Roles for biochemical and polymerase chain reaction technologies in diagnosis and control of bovine α-mannosidosis.
An α-mannosidosis testing programme was implemented to detect heterozygotes in a commercial Angus herd, in which a case of α-mannosidosis had been confirmed. The calf was homozygous for the 961T→C mutation. A plasma screening test and a polymerase chain reaction (PCR)-based, mutation-specific assay were used. Hair roots were used as a source of DNA for the PCR assay to determine the genotype of bulls at the 961T→C site. The mutation was detected in 3 of the 27 bulls examined, including the sire of the affected calf. The heterozygotes were sold for slaughter. Blood samples were collected from 747 heifers and cows in 11 grazing groups. Plasma α-mannosidase activity was examined within the groups. Blood samples in which plasma α-mannosidase activity was <70% of the group mean were selected, and DNA suitable for PCR analyses was prepared from leukocytes. Plasma α-mannosidase activity in 96 samples was <70% of the mean activity of the respective group. Of the 96 subjects, 46 were heterozygous at the 961T→C locus. All heterozygotes had plasma α-mannosidase activity <55% of the group mean. Plasma α-mannosidase activity was <55% in only 3 of the 50 animals that were shown to be homozygous wild-type (normal) at the 961T→C locus. Heterozygous heifers and cows were sold to slaughter. In this herd, the PCR assay was an ideal supplementary test to replace estimates of relative α-mannosidase activity in granulocytes which were previously used to establish the α-mannosidosis genotype of individuals that have low plasma α-mannosidase activity.