What is a sheep?

Writers Posted 16/01/19
Most of us would consider the wild ancestors of all our domestic sheep, the Urial, and the European Moufl on, from which all of the 2,000 plus sheep breeds around the world have descended, to be more akin to goats than the sheep we know.

Silly question? Maybe not quite so silly, I’m sure that on looking at the title of this most of you will immediately have a mental image of a sheep, probably of the sort of sheep with which you are most familiar. Ask the same question in another part of the world and it will conjure up a completely different set of mental images, some that we would probably just not recognise as a sheep.

Most of us would consider the wild ancestors of all our domestic sheep, the Urial, (a subspecies of the Asiatic Mouflon) and the European Mouflon, from which all of the 2,000 plus sheep breeds around the world have descended, to be more akin to goats than the sheep we know; however genetically they diverge by only a few percent. A divergence of around 4.5% for the former and 1.5% for the European lineage, the latter figure supporting recent zooarcheology and DNA evidence which suggests that European Mouflon are in reality a feral population of already domesticated sheep carried into Europe by migrating bands from their origins in the Middle East.

Certainly the Soay bears more than a passing resemblance (only woollier), to the European Mouflon, which would indicate a relatively close connection. There is a similar divergence in the genetic makeup of all of our domestic sheep breeds, probably somewhere around two percent i.e. a very small difference, but a difference in the genetic coding that makes a huge difference in the phenotype that we see; in reality there is probably as much variation within breeds as there is between breeds.

This in itself begs the question what is a sheep “breed” if there is so little difference in their genetic make up, the key is the way in which those genetics are arranged and coded in order to express particular traits in a way that is acceptable according to fairly arbitrary but established breed standards. The majority of traits can be manifest in a range of forms, e.g pink nose or black nose, small or big ears, it is what we select as being desirable for a particular breed that makes the breed what it is, i.e. how it conforms to breed type.

All those others arrangements are there within the genetic make up of the sheep, but the way in which we select and breed individuals results in the unwanted traits staying hidden, if it doesn’t conform to breed type we don’t breed from it (in theory). Almost any breeder, with the desire to do so, could, fairly readily, over time, change the appearance and nature of a breed, the development of the Beltex from the Texel clearly illustrates this point; all that is required is to, consistently and from generation to generation, select to a new set of criteria.

New Zealand breeders are far less precious about breeds than we are and have put a lot of effort into selecting for strains within breeds, so that the Romney now comes in a number of different formats, in particular high and low country Romney sheep, strains selected within the breed suited for differing conditions and production environments; some would say different breeds, but where do you draw the line? A breed is simply a group of sheep that conform to a particular set of breed characteristics determined by a breed society, but within which there is sufficient variation that will enable that breed to be changed completely.

This latter point may generate headaches for breeders and breed societies trying to ensure conformity to type, but without genetic variation breed development and progress ceases, the greater the diversity within a breed the better fitted it is to adapt to changing production environments, something we ignore at our peril in the current political and geo-climatic situation.

Breeds will develop and change, this may be achieved by small and gradual change, which can easily be generated from within, or from rapid and extreme change, which will generally be derived from the introduction of DNA external to the breed; the latter is probably the main cause of genetic erosion within breeds, particularly when it is employed covertly by unscrupulous breeders, simply for financial gain and is unrecorded. The introduction of alien genes into a breed may confer some advantage in the first cross, but certainly runs the risk of introducing undesirable characteristics that may take generations to eliminate.

So why do we bother with specific breeds? Breed societies, or good breed societies, are the focus for breed development and improvement, without them the national flock, apart from geographically isolated populations, would probably descend into a bunch of mongrels, we do make use of cross bred sheep quite widely within the national flock e.g. mules and half-breds, but for this system to work effectively and provide the hybrid vigour that gives them their productive advantage, does have a requirement for two distinct pure breeds, e.g. Swaledale and Blue Faced Leicester, without which the system would simply not work effectively.

If we are going to have pedigree and pure breeds then we do need to have breed standards. But, within those standards it is vitally important that we retain a degree of genetic divergence, without divergence and genetic variability we have no genetic progress. Homogeneity is the best way to fix a “type” genetically, but is a genetic Cul-de-sac; consider the Panda, an animal that has become so specialised that it has evolved itself into extinction. It is, and always will be, a difficult path to tread, maintaining a breed standard without inhibiting genetic progress, which often, by it’s very nature means change, sometimes small incremental changes at other times significant and rapid change, the former is very much easier to cope with than the latter. The flexibility to embrace positive change without compromising the breed and breed standards too much, but we do need to have the capacity to regulate this process and to discourage those breeders that feel that they can shortcut the whole process by the inclusion of external genetic resources.

The future success of sheep breeding does depend on us maintaining that genetic variation within our breeding stock without variation, nothing can change either for the good or bad. Within the UK we have both the curse and the benefit of more than 60 different sheep breeds, some of those currently regarded as rare breeds, simply because they are not currently fashionable; but many of those breeds have genetic compositions that have been modified over generations to suit particular management and environmental situations, genetic resources that we can ill afford to loose and whose maintenance we should all encourage. In this vein, it is really good to see that the Singleton Rare Breeds Show will be up and running again this year, on Sunday 14 July, a date for your new 2019 diary.


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