By Jeanie Muddle
Coloured lambs are occasionally born into pedigree white Southdown flocks. Since 2007, the Southdown Sheep Society have recognised and accepted registrations of these coloured Southdowns, identifying them in the flock book with the suffix "B" after the registration number.
Appearance
Coloured Southdown lambs are usually born very black but frequently become much paler as they get older. As the lambs grow, the black fleece gradually becomes paler with the tips of the fleece weathered to golden or coffee brown. Lambs may develop a pale noseband, pale tufts behind the ears and pale testicles in ram lambs. The fleece of mature coloured Southdowns can be any shade of grey from deep charcoal to silver, becoming lighter as the sheep ages but the head and legs remain dark. Like their white counterparts, the fleece of coloured Southdowns is short, dense and very fine. Coloured Southdown is ideal fleece for the production of a high quality natural-coloured woollen knitting yarn. With such a short staple, Southdown is not the easiest fleece for handspinning; however, experienced spinners can produce a very fine yarn.
The History of Colour in Sheep
The earliest domesticated sheep, like their wild ancestors, were frequently naturally coloured and the early fabrics made by man utilised natural wool colours. However, as the centuries passed, the development of a dying industry led to a demand for white wool which could be dyed to a range of attractive colours; as trade in wool became increasingly important in Britain, and white wool commanded a high price, the numbers of flocks of white sheep also increased. By the end of the 18th Century, coloured sheep were comparatively rare, the majority of British sheep breeds being predominantly white. However, the emergence of occasional coloured lambs in present-day sheep breeds is not surprising given their coloured ancestry.
The Coloured Gene in Southdowns
Although the registration of coloured Southdowns is recent, the occasional appearance of coloured lambs in white Southdown flocks is not new. Many white breeds have a recessive coloured gene and Southdowns are no exception. Throughout the history of the Southdown breed, coloured examples have been known; as with most white breeds, the existence of a recessive black gene is an integral part of the genetic makeup of the breed.
Southdown sheep of the 19th century and earlier frequently had coloured markings and produced coloured lambs. Youat ( "Sheep - Their Breeds, Management and Diseases" London 1883), writing about "South Downs" sheep notes:
"In almost every flock, notwithstanding the great care which has now been taken to prevent it, several parti-coloured lambs will be dropped, some with large black spots, some half black and some entirely black. A writer in the Annals of Agriculture states, that "he has frequently had twelve or fourteen perfectly black lambs, although he never kept a black ram or ewe".
Black Southdown lambs continued to be born into British Southdown flocks during the early and middle years of the 20th century. For example, Roberts and White (Journal of Genetics 22 p167, 1930) refer to "self-colour" Southdown lambs. ("Self-colour" is a genetic term for "all black".) When the British Southdown population declined dramatically in the latter part of the 20th Century, black lambs appeared to become increasingly rare.
The New Zealand Influence
In recent years, the frequency of coloured lambs appearing in British Southdown flocks, although not high, has been increasing. This re-emergence of the coloured gene is apparently associated with the Southdown sheep imported from New Zealand in 1980 since many black lambs can be shown to be descended from these imports and their progeny.
The most likely explanation is that the coloured gene was present in British Southdowns exported to New Zealand during the 19th and 20th centuries; it was perpetuated for many years in the extensive New Zealand Southdown flocks and has subsequently been re-imported back into UK Southdown flocks; these imports were bred freely with British Southdowns and were registered normally in the Southdown flock book. Now, many generations later, the descendants of these imported sheep must number well into the hundreds as the original rams were widely used in several significant flocks of the 1980s. The black gene has now been passed on through the generations to the present day sheep, a number of which will carry a black gene and are therefore capable of producing black lambs.
French Southdowns
Although coloured lambs have been reported from French Southdowns in the past, coloured Southdowns are not believed to occur in France at present. The French breeders' preference for pale faces may also mean that they are selecting against coloured genes, if present. (The presence of a coloured gene in a white-fleeced sheep can have an epistatic effect, enhancing face and leg colour.) So although a number of the recently registered coloured Southdown sheep in Britain have French import bloodlines in their pedigrees, it is not known if they have been a source of the coloured gene.
Background Information on Genetics of Colour
Colour in sheep is the result of the presence of specific combinations of genes on the chromosomes. It is known that there are a small number of important loci on the chromosomes which determine colour. Each locus comprises a pair of alleles, (which may be the same or different) and when a lamb is conceived, it receives one allele from each parent (i.e. half the genetic material from each locus). The main loci concerning fleece colour in sheep are the Agouti locus (A), the Extension locus (E) and the Brown locus (B). In addition, there are other loci which determine pattern or head and leg colour.
The A locus
One very important locus determining colour is the Agouti or A locus: the
reason all white sheep are white is because they have a dominant white allele
(the white/tan allele)
at this locus. Since this is a dominant allele the sheep will be white whether
they have one or two white alleles (And a white sheep which is homozygous for
white () having two white alleles
will generally be indistinguishable from one which is heterozygous for white
where only one of the two alleles is
.)
A recessive coloured allele
, known as the
nonagouti allele can be present at the A locus in many traditionally white
breeds including Southdowns. If a coloured lamb is produced in a white flock,
the lamb must be homozygous for recessive colour () having two recessive coloured alleles, and the lamb must have
inherited one recessive colour allele from each parent. The dominant white
which was present in
both sire and dam, is not present in the lamb so the recessive colour nonagouti
alleles can be effective in producing a black lamb. The breeder can also deduce
that the sire and dam of the black lamb must both be heterozygous for recessive
colour ().
Other Alleles and Loci
Most coloured sheep, including the primitive native British breeds, are
coloured or patterned as a result of various recessive colour alleles which
occupy the A locus, in the absence of dominant white
. The exceptions to
this are the Black Welsh and the Jacob breeds which have dominant colour as a
result of a dominant black allele (
) at the E locus; another locus, the B locus, is
responsible for the moorit colour found in breeds such as the Manx Loaghtan and
Shetland; these sheep are homozygous for the recessive brown alleles (
) which cause a black lamb (such as one with
alleles) to be brown.
Inheritance of the Recessive Coloured Gene
There are three genetic colour types of Southdown sheep (see Table 1).
| Table 1 | |||
| Genetic colour types in Southdown Sheep | |||
| Gene status: (simplified) |
Two white genes (most Southdowns) |
One white gene One black gene ("carrier" whites) |
Two black genes |
| Fleece colour: | White |
White |
Black |
| A locus alleles: | |
|
|
| Abbreviation: | WW | Wb | bb |
Since each parent contributes one half of its genetic material (one allele)
to each offspring, the results of the six possible crosses between the three
genetic colour types are shown in Table 2. (For simplicity, the dominant white
allele is abbreviated
to W and the recessive black allele
is
abbreviated to b.)
| Table 2 | ||||||||||||||
| Inheritance of Recessive Colour in Southdowns | ||||||||||||||
| Example | Cross | Result (%) | ||||||||||||
| 1 |
|
100% |
||||||||||||
| 2 |
|
|
||||||||||||
| 3 |
|
|
||||||||||||
| 4 |
|
|
||||||||||||
| 5 |
|
|
||||||||||||
| 6 |
|
|
||||||||||||
The important information that can be deduced from each example in this table is as follows:
Guidelines for breeders: In order to minimise infiltration of the coloured gene into the main white flock, breeders of coloured Southdowns should avoid registering and breeding from white rams bred from a coloured to white cross (as in Examples 4 and 5 above), although white ewes from this cross can be bred to a coloured ram to produce black lambs (Example 5). Breeders of coloured sheep should also be aware that black fibres downgrade commercial white wool; in order to minimise contamination, coloured sheep should always be shorn last. If white sheep have coloured fleece spots, where possible all coloured wool should be removed and disposed of either before shearing or before rolling the fleece.
Conclusion
The coloured gene, although most recently associated with the New Zealand imports, has been known to be present in Southdowns throughout the breed's history. The registration of coloured Southdowns has given this naturally-occurring minority variety of the Southdown breed recognition that they are a legitimate and historically well-established part of the heritage of the Southdown breed in Britain.