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  • AIS - Androgen Insensitivity Syndrome

    AIS stands for Androgen Insensitivity Syndrome - it is a recessive defect which causes females to be sterile.

    Mares will look and act like a stallion.   Heavily muscled, aggressive to other mares in heat and displaying other typical stallion behaviours.  These mares can be helped by gelding them.  They look like mares in every way but they also have internal male testicles.

    It has been documented in Quarter Horses, Throughbreds and Standardbreds,

    If you have an AIS mare or suspect you have one we would be very interested in her pedigree - please consider contacting us.

  • CHF - Congenital Hepatic Fibrosis

    CHF is Congenital Hepatic Fibrosis - a recessive disease

    CHF affects the liver - foals are small for their age and have a potbelly.

    There is no treatment and CHF foals are usually put down.

    To date, it has only been found in the Franches-Montagnes breed (all affected horses in that breed trace back to the stallion Elu, born in 1964, and he is an ancestor on both the sires side and the dams side) and it was also found in one Spanish Purebred foal.

  • CM - Congenital Myotonia

    CM is Congenital Myotonia - it is a recessive disease

    Myotonia slows the relaxation of muscles after voluntary contraction or electrical stimulation this shows up as difficulty rising to the horses feet, abnormal vocalization, a stiff gait, and rigin dlimbs, neck and trunk.

    Myotonia has been found in the New Forest Pony.

    There is no effective treatment.

    Genetic Testing is available.

    Genetic Codes:

    N/NThe horse is normal, and cannot produce affected offspring.

    N/cmThis horse carries CM and will pass the allele on to approx. 50% of its foals. If bred to another N/cm carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.

    cm/cmThe horse is affected with congenital Myotonia and will pass one copy of CM to every foal.

  • CSNB - Congenital Stationary Night Blindness

    CSNB stands for Congenital Stationary Night Blindness - it is a recessive disease

    CSNB causes an inability to see well in the dark - horses have it when they are born and it does not get worse as they get older.

    It is assicated with the LP pattern gene so it affects Appaloosas - horses with LP/LP (few spot) are affected. 

  • DSLD - Degenerative Suspensory Ligament Desmitis

    DSLD is also known as ESPA

    It is thought that DSLD is an inherited defect although some DSLD is environmental.  No genetic test has been developed for DSLD to date.

    DSLD/ESPA is a disease that affects the connective tissue (tendons & ligaments) and symptoms usually appear outwardly in the suspensory ligaments or tendons of lower legs, especially the fetlock area.  DSLD horses pasterns are usually parallel to the ground.  Also post legged is another common symptom of DSLD. Other subtle signs maybe be seen before the legs are affected outwardly.

    FLEX TEST & ULTRASOUND are used to confirm DSLD Diagnosis.Flex test of fetlock joints, ultrasound of suspensories. Dsld horses will fail the flex test in two or more legs. Palpation of suspensories will find them to be very hard & taut, maybe lumpy from calcification or could be mushy. Pain response is also noted.IRON BLOOD TESTING - Many DSLD horses have high iron levels and low magnesium levels.

    DSLD is a progressive condition and there is not much in the way of effective treatment.

  • FIS - Foal Immunodeficiency Syndrome

    FIS stands for Foal Immunodeficiency Syndrome - it is a recessive disease

    FIS affects the immune system - foals appear normal when they are born but an inability to fight infections means they will die within three months or less or they are put down in reponse to their inability to fight infections

    The condition is found in two rare related British pony breeds, the Fell and the Dales. 

  • GT Thrombosenia

    GT is Thrombosenia - a recessive disorder

    Thrombasthenia is a bleeding disorder where the horses blood doesn't clot properly, these horses bleed excessively. 
    Symptoms include weakness in the hind end, trouble getting up, cold limbs, low pulse

    There is no effective treatment.

    It is found in Throughbreds.

    Genetic Codes for GT:

    N/NNormal Cannot produce an affected foal

    N/gt1Horse is a carrier of GT, and can passto to approximately 50% of any offspring. If bred to another N/gt1 carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.

    N/gt2Horse is a carrier of GT, and can pass the allele on to approximately 50% of any offspring. If bred to another N/gt2 carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.

    gt1/gt1The horse is affected with GT. If bred to a normal animal, 100% of the offspring will be carriers. If bred to a N/gt1 carrier, 50% of the offspring will be carriers and 50% will be affected.

    gt2/gt2The horse is affected with GT. If bred to a normal animal, 100% of the offspring will be carriers. If bred to a N/gt2 carrier, 50% of the offspring will be carriers and 50% will be affected.

    gt1/gt2The horse is affected with GT. If bred to a normal animal, 100% of the offspring will be carriers. If bred to a N/gt1 or N/gt2 carrier, 50% of the offspring will be carriers and 50% will be affected.

    – Carriers may be bred to normal animals (N/gt1/gt2 x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
    – Breeding two carriers (N/gt1/gt2 x N/gt1/gt2) is not recommended due to the possibility of 25% of the offspring being affected.

  • HFH - Hydrocephalus

    HFH (known as Hydrocephalus, it is shortened to HFH for our purposes on this site)

    HFH stands for Hydrocephalus in Friesian Horses - it s a recessive trait
    HFH often results in stillbirths of affected foals and obstructed labor (dystocia) in dams, which can be fatal to the dam during birth. The condition is usually fatal and there is no effective treatment.

    HFH is found in Friesian horses with as many as 15% of Friesian being carriers. It has been seen rarely in other breeds but it is not known at this time if it is caused by the same genetics.

  • HWSD - Hoof Wall Separation Disease

    HWSD stands for Hoof Wall Separation Disease - it is a recessive disease

    Affected horses show separation and breaking of the dorsal hoof wall along the weight-bearing surface of the hoof during the first year of life. Horses are unable to carry their weight effectively and it often leads to laminitis and euthanasia.  It does not affect all horses with the same severity.  There is nottreatment that works long term for those that are strongly affected and putting them down is usually the only option.  

    This desease is found in Connemara ponies.

  • IAR - Impaired Acrosomal Reaction


    IAR is Impaired Acrosomal Reaction - genetic inheritance is still under investigation

    This gene impairs fertility - studies so far have only been carried out on males - IAR horses can reproduce but very erratically. .


    There are two mutaions 

    Etalon is testing for this on an experimental basis - if you have a horse with fertility issues contact them and see if you can be involved in their research project.


    Test Results look like this:

     /-, -/+   One    IAR Subfertility allele detected - NO KNOWN EFFECT
    /+, -/+  Two    IAR Subfertiliy alleles detected - NO KNOWN EFFECT
    +/+, +/- Three IAR Subfertility alleles detected - NO KNOWN EFFECT
    +/+, +/+ Four  IAR Subfertility alleles detected - MAY BE AFFECTED

  • IP - Incontinentia pigmenti

    IP stands for Incontinentia pigmenti - it is a dominant disease.

    IP causes skin lesions soon after birth that develop into warty areas with hair loss. Wooley hair may grow back in these areas. Affected horses have streaks of light and dark coat color from birth. (may be mistaken for a color pattern because affected animals have a striped appearance resembling the brindle pattern in dogs)In addition, there are abnormalities of tooth, hoof, and eye development.

    Only affected mares have been observed; affected males die before birth.  Affected mares also have trouble with aborting foals.

    Genetic Codes:

    XX     This horse is a normal female.

    XXIP    This horse is an affected female.  She will pass the mutation (XIP) to 50% of her offspring. She can become pregnant with foals of all four genotypes: normal female (XX), affected female (XXIP), normal male (XY), and affected male (XIPY).  Affected male fetuses are not viable and are spontaneously aborted during pregnancy.

    XY      This horse is a normal male.

    XIPY    Horses with this genotype are not viable, and XIPY fetuses spontaneously abort during pregnancy.  No live affected male foals are possible.

  • JEB - Junctional Epidermolysis Bullosa

    JEB stands for Junctional Epidermolysis Bullosa  - it is a recessive disease   Genetic Testing is Available

    JEB affects integrity of the skin. Affected horses have fragile skin that blisters easily. Blistering of the mouth and exungulation (loss of the hoof) are also seen. You can see the condition when the foal is born and foals are usually put down right away. There is no effective treatment.

    JEB1 affects Belgians
    JEB2 affects American Saddlebreds

  • LFS - Lavender Foal Syndrome

    LFS stands for Lavender Foal Syndrome - it is a recessive disease

    LFS causes seizures and the death of foals soon after birth. Symptoms include muscle spasms which cause backward arching of the head, neck and spine, and stiff or paddling leg movements. Foals are unable to stand and nurse and are euthanized. There is no effective treatment.

    Affected foals have a diluted coat color referred to as "lavender."

    LFS is found in Arabians.

  • LWO or OLWS - Lethal White Overo

    LWO stands for Lethal White Overo, also known as Lethal White Foal Syndrome (LWFS) or Overo Lethal White Syndrome (OLWS) - it is a recessive disease

    LWO is another disease associate with Pattern - in this case the Frame Overo patterning gene. Foals affected by Lethal White Overo  dies shortly after birth due to intestinal blockage. Their coat color is entirely white. There is no effective treatment.

    OLWS is found in any breed where the paint overo pattern is found such as Quarter Horses, Paints, Miniature Horses, and Thoroughbreds.

  • MCOA - Multiple Congenital Ocular Anomalies

    MCOA stands for Multiple Congenital Ocular Anomalies - it is a dominant disease

    MCOA affects horses with the Silver coat color dilution. Horses that have two copies of the Silver gene are more sseverly affected and a wide range of eye defects are seen including underdevelopment of the iris, greatly enlarged eyes,  small cysts in the eye and cataracts. Horses with only one Silver gene have less severe defects, usually just cysts..

    Breeds that have been diagnosed with MCOA include the Rocky Mountain Horse (including the two related breeds Kentucky Mountain Saddle Horse and Mountain Pleasure Horse), Icelandics, Shetland Pony, Exmoor Pony, American Miniature, Belgian Draft, and Morgans.

  • NFS - Naked Foal Syndrome

    NFS stands for Naked Foal Syndrome

    Foals are born with very sparse thin body hairs with little to no mane and tail hair.  They don't live past 3 years of age and they have delayed growth.  Their skin is dry and scaly in some areas and they have unusual tear activity..

    So far NFS has only been found in the Akhal Teke breed.

  • ODSD - Ovotesticular Disorder of Sexual Development

    ODSD means Ovotesticular Disorder of Sexual Development it is a dominant mutation

    ODSD produces sterile females - it only comes from the stallion - all foals born are either normal colts or fillys that cannot have foals of their own.

  • SCID

    SCID stands for Severe Combined Immune Deficiency - it is a recessive disease  Genetic Testing is Available

    SCID foals have a defect in their immune system - the look normal as foals as long as they receive antibodies from the mares colostrum but will die within six months from infections that they cannot fight. 
    There is no treatment.

    SCID is found in Arabians and related breeds..
  • SWO Splash

    SWO stands for Splashed White Overo - it is a recessive disorder

    SWO is another coat pattern defect - it applies to patterns that determine white.  Embryos that receive two of these genes will not complete development and will abort in the womb.

    Hearing loss is associated with White Patterned horses - horses white on the inside of the ear are affected - horses who's ears have pigmented hair inside the ear are not affected.

    Splashed White 2 (SW2) and Splashed White 3 (SW3) are found Quarter Horses and related breeds.

    Genetic Codes:

    SW1/SW1 Homozygous Horse has two copies of the SW-1 mutation
    N/SW1 Heterozygous Horse has one copy of the SW-1 mutation
    N/N Negative No copies of SW-1 mutation
    SW2/SW2 Homozygous Horse has two copies of the SW-2 mutation
    N/SW2 Heterozygous Horse has one copy of the SW-2 mutation
    N/N Negative No copies of SW-2 mutation
    SW3/SW3 Homozygous Possible homozygous lethal
    N/SW3 Heterozygous Horse has one copy of the SW-3 mutation
    N/N Negative No copies of SW-3 mutation
    SW4/SW4 Homozygous Possible homozygous lethal but no current information available
    N/SW4 Heterozygous Horse has one copy of the SW-4 mutation
    N/N Negative No copies of SW-4 mutation
  • WFFS - Warmblood Fragile Foal Syndrome

    WFFS stands for Warmblood Fragile Foal Syndrome - it is a recessive disorder  Genetic Testing is Available

    WFFS causes thin, fragile skin. Affected foals may be born with skin lesions and an open abdomen and are typically euthanized at birth or within a few days of birth. It is similar to HERDA except is shows up at birth.

    There is no effective treatment. 

    Warmblood Fragile Foal Syndrome is reported only in Warmbloods. 

    There are a few different Labs that test for it - enquire at your favorite lab.

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