Abstract
Twenty-five syndactylous Angus cattle, characterized pathologically, were 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, and 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 truncated cone, the base of which was located at the coronary band. Most hooves were fused completely with no indication of dual anlage. An occasional hoof had a distal notch, and other hooves had a dorsally located groove indicating dual embryonic origin. Lateral dewclaws were enlarged in most cases. Radiographs and dissections of limbs of 19 animals revealed a consistent pattern of fusion in most affected calves. Lesions included 1 or more of the following: disappearance of the large metacarpal and metatarsal intertrochlear notches, horizontal fusion of 1 or more carpals and tarsals, fusion of proximal sesamoids, 1 distal sesamoid, and fusion of paired phalanges. Evidence of a genetic cause consisted of 11 syndactylous calves among 70 offspring of 4 3/4 sib families, 8 preterm syndactylous fetuses among 148 preterm fetuses and 13 calves in progenies of 19 animals tested for possible heterozygosity, and 5 syndactylous calves from matings of an Angus syndactylous bull with 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 expression 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. Phenotypic effects on limb development were most dramatic in calves with the sy A/sy A genotype.