HERDA – Hereditary Equine Regional Dermal Asthenia – Buyer Beware!

HERDA – Hereditary Equine Regional Dermal Asthenia – Buyer Beware! Check the bloodline of any AQHA, APHA, ApHC and cross-bred horses of these breeds before you buy! Check your horses’ bloodlines before you breed, too! This is a heart-wrenching story from a woman whose mare was diagnosed with HERDA.

By Tara Flanagan and Robin Davison, March 2011: From across the paddock, Penelope (registered name, Quality Sensation) is a striking four year-old paint mare who has nothing but potential. Her athletic build, to-die-for lope and easy disposition indicate that she inherited all the right things.

Robin's horse, Quality Sensation. Click on image for larger view.

But get a little closer and you’ll notice the discoloration on her back from saddle sores. The skin around her withers feels corrugated. It’s easily manipulated and doesn’t snap back into place –almost as if the horse is severely dehydrated.

I bought my mare in November 2009 and had her hauled from Florida to Colorado. Penelope had an injury on her right hind leg from the trip that required a vet’s attention, and which was unusually slow to heal. Mostly, I was filled with the excitement that came with getting the horse I had dreamed about – Penelope and I were going to show at the National Western Stock Show someday.

Typical of many horses who are afflicted by HERDA, or hereditary equine regional dermal asthenia, Penelope started to show signs of the disorder when she developed saddle sores that did not heal in March 2010, about two months after she was started under saddle. A DNA test from UC-Davis revealed that Penelope is HRD/HRD – affected – meaning that she has two copies of the HERDA gene.

Robin's horse, Quality Sensation. Click on image for larger view.
Robin's horse, Quality Sensation, showing the skin not popping back into place. Click on image for larger view.

Affected horses develop severe lacerations, hematomas, and seromas from minor trauma, frequently resulting in disfiguring scars. Due to their persistent wounds, most horses cannot be ridden or shown competitively and are humanely euthanized. Many horses affected with HERDA are often not diagnosed until they are 1-2 years of age, but severely affected horses may develop signs shortly after birth. Symptoms include stretchy skin that feels “mushy” or “doughy” to the touch. Penelope’s mane, for example, has that doughy feel.  Contrary to what the name implies, the disease affects tissues throughout the horse’s body.  The proportion of carrier horses is high in certain Quarter Horse disciplines such as cutting, where 28.3% of elite cutting horses are carriers. Therefore, cutting horses that carry HERDA are more prevalent than halter horses that carry HYPP. In fact, 14 of the top 100 cutting sires are carriers whose offspring have earnings in excess of 116 million dollars. The performance traits of these select carriers bloodlines are highly desired, likely increasing the prevalence of HERDA. Although cutting horses have been the subject of most of the study and press about HERDA, the incidence of HERDA in pleasure and reining horses is on the rise. (information provided by Dr. Ann Rashmir)

HERDA is found in some descendants of the AQHA sire Poco Bueno. Researchers have named four deceased Quarter Horse stallions that were carriers and produced at least one affected HERDA foal. They are: Dry Doc, Doc O’Lena, Great Pine, and Zippo Pine Bar. These stallions all trace to Poco Bueno through his son and daughter, Poco Pine and Poco Lena. Other breeds affected are the American Paint Horse (APHA), the Appaloosa (ApHC) and any other breed registry that allows out-crossing to AQHA horses.  (this information found on http://www.angelfire.com/pa5/ment2befarms/herda.html).

As far as the odds go, if you breed a carrier to another carrier you have a 25 percent chance of producing an affected horse (HRD/HRD), 50 percent chance of producing another carrier (N/HRD) and a 25 percent chance of producing a normal horse (N/N). When a normal horse (N/N) is crossed with a carrier (N/HRD), 50 percent of the offspring may be carriers (N/HRD) and 50 percent may be normal (N/N); none of the offspring will be affected (HRD/HRD).

Quarter Horse
Quarter Horse
Quarter Horse
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Quarter Horse

I now board Penelope at a local farm, where she enjoys a shady enclosure. It’s too risky to turn Penelope out with most horses, but we have found a few equine companions for occasional turnout. For now, Penelope is doing well. I have learned that these horses can live many comfortable years with the disorder – provided they aren’t ridden and are kept in a very safe environment.

From the HERDA document from Dr. Ann Rashmir showing an affected horse. Click on image for larger view.

So, what can you do? If you plan to buy a quarter horse, paint or appaloosa 4 years old or younger that has several crosses to Poco Bueno, it’s wise to get him/her tested. Require a HERDA test as part of a pre-purchase exam if the horse has Poco Bueno as far back as seven or eight generations.  Just looking at the pedigree on registration papers might not be adequate to determine if the horse is at risk.  The test only costs $40 (here is the link:  http://www.vgl.ucdavis.edu/services/horse.php).  And it stands to reason that you can’t produce a HERDA affected horse if you don’t breed two carriers.

For more information please contact Dr. Ann Rashmir at the Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University G209 Veterinary Medical Center, East Lansing, MI 48824-1314, Office (517) 355-1866.

A few quick facts:

HERDA/hyperelastosis cutis was first reported by Lerner and McCracken in 1978.  The DNA test at UC-Davis has been available for 4 years.

2% of all Quarter Horses are carriers of the HERDA gene. (August 1, 2010 issue of Journal of the American Veterinary Medical Association)

AQHA has a ruling on HERDA currently up for review:


From the HERDA document from Dr. Ann Rashmir showing a severely affected horse. Click on image for larger view.

A few links on this rapidly emerging genetic disease:


HERDA – A Devastating Defect By Heather Thomas from the Equine Chronicle EC May/June, 2004 http://www.equinechronicle.com/health/herda-a-devastating-defect.html

An ABC News video interview with Robin:   mms://entriq0lax2wm.fplive.net/entriq0lax2/kmgh/video/20101015155800_45101_001041p1001239p9.wmv


I got this HERDA information from a colleague, Lisa Kemp, who is a multi-award winning writer and marketing consultant for the equine industry.  She blogs about equestrian business marketing at http://NoBizLikeHorseBiz.com.  She has included HorsesintheSouth.com in many of her articles, one of which was the award winning article about Gabrielle Boiselle that was a featured calendar promotion on my blog. We have more Gabrielle articles on my blog, too – she has her own category http://horsesinthesouth.com/blog/?cat=872. Lisa wrote a 3-part article for TheHorse.com for this HERDA issue.  You will need a login to TheHorse.com to read these articles (it’s free; you will just have to sign up).  Here is the first article:  http://www.thehorse.com/ViewArticle.aspx?ID=17175

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