White Ouessants .......or maybe not so white........

The breed standard is very clear on white sheep.They should be a solid white and as clear of marks and any pattern as posible, some red/tan ( phaeomelanin) is tolerated. As a general rule these lightly marked sheep with tan or red areas tend to fade as the sheep grow and so the adult sheep appears white. As I have started to learn more about sheep colour genetics there are a lot of things that I find interesting and far less that I find is written about phaeomelanin on the web. Of course all the information I seek may already be out there I just haven't found it ....yet For now heres a few things that I'm working on to try to understand.

Phaeomelanin is the tan part in the term Agouti White and Tan written AWt. I have come across various explanations or ways of viewing Agouti White and Tan I think I'm getting it, as a spectrum or range of colouration that runs from very deep red/ tan colour through to almost clear white. AWt is considered a pattern and not a colour and effectively it masks the black / brown ( eumelanin) colour of the sheep. So thats all there is to it ? ........I don't think so:-)

OK so my quest to understand more started with Elouan, link to previous posts on him Part One and Part Two . He's a white sheep and he has tan points. It was decided after some discussion that this was AWt even though until then I had thought of phaeomelanin as more red. He's just a bog standard white sheep although, there is a bit more to Elouan and his relatives but more of that later on.

So then I started keeping an eye out for white sheep and in particular white lambs. Phaeomelanin appears to be in most cases a transient pigment, it is broken down by light, It also doesn't hold well in wool fibre being retained more in hair fibres hence Elouans tan points and his creamy white wool. The phaeomelanin can get broken down leaving a washed out yellow behind. More so in the wool although even in the hair if you look closely at Gwenn whose photo is at the top of this post she has faint tan pigment on her head, its most noticeable when she is wet.

It seems even in white sheep the distribution and depth of colour of the red pigment is variable and no doubt covered by some genetic influence. So I got to thinking what could it be and wondering if it was possible to predict anything further about the inheritance of phaeo. First I looked at distribution of pattern.

Many ouessant lambs have a patch of red at the base of the neck this is acknowledged within the breed standard.

photo courtesy D Hendryckx
In most cases this type of colouration will quickly disappear or fade out as the lambs grow.
Sometimes the distribution of the phaeo varies and gives a more patchy covering.

Sometimes as with Elouan it is retained even into adulthood but this is most noticeable on the hair and not in the fleece.

and sometimes lambs are born with an all over red colouring.

Photo D Falck
At this point I also started noticing that there was much variation in the "red" pigment and that some lambs were born almost grey or perhaps platinum would better describe the colour.

Photo P Cottel
some seemed to have a combination of red and grey pigment
Photo D Falck
It was becoming clear that white sheep could be heavily coloured! Firstly if all these coloured ouessants are out there is the breed society correct in accepting only clear white or nearly clear white colours? Why would only clear white be considered acceptable? One explanation is likely to be that the prevalence of white sheep in general is a result of selection for the wool trade, a clear white fleece being the most desireable for commercial wool production. But does this mean the others are some how not ouessants or inferior? Not at all if anything their colouration or variation in colour is more likely to be indicative of the natural variation found in less selective or non-commercial flocks and so actually more representative of nature in all her splendour. Granted this may not fit with the "creation" of a breed of sheep.

Secondly is there any pattern or understanding of this type of expression of phaeomelanin? Well I'm sure its out there and someone knows but it seems its been a little overlooked, in part perhaps, because so many of the more commercial breeds have for generations selected out for this type of red colour variation prefering clear white sheep, so that the variants that would crop up within a population are few and far between. Why worry about patchy red sheep when clear white is so much nicer and simpler to understand, and then I came across an interesting association. Part of the features that go along with colour modified sheep is the intense expression of phaeomelanin, in some sheep.

Photo D Morzynski
Grey ( modified) ouessant ewe homozygous for colour modifier with white lamb, sire of the lamb was also a carrier for the colour modifier, pretty spectacular colours! It seems there is more to be understood about the colour modifying gene. So now all of a sudden the red phaeomelanin is clearly visible in not only white sheep but its very apparent in other colours too. The colour modifying gene can be carried in all colour sheep. In white ( AWt) sheep with the colour modifying gene the expression of phaeomelanin is often more vibrant. In other colours where traditionally it would be seen as a reddish cast for example in a black sheep suddenly, it is very apparent to the point that its expression can mask the underlying colouration of the black ( eumelanin) some turn around! It is also evident in the agouti greys even though the effects of the modifying gene on Ag grey sheep to lighten the eumelanin or black pigment is hardly noticeable, its effects on the red can be quite obvious.

Photo M Striepe
It also seems to persist for much longer and be more prevelant in wool fibre.It is also apparent that this expression of red is not directly linked to the colour modifying gene and any homozygous or heterozygous state. Its only in some sheep that this expression is seen even though others known to carry the colour modifying gene also have phaeomelanin the intense full on expression is only reserved for a select few. This probably says more about phaeomelanin or what it is that allows its expression than the colour modifying gene (I'm guessing!) .

So can a red pattern be repeated or predicted in a breeding and bred for? What controls the expression of phaeomelanin?
I wasn't able to come up with much but then my access to this type of information is limited so I may well be missing alot ( feel free to fill me in if you have any ideas!) In any event heres what I'm working on at the moment. I took the pattern exhibited by Elouan because its consistant symmetrical and seems to be repeated with a fair degree of similarity in a number of family members whats interesting however its that its also expressed in a lesser degree in other members and the depth of pigmentation also varies considerably would this give me enough to be able to form some consistant type of pattern enough to give me an idea of whats going on?

I started with Elouan, he was born essentially as seen in his adult fleece that is, with a clear white ( slightly off white) body but with darker phaeomelanin on both his face and legs.

Having worked out this was phaeomelanin I looked back at his closest relatives, they don't display the same degree of expression of pattern notably far less pigment on the face and much lighter legs almost a smudged colouration but still in essentially the same places, face and legs.

One or two were reported as having also small spots or ticking of darker pigment on a white body. The pigment was present at birth and didn't appear to fade greatly into adulthood. Could the deeper more extensive phaeomelanin be a cumulative effect? breed light to light and you get a darker expression but essentially in the same areas? The more intense the stronger and more defined the pattern? I then sought to see if I could find similar expression outside the flock and sure enough other ouessants displayed a varying degree of this pigment with the same pattern of distribution. Most were only mildly marked, is this because of selection for as clear a white as possible?

The trouble was the most intense expression of this pattern eluded an explanation for me.

Photo D Falck
As all Awt sheep are all lumped intogether irrespective of any apparent pattern or colouration, is it possible to sort this into something which can be expressed as a genotype within existing models? I put things on the back burner. Then this year a new crop of lambs and more information to get to grips with. However the same pattern was being repeated but with one noticeable difference. One lamb was born with not only the darker pigmented face and legs but also with an all over deep colouration or phaeomelanin. What struck me most about this picture was the symmetry of the facial markings. Also the vibrancy of the phaeomelanin and the apparent sugar frosted or light lips......hmm seen that before.

The pigmented head and legs pattern of colouration is seen in other breeds but not necessarily in red, Suffolks, Scottish blackface etc I can't find out much more than they are considered white sheep And that extension may be responsible for the black markings.

What would cause the same pattern distribution as that seen in the scottish blackface and its been noted that crosses do show signs of obvious phaeo as well as a diminished pattern or speckling but in the same areas, is it possible they are one and the same mechanism at opposite ends of the spectrum? Would the grey or platinum coloured lamb look essentially black when as deep as that of the lamb above with her dam that is almost brown? This all comes together in the Boreray sheep where both black faced white sheep and red/brown faced white sheep are seen and exhibit the same pattern of distribution.

So after a bit more reading and a bit more thinking, is it possible there is another pattern? Would this be located at agouti? That shows phaeo points on the face and legs but the eventual expression of this is controlled by a different locus (I'm surmising the extension locus would be a good place to look to start with) this locus and specific allele as yet not identifed controls whether you are looking at a smudge of colour or much greater expression through to my little anomoly the brown ( Awt or maybe Ax ) sheep and if you have black its because the extension locus allows for the intense expression of black? phaeomelanin or....? as in the scottish black face or suffolk but only on the points the rest of the sheep remains white. I am assuming that there would be more than one allele at the extension locus leading to differing phenotypes.

Is this possible I don't know, I am trying to see if this would work and fit with the very little that I do know ( I am easily confused!)

Next question is; would this work or shed any light on colour modification and the apparent link with phaeomelanin expression?

Edit Ok whilst pondering my navel, I got to thinking. Why would Gwenns phaeo be more obvious when its wet? because the water makes the hair more refractive so if that follows through and what I understand about the colour modifier is that it stretches the colour would it make the prescence of phaeo more vibrant as it refracts light better as it is also streched? Also gives greater penetration? This would also explain the accompanying lustre? Ok I'm getting a better picture of things here. So in that case the phaeo has always been present to a lesser or greater degree just not so apparent. Just need to get to grips with the depth of expression and that is I think something I can do in time.

If the prescence of eumelanin in the other agouti patterns and self coloured sheep pretty much cancelled out the effects at the extension locus of expression ( depth of colour) of phaeo, would the prescence of the colour modifying gene and its reduction in the influence of eumelanin. I am sure at this point there is a far more technical explanation like it changes the shape of certain molecules allowing greater penetration of phaeomelanin or less of eumelanin but thats a bit far for my little brain. Essentially allowing the extension gene to re-exert its influence on phaeo? I may really regret writing this when my little theory gets shot down in flames but for the moment its the best I've got to go on and until I can fall over some more information its a working theory under review ( be gentle with me!)

questions to answer

would this explain the appearance of some modifed sheep that are showing really heavy amounts of phaeo?

What have I missed? ( I am sure there is plenty!)

do I need to get out more......probably!