The clinical, pathological and biochemical manifestations of maple syr
up urine disease (MSUD) are similar in Poll Hereford and Poll Shorthor
n x Poll Hereford calves. No significant differences were observed in
branched-chain amino acid concentrations in plasma, or of branched-cha
in keto acid dehydrogenase activity in fibroblasts, between Poll Heref
ords homozygous normal and heterozygous for the mutation responsible f
or MSUD. Haemopoietic chimerism resulted in incorrect diagnosis of the
MSUD genotype in 30% of non-identical twins when blood DNA was analys
ed using allele-specific amplification. Hair roots are shown to be a s
uitable source of target DNA for genotyping Poll Hereford cattle for t
he MSUD mutation. Twelve of 203 (5.8%) aged Poll Hereford bulls, sampl
ed at saleyards during the last 4 months of 1993, were found to be het
erozygous for the mutation. In contrast, the mutant sequence was detec
ted in only 1 of 150 (0.7%) 2- and 3-year-old Poll Hereford bulls offe
red for sale at 2 stud sales held during 1993, suggesting that the pre
valence of the disease may decline over the next few years.