Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
The dorsal stripe
The dun dorsal stripe is a single, continuous dark line running from the base of the mane to the top of the tail, along the midline of the back. It is bilateral-midline-symmetric: one line, centered, consistent in width. It is darker than the body coat because it runs through the undiluted region where TBX3 does not suppress melanin.
Brindle stripes are multiple, irregular, and oblique. They run vertically along the neck and shoulder, across the barrel and flanks. They are not midline and not bilateral-symmetric. They follow the migration paths of the melanocyte clones that produced them, paths that are consistent in general anatomy but not in precise location from one horse to the next. A brindle horse will have stripes on the shoulder that a dun horse does not, and a dun horse will have one crisp midline stripe that no brindle mechanism produces.
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
How to tell them apart
The visual signatures are distinct when you know what to look for:
The dorsal stripe
The dun dorsal stripe is a single, continuous dark line running from the base of the mane to the top of the tail, along the midline of the back. It is bilateral-midline-symmetric: one line, centered, consistent in width. It is darker than the body coat because it runs through the undiluted region where TBX3 does not suppress melanin.
Brindle stripes are multiple, irregular, and oblique. They run vertically along the neck and shoulder, across the barrel and flanks. They are not midline and not bilateral-symmetric. They follow the migration paths of the melanocyte clones that produced them, paths that are consistent in general anatomy but not in precise location from one horse to the next. A brindle horse will have stripes on the shoulder that a dun horse does not, and a dun horse will have one crisp midline stripe that no brindle mechanism produces.
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
The molecular mechanism: TBX3
The genetic basis of equine dun was resolved in 2016 by Imsland and colleagues, published in Nature Genetics. The causative locus is a regulatory variant affecting expression of TBX3 (a T-box transcription factor) in melanocytes. The dun dilution results from directed, asymmetric distribution of melanin within individual hair shafts: melanin accumulates on the dorsal side of each hair and is reduced on the ventral side, producing the diluted appearance of the body coat. The primitive markings arise because TBX3 expression is regulated differently in the cells that produce the dorsal stripe, leg barring, and face-points, leaving those regions with normal (undiluted) melanin distribution. [Imsland et al., Nature Genetics, 2016, doi:10.1038/ng.3537; OMIA:001957-9796, Dun, Equus caballus]
This is a single gene affecting every melanocyte in the body through a positional distribution mechanism. It is the opposite of the mechanisms that produce brindle: dun operates uniformly across the coat, creating a consistent pattern determined by the horse’s genetic background; brindle arises from two distinct cell populations in the same coat, producing irregular stripes whose distribution is determined by developmental cell migration rather than by the horse’s constitutive genotype. [Murgiano et al., G3, 2016]
How to tell them apart
The visual signatures are distinct when you know what to look for:
The dorsal stripe
The dun dorsal stripe is a single, continuous dark line running from the base of the mane to the top of the tail, along the midline of the back. It is bilateral-midline-symmetric: one line, centered, consistent in width. It is darker than the body coat because it runs through the undiluted region where TBX3 does not suppress melanin.
Brindle stripes are multiple, irregular, and oblique. They run vertically along the neck and shoulder, across the barrel and flanks. They are not midline and not bilateral-symmetric. They follow the migration paths of the melanocyte clones that produced them, paths that are consistent in general anatomy but not in precise location from one horse to the next. A brindle horse will have stripes on the shoulder that a dun horse does not, and a dun horse will have one crisp midline stripe that no brindle mechanism produces.
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
What dun is
Dun is a coat modifier that dilutes the body color while leaving the primitive markings (dorsal stripe, leg barring, face masking, shoulder stripe, cobwebbing on the forehead) undiluted and often intensified by contrast. A bay dun (sometimes called “classic dun” or “buckskin dun”) has a tan body with black points, a dark dorsal stripe, and often dark barring on the legs. A red dun has a diluted chestnut body with red-orange primitive markings. A grullo (also grulla) is a dun on a black base: a smoky blue-grey body with black points and primitive markings. [Wikipedia: Dun gene; Wikidata Q5316479]
The Dun gene is dominant. One copy produces dun phenotype; two copies produce the same visible result (the trait is not additive in a way visible to the eye). A non-dun horse without the dilution does not carry primitive markings in the same form, though some non-dun individuals show a faint dorsal stripe that can create confusion. [Wikipedia: Dun gene]
The molecular mechanism: TBX3
The genetic basis of equine dun was resolved in 2016 by Imsland and colleagues, published in Nature Genetics. The causative locus is a regulatory variant affecting expression of TBX3 (a T-box transcription factor) in melanocytes. The dun dilution results from directed, asymmetric distribution of melanin within individual hair shafts: melanin accumulates on the dorsal side of each hair and is reduced on the ventral side, producing the diluted appearance of the body coat. The primitive markings arise because TBX3 expression is regulated differently in the cells that produce the dorsal stripe, leg barring, and face-points, leaving those regions with normal (undiluted) melanin distribution. [Imsland et al., Nature Genetics, 2016, doi:10.1038/ng.3537; OMIA:001957-9796, Dun, Equus caballus]
This is a single gene affecting every melanocyte in the body through a positional distribution mechanism. It is the opposite of the mechanisms that produce brindle: dun operates uniformly across the coat, creating a consistent pattern determined by the horse’s genetic background; brindle arises from two distinct cell populations in the same coat, producing irregular stripes whose distribution is determined by developmental cell migration rather than by the horse’s constitutive genotype. [Murgiano et al., G3, 2016]
How to tell them apart
The visual signatures are distinct when you know what to look for:
The dorsal stripe
The dun dorsal stripe is a single, continuous dark line running from the base of the mane to the top of the tail, along the midline of the back. It is bilateral-midline-symmetric: one line, centered, consistent in width. It is darker than the body coat because it runs through the undiluted region where TBX3 does not suppress melanin.
Brindle stripes are multiple, irregular, and oblique. They run vertically along the neck and shoulder, across the barrel and flanks. They are not midline and not bilateral-symmetric. They follow the migration paths of the melanocyte clones that produced them, paths that are consistent in general anatomy but not in precise location from one horse to the next. A brindle horse will have stripes on the shoulder that a dun horse does not, and a dun horse will have one crisp midline stripe that no brindle mechanism produces.
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map
The most common stripe on a horse is not brindle. It is the dorsal stripe: a dark line running from the mane to the tail, present in dun horses across nearly every breed on earth. A dun horse may also carry leg barring (zebra stripes), a transverse shoulder stripe, and darker face-points. All of these are primitive markings caused by a single dilution gene. None of them are brindle.
The confusion matters because the question “is this brindle?” comes up most often in the context of a horse with visible stripes, and in most cases the answer is: no, this is dun. Brindle is rare enough that a dun horse is statistically overwhelmingly more likely than a brindle horse in any given encounter. But the patterns are visually distinct once you know where to look, and the distinction has consequences: brindle involves two cell populations in the same coat; dun involves a single, inherited, dilution mechanism across the whole animal.
What dun is
Dun is a coat modifier that dilutes the body color while leaving the primitive markings (dorsal stripe, leg barring, face masking, shoulder stripe, cobwebbing on the forehead) undiluted and often intensified by contrast. A bay dun (sometimes called “classic dun” or “buckskin dun”) has a tan body with black points, a dark dorsal stripe, and often dark barring on the legs. A red dun has a diluted chestnut body with red-orange primitive markings. A grullo (also grulla) is a dun on a black base: a smoky blue-grey body with black points and primitive markings. [Wikipedia: Dun gene; Wikidata Q5316479]
The Dun gene is dominant. One copy produces dun phenotype; two copies produce the same visible result (the trait is not additive in a way visible to the eye). A non-dun horse without the dilution does not carry primitive markings in the same form, though some non-dun individuals show a faint dorsal stripe that can create confusion. [Wikipedia: Dun gene]
The molecular mechanism: TBX3
The genetic basis of equine dun was resolved in 2016 by Imsland and colleagues, published in Nature Genetics. The causative locus is a regulatory variant affecting expression of TBX3 (a T-box transcription factor) in melanocytes. The dun dilution results from directed, asymmetric distribution of melanin within individual hair shafts: melanin accumulates on the dorsal side of each hair and is reduced on the ventral side, producing the diluted appearance of the body coat. The primitive markings arise because TBX3 expression is regulated differently in the cells that produce the dorsal stripe, leg barring, and face-points, leaving those regions with normal (undiluted) melanin distribution. [Imsland et al., Nature Genetics, 2016, doi:10.1038/ng.3537; OMIA:001957-9796, Dun, Equus caballus]
This is a single gene affecting every melanocyte in the body through a positional distribution mechanism. It is the opposite of the mechanisms that produce brindle: dun operates uniformly across the coat, creating a consistent pattern determined by the horse’s genetic background; brindle arises from two distinct cell populations in the same coat, producing irregular stripes whose distribution is determined by developmental cell migration rather than by the horse’s constitutive genotype. [Murgiano et al., G3, 2016]
How to tell them apart
The visual signatures are distinct when you know what to look for:
The dorsal stripe
The dun dorsal stripe is a single, continuous dark line running from the base of the mane to the top of the tail, along the midline of the back. It is bilateral-midline-symmetric: one line, centered, consistent in width. It is darker than the body coat because it runs through the undiluted region where TBX3 does not suppress melanin.
Brindle stripes are multiple, irregular, and oblique. They run vertically along the neck and shoulder, across the barrel and flanks. They are not midline and not bilateral-symmetric. They follow the migration paths of the melanocyte clones that produced them, paths that are consistent in general anatomy but not in precise location from one horse to the next. A brindle horse will have stripes on the shoulder that a dun horse does not, and a dun horse will have one crisp midline stripe that no brindle mechanism produces.
Leg barring
Dun leg barring is horizontal and transverse: stripes that cross the leg perpendicular to its length, concentrated on the cannon and lower leg. They are dark on a lighter (diluted) limb background.
Brindle stripes on the legs run longitudinally, following the length of the leg rather than crossing it. The distribution reflects the vertical migration paths of the two melanocyte populations. A horse with horizontal leg striping has dun barring; a horse with lengthwise leg markings in a coat that is otherwise striped may have brindle.
Body color consistency
A dun horse’s body coat is evenly diluted: consistently lighter across the trunk and sides, with the primitive markings as the exception. The dilution is uniform because TBX3 acts on every melanocyte in the body coat through the same mechanism.
A brindle horse’s body coat is two-toned in stripes that vary in width and density. The non-stripe regions may be the base coat color; the stripes are where the second cell population expresses a different pigment level. The transition between stripes and base coat is typically softer and more irregular than the crisp contrast of a dun dorsal stripe.
Other dun markings
Dun horses may carry additional primitive markings that brindle horses do not: a shoulder stripe (a transverse dark bar across the withers and shoulder forming a cross with the dorsal stripe), cobwebbing (dark radiating lines from the center of the forehead), darker face-points, and frosted mane or tail hairs. These markings are part of the dun expression pattern and have no parallel in any of the brindle mechanisms. [Wikipedia: Dun gene]
The non-dun dorsal stripe: a third scenario
Some horses that do not carry the dun dilution allele nevertheless show a faint dorsal stripe. This is particularly common in certain breeds (Fjords, Przewalski’s horses, some Iberian breeds) and in horses with countershading (a general lightening of the ventral body that intensifies the contrast of the naturally darker topline). In these cases the stripe is typically narrow, faint, and lacks the full suite of dun primitive markings (no leg barring, no shoulder cross). Genetic testing that confirms the horse is non-dun (absence of TBX3 regulatory variant) separates this from true dun. [Imsland et al. 2016]
A horse with a faint midline stripe and no other primitive markings, no leg barring, and a non-diluted body coat is most likely non-dun with countershading, not brindle. The multi-stripe pattern across the shoulder and barrel is the diagnostic feature of brindle; a single midline stripe without other brindle characteristics should not be called brindle.
The statistical reality
Dun is present in virtually every horse breed on earth. In breeds where it is common (Fjord, Norwegian Dun, Dun Quarter Horse, Grullo, Buckskin), the majority of horses carry at least one dun allele. Brindle, by contrast, is rare enough that peer-reviewed studies are built around small numbers of documented cases. In a 2018 Spanish horse study, chimerism (one mechanism producing brindle-like coats) was documented at approximately 0.011% prevalence across 21,097 horses. [Anaya et al. 2018, via ScienceDaily]
This means that in any encounter with a striped horse, the prior probability strongly favors dun or dun-adjacent countershading over brindle. The diagnostic step is examining the stripe pattern: single midline stripe with horizontal leg barring and diluted body coat points strongly to dun; irregular vertical multi-stripes across the shoulder and barrel with two-toned body coat points toward brindle mechanisms. Both deserve evaluation, but the base rate should set the starting expectation.
Quick reference
| Feature | Dun | Brindle |
|---|---|---|
| Dorsal stripe | One, midline, crisp | Absent (brindle stripes are lateral, not midline) |
| Leg striping | Horizontal barring, transverse to leg | Longitudinal stripes, along leg length |
| Body coat | Evenly diluted across trunk | Two-toned in irregular vertical stripes |
| Shoulder marking | Transverse shoulder stripe possible | Heavy striping on shoulder/neck region |
| Mechanism | TBX3 regulatory variant, one gene | Two melanocyte populations (chimerism, mosaicism, BR1, or IP) |
| Heritability | Dominant, simple Mendelian | Depends on mechanism; BR1 is X-linked; others non-heritable |
| Rarity | Common, present in many breeds | Rare; documented cases number in the dozens |
Related reading
- Brindle Horses: Mechanisms, Genetics, and Patterns: the confirmed causes of brindle
- Brindle vs Roan Horse: How to Tell Them Apart: another common misidentification
- Brindle vs Rabicano: The Striping That Isn’t Brindle: the white-ticking pattern compared
- Blaschko’s Lines in Horses: why brindle stripes follow the developmental map