Highland Coat Colour Genetics Explained

There is little more perplexing to the Highland breeder than trying to understand coat colour in their animals. Unfortunately knowing a little bit about genetics can sometimes add to the confusion. In this article I will attempt to explain what is known about the genetics behind coat colour in Highlands and some fairly firm thoughts we have on what is as yet unproven. It will be in a simple fashion initially, but links to some more complex concepts will be available as well. This article is written with the help and guidance of Sheila Schmutz from the University of Saskatchewan, Canada who has been an incredible source of information on colour genetics, especially in Highland cattle.

General Concepts on Coat Colour Genes

All cattle have 30 pairs of chromosomes. Along these strings of DNA there are thousands of positions (each one known as a ‘locus’) that contain the genes for all characteristics that make up our cattle. Most genes are exactly the same between all breeds (genes that make a cow a cow, and not a horse), but a small percentage of genes account for the differences between breeds, and between animals of the same breed (like genes for marbling, temperament, horn shape, coat colour etc).

Sadly, there is not just one locus that controls coat colour in cattle. There are actually six major loci, and some other minor loci. In fact it is thought that the six major loci are shared among all mammals to determine their colouring. At each of these six loci there are numerous gene variations (alleles) that, in various combinations, will account for nearly all the colours that we see in Highlands. Currently only certain colour loci have been investigated in Highlands, and a few others in some other breeds. All this goes some way to explain why this is such a complex area to try to understand. There are certain facts that are known about coat colour in Highlands, and others that we can strongly postulate based on evidence from other breeds and the experience of breeders who have seen thousands of calves born.

I will use some nomenclature in these articles that need a brief explanation. The term ‘wild type’ refers to the default colour of cattle and usually has a default gene at each of the six loci to achieve this colour. Most other colours will be dominant over this ‘wild type’ base colour. The ancient aurochs of Europe (thought to be the ancestors of British breed cattle) were this colour – sort of a red/brown colour.

Each locus has a name and the first letter of that name is the abbreviation for that locus (e.g. the dilution locus is the ‘D’ locus). Each gene (or allele) at a locus will be given a symbol, usually using the letter of the locus and a superscript to define which variation it is is (e.g. E locus genes are ‘E⁺‘ for wild type and ‘E^D‘ for black, and ‘e’ for red). Generally dominant genes are written in capitals, recessive genes are in small letters. At each colour locus, 2 alleles will always exist and are written with a slash between them (E⁺/E⁺ or E^D/e, e/e for example).

The basics of the six loci are as follows:

‘E’ Locus

(Click here to know more about the ‘E’ or Extention locus)

		known in Highlands	suspected in Highlands
E^D	black (dominant)	yes
E⁺	wild type	yes
e	red	yes

This is the main controlling locus for the red and black base colours that we see in our cattle. It is thought that wild type and red animals can not be distinguished, although some wild type animals have a classical mask of black hairs on their face, and some black hairs on their neck and legs. We know that all brindle cattle are E⁺/E⁺or E⁺/e.

‘A’ Locus

(Click here to know more about the ‘A’ or Agouti locus)

		known in Highlands	suspected in Highlands
A^br	brindle	yes
A⁺	wild type	yes
a	black (recessive)		unknown

The wild type colour here is the agouti colour seen in Jersey cattle. A mutation at this locus has been reported to cause the brindle pattern in Normande cattle (1) and more recently this same gene has been identified in Highlands as the cause of their brindling pattern (Schmutz, personal communication).

‘K’ Locus

(Click here to know more about the ‘K’ locus)

		known in Highlands	suspected in Highlands
K	black (dominant)
K^br	brinde
k⁺	wild type		assumed

K^br is proven to be the gene controlling brindling in dogs. It has not been identified in Highlands though, so all Highlands are assumed to be K⁺/K⁺ at this locus.

‘D’ Locus

(Click here to know more about the ‘D’ or Dilution locus)

		known in Highlands	suspected in Highlands
D^c	dilutes red & black	yes
d⁺	wild type		assumed

The dilution gene, D^c, was first identified in Charolais cattle, and also Simmental cattle, but a similar mutation at the same locus has more recently been established to dilute red and black colours in Highlands (7). It dilutes red to yellow (one D^c gene) or white (two D^c genes). It also dilutes black to dun (one D^c gene) and silver dun (two D^c genes). This is not necessarily the same as the dilution genes for all other breeds (e.g. the grey colour in Dexter cattle is caused by a different gene).

‘B’ Locus

(Click here to know more about the ‘B’ or Brown locus)

		known in Highlands	suspected in Highlands
B	black (dominant)
b	brown / chocolate		?

As yet there is no known influence on Highland cattle colouring at this gene locus. This brown colour is known to occur in Dexter cattle (they appear a rich, reddish brown colour), but in that breed it is confusingly called ‘dun’.

‘S’ Locus

(Click here to know more about the ‘S’ or Spotting locus)

		known in Highlands	suspected in Highlands
S⁺	wild type		assumed
S^P	piebald (particolour?)		assumed

This locus is thought to be involved with most of the white patches that appear in cattle breeds – Pinzgauer colouring, and the piebald colouring of Herefords, Guernseys and Holsteins. This piebald colouring looks very similar to the parti colour colouring that pops up in Highlands from time to time. The white udder or underbelly that we see in some Highlands could have an inherited basis or may simply be a change pigment migration in some animals.