HERDA (HC)

What is HERDA (HC)? Hereditary equine regional dermal asthenia (HERDA) is a genetic skin disease predominantly found in the American Quarter Horse. Within the breed, the disease is prevalent in particular lines of cutting horses. HERDA is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected (H/H) horses. Affected (H/H) foals rarely show symptoms at birth. The condition typically occurs by the age of two, most notably when the horse is first being broke to saddle. There is no cure, and the majority of diagnosed (H/H) horses are euthanized because they are unable to be ridden and are inappropriate for future breeding. HERDA has an autosomal recessive mode of inheritance and affects stallions and mares in equal proportions. Research carried out in Dr. Danika Bannasch's laboratory at the University of California, Davis, has identified the gene and mutation associated with HERDA. (UCD)

The diagnostic DNA test for HERDA that has been developed allows identification of horses that are affected (H/H) or that carry (N/H) the specific mutation. UCD is capable of performing this simple test via a hair pull w/follicle submission. Other skin conditions can mimic the symptoms of HERDA. The DNA test will assist veterinarians to make the correct diagnosis. Any horse with the below mentioned bloodlines should be HERDA tested prior to breeding. (UCD)

HERDA results are reported as follows:

Research suggests that the Poco Bueno bloodline is responsible for the spread of HERDA (HC).

Just where along the line did HC occur? Winand says: As of this writing, pedigrees from approximately 100 well-documented cases have been examined. These show that 95% of the horses identified with HC trace back to Poco Bueno through both their sires and dams. The other 5% trace back to other horses in this sire line, including King, Zantanon, Little Joe, and Poco Bueno’s full brother Old Grand Dad. While this suggests that Poco Bueno may have inherited the HC mutation from his sire, this may not be the case. With the available information, it is difficult to rule out the possibility of Miss Taylor, Poco Bueno’s dam, transmitting the HC gene to Poco Bueno. It may never be possible to scientifically identify the origin for several reasons. We have no pedigrees to date that completely differentiate the lines of King versus Miss Taylor, and even if we did, it is difficult to verify the accuracy of pedigrees this far back, or further. (Bringinglight)

 It has been established, say Rashmir and Winand, that the recessive gene was passed on to Doc O’Lena through his dam, Poco Lena, rather than through his sire, Doc Bar. There is no evidence that Doc Bar was a carrier, they say. Poco Lena had only one other foal, Dry Doc, and he, too, was a carrier, according to the researchers. (Bringinglight)

There is some good news, the two researchers say. The genes that cause HC are recessive, and it takes two to tango. This means that both sire and dam must possess the recessive gene in order for an offspring to possibly be afflicted (H/H) with HERDA. In this way, the disease differs from hyperkalemic periodic paralysis (HYPP), which descended through the bloodline of the Quarter Horse stallion Impressive. HYPP is caused by a dominant gene that can be carried by only one of the parents and still cause the affliction. With HC, both parents must carry the recessive gene for the horse to be afflicted. (Bringinglight)

Responsible Breeding is a must!

Under the genetic law of averages, here’s how it works, according to the two researchers:

The first line of defense by horse owners is to avoid breeding a known carrier (N/H) to a known carrier (N/H) and avoid breeding known afflicted (H/H) altogether – remember (H/H) foals should be put down for humane reasons and should never be allowed to possibly reproduce themselves.

References

http://www.vgl.ucdavis.edu/services/herda.php
http://www.bringinglighttohypp.org/HERDA.html

NOTE: All of Flying V Ranch mares carrying the above bloodlines are HERDA tested N/N and all outside mares who carry the above bloodlines looking to breed to Jaz (N/H) must also test N/N. A UCD HERDA certificate must be submitted before semen will be shipped to mares that carry the above bloodlines.