True Classic Roan & Lp Roan ~ by Sheila Archer

Some Observations on Classic Roan (Rn):

Not all horses that have inherited this form of roaning display the pattern at the expected time - when the foal coat is shed. A small percentage of classic roan horses will exhibit a slightly later development. This is similar to the occasional late onset of grey (about 7% do not show for at least 5 years). Appaloosas also can show delayed expression of Lp-caused traits and roaning, by as much as 10 years in some cases.

The genetic reasons behind a delay in dispersed white pattern development are not understood, and there's very little information available on this. I suspect that basecoat colour has some effect, and that horses which are homozygous black (E/E) are potentially the slowest to roan, but there must be other, as yet unidentified genetic causes. Personally, I have observed slow roaning in a classic roan horse first hand, in Spanish Mustang I purchased as a yearling. He did not develop classic roan patterning until he shed his winter coat, the spring he was a yearling. It was not apparent with the shedding of his foal coat. He is a dark grulla, has a bay classic roan sire, and a normal, non-roan grulla dam. I suspect he's just a "late bloomer", and that this does happen from time to time with classic roan horses (the kind that have the Rn mutation).

One might argue that this horse isn't actually carrying classic roan (Rn), but has instead some other sort of roan-causing pattern gene. I suppose it is possible that there's more than one gene that can cause roan patterning of a kind similar enough to classic roan that they are hard to tell apart from each other by physical appearence alone. If there are other genes that cause similar kinds of roaning, there is no way of knowing for sure until the Rn gene has been isolated and can be DNA tested for. Right now, all we know is that Rn is most likely a mutation at the KIT locus, but that's all that is known at this time. The only way to find out if there's more than one type of roaning gene at work that makes similar looking horses that all sort of seem to be classic roan, but aren't genetically the same, would be through lab-based research to isolate the genes. To the best of my knowledge, no one is doing this right now.

For more information on coat colour and pattern in the horse, I recommend the following text by Dr. Phillip Sponenberg, the world's most-recognized equine coat colour and pattern phenotype-based researcher.

Equine Color Genetics - 2nd edition

D. Phillip Sponenberg

2003 Iowa State Press (Blackwell Publishing)

ISBN 0-8138-0759-X

The Occurrence of Appaloosa Patterning in Horse Breeds:

The main gene responsible for Appaloosa patterning is called "leopard complex", symbolized by "Lp". This gene occurs in other breeds of horses and ponies, yet it is the "appaloosa" gene, in the sense that all breeds which have this mutation will show one or more of the patterns associated with the leopard complex. The following is a partial list of breeds in which Lp occurs:

Spanish Mustang (also called the Spanish Colonial Horse)

Knabstrupper (Denmark)

Noriker (Austria)

Fallabella (Argentina)

British Spotted Pony (UK)

Karabair (Turkmenistan)

Altai (Russia)

There are others, but these are some of the most common ones. There are also still a few undetected LP-carriers in the following breeds that once had many more of them, but have now outlawed that coat pattern gene in their registration rules:

Andalusian (Spain)

Lusitano (Portugal)

Lippizan (Austria)

Quarter Horse (N.America)

With regard to the Quarter Horse, at one time, before the weeding out process was complete, there were a number of registered QH's with Lp. They were allowed to be registered because back then no one paid much attention to what sort of roaning a horse had, as long as it was not "obviously" Appy (or Paint) in appearence. These horses inherited Lp from unregistered Appaloosa-patterned ancestors - the Spanish Mustangs that were part of the recipe the QH was created from. There were a number of LP-roans in the early days of the AQHA, but they are now virtually all gone. I know of no recent cases being reported. The AQHA has done its best to remove all "paint" and "Appy" genetics from their gene pool, and perhaps that work is now complete.

It is extremely hard to hide Lp in a line of horses, unless the breed has an obscuring trait. For example, the Lippizan and the Andalusian are now almost entirely grey carriers, and Lp hides there well. However, if obscuring genes like grey are not present, and/or when the right two horses are crossed, a modifying gene that helps to produce white patterning is also inherited, from the other parent, and presto - a blanket, and a very obvious-looking horse. Several famous lines of Appaloosas started out this way, the result of a cross between two AQHA parents.

Regarding LP-caused Roaning:

It is incorrect to say that eventually all Lp-carrying horses "roan out completely". Some amount of roaning normally occurs when Lp is present, but the amount varies greatly. Most horses get a moderate amount of roan hairs, some get very very few - a handful sprinkled through the coat. Also, in ALL cases, no matter how much roaning LP causes, the horse never roans completely to an all-white appearence. It retains "varnish marks", and this pattern cannot be mistaken for any other type of roaning, nor does it look like the pattern caused by the grey gene. "Varnish" marks are dark areas where less roaning occurs, and are located over the bony, prominant areas of the body, an important distinguishing feature of LP-roaning. Horses that are homozygous for LP roan more evenly, because they get no dark body spots, just white hairs, and they have unpigmented hooves, but they still keep their "varnish marks".

Photo of an LP-roan by Sheila Archer.

Another horse, much older, and homozygous for LP, so she has no spots, only a lot of white hairs. Still, she has retained her varnish marks. Note the extreme loss of pigment in her face. Some homozygous Appaloosas get this way as they age. Photo by Sheila Archer.

Readers who would like to learn more about the Appaloosa and its genetics,

please consider joining our research team's electronic classroom:

http://groups.yahoo.com/group/theappaloosaproject/

To learn more about the current research being conducted in Appaloosa genetics:

www.theappaloosaproject.org

The Appaloosa Project research team is made up of ten equine genetics researchers from all over N. America. Sheila Archer is the phenotype researcher (studies the inheritance of obvious physical traits), working with photos and pedigree analysis. The other nine members of the Appaloosa Project research team are molecular biologists, headed by Dr. Rebecca Bellone (was Terry). They do lab-based genetic research on the DNA samples Ms. Archer finds for them from selected groups of horses.

Funding for the Appaloosa Project comes through the participating universities (U of Tampa, U of Kentucky and Texas A&M), as well as a yearly research grant from the Appaloosa Horse Club of Canada (ApHCC), and private donations from breeders and Appaloosa enthusiasts.

If you would like to donate to our research, we would really appreciate it. All ten of our researchers are volunteers. Not one cent of the money we raise for research goes to us - only to the purchase of lab materials, chemicals and sample shipping costs. To find out how to donate, please visit this link:

http://www.theappaloosaproject.org/shirts.htm#Donate

Sincerely,

Sheila Archer