Aurochs cow colour schemes

While the colour of aurochs bulls is easy to determine (black or very, very dark brown), there is a larger spectrum for the possible colour of aurochs cows. Historic evidence indicates that there was variation, which is also in accordance with the colour of wildtype-coloured domestic cows. 

I tried to illustrate this variation on with a drawing. It shows an aurochs cow which is based on the Camebridge specimen in four different colours, representing the spectrum which is documented by cave paintings and the report from Schneeberger in Gesner 1602. They mainly differ in the degree of eumelanisation. Eumelanin is black pigment, and in wildtype coloured cattle black hair starts to grow on the sides of the trunk, legs, head and neck and continues to grow up to the top of the body, leaving only a dorsal stripe of a lighter colour. Wildtype coloured cattle can either be fully eumelanised (“bull colour”), not eumelanised at all or somewhere in between, depending on when this process stops.

Top left: This colour scheme is completely reddish brown with a dark eel stripe and dark forelocks, and having no black hair except for the tail tip. This colour scheme is similar to that of banteng cows and found in wildtype-coloured domestic cows (see here for a Taurus cow showing this colour). There are cave paintings which might show this variant. The other colour variants, or actually all wildtype coloured cattle, also have a dark eel stripe but reduced to a very fine line that is not always discernable. 

Top right: This is the “standard” colour scheme. Reddish brown with black or very dark brown head, neck, legs, sides of the trunk and tail tip. This colour is very common in wildtype-coloured domestic cattle and you can see it in this Heck cow. It is also illustrated in cave paintings and therefore was most likely present in wild aurochs. Some wildtype-coloured domestic cattle have dark brown hair instead of reddish brown hair, which can be seen in Maronesa cows or some Heck cows (I know of no cave painting that unambiguously shows this colour but it might have belonged to the natural variation of wild aurochs as well). 

Bottom left: This colour scheme is basically black with a reddish brown colour saddle. This colour variant has been illustrated in cave paintings and is nicely shown by the Taurus cow Lerida. 

Bottom right: “Bull colour”. Apparently, aurochs cows sometimes also had a colour identical to that of bulls. Cave paintings show a black cow and Schneeberger also reports this. This Taurus cow shows this colour. 

There is a continuum between those colour schemes. They represent a spectrum and all possible colours along this spectrum can be found in wildtype coloured domestic cattle, and probably also the aurochs. Apparently there was less selective pressure on the exact colour of aurochs cows so that we find this variation. 

That means that “breeding-back” has room for variation concerning which cow colours are to be permitted in breeding. Other, lighter, colours like beige or very light brown indicate dilution alleles (f.e. see this Taurus cow) and should be selected out as they are most likely domestic mutations.