Friesian Horse Dwarfism

Quick Summary

Dwarfism in Friesians is an inherited disorder characterized by a disproportionate growth with reduced bone length of limbs and ribs while the size of the head and length of the back are normal.

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Phenotype: Dwarfism is characterized by a disproportionate growth with reduced bone length of limbs and ribs while the size of the head and length of the back are normal. Affected horses have hyperextension of fetlock joints of all limbs with varying degrees of severity.

Mode of Inheritance: Autosomal recessive

Alleles: N = Normal/Unaffected, D = Dwarfism

Breeds appropriate for testing: Friesian, Friesian crosses

Explanation of Results:

  • Horses with N/N genotype will not be affected by Friesian dwarfism and cannot transmit this dwarfism variant to their offspring.
  • Horses with D/N genotype will not be affected by Friesian dwarfism, but are carriers. They may transmit this dwarfism variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a foal with Friesian dwarfism.
  • Horses with D/D genotype will have Friesian dwarfism.

Turnaround Time
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Price

$45 one test per animal
$60 this test + one test from list below

$75 entire Friesian Health Panel (all 3 tests)

Sample Collection

Horse DNA tests are carried out using cells from the roots of a hair sample (roughly 20-30 hairs).

1. Grab about 10 hairs at the base.

2. Wrap the hairs around your finger and give it a quick pull.

3. Check the ends to make sure the pulled hairs have roots.

4. Repeat the process until you have collected about 20-30 hairs with intact roots.

5. You can choose different places on the mane or tail. NOTE: For foals, we recommend pulling all hairs from the tail only. 

6. Tape the hairs to the submission form and fold the form along the dotted line to protect the sample. Do not use ziploc bags as they can cause condensation that allows mold to grow on the hair.

Hairs with roots

7. Place the folded form containing the sample in a paper envelope and mail it to the laboratory.

 

Additional Details

Dwarfism in Friesians is characterized by a disproportionate growth with reduced bone length of limbs and ribs while the size of the head and length of back are normal. Microscopic analysis of growth plates in affected animals shows irregular transition from cartilage to bone and abnormal arrangements of chondrocytes (cartilage cells). Affected horses have hyperextension of fetlock joints of all limbs with varying degrees of severity. A mutation (c.50G>A) in exon 1 of the Beta-1,4-Galactosyltransferase 7 (B4GALT7) gene has been identified that is associated with this disorder. B4GALT7 plays an important role in proper formation of extracellular matrix, a key element for bone development. The mutation affects normal functioning of the gene which interferes with proper collagen formation.

Friesian dwarfism is inherited as a simple autosomal recessive trait. This means that affected foals have two copies of the defective gene and that the disorder occurs in males and females. It is estimated that about 12% of the Friesian population are carriers (N/D) of the mutation.

Testing for Friesian dwarfism assists owners and breeders to identify carriers and to make informed mate selection to avoid producing affected foals. Matings between carriers have a 25% chance of producing affected foals. Breeding carriers to normal horses is safe and a means to maintain genetic diversity in the breed and avoid production of affected foals.