Name: A Agouti – facteur bai/noir
Brand: Equigerminal
Price: 43.05 EUR

À propos du test

Le locus Agouti contrôle la répartition du pigment noir. L'allèle dominant A limite le pigment noir aux extrémités. L'allèle a est récessif.

Pourquoi tester ?

Les chevaux n'ont que trois couleurs de base : bai (A/- E/-), alezan (-/- e/e) ou noir (a/a E/-). La couleur de base ne détermine pas à elle seule la robe du cheval, car de nombreux autres gènes la modifient : ils peuvent la diluer, la dépigmenter ou y ajouter des taches blanches ou d'autres motifs.

En l'absence de variantes dans les autres gènes modificateurs, le cheval présente le phénotype de la couleur de base.

La couleur de base de la robe est déterminée par la somme de deux loci, Agouti et Extension.

Le locus Agouti contrôle la répartition du pigment noir. L'allèle dominant A limite le pigment noir aux extrémités. L'allèle a est récessif.

A/- E/- : couleur de base baie. L'allèle dominant A limite aux extrémités le pigment noir produit par l'allèle E.
a/a E/- : couleur de base noire. Le récessif homozygote a/a ne donne une couleur de base noire que parce qu'Extension impose la production de pigment noir.
-/- e/e : couleur de base alezane. Un cheval e/e ne produit que du pigment rouge et, n'ayant pas de pigment noir, il n'est pas influencé par Agouti.

Signes cliniques

Bai (A/- E/-). L'allèle dominant A limite le pigment noir aux extrémités : crinière, queue, bas des membres et bord des oreilles. Le corps va du bai clair au bai très foncé.

Noir (a/a E/-). Noir uniforme sur tout le cheval, y compris crinière, queue et membres.

Alezan (-/- e/e). Pigment rouge uniquement, de l'alezan clair à l'alezan très foncé, avec crinière et queue plus foncées, de même teinte ou lavées. Agouti n'a aucun effet visible sur un cheval -/- e/e.

La couleur de base ne détermine pas à elle seule la robe du cheval, car de nombreux autres gènes la modifient : ils peuvent la diluer, la dépigmenter ou y ajouter des taches blanches ou d'autres motifs. Phénotypes pouvant prêter à confusion :

Bai très foncé (A/- E/-) et noir (a/a E/-)
Noir (a/a E/-) décoloré par le soleil
Alezan très foncé (-/- e/e) et noir (a/a E/-)
Sooty (charbonné), qui assombrit le dos
Dilutions, qui modifient la couleur de base
Gris, qui dépigmente progressivement la couleur de base

Transmission

What breeders need to know about base coat colour:

Two black base colour a/a E/e horses mated together can produce foals with a black (a/a E/-) or chestnut (a/a e/e) base colour.
Two chestnut base colour (-/- e/e) horses mated together can only produce foals with a chestnut base colour (-/- e/e).
Two bay base colour A/a E/e horses mated together can produce foals with a bay (A/- E/-), black (a/a E/-) or chestnut (-/- e/e) base colour.
A bay base colour A/A E/E horse can never produce foals with a black (a/a E/-) or chestnut (-/- e/e) base colour, whatever the mating partner.

Mendelian probability for each foal from mating two bay base colour A/a E/e horses:

56.25% bay base colour: A/- E/-
18.75% black base colour: a/a E/-
25% chestnut base colour: -/- e/e

Why is it so important to test bay and black base colour horses?

Because horses with the same base colour can have different genotypes, and that changes the foals they can produce.

Bay base colour horses:

A/A E/E: only produces foals with a bay base colour (A/- E/-), whatever the mating partner.
A/a E/E: carries the recessive a allele. Never produces foals with a chestnut base colour (-/- e/e). Mated with another carrier of the a allele, or with an a/a horse, it can produce foals with a black base colour (a/a E/-).
A/A E/e: carries the recessive e allele. Never produces foals with a black base colour (a/a E/-). Mated with another carrier of the e allele, or with a -/- e/e horse, it can produce foals with a chestnut base colour (-/- e/e).
A/a E/e: carries the recessive a allele and the recessive e allele. Can produce foals with a bay (A/- E/-), black (a/a E/-) or chestnut (-/- e/e) base colour.

Black base colour horses:

a/a E/E: never produces foals with a chestnut base colour (-/- e/e), whatever the mating partner.
a/a E/e: carries the recessive e allele. Mated with another carrier of the e allele, or with a -/- e/e horse, it can produce foals with a chestnut base colour (-/- e/e).

By appearance, these horses are identical. Only the DNA test shows which is which.

And that is why it is important to choose the mating partner carefully.

Prévention

100% probability of foals with a chestnut base coat -/- e/e. Both parents must have a chestnut base coat -/- e/e. The parents' Agouti genotype does not change the foal's base coat, but it is passed on.

Foals with a black base coat a/a E/-. Each parent must have at least one recessive a allele (A/a or a/a) and at least one of the parents must have the E allele. For a 100% probability of foals with a black base coat, both parents must be a/a and at least one must be E/E. Two a/a E/e horses mated together: 75% black base coat a/a E/- and 25% chestnut base coat a/a e/e.

100% probability of foals with a bay base coat A/- E/-. At least one parent must be A/A and at least one parent must be E/E. An A/A E/E horse produces 100% foals with a bay base coat, whatever the mating partner.

Base coat selection. To select against a chestnut base coat, use at least one E/E parent. To select against a black base coat, use at least one A/A parent.

The Agouti genotype of a chestnut base coat horse matters. An a/a e/e horse passes the a allele to 100% of its foals. Mated with a black base coat a/a E/E horse, it produces 100% foals with a black base coat a/a E/e.

Base coat should not be the only criterion for choosing a mating partner.

Résultats

Bai : A/- E/-
• Agouti : A/A ou A/a

Noir : a/a E/-
• Agouti : a/a

Alezan : -/- e/e
• Agouti : A/A, A/a ou a/a

Exigences d'échantillon

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Crins avec racines : 20 à 40 crins arrachés (et non coupés) de la crinière ou de la queue, avec leur racine. Fixez-les avec du ruban adhésif dans la zone prévue du formulaire d'envoi imprimable. Les crins sans racine ne peuvent pas être analysés.

Sang : 5 mL de sang total dans un tube K3-EDTA, prélevé par un vétérinaire. Étiquetez le tube avec le nom du cheval et envoyez-le avec le formulaire d'envoi.

Conservez les échantillons au sec et à température ambiante, sans les congeler. N'envoyez pas de crins mouillés, moisis ou souillés par la litière ou les crottins.

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Délai d'exécution

Traitement standard : résultats sous 5 à 10 jours ouvrés après l'arrivée de l'échantillon au laboratoire. L'envoi est organisé et payé par le client, et le délai de transport n'est pas compris dans ces 5 à 10 jours ouvrés.

Les échantillons dont l'extraction ou l'amplification de l'ADN échoue sont repris sans frais supplémentaires, ce qui peut ajouter quelques jours ouvrés. Nous vous contacterons si un nouvel échantillon est nécessaire.

Comment ça marche

🛒 Achetez le test : sélectionnez et achetez le test en ligne.

📧 Recevez les instructions : une fois le paiement confirmé, vous recevez par e-mail les instructions de prélèvement de l’échantillon.

📄 Remplissez le formulaire : imprimez et remplissez le formulaire de soumission avec l’identification de l’animal.

✨ Prélevez l’échantillon : arrachez 20 à 40 racines de poils avec le bulbe et collez-les dans la zone indiquée du formulaire, ou demandez à votre vétérinaire de prélever du sang dans un tube K3-EDTA.

📮 Envoyez-le au laboratoire : Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.

📊 Recevez le rapport : le rapport certifié est émis dès que l’analyse est validée.

Questions fréquentes

What is the difference between genotype and phenotype?
The genotype is what is written in the horse's DNA. It cannot be seen. The phenotype is what can be seen: in this case, the coat.
For each gene, the horse has two alleles: one inherited from the dam and one from the sire. We write, for example, A/a E/e.
Two horses can look the same and be different in their DNA. An A/A E/E horse and an A/a E/e horse both have a bay base coat. The A/a E/e horse can have foals with a black or chestnut base coat; the A/A E/E horse only has foals with a bay base coat.

What is the difference between base coat and the animal's coat?
The base coat is the starting point. There are only three: bay, black and chestnut. It is decided by two genes, Agouti and Extension.
Then other modifier genes can change the base coat: dilute it (make it lighter), depigment it (remove colour) or add white spotting and other patterns. The end result is the animal's coat, the one we see.
Examples:
• Palomino: chestnut base coat with one Cream allele.
• Buckskin: bay base coat with one Cream allele.
• Grey: any of the three base coats, progressively depigmented by Grey with age.
If the other modifier genes have no variants, the animal's coat is the same as the base coat.

What does each locus do?
The horse can produce two pigments: black pigment and red pigment.
Extension decides which one is produced. With at least one E allele, the horse produces black pigment. With e/e, the horse only produces red pigment.
Agouti decides where the black pigment goes. With at least one A allele, black pigment stays only on the points (mane, tail, lower legs and ear rims): bay base coat. With a/a, black pigment covers the whole body: black base coat.

Why is an e/e horse always chestnut base coat?
An e/e horse only produces red pigment. Agouti only acts on black pigment. Without black pigment, Agouti has nothing to act on, and the horse has a chestnut base coat -/- e/e, whatever its Agouti. But the Agouti alleles remain in the DNA and are passed on to the foals.

Why is an a/a horse black base coat only if it has the E allele?
a/a puts black pigment over the whole body. But there is only black pigment if the horse has at least one E allele. So: a/a E/- is black base coat; a/a e/e is chestnut base coat.

What does the dash in A/- or -/- mean?
The dash means "any allele". It is used when that allele does not change the base coat.
• A/- E/- can be A/A E/E, A/a E/E, A/A E/e or A/a E/e: all have a bay base coat.
• -/- e/e can be A/A e/e, A/a e/e or a/a e/e: all have a chestnut base coat.

If I can already see my horse's coat, what is the test for?
Because looking at the horse does not show what it can pass on to its foals. An A/A E/E horse and an A/a E/e horse look the same, but have different foals. Only the DNA test shows which is which.

Can two bay base coat horses mated together have a foal with a black or chestnut base coat?
Yes, if both are A/a E/e. Mendelian probability for each foal:
• 56.25% bay base coat A/- E/-
• 18.75% black base coat a/a E/-
• 25% chestnut base coat -/- e/e

Can two black base coat horses mated together have a foal with a chestnut base coat?
Yes, if both are a/a E/e. Mendelian probability for each foal:
• 75% black base coat a/a E/-
• 25% chestnut base coat a/a e/e

Which horse has 100% foals with a bay base coat?
An A/A E/E horse. It always passes the A allele and the E allele to every foal. So all foals have a bay base coat A/- E/-, whatever the other parent.

How to get foals with a black base coat?
For it to be possible: each parent must have at least one a allele, and at least one of the parents must have the E allele.
For a 100% probability: both parents must be a/a and at least one must be E/E.

Why does this test matter to breeders of black horses?
The Friesian horse is always black. In Portugal, the Coudelaria Ortigão Costa breeds only black Pure Blood Lusitano horses. To keep a black base coat in every foal, the breeder must know which breeding horses are a/a E/E and which carry the e allele (a/a E/e). Two a/a E/e horses mated together have a 25% probability of a foal with a chestnut base coat a/a e/e. An a/a E/E stallion has 100% foals with a black base coat with any a/a mare. Only the DNA test identifies the carriers.

Can a chestnut base coat horse have foals with a black base coat?
Yes, if it has the a allele (A/a e/e or a/a e/e). Example: an a/a e/e horse mated with an a/a E/E horse has 100% foals with a black base coat a/a E/e. That is why the Agouti of a chestnut base coat horse counts when choosing the mating partner.

How to tell a very dark bay base coat from a black base coat?
By eye it can be difficult. With the DNA test it is certain: bay base coat A/- E/-; black base coat a/a E/-.

My grey horse does not show its base coat. Can it be tested?
Yes. Grey progressively depigments the coat with age, but the DNA does not change. The test determines the base coat the horse was born with.

At what age can a horse be tested?
At any age. The DNA is the same from birth.

When will I receive the results?
Within 5 to 10 working days of the sample arriving at the laboratory. The certified report is sent as soon as the analysis is validated.

For Professionals

Genetic information for veterinarians, geneticists and laboratories.

Agouti (A) locus – ASIP gene (agouti signalling protein), ECA22

Function: controls the distribution of black pigment. The ASIP protein blocks the MC1R receptor.
A allele: functional dominant allele. Restricts black pigment to the points.
a allele: recessive allele. In a/a E/-, black pigment is distributed over the whole body.

Variant at the Agouti locus

a (Rieder et al., 2001): 11-bp deletion. NC_009165.3:g.26067463_26067473del; NM_001164017.1:c.187_197del. Originally published as g.2174_2184del and c.191_201del (Rieder et al., 2001); OMIA gives c.187_197del. Identifiers: rs3091770233; OMIA variant 509.

Inheritance

The e and a alleles are autosomal recessive (OMIA: code A, autosomal).

Breed distribution

Avila et al. (2022) tested 11,281 horses from 28 breeds and found the e and a alleles in all of them: Andalusian, Appaloosa, Arabian, Connemara Pony, Dutch Warmblood, Gypsy Cob, Gypsy Vanner, Hanoverian, Icelandic Horse, Knabstrupper, Lusitano, Miniature Horse, Missouri Fox Trotter, Morgan Horse, Mustang, Norwegian Fjord Horse, Oldenburg, Paint Horse, Percheron, Pony of the Americas, Pura Raza Española, Quarter Horse, Rocky Mountain Horse, Shetland Pony, Standardbred, Tennessee Walking Horse, Thoroughbred and Welsh Pony.

Key references

Rieder S, Taourit S, Mariat D, Langlois B, Guerin G (2001). Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses. Mamm Genome 12:450-455. doi:10.1007/s003350020017. PMID 11353392.
Avila F, Hughes SS, Magdesian KG, Penedo MCT, Bellone RR (2022). Breed distribution and allele frequencies of base coat color, dilution, and white patterning variants across 28 horse breeds. Genes 13:1641.
Henner J, Poncet PA, Aebi L, Hagger C, Stranzinger G, Rieder S (2002). Horse breeding: genetic tests for the coat colors chestnut, bay and black. Schweiz Arch Tierheilkd 144:405-412.