Original
Article About Dexters
"Grade One - and the Colour Dun"
by Beverley McCulloch and Michael
Trotter
Beverley McCulloch and
Michael Trotter are both
retired scientists who used to work for the Canterbury Museum in
Christchurch, New Zealand. They have an active interest in Dexters, rare breeds conservation, and smallfarming. Together, they
operate Summer Wine Dexter stud on 10 acres in North Canterbury. See their
website, Summer Wine Dun Dexters www.dundexters.co.nz.
This article was written in May 2005 and has yet to be published elsewhere.
The photos have been added by the Webmaster.
Note: Reference is made in this article to
"grading up" and G1 Dexters. In
New Zealand, when people wanted to breed Dexters in the 1970s, only Dexter
semen could be imported at that time. This semen was placed in cows from
another breed and a "grading up" process was undertaken. A Grade One or G1
Dexter is 50% Dexter; Grade Two (G2) is 75% Dexter; Grade Three (G3) is
87.5% Dexter; and Grade Four (G4) is accepted as a purebred.
Dexter Cattle Societies throughout the world recognize three colours in
purebred Dexters – black, red, and dun. Relatively recent research into the
genetics of the dun colouring in Dexters has shown that it is the result of
a mutation that is unique to the Dexter breed and is quite different
genetically from the dun colouring exhibited by some other cattle breeds.
The genes which cause an animal to exhibit the dun colouring are quite
separate from the normal black or red colour genes in cattle and are carried
in addition to those for black and/or red.
In accepting this finding (and no-one has argued against it) we must then
accept the premise that the dun colour recognized in the Dexter breed
description is this unique ‘Dexter dun’. (The term ‘Dexter dun’ is used
throughout the remainder of this article to denote the dun colour unique to
the breed.)
A second finding of the same research is that the ‘Dexter dun’ gene is
recessive, which means that animals have to be carrying two such genes, one
passed on to it by each parent, in order to exhibit the ‘Dexter dun’ colour.
Again, no one has argued with this. (It should be noted however, that where
an animal carrying two dun genes also carries two red genes, it will exhibit
the red colour. This does not affect the conclusions reached from the
argument presented here, which is concerned only with Dexters exhibiting
dun.)
In accepting both the above findings, we must also accept a further premise.
This is, that in any Dexter grading-up programme, it is simply not
genetically possible to have a ‘Dexter dun’ Grade One animal. This is
because while it is possible for the Dexter sire to pass on a ‘Dexter dun’
gene, it is not possible for the dam of another breed to do so. In simple
terms, you cannot have a ‘Dexter dun’ G1.
This is all quite straightforward until you examine the Appendix for Grade
One registrations in the Herd Book of the Dexter Cattle Society New Zealand
(DCSNZ) where we see that a number of animals are described as dun. Whatever
shade of brown these animals are (or were) they cannot be the true ‘Dexter
dun’ of the breed description.
The obvious conclusion is that the colour of these particular Grade One
animals must be derived from their non-Dexter dams. This is not really
surprising. We accept that a Grade One animal gets half its genes from its
sire and the other half from its dam, and that its coat colour may be
inherited from its Dexter sire or its non-Dexter dam. If a Grade One calf is
showing its Dexter sire’s colour it can be only black or red (remember, even
if the sire passes on a ‘Dexter dun’ gene, the calf can’t exhibit dun
without another such gene from its dam) but if it shows its foundation dam’s
colour, it could, for example, be Jersey ‘fawn’ or ‘brown’ or Shorthorn
‘roan’ or Murray Grey ‘grey’. (These ‘colour’ terms are used here for
convenience – they are not a genetic description of a colour.) Non-Dexter
colours may also be found in the higher grades but in lower numbers.
The fact that solid colours other than black, red, and dun can be exhibited
by grade Dexters is recognised the Society’s current Regulations (7.4 Stud
Management). But while something like ‘brown’ or ‘grey’, for example, is
acceptable in grade animals, breeders are actually registering all non-black
or non-red animals as ‘dun’. They are currently being recorded as such in
our Grade One herd registrations and these animals are being purchased in
the belief that they are the true dun Dexters.
If we look at the colours recorded in our Grade One registrations we find
that at an earlier period a number of animals were registered as their
actual colour, e.g. roan, grey, light brown etc. But the more recent
registration forms require breeders to choose one of the three standard
colours for their animals – there is no mention of, or allowance for, the
nomination of any other solid colour for grade animals – despite the fact
that this is specifically allowed in the Regulations.
All registered animals, including grades, are being shoe-horned into the
black, red, dun straightjacket, regardless of their origins, and breeders
registering grade animals are not being reminded that they can depart from
this, even though the naming of another colour may be a more genetically
accurate description of the animal. This is particularly unfortunate in the
case of Grade One animals being registered as ‘dun’, because as has been
shown above, it is not genetically possible for a G1 to be ‘Dexter dun’.
This whole matter arose from an enquiry we received from a new member who
had just purchased a “dun G2 heifer.” The substance of the enquiry is
irrelevant to this discussion; what did concern us was the added information
that the heifer’s Grade One dam was also described as dun – which we
realized was not possible. Genetically, it is possible that the Grade Two
heifer is ‘Dexter dun’, but if that animal’s mother is a brown colour there
is a better than even chance that the daughter is actually of the same
non-Dexter shade. ‘Dexter dun’ genes are not all that common in the New
Zealand herd.
There is only one certain way to resolve this sort of question and that is
by DNA colour testing, but we are not aware that this is yet available in
New Zealand, although it is routine in North America.
It is important to note here that there is nothing semantically incorrect in
describing the phenotype (physical appearance) of brown-coloured G1s as dun
– dun simply means brown, as indeed such animals are. But it is genetically
misleading, because such brown animals will not breed genetically true for
‘Dexter dun’. This is, of course, why everyone told us that it was not
possible to breed for a dun herd – because for so many years New Zealand
breeders were dealing with grade animals, and very many of the so-called
‘duns’ they were breeding from (including all those at Grade one level) were
not true ‘Dexter dun’ at all. The genetically pure dun Dexter follows
pre-determined genetic rules, as does any other colour – something we are
currently proving in practice with our all-dun purebred herd.
Whatever the Society’s reaction may be to this situation – one thing is
quite clear. The genetics of the dun colour in Dexter cattle, as currently
accepted, means that it is not possible to have a Grade One Dexter calf of
the dun colour required in the Society’s Breed Description, and a decreasing
proportion of animals at higher grades, registered as dun, will also be
incorrectly so described.
Acknowledgements:
We would like to thank John
Paterson, who so effectively commented on our first draft of this article –
including checking with Sheila Schmutz on the validity of our conclusions.
Notes:
1. Our conclusion that a Grade One Dexter, the product of a Dexter sire
and a non-Dexter dam, cannot exhibit the ‘Dexter dun’ colouring was
confirmed by geneticist, Sheila Schmutz, in an e-mail to John Paterson on 4
May 2005. Schmutz is one of the authors of a major scientific publication on
the dun Dexter gene.
2. Owners of ‘graded
up’ Dexters registered as dun, can find out if an animal is the unique
‘Dexter dun’ by checking the registered colour of each Grade one cow on its
pedigree. If only red and black G1s occur, then a dun colour that appears at
a higher grade is almost certainly ‘Dexter dun’. If a dun G1 appears on a
pedigree, then the apparently dun colouring of any descendant could be
suspect, although the higher the grade, the statistically less likely this
becomes. It is important to note, however, that any animals which may have
been wrongly identified as to colour, are nevertheless still officially
registered Dexter cattle – whatever their grade.
3. An analysis of the percentage of females of various grades registered as
dun in the DCSNZ Herd Book up until 31 March 2005, gives the following
results.
Grade 1 - 4.8%
Grade 2 - 3.3%
Grade 3 - 3.7%
Purebred - 6.5%
Statistically these results are very crude – mainly because of the selection
both for and against sires – including selection for and against colour –
plus the introduction into the gene pool of imported ‘fullblood’ animals
carrying the dun gene.
However, if animals that carry the genuine ‘Dexter dun’ gene were the only
ones registered as dun, the results would certainly be very different. They
would start off with 0% at Grade 1 and the percentage would gradually
increase as the proportion of Dexter blood increased with each grade. The
greatest distortion in the percentages shown above is at the Grades 1 and 2
levels, which is much as we would expect using the current registration
system.
Reading:
“Color Genetics and the
Registration of Dexter Cattle” by John Potter.
www.dextercattle.org/colorgenetics.htm [Viewed 10.5.2005]
“TYRP1 is associated
with dun coat colour in Dexter cattle or how now brown cow?” by T. G.
Berryere, S. M. Schmutz, R. J. Schimpf, C. M. Cowan and J. Potter. Animal
Genetics, Volume 34 Issue 3, pages 169-175, 2003.
“Genetics of Coat Color
in Cattle” by Sheila Schmutz.
http://skyway.usask.ca/~schmutz/colors.html [Viewed 10.5.2005]
“How Now, Dun Cow” by
Carol Davidson. Paper presented at the Second World Dexter Congress,
Australia, 2002. Also on Congress CD.
“Dun Colouring in
Dexters” by Beryl Rutherford. In My Love Affair with the Dexter,
Triple D Books, Australia, 2005, page 92. Previously published in The
Dexter Cattle Society Bulletin, No.157, 2004.
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