HETEROZYGOTE DETECTION FOR MAPLE-SYRUP-URINE-DISEASE IN CATTLE

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.