GENETIC TESTING FOR HORSES
Sponsored by the American Quarter Horse Association .
Screening for genetic disorders can help improve the overall health of your horse herd . The American Quarter Horse Association recommends owners screen Quarter Horses for six genetic disorders , and testing can be simplified through a health panel test .
When a test is ordered through AQHA , the owner receives the kit by email , then mails a hair sample directly to the Veterinary Genetics Laboratory at the University of California-Davis . AQHA notifies the owners and adds the results to the horse ’ s record and certificate of registration . The genetic health panel test costs $ 100 for AQHA members and $ 165 for nonmembers . If the testing is done in conjunction with the DNA parentage test , there is a reduced rate of $ 120 for the combined tests .
The effects of these genetic diseases are wideranging , from mild and manageable to severe and terminal . Read on to learn about the six diseases covered in the AQHA panel test . GBED : Glycogen Branching Enzyme Deficiency Disorder
GBED is a fatal disease where affected animals may be aborted or stillborn . Foals that survive to term typically die or cannot stand or nurse on their own . Foals may appear healthy for a time but eventually may develop seizures , become too weak to stand , or in some cases , die suddenly .
GBED affected horses lack an enzyme that is used to properly make the necessary sugars muscles need to function and cannot store the sugar needed for numerous tissues in the body . This means the tissues are energy impaired , resulting in muscle weakness and organ failure .
GBED is a recessive mutation , which means a horse must inherit two copies to be affected . A horse with one copy is known as a carrier . It will not experience symptoms of the disorder but can pass the mutation to its offspring . HERDA : Hereditary Equine Regional Dermal Asthenia Disorder
HERDA is a skin condition characterized by hyperextensible ( more elastic than normal ) skin , severe scarring , and open and slowhealing wounds along the back of affected horses . HERDA causes collagen between skin layers to not form properly , resulting in a horse that is easily injured . HERDA is a recessive mutation , which means your horse must inherit two copies to be affected . A horse that inherits one copy is known as a carrier and will not experience any symptoms caused by the mutation . HYPP : Hyperkalemic Periodic Paralysis Disorder
HYPP is characterized by sporadic attacks of muscle tremors ( shaking and trembling ), weakness and / or collapse . Attacks can also be accompanied by loud breathing noises resulting from paralysis of the muscles of the upper airway . This genetic mutation disrupts the muscle ’ s sodium channel resulting in too much potassium in the blood . This causes severe muscle cramping , pain and , in extreme cases , paralysis resulting in death . HYPP is a dominant mutation , which means a horse with one copy of the mutation may be affected . MH : Malignant Hyperthermia Disorder
MH is a genetic mutation that causes a life-threatening condition triggered by certain anesthesia drugs such as halothane or isoflurane . MH can also be triggered by stress or excitement . During an episode , a horse with MH will release uncontrolled amounts of calcium into the bloodstream , which results in painful muscle
Courtesy of Bee Silva .
cramps , extremely high temperature up to 113 degrees Fahrenheit , irregular heart rhythm , excessive sweating and shallow breathing . A horse that has PSSM or MYHM in conjunction with MH will likely have much more severe episodes . MH is inherited as a dominant trait , which means it can be affected with only one copy of the mutation . PSSM : Polysaccharide Storage Myopathy Disorder
PSSM is a disease causing an abnormal accumulation of glycogen , the form of sugar stored in the muscle . This excess sugar causes mild to severe muscle cramps , sore muscles and / or muscle weakness . Horses that are managed properly can generally go on to have successful performance careers . Two types of PSSM have been classified : PSSM1 and PSSM2 . The genetic test used by AQHA identifies PSSM1 mutation . PSSM is a dominant mutation , which means horses with just one copy may experience effects . MYHM : Myosin-Heavy Chain Myopathy
MYHM is a relatively newly discovered genetic disorder , which can result in two distinct clinical disease presentations that both involve muscle loss or damage and are linked to the same genetic variant . A horse with MYHM is prone to presenting with one or both during their lifetime , while some horses with the mutation may never experience symptoms . Immune-Mediated Myositis ( IMM ) is one form of clinical disease caused by MYHM , resulting in muscle atrophy often as the result of a response to a vaccine or infectious agent such as strangles . The immune system misinterprets the muscle cells as foreign and rapidly attacks them . Horses initially experience stiffness , weakness and a decreased appetite followed by the rapid loss of 40 % of muscle mass within 72 hours . The second presentation of MYHM is Nonexertional Rhabdomyolysis and often presents as stiffness , like “ tying up ,” and possible swelling of muscles along the back and haunches without exercise . MYHM is a dominant mutation , which means your horse only needs one copy to be affected . A horse must be exposed to a trigger to experience symptoms . AQHA Genetic Health : New Online Resource
AQHA now offers an interactive tool at www . aqha . com / genetics that educates owners and breeders about how genetic diseases affect an American Quarter Horse . The online resource provides information about special care a horse might require and prompts thoughtful breeding decisions .
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