The Veterinary Genetics Laboratory offers genetic tests specific to Dexter Cattle.

Dexter Dun

The Dun coat color in Dexter cattle is a dilution of black pigment (eumelanin) caused by a recessive mutation in the gene tyrosinase related protein 1 (TYRP1), also known as the Brown locus. The hair color is diluted to shades of dark brown to golden. Red pigment is not diluted by this mutation. A genetic test specific for the Dexter Dun mutation is available from VGL.

SUBMISSION FORM - Allow 5-10 business days for test results.

Results reported as:

B/B: Animal does not have the Dun mutation

B/b: Animal carries one copy of the Dun mutation. Color is not diluted.

b/b: Animal is homozygous for the Dun mutation.

A second test for red/black pigment (MC1R or Extension gene) may be needed to determine the complete coat color genotype and possibilities for offspring color.

Reference:

Berryere TG, SM Schmutz, RJ Schimpf et al. TYRP1 is associated with dun coat colour in Dexter cattle or how now brown cow? Animal Genetics 34: 169-175, 2003..

Extension (Red/Black)

Several genes are involved in the process of creating the complex coat colors and patterns found in domestic cattle. One of these is the Melanocortin 1 Receptor (MC1R) gene, also called Extension, that controls the production of black (eumelanin) and red (phaeomelanin) pigments. The three alleles (forms) of this gene are dominant black (ED), Wild type (E+) and recessive red (e). Dominant black (ED) is dominant to the other two alleles and animals with this allele are jet black (solid or spotted). The Wild type (E+) produces cattle with reddish brown to brownish black coloration with a tan muzzle ring. Two copies of the recessive red (e) allele will result in red color. The other coat color genes act as modifiers of these base colors adding white spotting patterns, reorganizing the distribution of red and black pigments (Brindle and Agouti) or diluting the pigments (Dun, Charolais dilution and Simmental diution).

Coat color results are reported as:

ED/ED:	Dominant black. This animal cannot produce red offspring
ED/E+:	Dominant black, carrier of red
ED/e:	Dominant black, carrier of red
E+/E+:	Red
E+/e:	Red
e/e :	Red

Bulldog Dwarfism (Chondrodysplasia)

Inheritance of a form of chondrodysplasia known as bulldog dwarfism has been documented in Dexter cattle since the early 1900s. Among other defects, affected fetuses have severe disproportionate dwarfism, short vertebral column and a large head, and are naturally aborted around the seventh month of gestation.  The defect is a major problem for Dexter breeders, as one copy of the defective allele produces the favored short-legged phenotype of Dexter cattle. Thus, selection for the preferred Dexter phenotype maintains a lethal allele in high frequency in the population. Breeding carrier animals together will produce 25% affected fetuses.

Research by investigators in Australia determined that the bulldog dwarfism in Dexters is caused by two mutations in the aggrecan gene (ACAN). The most common mutation is BD1 (2266_2267ins-GGCA). A second mutation in the same gene – BD2 (–198C>T) – accounts for bulldog dwarfism in one particular bull lineage. A diagnostic test for BD1 has been developed and is available to help Dexter breeders avoid production of bulldog calves.

The results of testing at VGL are reported as:

N/N: Normal, does not have the bulldog gene.

N/BD1: Carrier, has one copy of the BD1 bulldog gene. Breeding to another carrier will produce 25% affected bulldog calves.

BD1/BD1: Affected fetus, has 2 copies of the bulldog BD1 mutation.

Reference:

Cavanagh  J.A.L., I. Tammen , P.A. Windsor, J.F. Bateman, R. Savarirayan , F.W. Nicholas, H.W.  Raadsma. Bulldog dwarfism in Dexter cattle is caused by mutations in ACAN. Mammalian Genome 18:808-814 (2007)