HEREDITARY SYNDACTYLY IN ANGUS CATTLE

Twenty-five syndactylous Angus cattle, characterized pathologically, w ere reported from 16 herds in 10 states from 1979 to 1994. Twenty-one (84%) had all 4 legs syndactylous, 3 (12%) had 3 legs syndactylous, an d 1 (4%) had 2 legs syndactylous. All syndactylous cattle walked with considerable difficulty. Hooves of aged animals became curled and bent laterally or medially. Affected hooves had the appearance of a trunca ted cone, the base of which was located at the coronary band. Most hoo ves were fused completely with no indication of dual anlage. An occasi onal hoof had a distal notch, and other hooves had a dorsally located groove indicating dual embryonic origin. Lateral dewclaws were enlarge d in most cases. Radiographs and dissections of limbs of 19 animals re vealed a consistent pattern of fusion in most affected calves. Lesions included 1 or more of the following: disappearance of the large metac arpal and metatarsal intertrochlear notches, horizontal fusion of 1 or more carpals and tarsals, fusion of proximal sesamoids, 1 distal sesa moid, and fusion of paired phalanges. Evidence of a genetic cause cons isted of 11 syndactylous calves among 70 offspring of 4 3/4 sib famili es, 8 preterm syndactylous fetuses among 148 preterm fetuses and 13 ca lves in progenies of 19 animals tested for possible heterozygosity, an d 5 syndactylous calves from matings of an Angus syndactylous bull wit h 1 Angus and 4 Holstein syndactylous cows. Data were consistent with recessive inheritance at a single locus. Angus cattle with sydactytly had a larger number of affected limbs than did syndactylous Holsteins and their Angus crosses, suggesting existence of 2 recessive alleles. The allele of Holsteins (sy(H)) appeared to influence phenotypic expre ssion in a dominant pattern over the Angus allele (sy(A)). Both sy(A) and sy(H) alleles acted as reccessives to the normal SY allele. Phenot ypic effects on limb development were most dramatic in calves with the sy(A)/sy(A) genotype.