Homozygous, Lethal White (OWLS), HYPP, Color Determination Testing
What does it mean if a Paint is homozygous for the tobiano gene?
When an animal is determined to be homozygous for the tobiano gene, it means that the animal will produce a foal inheriting the tobiano gene each time, no matter whether the other parent is another Paint, a QH or a Thoroughbred. The gene may express itself minimally or loudly on the foal. The determination of homozygous status can only be reached in a horse with the tobiano or tovero coat pattern that has two tobiano or tovero parents.
How do I test my horse to determine if it is homozygous?
This testing is not done through the APHA offices. It can be obtained by contacting UC Davis. You can contact them by phone at 530-752-2211 or by writing Veterinary Genetics Laboratory, Tobiano Testing, Old Davis Road, University of California, Davis, CA 95616. You can also visit the UC Davis web site at www.vgl.ucdavis.edu . Homozygous testing is an agreement strictly between the laboratory and the horse owner. Only a tobiano or tovero who has two tobiano or tovero parents can be homozygous.
You can contact UC Davis or APHA to send you the required information. You will find a link to the UC Davis web site from our site. Look under LINKS.
Can the DNA test be used to determine if a horse is homozygous or can tobiano homozygous testing results be used for the DNA requirement?
DNA testing is most commonly done using a hair sample. Homozygous testing must be conducted using blood. Tobiano testing results to determine if an animal is homozygous record protein markers. Parentage verification testing (DNA) uses genetic chromosome markers. They require separate testing procedures. Both can be obtained from a blood sample, but a hair sample can only yield DNA markers.
At this time, APHA has designated Maxxam Analytics as the approved lab for DNA testing. Homozygous testing is available through UC Davis. Since two labs are involved and only one is designated for providing DNA to APHA, it would be necessary for you to submit samples to each lab separately for the testing you require.
What is OLWS or Lethal White Syndrome?
Overo Lethal White Syndrome (OLWS) is an inherited genetic defect that can occur in the offspring of Paint Horses with overo lineage. Normally associated with frame overos, it can also be found in other overos, solid horses or Quarter Horses. OLWS can occur if both parents are carrying the gene and both pass it along to the foal. Also known as congenital intestinal aganglionosis, the foals are solid white or nearly solid white. Foals inheriting OLWS appear normal, but after a short period of time (usually within 12 hours) show signs of colic due to an inability to pass feces. OLWS is always fatal.
A simple DNA test can be done with a hair sample to determine is your horse is at risk for producing lethal white foals. (The March 2004 issue of the Paint Horse Journal has a very good article concerning this testing procedure.) If the horse is determined to be at risk for producing a lethal white foal then precautions can be taken to select a suitable horse to breed to that has been shown not to be a carrier of the gene. By exercising sensible precautions in selecting which horses are bred it is possible to avoid producing a lethal white foal.
How do I obtain a lethal white gene test kit?
There are no test kits available through APHA. There is currently one university, UC Davis, which has developed a test kit relating to lethal white gene testing. APHA can provide you with an information sheet provided by the university describing their product and how to contact them to request a kit or you can visit their web site for more information. The test costs $50. Please contact Field Services at ext. 777 to request this information.
You will find some information about Overo Lethal White Syndrome on our web site under the section entitled THE BREED, RELATED GENETICS. You will also find a link to the UC Davis web site for additional information and forms under LINKS.
How do I test my horse for HYPP?
If you own a horse with an ancestor tracing back to the AQHA stallion Impressive you may wish to test your horse to see if it is HYPP positive or negative. Testing can be done by Maxxam Analytics, Inc. for a fee of $35. Please contact Field Services at ext. 777 to request information about HYPP and testing.
Can APHA tell me the HYPP status of a particular horse?
Currently, APHA does not require or record the HYPP status of any horse. You should contact the owner of the horse to inquire if the horse has ever been tested and to obtain those test results.
What is Red Factor testing and what is it used for?
Equine coat colors fall into two basic families of red pigment or black pigment. The red family includes sorrel and chestnut. The black family includes black, brown and bay. Red factor testing can be used to tell if a dark horse is homozygous for the black color gene, meaning it will only produce foals in the black coat color family.
Red Factor testing can also be used to tell if a diluted horse is in the black family or red family. Perlino belongs to the black-brown-bay color family, and cremello belongs to the chestnut-sorrel (red) family. It can be difficult to correctly determine visually if a horse is cremello or perlino. At times, the pedigree can assist in making that determination. The only method of certainty is to perform the Red-Factor Test or conduct test breeding.
Information can be obtained by contacting APHA Field Services for a Red Factor Test Submission Form. Testing is completed with a hair sample.