Color Genetics in Coopworth Sheep
By D. P. Sponenberg
Coopworth sheep are an interesting breed resource that is widely used throughout the world in both purebreeding and crossbreeding systems. Most of this activity is geared towards the production of lamb and mutton, but the wool of Coopworths has become an important component of the international specialty wools market. The wool is especially highly regarded by handspinners, who appreciate colors as much as they do white wool.
Coopworth color is determined mainly by two separate genetic mechanisms, with another two that are common enough to warrant some attention. Color genetics of the Coopworth is consistent with the genetics of the parent breeds - Border Leicester and Romney. The genetic mechanisms interact to give a fairly wide range of colors.
The main color control in the breed is the result of the instructions at two genetic sites: Agouti and Brown.
One mechanism for color is the Agouti locus (locus is Greek for address, and just means a specific site), which controls the distribution of white and dark fibers over the body of the animal. What this means, in practice, is that the darker patterns can pop up as surprises following mating of the paler patterns, but the paler patterns do not pop up out of the darker ones.
The Agouti patterns in the Coopworth are most likely limited to about three choices. The first of these is the familiar white, which is white all over and has pigmented skin. White sheep, obviously are the palest of the Agouti patterns, and so can mask the other choices. This masking phenomenon is the reason that the darker patterns can occur as surprises.
white Coopworth lamb.
A second reasonably common Agouti pattern in the Border Leicester and Romney, as well as the Coopworth, is the blue pattern, sometimes called English blue. This pattern is very common in all longwool breeds. The blue pattern consists of subtle gradations of pale and dark areas, so that the fleece has a variety of shades of grey in it. Most blue sheep have distinctive pale areas under the eyes (tear drops) and pale areas on the muzzle. Blues vary from light and nearly white, to very dark and nearly black.
A third option at Agouti is the "no pattern" or black choice. This is reasonably rare in most Longwools, and results in black lambs without the distinctive pale areas of the blue pattern. In most situations the black sheep are born black, but then fade to some shade of grey with age. This fading is controlled by other, poorly characterized, genetic factors.
"Blue" Coopworth ewe and lambs- one black, one blue.
A second locus, Brown, interacts with the Agouti locus to give the final color of the sheep. Options at Brown include black, which is dominant, and brown, which is recessive and can therefore occur as a surprise among black-based matings. The combination of the black choice here with the various Agouti patterns includes white, blue, and black. With the brown choice at this locus, the Agouti patterns become white, pale beige, and darker brown. The browns are usually called moorit in wool parlance. Moorits vary from a dark chocolate brown through fairly warm honey colors, to beige.
It is important to note that with white sheep it is difficult to tell if they are black-based or brown-based. A few hints can help, though. One is that the skin of black-based sheep is usually dark, while the sheep of brown-based sheep is usually much lighter. This detail can be important to breeders specifically aiming for certain colors of lambs.
A third mechanism for color variation is more rare, and this is called "dark brown." It is a dominant modification of black. The lambs with one copy of this gene are born nearly black, and then lighten a little to a distinctive dark brown. The brown carries all the way to the skin, and the hair on the face and ears is also brown rather than black. When dark brown sheep are mated together a few of the lambs can come out black, some dark brown, and some are a pale silvery brown. These pale lambs are the result of two doses of the gene - and are pale rather than dark brown.
To slightly confuse the issue even further, on some occasions colored x colored matings give white lambs. This happens in Romney and Border Leicester flocks as well, and the most likely culprit is the Extension locus with two choices: dominant black, and "normal" or "wild" type. This genetic variant is not usually associated with Longwools, and it could have arrived in them either by mutation or by some crossing in the past. Regardless of how it came into the breeds, it is in them, and the animals with the variant appear to be typical purebreds with no obvious outside breeding.
The dominant black is just that - completely black unless modified to be brown by the genetic mechanisms for moorit or dark brown. The "wild type" alternative allows the Agouti instructions to come through, leading to the familiar white, English blue, or black at that locus. The trick here is that it is impossible to distinguish the blacks that have dominant black from the blacks that have recessive Agouti black, and this can create unusual lambs popping out in some breeding programs. A dominant black sheep can carry white, so that when mated to a blue or recessive black mate it is possible to get white lambs back again. On the other hand, colored sheep from white parents are certain to have missed the dominant black gene, as white cannot cover it up.
Breeding for Color
Breeders interested in colored wool production can use genetics to their advantage, and can make previously rare colors relatively common in their own flocks. Throughout the entire world, colored lambs are relatively common in Border Leicester, Romney, and Coopworth flocks. The fate of these depends on the breeder's goals. In commercial sheep production, especially in Australia and New Zealand, it is critically important to keep colored sheep out of white flocks. Even a few colored sheep can contaminate the whiteness of the clip of an entire flock. In those countries, colored lambs are culled early.
Breeders interested in the colored wool market can use these colored lambs to good advantage. When mated to one another, color is going to always produce color in most Longwool breeds. The only exception is those flock which have the dominant black. While colored to colored matings generally assure the production of colored lambs, it can be important to introduce fresh genetics into a colored flock. One way to do this is to introduce a white sheep that has been highly selected for traits that need to be strengthened in the colored flock. This white sheep will likely produce only white lambs, but each of them is assured of carrying color from the colored parent. These lambs can then be used with colored mates to produce white lambs about half of the time, and colored lambs half of the time. An alternative is to mate these "color carriers" to one another, and produce colored lambs in about one fourth of the lamb crop.
Another strategy is to try to locate sheep in white flocks that have previously produced colored lambs. These are assured of carrying color, and can be used to more rapidly introduce desired traits into a colored flock.
The range and depth of color in the wool is subject to age-related changes as well as to genetic factors. In most flocks producing colored wool it is an advantage to have a variety of colors available. It appears that the darker shades are generally recessive, and so some selection for the darker end of the spectrum is going to be necessary if good, dark blacks are going to be produced.
The moorit colors are also interesting, and generally more rare than the black based colors. These moorits can be used with one another to produce only moorits, but their rarity usually assures that they will also be mated to other color types. If moorits are mated to white sheep, white lambs are the usual result. If these white lambs are mated back to a moorit, the usual ratio is going to be 50% white lambs, 25% black based lambs, and 25% moorits. When moorits are mated to black-based colors the usual result is black based lambs. When these lambs are mated back to moorits, they produce 50% black based and 50% moorit lambs. Moorit colors are therefore more difficult to produce from mots other colors, but will consistently produce moorit when mated to one another.
Moorit colors present another challenge to the breeder, which is that the moorit color is generally somewhat "weaker" than the corresponding black-based color. So, a "moorit-blue" combination is likely to be very pale. A "moorit-no pattern" combination is going to be darker, but still might fade considerably from a rich chocolate brown birth coat.
One strategy to darken the moorits is to use very, very black sheep as the outcross to these. In most flocks the darker end of the spectrum is more difficult to secure, so put pressure on this end rather than the lighter end which usually takes care of itself. If pale moorits are mated to dark blacks, the result should be blues and blacks that tend to grey with age. If these are mated to one another, or to dark moorits, the result is going to be a low percentage of moorits that are dark and remain that way. Once these are produced, they can be mated again to dark blacks, and using the resulting lambs in a breeding program will increase the percentage of darker moorits.
Color genetics is intricate and complicated. Considering the different components of the final color makes it possible to understand how the color arises. The basic components are pattern (Agouti locus), black-based or brown-based (Brown locus), or rarely dark brown and Extension, and then the relative depth of the color (control of this is unknown). It is fascinating that a few controls can result in the incredible wealth of colors and shades available in Coopworth wool.
D. Phillip Sponenberg, DVM, PhD
For more on color genetics, see our Sheep Links Record Keeping, Selection, Genetics/Breeding page
Jim and Martha McGrath
178 Lough Rd.
Franklin, WV, 26807