Mare and foal

 

Horse Genome Project

RECENT NEWS

International Equine Genome Mapping Workshop
The 8th Dorothy Russell Havemeyer Foundation International Equine Genome Mapping Workshop took place near Newmarket, UK from July 22 to 25, 2009...[more]

MEDIA ECLIPSE AWARD
Writers at the Louisville Courier Journal recently won the 2008 Media Eclipse Award for journalism based on an article about Thoroughbred racing and break-downs. They published a 3 part story, including genetics, track surfaces and medications. In connection with the genetics section they interviewed several members of the Horse Genome Project. See the accompanying links for the full stories on the 2008 Media Eclipse Award and the article itself.

Courier-Journal Web site wins award for horse project
Genetics may hold key to Injury-prone horses
[December 2008]

HORSE GENOME SEQUENCE COMPLETE
The first draft of the horse genome sequence was recently completed and deposited...
[JAVMA News, April 2007]

HORSE GENOME ASSEMBLED
Data on Equine Genome Freely Available to Researchers Worldwide
[NIH News, February 2007]

HORSE GENOME SEQUENCED
The first genome map of a horse is complete, providing scientists with new tools for investigating equine disease. [ April 2006]

 

SOME DEFINITIONS OF GENETIC TRAITS AND CONDITIONS CURRENTLY UNDER STUDY

Allergic Eczema:  Also known as allergic dermatitis and is characterized commonly in horses as “sweet itch”, “summer eczema”, “Queensland itch” in Australia, summer mange and “kasen” in Japan.  This is a hypersensitivity reaction to the bite of insects, especially biting midges (Culicoides spp.) The condition has been shown to have a hereditary aspect.  (taken from Rooney & Robertson, Equine Pathology, Iowa State University Press, Ames, Iowa. 1996)

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Athletic Performance:  Horses are prized for their athletic performances in racing, jumping, High School riding and for the ability to perform variations of different gaits.  Heredity plays a major role in performance and enhancing performance will entail understanding the genetics of performance traits.

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Anterior Segment Dysgenesis This is a congenital eye disease, apparent at birth but not progressive. It appears to have a hereditary component and is under investigation in Rocky Mountain Horses and Miniature Horses.  (learn more...)

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Trichothiodystrophy (TTD) is sulfur-deficient brittle hair. Individuals with trichothiodystrophy have brittle hair (because of reduced content of cysteine-rich matrix proteins) which results in hair loss and ichthyotic (scaly) skin. Approximately half of the patients display photosensitivity, correlated with a nucleotide excision repair (NER) defect. In horses TTD is associated with curly hair, and hair loss (although it does not occur in all curly horses) usually occurs in the summer.

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Behavior:  Some performance traits might be considered inherited aspects of behavior.  Behavior also encompasses stable vices and stereotypic behavior.  The occurrence of different behaviors among horses under the same management conditions suggests a hereditary component.

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Cerebellar Abiotrophy: This congenital condition is thought to be caused by an autosomal recessive gene that results in loss of substance and organization of the cerebellum.  Foals with this condition develop progressive neurological dysfunction after birth.  (taken from Rooney & Robertson, Equine Pathology, Iowa State University Press, Ames, Iowa. 1996)

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Cervical Stenosis:  Cervical stenosis is a narrowing of the spinal canal that pinches the spinal cord within the neck region.  The resulting spinal cord injury causes proprioceptive deficits and ataxia.  It is a primary cause of what is referred to more commonly as Wobblers Syndrome.  Magnetic resonance imaging studies should provide new insight into the specific anatomical events that lead to spinal cord pinching.  Variables that cause cervical stenosis, environmental and perhaps genetic, need to be specifically identified.

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Chronic Progressive Lymphedema:  A condition characterized by progressive swelling, hyperkeratosis and fibrosis of distal limbs has been recognized in Shires, Clydesdales and Belgian Draft horses.  (learn more...)

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Contracted Foal Syndrome:  Flexor tendon disorders are associated with postural and foot changes, lameness, and debility. There are congenital and acquired causes. Uterine malposition, teratogenic insults (arthrogryposis), and genetic defects have been either implicated or proved to cause contracted limbs in newborn foals. (learn more...)

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Dwarfism:  Dwarfism is associated with many different genetic defects in people that cause reduction in skeletal growth.  Dwarfism exists among horses and is regarded as a problem among miniature horses which have been selected for small stature. 

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Equine Placental Development:  The health of the placenta determines the health of the foal. Understanding gene expression of the placenta during development is of major interest to horse breeders.

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Fell Pony Syndrome:  A recessive immunodeficiency trait has been identified among horses of the Fell Pony population. 

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Fertility and Reproduction:  Fertility and reproduction are major aspects of horse husbandry.  Genetic defects may result in poor fertility or infertility in stallions or mares.

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Fracture and Tendon Injury:  Horses are athletes and their activities subject them to risk of bone or tendon injury.  Identifying those factors which lead to stronger bones and tendons will make horses and riders safer.

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Immune Mediated Myopathy: IMM is a newly recognized inflammatory myopathy in horses that causes malaise and rapid muscle wasting of epaxial and gluteal muscles. In some, but not all cases, it develops after exposure to Streptococcus equi. Quarter Horses have a statistically significant over-representation amongst cases of IMM relative to other breeds.

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Immunity to Equine Herpes Virus Type 1:  When a horse is infected with herpes viruses, the virus invades different tissues and alters normal cell function.  An immune response is mounted by the horse which is usually successful in eliminating the viral infection.  But the natural immune response is often too late to avoid abortion, respiratory disease or neurological diseases.  Understanding the molecular events associated with infection and immune response may help provide better vaccines and therapies. 

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Immunity to Rhodococcus equi in foals:  Foals are susceptible to rhodococcus infections when young and their immune systems are not fully developed.  Understanding the molecular events that lead to survival from the disease may provide insights for better therapies or even effective vaccines.

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Improved Safety of Intra-articular Glucocorticoid Therapy:  Glucocorticoids are potent anti-inflammatory agents widely used as a drug therapy for synovitis and osteoarthritis, targeting primarily cells in the synovium and joint capsule.  Although these drugs provide symptomatic pain relief while also reducing the production of damaging inflammatory mediators and enzymes, they can concurrently compromise the function of chondrocytes – the cells that synthesize and maintain articular cartilage.  Evaluating new drug candidates that retain beneficial anti-inflammatory properties, but have reduced detrimental effects on the function of cartilage cells offers the potential for an advance in joint disease therapy.

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Laminitis (founder): “Traditionally defined as inflammation or edema of the sensitive laminae of the hoof, laminitis is now thought to be a transient ischemia associated with coagulopathy that leads to breakdown and degeneration of the union between the horny and sensitive laminae. In refractory cases, rotation of the pedal bone is a common sequela that may progress to perforation of the sole. The disease is a local manifestation of a more generalized metabolic disturbance, and the hoof problems are classified as acute, subacute, or chronic.”  “The most common causes of laminitis are ingestion of excess carbohydrate (grain overload), grazing of lush pastures (especially in ponies), and excess exercise and concussion in an unfit horse. It also may develop secondary to postparturient metritis, endotoxemia, colic and enteritis, or administration of an excess of corticosteroid or some other medicament. The risk is higher in ponies and in horses that are overweight and unfit. Incidence of the acute and subacute forms is higher whenever there is a flush of new grass.”  (learn more...)

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Lavender Foal:  “This is a disease that causes Arabian foals to be born with an unusual coat color.  Affected foals usually die within a few days of birth from serious neurological problems.  It is a lethal genetic disorder that seems to require both parents to be carriers and affects both male and female foals.”
(learn more...)

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Lordosis:  (Also called low back, soft back or swayback) Occasionally horses are born with extreme curvature (lordosis) of the back or develop them shortly after birth.  This condition may be the result of congenital malformation of vertebrae and be under genetic control.

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Maturation of Articular Cartilage:  In the first year of life, maturation of articular cartilage in the horse is characterized by structural and organizational changes of matrix molecules and functional changes in cartilage cells.  These changes quite likely are important for the long-term function and durability of synovial joints.

 Repair of Articular Cartilage:  The inability of structural lesions in articular cartilage to fully repair is a primary cause of osteoarthritis and the main reason for why degenerative joint disease is chronic and progressive in all mammals.  It is unclear why cartilage cells are unable to restore normal cartilage following structural injuries, but they are a primary target for therapeutic advances.

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Muscle Response to Exercise:  The horse is an athlete and its activity is dependent upon muscle action.  Understanding gene expression of muscle in response to exercise will provide information to guide training and avoid injury.

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Navicular Disease:  “Navicular disease is essentially a chronic degenerative condition of the navicular bursa and navicular bone that involves damage to the flexor surface of the bone and the overlying deep digital flexor tendon with osteophyte formation on the lateral and proximal borders of the bone. Thus, it is a syndrome with a complex pathogenesis rather than a specific disease entity. It is one of the most common causes of chronic forelimb lameness in horses but is essentially unknown in ponies and donkeys.”
 (learn more...)

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Osteochondrosis Dessicans:  “In osteochondritis dissecans (OCD), a focal area of the immature articular cartilage is retained, and the matrix in the basal area of this region becomes chondromalacic and acellular. The immature articular cartilage separates from the underlying trabecular bone. The chondral fracture extends horizontally and vertically until a flap is formed. Synovial fluid gains entrance to the underlying medullary space, and subchondral cysts may form (usually only in larger animals). The flap of immature articular cartilage may break away completely (“joint mice”) or may reattach by endochondral ossification to the underlying bone.  The exact cause is unknown but is assumed to be multifactorial. Factors include genetic predisposition, fast growth, high caloric intake, low copper and high zinc levels, and endocrine factors.”
(learn more...)

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Polysaccharide Storage Myopathy:  “PSSM is a debilitating muscle disease in many breeds of horses.  Clinical signs vary, but can range from muscle atrophy and progressive weakness that is most common in Draft breeds, muscle soreness and gait abnormalities in Warmbloods, and acute post-exercise muscle cramping and muscle necrosis in Quarter Horses. All forms of PSSM are highly associated with deposits of an abnormal polysaccharide in skeletal muscle fibers, and are typically characterized by an increased content of glycogen in skeletal muscle.  A heritable basis for PSSM in Quarter Horses was established in a prospective breeding trial. Approximately 10% of all American Quarter Horses and 36% of all Belgian Draft horses have PSSM.  Other breeds of horses have also been reported to have PSSM, although the prevalence within these breeds is unknown. A mutation in the equine GYS1 gene, encoding the skeletal muscle glycogen synthase enzyme, is highly associated with PSSM in a number of breeds, but there is another form of PSSM that is not caused by this mutation (learn more...)

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Recurrent Airway Obstruction (Heaves):  “Recurrent airway obstruction (RAO) is a common, performance-limiting, allergic respiratory disease of horses characterized by chronic cough, nasal discharge, and respiratory difficulty. Episodes of airway obstruction are observed when susceptible horses are stabled, bedded on straw, and fed hay, whereas elimination of these inciting factors results in remission or attenuation of clinical signs.  The average age at onset is 9 yr. Approximately 12% of mature horses have some degree of allergen-induced lower airway inflammation. There is no breed or gender predilection; however, there does appear to be a heritable component to susceptibility.”
(learn more...)

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Recurrent Exertional Rhabdomyolysis (tying up): “RER is likely the most common form of “tying-up” and the most important muscular disorder of Thoroughbred racehorses. Epidemiological studies at a small mid-western US racetrack, and in the United Kingdom, have both determined that 5 –10% of all Thoroughbred horses develop ER at some point during a racing season, up to 75% of trainers have at least one horse with RER, and recurrence is so frequent in 17% of the affected horses that they never race again that season.  Clinical evaluation and computer analysis of pedigrees containing RER horses from across the US, and a breeding trial that mated RER and unaffected horses, indicate that RER is a dominant disorder, with environmental influences playing a role in the sporadic expression of the clinical phenotype. An in vitro alteration in the regulation of muscle contraction has been found in RER horses, manifested as a significantly increased sensitivity to the development of potassium-, caffeine- or halothane-induced contracture.”
(learn more...)

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Recurrent Uveitis:  “Equine recurrent uveitis is an immune-mediated disease with many potential initiating causes. The common denominator is damage to the uveal tract, which may be initiated by trauma (both penetrating and blunt) or systemic disease. Specific conditions or agents implicated in the pathogenesis include leptospirosis, brucellosis, strangles ( Streptococcus equi infection), onchocerciasis, equine influenza, tooth root abscess, and hoof abscess.”  “Even though the immunologic basis for the recurrent nature of uveitis has been extensively studied, detailed understanding of the factors involved remains elusive. Sequestration of organisms, antigen, or antibody-antigen complexes within the anterior uvea has been advanced as an explanation for the chronicity of the ocular inflammation long after the initiating cause has resolved. Additionally, T lymphocytes have been found to be the predominant inflammatory cell type in clinical cases; their presence suggests a cytokine-driven, immune-mediated inflammatory response. The mechanisms by which this response is activated (or deactivated) remain unknown.” 
(learn more...)

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Sarcoid Tumors:  “Equine sarcoid is the most commonly diagnosed tumor in horses and accounts for up to 33% of all reported equine tumors. Sarcoids may arise either spontaneously, or at a site of previous skin trauma. They develop from a specific cell in the skin called the fibroblast. The mechanism of this uncontrolled growth of fibroblasts in unknown, but a virus (papillomavirus) has been implicated. There is no sex or breed predilection, however, age may play a role as the majority of sarcoids (~ 70%) occur in horses less than 4 years old. The most common sites of the occurrence are the head, ears, limbs, and ventral abdomen.” (learn more...)

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Shivers Muscle Tremors:  “Shivers is a devastating disorder in draft and warmblood horses whereby horses develop muscle tremors and flexion beyond normal limits of the rear limbs during shoeing, after standing still or when backing up. Many affected horses also show concurrent tail tremors. In some horses, Shivers never progresses, while in others it leads to weakness, muscle atrophy and an inability to get up.” (learn more...)

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Stereotypic behavior:  These are also known as stable vices and include behaviors such as  cribbing, weaving, air-sucking, kicking and other repetitive non-productive or self-destructive behaviors.   Investigations are underway to determine why some horses exhibit stable vices and other do not.  A hereditary component is suspected. 

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Suspensory Ligament Desmitis:  “Degenerative Suspensory Ligament Desmitis (DSLD) is a syndrome recognized in the Peruvian Paso, Peruvian Paso crosses, Arabians, American Saddlebreds, American Quarter Horses, Thoroughbreds and some European breeds such as the Irish Thoroughbred and Swedish Warmbloods.” “Speculation is that, at some point in the life of a predisposed horse, a previously normal suspensory ligament begins to undergo failure when resisting normal forces of tension (strain). With normal tissue, a strain is repaired with fibroblasts (cells that produce type III collagen). Fibroblasts 'bridge' the damage and, in time, repair the damaged tissue. The new collagen fibers then orient themselves in line with the stress on the tissue as the healing progresses. Horses affected with DSLD have an abnormal healing response. Regardless of the causes of the injury or strain, the damaged tissue heals with cartilage instead of collagen. Fibroblasts defect and become chondrocytes and the ligament is unable to restore itself to normal tissue strength. The ligaments continue to 'break down' even with just the strain of normal weight bearing. Some Peruvian Pasos have spontaneously exhibited DSLD as yearlings.” (learn more...)

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White Markings:  White markings on horses are sometimes valued by horse owners.  The genetic basis for some white markings (e.g., overo, tobiano, sabino-1) are well known.  The genetic basis for other white markings, such as blazes, socks, stockings, other sabino patterns, roan and appaloosa remain under investigation.

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running horses

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