1. GENETICS OF BAY, BLACK, AND CHESTNUT

Linda Newell writes:

This is very interesting to me. Can anyone explain to me why my horse, who is the output of one chestnut and one black is a bay. I have heard several explanations, but still don't understand. The black is a Percheron, so I am sure he didn't have any bay in his background (Percherons can only be black or gray). The chestnut had a bay mother and a chestnut father. The mother and father of my horse's mother had six foals and all were chestnut. My other horse is the product of a gray mare and the same black father. Also, I have seen several Belgian/ Percheron crosses, and all were bay, sometimes with washed out looking noses and flanks. In the winter time, my horse gets blondish hairs on his legs and his belly, but in summer he is a bright mahogany bay with black points and no white markings.

Linda

Hi, Linda, this is going to get somewhat complicated but bear with me. There are several gene locuses at work here, your horse's parents were of genotype: A- ee in the case of the chestnut and aa E- in the case of the black. A, means that the body color is red or reddish and the points are black, as in a bay horse. a, means the horse is black all over. But another locus, the chestnut locus can cover up the affects of 'a' black genes or 'A' bay genes. The 'E' gene does not cover up black or bay, the 'e' gene does cover up black or bay and makes the horse red, chestnut. Because 'e' is recessive you need two ee's to make the cover-up work. So your horse's father carried the aa black genes and the E- that allows either black or bay. Your horse's mother carried A- which is bay and ee which is chestnut that covers up black or bay. Now each horse contribute one of each gene pair to the baby. Thus your horse's father contributed an 'a' and the 'E' which prevented your horse from being chestnut. Your horse's mother contributed the 'A' which made your horse bay instead of black and an 'e' which because it was recessive to 'E' doesn't show up. Thus your horse's genotype is Aa Ee and will be able to produce blacks, bays, and chestnuts if mated to horses carrying these genes though because of the complicated interactions prediction of which color will come through may be difficult. For example if mated to another Aa Ee bay horse this horse will produce bay, chestnut, and black in the ratio of 9 bay: 4 chestnut: 3 black. But if mated to a bay whose genotype is AA Ee your horse will produce only bays and chestnuts though some of those could produce blacks. By the way grey is caused by another locus the 'G' causes grey, 'g' causes non-grey.

Kinda complicated but it really makes sense, honest.

Tracy

Question: Bay x chestnut -- what are chances of black foal? >From Tracy:

Let's take the case of a black horse, which is one of the most difficult colors to achieve in most breeds. Remember that chestnut ee covers up black aa and bay A-. So, a chestnut horse with a black ancestor is bred to a bay horse with a black ancestor. The chestnut's gene pattern looks something like a?ee (a? because it had a black ancestor, ee because it is chestnut). The bay's gene pattern looks something like AaE? (A because it is bay, a because it had a black ancestor, E? because it is not chestnut). When they breed, there are 16 different combinations possible, of which 4 are definitely bay, 4 are bay or chestnut depending on what genes the ? are, 4 are chestnut or black, 2 are bay or black, and only 2 are definitely black. If we make the first ?=A and the second ?=e then, the possible offspring are 8 chestnuts, 6 bays, and 2 blacks in other words a ratio of 4:3:1. When you add more color genes it becomes more complicated.

>b) is Bay also a dominant gene such that two bay horses should

>always produce bay?

Bay is a dominant gene, however the only colors that always breed true are the recessives such as ee chestnut, if you breed two chestnuts together you will get chestnut, no exceptions. Dominant genes such as A bay can hide or cover up the presence of recessive genes such as a black, or e chestnut. Other dominant genes located at different locuses can cover up bay, for example G grey. My yearling filly was born bay and is turning grey, by the time she is six or seven she will be almost white with very little to show for the bay color she carries.

Also, Tracy, I have a red chestnut mare. I am breeding her next year to a chestnut stallion so I will certainly get a chestnut baby. If I breed her to a black/bay (Arabs that are black with brown muzzle are called black/bays), what kinds of color can I expect. I am fairly sure the stallion's sire or dam was a solid black. Oh, yes, he is a purebred Arab...

The black/bay color is also known as seal brown, dark brown, etc. it appears to be caused by the action of the P pangare gene on aa black horses. So this stallion is probably aa E- Pp. We don't know whether he harbors an e chestnut gene, or whether your chestnut mare ee harbors a a black or A bay gene. So your most likely possibilities are: black (difficult, but possible), black/bay, chestnut possibly even liver chestnut depending on whether the stallion has an Sty gene, or normal bay. I can't give you percentages because it depends on the genes we don't know about.

Tracy

Melanie Dresser writes: And how common are true black horses as opposed to ones that are just black/brown.

>From _Horse Color_: True blacks are rare in most breeds except the Percheron, the Fell Pony, the North American Spanish Horse, and a few others such as the Morgan. The Friesian is always black. There appear to be two genetically distinct blacks, "regular" black, which can fade in the sun, and "jet black", a glossy black which doesn't fade. Jet black is found just in a few breeds such as Clydesdale.

I have been reading with interest all the messages on colours in horses. As with any arbitrary system of classification it does little justice to the beauty it attempts to describe. It does however do credit to people's imagination and inventiveness.

I would like to add to the body of knowledge we have developed here and give you the colours and definitions that are recognized by the Canadian Horse Breeders Association (the association of people who breed horses of the Canadian Breed), the (Canadian) Department of Agriculture and the Canadian Livestock Records Corporation:

• Black : which includes 'fading' blacks. Fading blacks are black horses whose coats burn to a mixture of browns ranging from mahogany to sandalwood when kept outdoors all summer long. The browns are evenly mixed so that the coat does not appear patchy and if you look closely the coat is an even mixture of all the different brown colours. It can be quite beautiful. The mane, tail and legs stay jet black as well as the coat under the mane which is protected from the sun.

• Dark Bay: Very dark brown with black mane and tail, may or may not have some black on the legs. The coat is usually the colour of a beaver pelt.

• Bay: Reddish-brown hairs with black tips on the body and legs. The mane and tail are black.

• Chestnut: A Chestnut is any horse with a mane and tail that are not black. The mane and tail can be dark brown to light brown, blond to red or any mixture of the four. This designation is further defined by the colour of the coat: clear, golden, dark, or burnt (see next section for descriptions).

Of course the horses don't all fall neatly into these artificial pigeonholes and their colours are sometimes hard to place, especially the chestnuts.

There are no white or grey Canadians. The colours for the breed break down as follows:

Mares:           48% black        23% chestnut           29% bay
Stallions:       58% black        22% chestnut           20% bay
Geldings:        41% black        22% chestnut           37% bay

There are approximately 1100 Registered Canadians in the world, most of which are in Quebec.