Sunday, September 24, 2017

The Roan Modifier


We will begin with an in-depth description of the Roan Modifier including genetics. Examples of roans will be provided in as many colours as we could find in the wild horse herds. We will conclude with other types of 'roaning' as well as confusing colours.  As with all the horse photographs presented here, we do not know the genetics of the animals; we rely solely upon the phenotype (physical appearance) of the animal.

The term roan or roaning refers to any horse with white hairs intermixed on a base coat.  It can be applied to horses going grey, sabinos patterns, Rabicano, varnish-rain appaloosa, or the dark-headed or ‘classic’ roan.  The classic roan modifier acts on any base coat colour and changes the body to varying degrees of white; leaving the head, mane, tail and lower legs the original colour in most cases. The colour does not change after birth; these horses are roan from birth or after their first foal coat sheds. Grey horses get progressively lighter as they age whereas some roans actually get darker as they age. This darkening appears in some roan lineages and mares seem to darken more than stallions or geldings. Hereafter, "roan" will refer to the classic roaning patterns which are nonprogressive and heritable (Sponenberg, D, 1996).

A bay (left), and a bay roan (right)

The Roan Modifier acts upon an existing coat colour. It causes the intermingling of white hairs amongst the base colour except on the mane, head, tail and lower legs (points). In the image above, we have a bay horse on the left and a bay roan on the right. You can easily see how the colour is lightened by the presence of white hair. Some horses have nearly white body colour, while some have just a dusting of light hair along the back and flank. The amount of white can be quite variable. Additionally, any scars that are acquired in the roan area grow back in the base coat colour (Gower, 2016).


The genetic control is autosomal dominant which means if one parent has the trait, the offspring will have the trait. If both parents have the trait, then all the offspring will have the trait. Roans tend to become common in populations where a dominant stallion has a large harem. He will pass the roan trait to his offspring. For a long time, 'dominant roans' were thought to be associated with a lethal gene similar to the Lethal White Syndrome found in. Homozygous roans, or those with two genes for the roan trait (RR), were believed to die in utero because homozygosity was linked to a trait incompatible with life. Since the discovery of, and the mapping of the equine genome, there have been several homozygous roan stallions discovered (Bailey & Brooks, (2013). (See also: https://www.vgl.ucdavis.edu/services/Roan.php). 

The KIT region of the third equine chromosome is the site of several traits. The Roan trait, the Extension trait (which controls chestnut or 'not chestnut'- black or bay), Sabino 1 trait, Dominant white, Tobiano, and proteins used in blood typing. 
The roan trait effects the main coat, not the points (lower legs, mane and tail) as the extension trait effects the red coat of bays leaving the points dark. The roan trait also darkens the head. occasionally tobiano paints will have areas of roaning mixed within the paint pattern (examples below). Sabinos have a roan-like pattern with a frosted appearance to the patches of colour. All these traits are found on the same chromosome in close proximity, and the effects are similar although they may be caused by different genes (Hauswirth et al., 2013; Marklund, Moller, Sandberg, & Andersson, 1999; Negro Rama et al., 2016; Reissmann & Ludwig, 2013; Waud et al., 2009.).

Nomenclature


Roans have many names and these names are often interchangeable. Blue roan, strawberry roan, red roan, sorrel roan and dun roan are some of the terms to describe roans. For the purposes of this post, we will use the base coat+roan to describe the horses. So a roan modifying a grullo coat will be called a "grullo dun" and a chestnut coat modified by roaning will be a "chestnut roan".).

Black Roan/Dark Bay Roan

A horse with a black, dark bay, or any other dark colour with the roan modifier.
A black roan from Great Desert Basin, Utah 2016
Here we have a normal Black/Dark Bay in front and a Blue Roan in the middle. In the back is a Bay Roan.

'Blue' from Sand Wash Basin (2014). A lovely dark bay/black roan


A grey and a Black Roan. Greys may be confused with roans because of the similar white 'ticking' appearance but the greys often have more white in the tail and lighter faces. This can vary from grey to grey but they generally get lighter with age. Great Desert Basin, Utah 2017

Close-up of the legs. The roan (behind) has a more colour on the legs than the grey stallion in front. Great Desert Basin, Utah 2017

The Bay Roan


Roan Foal and her dam. This foal looks more roan in other photos but it is still very subtle. Sand Wash Basin, Colorado 2014
Bay Roan Paint foal. Noter the tendency for even young foals to look distinctly roan. Great Desert Basin, Utah 2017

A bay roan foal, a grey mare, and chestnut roan paint foal behind. This chestnut roan may be a dun as they are several duns in the band. It is hard to see because the legs are white so we cannot see any primitive markings but there is a faint dorsal stripe.
A Bay Roan Paint foal. This youngster may have some grey in the mix as well as roan. The mane and tail are very dark, which is consistent with roan but the face is light. In the roans that have more white- it is usually distributed along the mane, tail, and face. It is hard to assess the points (legs) because there is a great deal of white present. Sand Wash Basin, Colorado 2016.


This is the same bay roan mare as the photo directly below and a good example of how lighting can alter the perceived colour of a horse.  If possible, try to view the horse with direct midday lighting with the sun behind you. Pilot Butte/Rock Springs, Wyoming 2013


A beautiful bay roan mare from Pilot Butte (Rock Springs, 2011). She demonstrates the inverted 'V' on the black points of her forelegs. She is very light with very dark points- this image was not enhanced in Photoshop but it was taken at dawn.


A beautiful mare from Great Desert Basin (2017). She has an interesting pattern of the 'corn spots' on her left flank. These marks can represent injuries that heal with the base colour replacing the white, or they can occur spontaneously. (Sponenberg, 2009).

This stallion has a very sandy base colour which may be a yellow-bay, or a buckskin/dun. The photo doesn't allow us to look for any primitive markings. Sand Wash Basin, Colorado 2014. Also, he shows minimal roaning. However, you'll see him again two photos below chasing another horse.

A handsome Bay Roan from Sand Wash Basin. He has a moderate amount of white as opposed to the stallion in the photo below (2015)

A dun  (?) roan chasing a light bay roan.- he does have a dorsal stripe which would make him a dun, but we cannot see any zebra striping on the legs in this photograph...
The Chestnut Roan
A chestnut roan- from Pryor Mountain.


Chestnut roan stallion from Sand Wash Basin.


The bay mare from earlier photos and her chestnut foal from Pilot Butte/Rock Springs. Some roans have greyish manes and tails. 


The same foal from the photo above.


A Alovely light chestnut, possible dun, from Pyror Mountain.


A liver chestnut stallions from  Great Desert Basin, Utah. Note the dark mane and tail.



'Cody' -a lovely dark liver chestnut roan from Sand Wash Basin, Colorado 2011. In this photo, Cody looks like a bay. However, in the photo below, he has reddish legs.


More Cody, the liver chestnut roan from Sand Wash Basin, 2014. Note how the colour changes based on season and lighting. Roans usually look darker in winter coats. In this photo, Cody has very light red legs- he may be a liver chestnut with a very dark mane & tail.
A foal who may be a roan. Until the first foal coat sheds, all bets are off. She may be greying out early, or she'll become darker on her head, legs, mane & tail. Sand Wash Basin, Colorado.


Running to the waterhole, a chestnut roan leads the way. Sand Wash Basin, Colorado.

The Palomino Roan

A foal from Sand Wash Basin, Colorado. This may be a future roan based on the darker head, and legs. The mane and tail are often very light in normally coloured palomino horses and so the roan colour may become nearly the same colour as the mane and tail. 



Another Palomino roam foal from Great Desert Basin.

The Dun/Grullo Roan

The dun (grullo) stallion in the back (sparring with a bay) tend to have a warmer tone to their coats then black/blue roans. To identify the dun roans, look for primitive markings on the legs.


A dun roan- here we can clearly see the zebra striping at the top of the black on the forelegs of this stallion. Primitive markings occur in dun horses and consist of zebra stripes on the legs, shoulders or wither stripes, 'dorsal stripe from withers to dock, cobwebs' on the face, and lighter guard hairs on the outside of the mane and tail. Additionally, there is a dorsal stripe along the top line and into the tail.

Nice dun roan with striping visible on the legs and withers/shoulders


A lovely grullo roan from the Pryors. Again they often have a warmer tone to their colouration.


The same grullo roan as above- noted the change in colour due to lighting- from the Pryors.

Other Roans

A frosted roan. The roaning incorporates the mane and tail. The effect is fine patina of white air brushed over the entire horse.

A varnish Appaloosa- similar to roans but they tend to have darker colour over bony prominences.They generally do not have darker legs, manes, or tails.

A fantastically marked roan bay pain from Great Desert Basin.


THe mare is a buckskin roan. The buckskin colour is caused by the presence on one cream gene on a bay horse. The cream gene acts on red base colour of bay turning it lighter yellow nbut leaves the black alone. In a chestnut horse, the cream gene lightens red to a gold to pale cream colour. This includes the mane and tail which are red in chestnut horses. There is clearly no dorsal strip in this horse so it is unlikely to be a dun. 


CONFUSING COLOURS


This grey paint resembles a roan but it is more lilely this horse is a sabino (a type of paint similar to roan) that may be greying out slowly.  Grey horses get lighter each year whereas roans do not. Grey horses are born dark and lighten with age, roans are either norn roan or shed into roan after their first foal coat.


At first glance I thought this horse was a roan but it turns out he is just very muddy...


Another almost roan... but it was just water and the sun reflecting off a dusty coat.


A grey sabino paint- note the light head.


A paint with a speckled pattern reminiscent of a roan from the Black Hills Wild Horse Sanctuary. This horse is a paint, possible sabino and/or frame overo.


Another sabino/frame overo (?) paint from Black Hills Wild Horse Sanctuary.


A chestnut paint Sabino from the Black Hills Wild Horse Sanctuary.

Roaning Patterns in other coat types

Picasso, a well-known stallion from Sand Wash Basin is a Tobiano paint. He may have other genetics as well as Tobiano. Because the KIT gene controls roaning as well as Sabino and Tobiano, those traits tend to have similar characteristics.  Many Tobiano  paints have roaning intermingled in their paint pattern. Below are several photographs of Picasso and Cowboy.



Picasso, left side and mud


Picasso, right side


Cowboy, a frame overo with roaning mixed in the paint pattern.


Cowboy left side


Cowboy, right side


Cowboy, right side



Kokomo, Picasso's son.


References

Bailey, E & Brooks, S. (2013). Horse Genetics (2nd ed.). Boston, MA: CAB International.


Dürig, N., Jude, R., Holl, H., Brooks, S., Lafayette, C., Jagannathan, V., & Leeb, T. (2017). Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes.

Gower, J. (2016). Horse Color Explained: A Breeder's Perspective. Brattleboro, Vermont: Echo Point Books & Media, Inc.

Haase, B., Brooks, S. A., Schlumbaum, A., Azor, P. J., Bailey, E., Alaeddine, F., . . . Leeb, T. (2007). Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses. PLOS Genetics, 3(11), e195. doi:10.1371/journal.pgen.0030195

Haase, B., Jude, R., Brooks, S. A., & Leeb, T. (2008). An equine chromosome 3 inversion is associated with the tobiano spotting pattern in German horse breeds. Animal Genetics, 39(3), 306-309. doi:10.1111/j.1365-2052.2008.01715.x

Hauswirth, R., Jude, R., Waud, R Bellone, R., Archer, S., Holl, H., . . . Leeb, T. (2013). Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes (Vol. 44).

Kathman, L. (2012). The Equine Tapestry: Volume I- Draft and Coaching Breeds. Charlotte, NC: Blackberry Lane Publishing.Marklund, S., Moller, M., Sandberg, K., & Andersson, L. (1999). Close association between sequence polymorphism in the KIT gene and the roan coat color in horses KIT sequences: AJ224642–AJ224645 (Vol. 10).

Negro Rama, S., Imsland, F., Valera, M., Molina Alcalá, A., Solé, M., & Andersson, L. (2016). Association analysis of KIT, MITF, and PAX3 variants with white markings in Spanish horses (Vol. 48).

Reissmann, M., & Ludwig, A. (2013). Pleiotropic effects of coat colour-associated mutations in humans, mice and other mammals (Vol. 24).

Santschi, E. M., Vrotsos, P. D., Purdy, A. K., & Mickelson, J. R. (2001). Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. Am J Vet Res, 62(1), 97-103.

Sponenberg, D. (2009). Equine Color Genetics (3rd ed.). Ames, Iowa: Wiley-Blackwell.

Thiruvenkadan, A., Kandasamy, N., & Panneerselvam, S. (2008). Coat colour inheritance in horses (Vol. 117).

Waud, Brooks, S., Tozaki, T., Burger, D., Poncet, P.-A., Rieder, S., . . . Leeb, T. (2009). Seven novel KIT mutations in horses with white coat colour phenotypes (Vol. 40).

Waud, Rieder, S., Tozaki, T., Hasegawa, T., Penedo, C., Jude, R., & Leeb, T. (2011). Five novel KIT mutations in horses with white coat colour phenotypes (Vol. 42).






About the Author & Photographers

AUTHOR & PHOTOGRAPHER

Dr. Meredith Hudes-Lowder,
 DNP, WHNP-BC, MSN, BSN, RNC, BS Biology

Meredith received a Bachelor of Science Degree from Binghamton University with an emphasis in ethology and genetics. She received a Bachelor of Science in Nursing also from Binghamton and a Masters of Nursing in Perinatal/Women's Health from Stony Brook University. She has a Research Doctorate of Nursing Practice from Stony Brook University. Her doctoral thesis was a research study on cervical cancer screening intervals. She was invited to present her research findings at the podium for the Nurse Practitioners in Women's Health Annual Conference in New Orleans, October 2016. She is a member of several professional organisations and was inducted into Sigma Theta Tau- the Nursing Honor Society in 2007.






PHOTOGRAPHER

Karen McLain: Painter, artist, photographer

Karen McLain is a third generation Arizona native. Growing up in Arizona, she developed a deep appreciation for the outdoors, and for the rural and ranching lifestyle. Karen graduated from Arizona State University with a B.A. in Studio Art. She went on to pursue more traditional and realistic styles, and to create a style of her own. A number of commissioned works are accepted from collectors. The rest of the time, Karen can be found drawing or painting en plein air. These landscapes and life studies of wild horses are then developed into larger works in her studio.

McLain states: ”Painting from life not only reveals natures beauty first hand, but it also challenges me to focus and see clearly the light, form, and wonderful color present.  Time spent in the saddle, and painting en Plein air, results in an outlook that McLain describes as “Drawn from life, and inspired by life”, which is reflected in her work. See Karen’s “studio tour” here












The Roan Modifier

We will begin with an in-depth description of the Roan Modifier including genetics. Examples of roans will be provided in as many c...