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Mannosidosis in Cattle
Peter J. Healy, B.V.Sc., Ph.D., Veterinary Research Station, Glenfield.
Mannosidosis (pseudolipidosis) is a lethal disease that has been reported in Angus-type cattle in Australia and New Zealand. Calves affected with the condition show tremor of the head and neck, an unsteady gait and a tendency to be aggressive. The animals die before reaching breeding age. The disease was first described in Australia by Whittem and Walker (1957) then studied in New Zealand by Jolly (1976). Jolly and co-workers have established that the disease is an inborn error of metabolism caused by a deficiency of alpha-mannosidase in tissue lysosomes. They have shown that the condition is inherited in a simple mendelian manner. Homozygous recessive animals are clinically affected and heterozygotes, although clinically normal, have a partial enzyme deficiency. Activity of alpha-mannosidase in serum or plasma generally reflects tissue enzyme activity. Detection of heterozygotes can be achieved by means of a serum (or plasma) test, or a lymphocyte test. When testing a whole herd, the serum test can be expected to allow definition of the genotype of approximately 97% of subjects, providing information is available concerning breeding, age, sex and grazing history of each of the subjects. In practice it is usually possible to cull the remaining 3% of subjects that give en equivocal test result. However if these animals are considered to be valuable then they can be subjected to the more complicated lymphocyte test that will allow definition of their genotype. If animals are tested as individuals, or in small groups, the serum test will allow definition of only 70% of subjects. In these circumstances it may be economical to apply the lymphocyte test. Testing of individual sires can best be managed by subjecting 10 of their progeny to the serum test, but the progeny must be of the same age and sex and be grazing under almost identical conditions.
In New South Wales, 10 cases of mannosidosis have been confirmed at Glenfield over the past 10 years, 2 of the calves being Murray Greys and 8 Angus. Testing of 10 herds, 6 Angus and 4 Murray Grey (clinical cases reported in only 1 herd) has revealed that approximately 5% of animals in these were heterozygotes. In a random-breeding population an incidence of 5% heterozygotes would mean that 1 in every 1600 calves born would die of mannosidosis, so that this disease would be of little economic significance under these circumstances. However, stud breeding is not conducted in a random manner and at various times different families of cattle predominate in the stud books. If, by chance, a fashionable family contained a relatively high proportion of heterozygotes, the prevalence of heterozygotes in the population could increase rapidly.
In New Zealand, estimation of serum alpha mannosidase activity is being used as a basis for a disease control scheme, based upon detection and elimination of heterozygotes from bull-breeding herds. This scheme is being conducted by the Ministry of Agriculture and Fisheries with the support of the Angus Association. The Australian Angus Association and the Murray Grey Beef Cattle Society have been informed of recent developments concerning this disease and are awaiting the response from their members before deciding to support a disease control scheme, as in New Zealand, In the meantime, it is the intention of the New South Wales Department of Agriculture to offer a testing service to interested breeders, on a fee-for-service basis.