Bienvenue chez Spered Breizh Ouessants. La race est originaire de l’île d’’Ouessant qui fait parti d’un petit archipel au large du Finistère, Bretagne. L’île de l'épouvante comme c'était connu par certains était balayé par les intempéries de l’atlantique, ces moutons rustiques s'adaptaient à survivre sur les pâturages pauvres des falaises salées. C’était les femmes de l’île qui élevaient les moutons réputés pour leur laine noire à tisser « la berlinge » une étoffe régionale et leur viande avec un goût doux et délicat.
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mardi 12 mars 2013
Forensics (4) - Selection Criteria
I was asked recently why wattles are in the breed standard and listed as a fault for which there is disqualification but a poor horn set isn't listed as grounds for disqualification.On the face of it neither would be considered desireable and many a breeder would not breed from a ram with poor horns any more than they would from a Ouessant with wattles. To disqualify one but not the other seems quite harsh.
There is a reasoned logic behind the disqualification of one but not the other which may not be apparent immediately. Without delving deeply into the origins of wattles in the breed, it is safe to say that wattles are not a primitive european short tail breed trait, that might seem like a reason for disqualification that could justify their specific mention in the breed standard in itself. There is however a rational argument for disqualifying wattles and not horn set and that has to do with genetics. Only once it is possible get to the root of the inheritance of both wattles and other breed traits like horns does the breed standard truly make sense.
The inheritance of wattles has been studied by JJ Lauvergne LINK it is a dominant gene this means it can be considered a single trait gene even though it can ocasionally through a quirk in genetics skip a generation, in general by eliminating the sheep carrying wattles from the breeding programme you can virtually guarantee to eliminate wattles in one generation.
By disqualifying those sheep that have wattles there is a strict control on what would otherwise be a gene that would proliferate rapidly. On the other hand traits such as horn shape and set are considered to be polygenic that means that their expression is controlled by a number of genes many of which are not readily identifiable and selection for the most desireable horn trait is likely in the longer term to improve horn set but disqualifying any that don't meet the breed standard is no guarantee of success in eliminating bad horns and may in fact also be counter productive in some cases.
The understanding of the breed standard at a genetic level has both in the past and today influenced its interpretation and demonstrated its validity.
There is another selection criteria that has to be mentioned and it can be considered a single gene trait however it operates on a continuum, white spotting would be considered one such gene. Whilst white spotting can be easily identified as a single gene trait its expression can be considered on a spectrum if the complete expression of white spotting is understood. I have previously covered how it can be possible with selection to increase the degree of white spotting over time by always selecting for the greatest area of white spotting. HERE in cases of genes where variation is along a spectrum and the standard dictates a certain maximum or minimum level there will always be variation on either side of that level of acceptance. This waxing and waning is part of the fluidity of expression or variance that will naturally occur, the tighter the selection criteria the smaller that variation will be but it will consistantly be there. Within the breeds history these selection criteria have developed often in conjunction with the breeds purpose or history of development. For example white spotting in black sheep is considered undesireable when a uniform dark coloured wool is required and so whilst the white spotting gene as a single gene with recessive expression in black sheep would be hard to eliminate, its effects can be mitigated by the limits placed on it in the standard. This could be considered an arbitrary decision but it has an historical relevance and also a relevance ultimately to maintaining the validity of the breeds heritage.
Once again the standard proves itself to be well observed and conspires to maintain within the breed those essential references to history without ever mentioning them expressely.