
Perosomus elumbis is an occasionally found congenital anomaly of unknown etiology characterized by partial or complete agenesis of lumbar, sacral, and coccygeal vertebrae. It is accompanied by posterior bimelic (affecting bilateral limbs) arthrogryposis, characterized by ankylosis of joints with associated muscular malformations.
Affected calves cannot use their hindlimbs and must be euthanized. The condition has also been reported in sheep and pigs.
The defect is suspected to be inherited.
A decreased number of vertebrae also has been reported rarely but is believed to be a genetic defect.
Lysosomal Storage Diseases Affecting the Skeleton in Large Animals
A large group of inherited/genetic diseases results from the deficiencies of specific lysosomal enzymes, culminating in the accumulation of substrates within cells, particularly partially catabolized glycosaminoglycans.
GM1 gangliosidosis occurs in cattle and sheep and is due to a deficiency of enzyme beta-galactosidase. Skeletal lesions may include proportionate dwarfism, irregular intervertebral spaces, and degenerative changes of the articular cartilage.
Congenital erythropoietic porphyria is an inherited condition in cattle, sheep, and pigs that results in abnormal porphyrin metabolism. Porphyrins are organic compounds that include heme, a precursor to hemoglobin, which is essential for oxygen transport in the blood.
A genetic mutation preventing porphyrin metabolism leads to accumulation of porphyrins in the blood, resulting in red-brown discoloration of teeth, bones, and urine, and within other tissues. Excess porphyrin in the skin results in dermatitis after sunlight exposure.
Congenital and Inherited Disorders of Muscle in Large Animals
Several inherited disorders affect skeletal muscle in animals, including defects of skeletal muscle, inherited and congenital myopathies, myotonia, metabolic myopathies, malignant hyperthermia, and disorders resulting in abnormal development of lower motor neurons (see the table Muscular Disorders Affecting Large Animals).
Further details on species-specific disorders are provided in the species-specific chapters; conditions affecting multiple species are detailed in the text.
Muscular Disorders Affecting Large Animals
Disorder Type | Definition | Examples | Species Affected |
|---|---|---|---|
Muscular defects | Defects in the formation and disposition of muscle not associated with a lesion in neuronal tissue | Myofibrillar hypoplasia (splay leg) | Pigs |
Muscular hyperplasia (double muscling) | Cattle, sheep | ||
Muscular steatosis | Cattle, sheep, pigs | ||
Inherited and congenital myopathies | Genetic muscle disorders that are present at birth, although onset may be delayed | Myopathy of the diaphragmatic muscle | Cattle |
Muscular dystrophy of Merino sheep | Sheep | ||
Myotonia | Temporary inability of skeletal muscle fibers to relax, resulting in muscle tension | Myotonia of the goat (“fainting goats”) | Goats |
Hyperkalemic periodic paralysis | Horses | ||
Myotonic dystrophy-like disorder | Horses | ||
Spastic paresis of cattle | Cattle | ||
Metabolic myopathies | Abnormal skeletal metabolism leading to neuromuscular dysfunction | Equine polysaccharide storage myopathy | Horses |
Glycogen branching enzyme deficiency | Horses | ||
Myophosphorylase deficiency (glycogen storage disease) | Horses, cattle, sheep | ||
Malignant hyperthermia | Results in sudden increase in myoplasmic calcium concentration, prolonged contraction, and life-threatening hyperthermia | Malignant hyperthermia (porcine stress syndrome) | Pigs |
Malignant hyperthermia-like syndrome | Anesthetized horses | ||
Primary CNS conditions | Neuroectodermal defect leading to denervation of muscle | Arthrogryposis | Horses, cattle, sheep, pigs |
A muscular dystrophy is "an inherited progressive myopathy characterized histologically by ongoing muscle fiber degeneration and regeneration" (1). While some myopathies of large animals have similar features, they cannot be classified as dystrophies. For example, a myopathy of Merino sheep is often referred to as a muscular dystrophy; however, ongoing fiber degeneration and regeneration is not a hallmark figure of this disease. Instead, there is progressive atrophy of muscle fibers and replacement with adipose cells.
Muscular defects in large animal species include myofibrillar hypoplasia, muscular hyperplasia ("double muscling"), and muscular steatosis.
Muscular steatosis, a condition in which muscle fibers are replaced by fatty deposits, occurs occasionally in cattle, sheep, and pigs at slaughter. Sometimes muscular steatosis is indicated before slaughter by an abnormal gait, but usually the condition is not found until carcass inspection.
The condition may be difficult to establish; often, only the restriction of muscular steatosis to a single muscle group in an otherwise poorly marbled carcass makes it conspicuous.
In pigs, there is evidence that the onset of muscular steatosis is accompanied by lipid accumulation in muscle fibers.
No clinical signs of disease occur, and the cause is unknown.
Gross lesions are symmetric, pale areas in affected muscles, especially of the back, neck, and upper limbs. Microscopically, many muscle fibers are replaced by fat cells.
Arthrogryposis is caused by abnormal development or structure of skeletal muscle resulting from lack of stimulation by an abnormal lower motor neuron. An underlying neuroectodermal defect causing denervation of the corresponding muscle results in one or more limbs being severely rotated or curled back or forth, with or without curvature of the thoracolumbar spine (scoliosis or kyphosis) or neck (torticollis).
Affected animals are usually born dead, and the rigidity of affected limbs frequently results in dystocia.
Arthrogryposis may be genetic or due to the dam's exposure to viruses or toxins.
Arthrogryposis occurs with some frequency in horses, cattle, sheep, and pigs.
Myophosphorylase deficiency, or glycogen storage disease (GSD), occurs in horses, cattle, and sheep. This disease is the result of defects in the processing of glycogen synthesis or breakdown within muscle, liver, and other cell types.
GSD may be genetic or acquired. Genetic GSD is caused by any inborn error of metabolism (genetically defective enzymes) involved in these processes.
In production animals, acquired GSD is caused by intoxication with the alkaloid castanospermine. Castanospermine inhibits enzymes involved in glycogen metabolism, leading to abnormal glycogen accumulation in tissues. Animals can be exposed through ingesting certain leguminous plants. In some cases, seeds and plant debris can spread to previously safe grazing lands through water runoff, flooding, or soil movement. If plant material from castanospermine-containing species is harvested along with forage crops, it can become part of hay, silage, or grain mixtures. This is more likely if toxic plants grow in mixed pastures or if improperly sourced feed is used. Exposure typically occurs from contaminated pastures or feedstuffs containing these plants or their seeds.
Progressive muscular weakness and inability to rise properly may be evident in animals with GSD.
Of 11 types of glycogen storage diseases characterized in humans, 5 (types I, II, III, VII, and VIII) have been identified in animals. Type II glycogenosis in Shorthorn and Brahman cattle has been well documented and is inherited as an autosomal recessive disorder.
Affected cattle develop muscular weakness and die at 9–16 months old, often with accompanying cardiomegaly and congestive heart failure. Morphological and biochemical studies have revealed extensive intraliposomal and cytoplasmic glycogen deposits.
Corriedale sheep also develop type II glycogenosis.
Myophosphorylase deficiency (type V glycogenosis) is an autosomal recessive disorder in Charolais cattle. Affected cattle show exercise intolerance and may have increased serum activities of skeletal muscle–origin enzymes. Elevated AST, CPK, and LDH enzymes suggest muscle damage due to the metabolic dysfunction caused by glycogen storage and utilization defects.
References
Cooper BJ, Valentine BA. Muscle and tendon. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals. Vol. 1. 6th ed. Elsevier; 2016:192-196.
