The dun coloration in Dexter cattle is caused by the dilution of black pigment in the hair, producing shades of dark brown to gold. This color dilution is caused by a recessive mutation. Dexters come in three different colours; black, red and dun.
But what makes a Red Dexter red or a Dun Dexter dun? Or for that matter allows a Black Dexter to have a coloured calf? Two major genes are involved in producing these colors. Clear as mud? Well it actually is not that confusing when we break it down. Dun is widely believed to have come into the breed through introgression of non Dexter blood into the breed.
The primary colour gene in the Dexter has two principal alleles, red and black. Dun comes in shades of blond, cocoa brown, strawberry blond, and mahogany. Duns always have a tannish brown nose and brown eyeliner, although their eyes are typically lighter in color than the eyes of other Dexters.
Black and red, are a simple either / or", but then there is the color Dun which is more like an on / off". The genetics of Dexter cattle are fascinating as they showcase the interplay of several genes that determine coat color, one of the most visible traits. The color variations in Dexter cattle are typically black, red, and dun, traits governed by specific genes located on separate chromosomes.
B/B = normal looking black Dexter B/b = normal looking black Dexter (carries dun) b/b = brown Dexter Dun Dexter dun is a different dilute mutation than dun found in other breeds of cattle. It is unique to the Irish Dexter breed. Dexter Dun affects only black Dexters, making them appear different shades of tan to chocolate color pigment.
When we started breeding Dexters, the genetics of the dun colouring was not understood - dun calves sometimes cropped up unexpectedly, from either black or red parents. However, research showed that the colour is caused by a recessive gene that modifies the black colour gene to produce dun. The Dexter dun study concluded with the publication in 2003 of TYRP1 is associated with dun coat color in Dexter cattle or how now brown cow? by the International Society for Animal Genetics in their journal, Animal Genetics, 34, 169.
Dexter Dun Coat Color Research Project presented by Jessica Peterson and Anna Fuller from the University of Nebraska.
