Download Coloured Southdown Sheep - Twisty Tree Ranch Fiber Farm

Coloured Southdown Sheep
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 AWt (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 (AWt AWt) having two white alleles will generally be indistinguishable
from one which is heterozygous for white where only one of the two alleles is AWt .)
A recessive coloured allele Aa, 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 (Aa Aa) having two recessive coloured alleles, and the
lamb must have inherited one recessive colour allele from each parent. The dominant white AWt 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 (AWt Aa).
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 AWt.
The exceptions to this are the Black Welsh and the Jacob breeds which have dominant colour as a result
of a dominant black allele (ED) 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 (BbBb) which cause a black lamb (such as one with Aa Aa 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
White
White
Black
Fleece colour:
AWtAWt
WW
A locus alleles:
Abbreviation:
AWtAa
Wb
AaAa
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 AWt is abbreviated to W and the recessive black allele Aa is abbreviated to b.)
Table 2
Inheritance of Recessive Colour in Southdowns
Example
Cross
Result (%)
X
1
WW
100 % WW
WW
X
2
WW
Wb
50 % WW
50 % Wb
X
3
Wb
Wb
25 % WW
50 % Wb
X
4
WW
bb
100 % Wb
25 % bb
X
5
Wb
bb
50 % Wb
50 % bb
X
6
bb
bb
100 % bb
The important information that can be deduced from each example in this table is as follows:
1. Two white sheep without the coloured gene will breed pure.
2. White sheep with a recessive coloured gene (Wb sheep) will pass on the coloured gene to about
half of their progeny even though no black lambs are born. These white sheep cannot be
distinguished from the WW white sheep without a colour gene; therefore coloured genes can be
present over many generations without the breeder being aware of them.
3. Two white sheep both carrying the recessive coloured gene can produce occasional coloured
lambs (about 1 in 4). The sudden appearance of a coloured lamb in a white flock may be the first
indication that coloured genes are present in the flock. However, there will inevitably be
numerous unidentified carriers, including those throughout the pedigree of the sire and dam of the
coloured lamb.
4. White sheep which do not have the coloured gene (WWs) will produce all white lambs if bred to
a coloured sheep (bb). These white lambs will all be carriers of the coloured gene (Wbs).
5. When a coloured sheep is mated to a white “carrier” sheep (Wb), about half the lambs will be
black.
6. Two coloured Southdowns (bbs) will breed pure, producing only black lambs.
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.