Horse Coat Colours and Markings Cindy Harper Onderstepoort Laboratory for Applied Veterinary Genetics
Basic Colours Black Bay Chestnut
Genetic Control of the Basic Colours Melanocytes produce melanin pigment 2 Pigments responsible for coat and skin colour eumelanin (black and brown) and phaeomelanin (red and yellow) Colour genes control either the pigment producing cell or pigment production 2 genes control the main colour switches in horses Extension (E) and Agouti (A)
Genetics Sire Dam Locus (address of a gene and each has a name) occurs on a pair of chromosomes 1 from sire and 1 from dam Form of gene (allele) on 1 chromosome of pair can be same as on other homozygosity Or different heterozygosity Different dominant and recessive where 1 allele is expressed and other is not Function: Gene that codes for protein Protein: Effect e.g. stimulates melanocyte to produce eumelanin Chromosome pair Result: Black horse
The Extension Gene/Locus (E) Difference between black and red lies in the action of 1 gene MC1R Allele symbols are E and e E extends black (eumelanin( eumelanin) ) in coat e extends red (phaeomelanin( phaeomelanin) ) in coat Combination of alleles at the extension locus: EE Ee ee Allows black in the coat: Black, brown, bay, buckskin, grullo Black in the skin but not in the coat: Chestnut, palomino
Black Pattern The Agouti Gene / Locus (A) AA Aa Black pattern limited to the legs, mane and tail aa Black distributed uniformly through the coat The combination of alleles at the extension and agouti genes / loci control the basic colour of the horse
Interaction between Extension and Agouti EEAA EEAa EeAA EeAa Black in coat Black at the points Bay, Brown EEaa Eeaa eeaa eeaa eeaa Black in coat Black throughout coat Only red in the coat coat Black, Chestnut,
Red Factor (e) Extension locus 2 alleles E and e ee breeding principles Chestnut + chestnut = all chestnut e e e ee ee e ee ee
Red Factor (Ee( Ee) and Black Pattern factor (Aa( Aa) Sire: eeaa chestnut ea ea chestnut + chestnut = All chestnut Extension (red) locus dominant over the Agouti (black) locus Dam: eeaa chestnut ea ea eeaa eeaa eeaa eeaa
Red Factor (Ee( Ee) and Black Pattern factor (Aa( Aa) Sire: EEaa black Ea Ea Dam: eeaa chestnut ea ea EeAa Bay EeAa Bay EeAa Bay EeAa Bay
Red Factor (Ee( Ee) and Black Pattern factor (Aa( Aa) Sire: Eeaa black Ea ea Dam: Eeaa black Ea ea EEaa Black Eeaa Black Eeaa Black eeaa Chestnut
Breeding Black Avoid recessive e! Genetic test for E/e Is this a true black (aa( aa) ) or dark bay / brown (Aa)? Genetic test for A/a
Principle Each horse has all the genes that can possibly code for any colour, BUT an individual allele combination that in total gives it a specific appearance! Extension Locus E e Agouti Locus A A Cream Locus CR N Grey Locus g g Tobiano Locus TO N 1 2 3 4 5 Genotype: E/e A/A N/CR g/g N/TO Phenotype: Diluted Bay (Buckskin) Nongrey with a Tobiano Paint pattern
What colour?
Basic Colour Modification Sooty / Shaded Black hairs between coat hairs Bay topline to extensive covering most of the body
Basic Colour Modification Sooty / Shaded Bay extensive shading Brown How to distinguish from true black? Genetic test aa black / Aa or AA - brown
The Brown Gene There is a brown gene (TYRP1) dilutes black to chocolate Most obvious in dogs, but not common colour in horses and chocolate and dun horses are caused by other genes
When is a horse Brown?! Brown in horses is a term used to describe a shade of bay in horses. Some breeders describe all bays with shading / sootiness as Brown Some breeders describe all bays regardless of shading as bays Most commonly breeders describe the dark, extensively shaded bay as brown and all other bays as bay Heritability?
Brown Heritability Some believe that brown can be bred and is in fact a sub-division of the agouti locus or extension locus (A t or E B ) Black is allowed in the coat and is more extensive than the points in a bay This would support the proposal that brown ( extensive( bay ) ) is heritable and breedable
Colour terms Terms that describe a phenotype what you see Depend on breed / society / country / individual Only right or wrong is to find and test the actual genetic control! FEI rulebook states that the definition of colour differs according to country.
Basic Colour Modification Sooty / Shaded Chestnut usually distributed throughout the coat Liver Chestnut
Basic Colour Modification Mealy Mealy causes lighter areas on the belly, muzzle, inner legs, and over the eyes. It is usually ignored in color description. Black - Seal brown (test aa is modified black / Aa or AA is bay with lots of shading) Chestnut to sorrel for breeders of draft horses
Mealy Dun Bay
Bay Black Points Legs Ear tips Mane Tail
Variations of Bay
Black No Brown in coat White markings are allowed Genetic test aa vs Aa or AA and EE or Ee
Feature of Bay vs Black A black horse, even with a sun-bleached hair coat will have solid black hairs around the eye. Bay Black
Chestnut e e e ee ee e ee ee Recessive traits are expressed phenotypically when in homozygous form! Red coat throughout no black points.
Chestnut Modifications Liver Flaxen Flaxen and mealy
White on basic coat Any white or white pattern is SUPERIMPOSED on a basic colour Cover the whole or part of the horse Pattern name Grey Roan Roaning Spotting Paints White markings
Grey Born any colour becomes grey Usually starts on head and is progressive Speed of greying individual Gradual process completely white with pigmented skin
Grey Breeding Dominant trait GG and Gg always grey i.e. a horse does not carry a hidden grey gene A grey foal must have at least 1 grey parent! Homozygous grey + non grey 100% Grey g G Gg G Gg g Gg Gg
Grey Breeding A horse can have any combination of base coat genes, but G overrides all e/e a/a N/RN to/to C/C G/g = GREY Grey is going to obliterate any other colour pattern 2 greys can produce a non-grey DNA Test available G G GG g Gg g Gg gg
Grey Variations Variations of grey can given different names: Rose grey Steel grey Fleabitten grey Dapple grey
Roan Permanent colour,, white does not progress with age! Dark head and limbs Characteristic inverted V above knees
Roan Genetics RN is caused by a dominant gene. RNrn or rnrn (not roan) no test yet THUS: A roan must have 1 roan parent! Homozygous dominant roan RNRN = lethal resorption?
Roan Variations Chestnut Roan Blue Roan
Rabicano / Roaning Rabicano,, also called white ticking or roaning,, is characterized by limited roaning in a specific pattern, usually in the flank, sides and the tailhead Also in breeds which do not possess any true roan Thoroughbreds and Arabians
Spots THE LEOPARD COMPLEX Produced by a the leopard gene complex (Lp( Lp) It is a dominant trait patterns produced by modifier genes Not all horses with the dominant leopard allele (Lp)) will be spotted but indicators of this gene include: White sclera Mottled skin Striped hooves
Leopard Breeding Occurs in many breeds but in some it is a fixed characteristic Appaloosa, Knapstrup, Noriker Dominant Lp allele expresses a pattern Pattern depends on modifiers Horse with a specific pattern can produce the whole range of patterns depending on the modifiers in its gene complex No specific test
Leopard Patterns Leopard
Blanket
Varnish Roan Not Rn or G Lp spotting complex gene with characteristics and may have leopard spots Mottled skin, color mainly on bony points (on the face, usually in a distinct V on the bridge of the nose; on the cheeks, point of shoulder, elbows, knees, point of hips, hock) and it can be seasonal as well Roans (RN) are roan from birth, varnish roans are born quite solid with some spots and "roan out" as they age
Varnish Roan Variations
Leopard Variations Small Blanket Extensive Solid Blankets Extensive Spotted Blanket or Near Leopard Leopards with various sized spots
Paints Basic colour with a white pattern superimposed Patterns are controlled by separate genes and are heritable Extent of pattern can vary
Tobiano Most legs white White crosses the topline General head markings (may have no head markings) Mixed tail Regular Edges Dominant gene TO/TO or N/TO Direct Genetic Test available
Tobiano Variations
Frame Overo Dark legs White patches on the sides Irregular Edges Extensive head markings Tail one colour
Frame Overo
OLWS Frame Overo is associated with Lethal White Foal Syndrome (LWF) Mutation in gene supposedly produces frame overo O/O Test for this mutation Some solids carry the O mutation (N/O) N/O x N/N always to avoid lethal O/O solid white foal with incomplete intestinal development
Sabino Legs extensively white edges mottled White mottled body spots with ticking and roaning Extensively marked faces with white chin Polygenic trait 1 sabino pattern test available N/SB1 or SB1/SB1 extensive white sabino but no lethal
Sabino Variations Paint pattern but occurs in many breeds
Splashed White Legs, body and face are white Edges of markings are crisp Dipped into white paint
Dilution Factors Cream Dun Silver Champagne
Cream Dilution Caused by Dilution factor Cr at the cream locus Incomplete dominant gene, which means that it is expressed to some degree when there is only one copy of the gene and to a greater degree when there are 2 copies DNA test available 1 copy of dilution factor N/Cr Dilutes only red to yellow Does not dilute black
Palomino ee N/Cr Chestnut
Buckskin EEAa or EeAa and N/Cr Bay
Sooty Buckskin EEAa or EeAa and N/Cr Shaded Bay
Smoky Black Ee or EE and aan/cr Both tested to carry the cream dilution factor Can produce palomino, buckskin and double dilutes even though it looks black
Cream Dilution 2 copies of dilution factor Cr/Cr Dilutes red and black Pink skin and blue eyes (not albinos) Diluted Chestnut = Cremello Diluted Bay = Perlino
Cream Dilution DNA-tested: TOto EE aa Cr/Cr Diluted Black = Smoky Cream
Grey vs. Cremello
Dun Dilution Factor + Primitive Marking Factor: Linked Primitive marks are the colour of the undiluted base colour Simple dominant gene DNDN dun DNdn dun dndn not dun Dilutes all colours to a certain extent Yellow colour more tan than cream dilution Manes, tails and primitive markings colour of non- diluted base colour No direct DNA test (zygosity( test based on pedigree and other markers)
Primitive Markings List (dorsal stripe) Zebra stripes Withers stripe Cobwebbing on face
Bay with dun gene zebra dun Classic Fjord colour Dun Variations
Dun Variations Chestnut : orange + red points Red Dun Black : mouse / smoky coloured horse with black points Grullo
Silver / Taffy (aus( aus) Silver gene (Z) is a simple dominant Dilutes black but not red Results in colors that are frequently confused with chestnut, but that lack the redness of chestnut Lightens manes, tails, and lower legs to flaxen or silver grey, or can leave them relatively unchanged Gene has been identified and test is available N/N no silver mutation present Z/N or Z/Z silver mutation present
Silver Variantions N/Z or ZZ Bay-based horses will have chocolate lower limbs with flaxen mane and tail and red body Red Silver
Silver Variantions N/Z or ZZ Black-based / Brown horses will be chocolate with flaxen mane and tail Chocolate Silver or Silver Dapple
Silver Characteristics Progressive colour that changes with age Foals often have silver eyelashes
Silver Variations Chestnut will not be affected but may be confused with bay silver Chestnut confirmed silver carrier
Champagne Simple dominant gene that dilutes hair pigment from black to brown and red to gold N/Ch and Ch/Ch The skin of Champagne-diluted horses is pinkish/lavender toned and becomes speckled with age; the speckling is particularly noticeable around the eye, muzzle, under the tail The eye color is blue-green at birth and darkens to amber as the horse ages. DNA test is available
Champagne Variations Chestnut (red) diluted to gold body colour with flaxen mane and tail Bay diluted to a tan body color with brown points Black to a darker tan body with brown points
Champagne Variations Pinkish skin Blue to amber eyes Speckles
Horse Colour can be confusing without genetic testing Palomino N/Cr Chocolate Silver Z/Z or N/Z Flaxen Chestnut
Horse Colour can be confusing without genetic testing Smoky Cream E a/a Cr/Cr Perlino E A Cr/Cr Champagne Grullo a/a DN Ch
White No albinos No W/W lethal N/W true white Spot and paint patterns extensive Grey pigmented skin and eyes Cremello and Perlino