The Complicated Mystery of Mouse Dun in Primitive Horses

Mares and foals on the Ravenseyrie Sorraia Mustang Preserve
(photo: summer 2010)

In doing a bit of online research into the Polish Konik horses, I have been impressed how the history of the Polish Konik horse has many parallels to the history of the Sorraia horses, with Tadeusz Vetulani performing a role similar to that which Dr. Ruy d'Andrade undertook in Portugal, in the recovery of remaining regional horses who displayed tarpan-like characteristics (most having known to descend from the European wild horse that inhabited the region) and giving them back the opportunity to reproduce in a semi-wild setting with careful removal of off-types.

Though the Polish Konik tends toward a little coarser, pony-like build with more varying profiles than that of the Sorraia, there are, even so, Sorraia types that are present among them, suggesting each are representing regional variations of the same wild equine. See for yourself below:

A large herd of Konik horses at the Oostvaarderplassen nature preserve.
Many in this photo appear to share common phenotypical characteristics with the Sorraia and Sorraia Mustangs.
(Photos: A. Stuart)

Compare the above scene with one from Ravenseyrie:

Bella, Segura and Zorita
Ravenseyrie Sorraia Mustang Preserve

In the next photo, you will see Konik horses which differ quite a bit from the more refined, longer build of the Sorraia, giving the impression of rustic ponies. This morphological variation among the Koniks is an interesting feature that prompts curious conjectures on my part which are better left unmentioned for now.

Konik horses on a nature preserve near Arnhem in the Netherlands.
Note the difference in these Koniks, less refinement, shorter and of heavier build than the Sorraia
(Photos: A. Stuart)

In his book, VALLEY OF THE WILD HORSES, Hardy Oelke wrote:

"The Sorraia horse (zebro) is best classified as a subspecies of Equus ferus, and is according to newest DNA analyses an Iberian variant of the Tarpan. It was an important ancestor of the Andalusian and Lusitano. Its phenotype is similar to that of the Polish Konik (which is known to be a direct Tarpan descendent) but averages about 14 hands in size, and is more uniform in type."

Part of my foray into the world of the Polish Konik horses lead me to two research papers published online which attempt to unravel some of the mystery of the primitive colouring of these equines.

THE ISSUE OF BLUE DUN SHADE INHERITANCE IN THE HORSE and SELECTION OF POLISH KONIK HORSES FOR COAT COLOUR AND THE WAYS TO IMPROVE ITS EFFECTIVENESS are authored by Anna Stachurska and Antoni Brodacki. Both articles offer interesting data compiled from the Polish Konik studbook regarding the primitive "blue dun" coat colour more universally referred to as "grulla" or "mouse dun" (In Portugal this colour is defined as "rato" i.e rat coloured.)

With the phenotypical similarities between the Sorraia and the Konik horses in mind, I believe the results of our preservation efforts offer an additional window into the documenting of how the grulla colour expresses itself. Might the Polish researchers be interested in being made aware of the varying hues of grulla present in the offspring of our purebred Sorraia stallion, Altamiro and his harem of carefully selected Sorraia Mustang mares? I decided to write Anna Stachurska at the Department of Horse Breeding and Use, Agricultural University, Lublin, Poland. (Anna is one of the authors of the papers listed above.)

Shades of mouse dun among some of the Ravenseyrie herd members...even Kevin shows a little bit of grullo colouring!

Specifically, I had noted that in our small closed group of Sorraia and Sorraia Mustang horses, there are colours that have resulted which do not conform to the summations published in the inheritance paper.

The Issue of Blue Dun Inheritance in the Horse paper relays the following:

"...a distinct tendency appears the darker the parents the darker the progeny, and vice versa: lighter parents produce lighter progeny."

and

"Regarding the sex in the parents and foals it should be noted that dark sires did not sire light colts..."

and

"It could be concluded that the dark sires marked their offspring with the dark shade character more distinctly than dams, whereas the dams transferred the light shade more easily, though the differences were not significant (p>0.05). Besides, there is a visible tendency of a greater percentage of dark daughters than dark sons, produced by dark sires or dark dams."

Of the nine foals Altamiro (a dark grullo) has sired, only two are darker than he is--Fada and Interessado. Silvestre is a slightly lighter grullo than Altamiro. Animado and Encantara are medium shades of grulla and Segura, Pinoteia, Tocara and Levada are all light grulla shades.

Grazing at the bluff's edge in the summer of 2010
Ravenseyrie Sorraia Mustang Preserve

Anna Stachurska has been very gracious to engage in an email correspondence and is surprised that Altamiro would have sired light colts and fillies. Anna says, that "nature is very complicated," and added, "Fine, you noticed it. And thank you for the report."

So far, the complicated mystery of the mouse dun colouring eludes definitive understanding and despite numerous studies being undertaken by talented scientists, the "dun gene" has yet to be isolated. However, particular DNA markers have been identified, and this in conjunction with photo identification, a three generation pedigree and hair root samples are providing the University of California Davis' Veterinary Genetics Laboratory with enough confirmation to offer a dun zygosity test. It should be noted that other labs question the reliability of this type of test.

Mares and foals on the Ravenseyrie Sorraia Mustang Preserve
(photo from the summer of 2008)

Because of the exchanges I have been having with Anna Stachurska, I have been inspired to place within the Journal of Ravenseyrie a pictorial documentation of each of Altamiro's foals, showing how their colour alters as they mature and how variations in light and the time of season also affect the appearance of their mouse dun colour. I will devote separate entries for each foal in the upcoming days.

Esteemed laboratories are working hard to understand more completely the complicated mystery of this primitive-colour-with-so-many-names, and their amazing diagnostic techniques are providing greater illumination of the genetics behind the grulla coat colour in horses. Of what possible good are studies which appear more anecdotal by documenting the colours of offspring between grulla dams and sires? These less sophisticated compilations are valuable for their ability to remind us that it is the horse and his environment that we are actually studying. Laboratory results from isolated components of equine hair samples provide just one window into the possible reasons for the way colour is expressed in horses. I feel it is important to also monitor and report on the outward appearance of coat colour as it is influenced by factors other than inherited genetics...after all we are just now beginning to realize (through the study of epigenetics) that environmental, dietary and even behavioural factors trigger the way genetics express themselves. These factors are not observable through a microscope, but only through long term observation of horses living in a natural habitat.

Animado is a light grullo, while both Interessado and Fada are very dark grullo
Ravenseyrie Sorraia Mustang Preserve

To learn more about this primitive coat color, readers may find these links helpful:

>> EQUINE COLOR GENETICS

>> http://www.dungenes.org/

>> http://www.horsecolor.com/dilutions/dun/index.html

>> http://www.vgl.ucdavis.edu/services/dunhorse.php

>> http://en.wikipedia.org/wiki/Dun_gene

>> http://en.wikipedia.org/wiki/Grullo