Bulldog Dwarfism (Chondrodysplasia) in Miniature Zebus

Inheritance of a form of generalized chondrodysplasia known as bulldog dwarfism has been documented in several breeds of cattle including Miniature Zebus. Among other defects, affected fetuses have severe disproportionate dwarfism, a short and compressed vertebral column, a large head, and short, stocky limbs. Fetuses with this genetic defect are naturally aborted around the seventh month of gestation.

A mutation in the cartilage development gene Aggrecan (ACAN) was identified as the cause of bulldog dwarfism in Miniature Zebu cattle. The mutation is one base pair insertion (ACAN:c.5686insC) in the sequence of exon 12 of the gene which results in production of truncated protein and loss of its critical function needed for normal bone and cartilage development. This mutation (named here BDz for simplicity) has an autosomal recessive lethal mode of inheritance. This means that both males and females are equally affected and that affected fetuses are not viable and are aborted later in pregnancy. Two other mutations (BD1 and BD2) in the same gene are responsible for bulldog dwarfism in Dexter cattle.

Testing for this bulldog dwarfism variant in miniature Zebus can help breeders determine if carriers are present among breeding stock and to use mating strategies to avoid producing affected calves. Breeding carrier animals together is not advised because this type of mating has a 25% chance of producing affected calves. The test can also be used by veterinarians to confirm bulldog dwarfism diagnosis of aborted fetuses.