Colour coded
Is is possible to breed the colour of horse you’ve always dreamed of?
Grey, black, palomino, roan… We explore how the colour of your horse is not always about chance
AFTER BREEDING YOUR mare, it will take 11 long months for her foal to show himself. While she’s busy munching grass in the paddock and enjoying her expectant mum status, you’re left with time to plan and dream… Will the foal have dressage potential, perfect conformation, a good temperament and, more importantly for some, what colour will he be? Your mare is bright bay, the stallion dark bay, so he’s going to be another f lashy little bay, right? So, what a surprise when the new arrival is chestnut. How did that happen? The answer lies in colour genetics and Your Horse magazine unravels the code.
It’s all in the cells
Within each of your horse’s cells are millions of genes (think of them as biological instructions for making the different parts and characteristics of an animal) and each cell has two copies of each gene — one from either parent. The two copies are not always the same, and these alternatives are called alleles. When they are the same, the horse is said to be homozygous for that gene — which could be colour, his big ears, height and so on. If the genes are different, the horse is heterozygous. In heterozygous horses, one allele may be visible in the horse, but the other is not. The visible allele is
“Within each of your horse’s cells are millions of genes and each cell has two copies of each gene — one from either parent”
“In the end, movement, temperament and conformation are far more important than colour”
known as dominant, the other recessive, and it’s these recessive alleles that can result in an unexpected coat colour in a foal. All horse colours stem from three base coat colours — black, brown and red — and the genes that determine these colours are known as A, B and E.
Genes explained
Each gene is allocated a letter to identify it and when genes combine, this is what gives a horse its colour. A dominant allele (bossy boots) of a gene is shown by an italicised capital letter, and the recessive (shrinking violet) one by an italicised lower-case letter. Grey horses have the G gene, which is a modifying gene and means foals that are GG or Gg are any colour and will go whiter/ greyer as they age. A grey horse with pink skin has the W (or white) gene and Ww horses are white from birth. Black, brown or bay horses have the EE or Ee gene. If they have black pigment in the skin, but not in the hair, then they
are ee, a variation of chestnut. The agouti is a modifier gene and controls the distribution of black pigment. The dominant allele A restricts black pigment to the points of the horse (mane, tail, lower legs and ear rims), as seen, for example, in bays. The recessive allele a uniformly distributes black pigment over the entire body. Then there are the diluting genes, which are C and D. They can change solid colours to yellow, light red, grey or cream, such as cremello, dun, palomino and so on. A chestnut, ee, becomes a palomino by the dilution of the red pigment in the body to yellow, with the mane and tail being diluted to flaxen. A bay horse, EA, becomes a dun by the dilution of the body to yellow without it changing the colour of the dun’s black mane and tail.
Grey and broken colours
Grey horses are not born grey, but more and more white hairs will appear until eventually they become grey. Some show signs of changing colour within three to four months, while for others it could take years. If one or both parents was grey, but your foal isn’t, watch out for white hairs appearing around the temples, ears and hocks, as this is often the first sign that he’s going to be grey. The skin of a grey, even when he’s become much lighter, will match his birth colour. This is one way of telling him apart from a white horse or a grey with the white gene. Truly white horses are born and stay white. Great care must be taken when breeding two white horses together as possession of a double white gene (‘lethal white’) can be fatal. In skewbald and piebald horses, the white markings are simply laid over the top of the horse’s other colour. A roaning pattern is where individual white hairs are mixed into the normal coat.
It’s not all about colour
Although some people can get hot under the collar about breeding a foal of a particular colour, everything else needs to be in order too. In the end, temperament, movement and conformation are far more important than colour. See the prospective mare and stallion in action and ensure they’ve got what you need from your new baby. If not, wait and keep looking until you find the right parents.
Colour versus type
There is no direct relationship between a horse’s type and his colour, but there are different expressions of the genes involved. For example, C and D genes are rarely seen in racehorses, but E and A are seen a lot, which is why there are so many bays and chestnuts on the racetrack. Often, colours are selected because of registration in a studbook. Weatherbys, for instance, only accepts certain colours, which is why you’re unlikely to see a dun racehorse.