Effects of altered dietary iron intake in Mycobacterium paratuberculosis-infected dairy cattle: sequential observations on growth, iron and copper metabolism and development of paratuberculosis.

Twenty calves were orally inoculated with Mycobacterium paratuberculosis at six weeks old. At six months old, 10 of these, plus four uninfected controls were maintained on limited dietary copper and supplemented iron intake for a further 27 months. During this time all these animals, together with a further four untreated controls, were bred before being killed and examined for evidence of paratuberculosis. Despite significant reduction in weight gain, attributable to both iron supplementation and infection, no significant difference was found in the numbers of iron-supplemented and unsupplemented animals that developed clinical signs nor in the extent and severity of intestinal lesions between groups. Accumulation of iron in paratuberculosis lesions was not affected by iron supplementation but was positively correlated with the frequency of shedding of M paratuberculosis in faeces (P less than 0.05). Dietary iron supplementation alone resulted in serum hyperferraemia, hepatic siderosis and slight hypocuprosis, whereas, in infected animals, this resulted in marked hypocuprosis and anaemia within groups (P less than 0.05). Infection alone resulted in serum hypoferraemia and intestinal and hepatic siderosis which was positively correlated with the severity of infection within groups (P less than 0.05). Susceptibility to paratuberculosis may result from failure ultimately to limit monokine-mediated iron sequestration in intestinal tissue.

Studies of the pathogenesis of Rhodococcus equi infection in foals.

Pyogranulomatous pneumonia was induced in Thoroughbred foals by intranasal challenge with freeze-dried cultures of Rhodococcus equi (previously Corynebacterium equi). The incubation period was about 18 days and clinical signs were not seen for a further week. There were marked seasonal and individual foal differences in responses to infection. Elevations in serum caeruloplasmin oxidase activity and copper concentrations appeared to be sensitive indicators of infection. Serum zinc concentrations and serum alpha-mannosidase and alkaline phosphatase activities fell in the more severely infected foals. Use of trace elements and trace element-related parameters along with faecal culture for R. equi could prove useful for early diagnosis of field cases.

Mannosidosis in Galloway calves.

Mannosidosis was diagnosed in four stillborn Galloway calves and an autolyzed full-term fetus from experimental matings of carrier animals. Gross lesions were moderate internal hydrocephalus, and pallor and enlargement of the liver and kidneys and arthrogryposis. Histologic changes in the central nervous system of each calf were marked foamy vacuolation of the cytoplasm of neurones in the cerebral cortex, thalamus and brainstem, and vacuolation of the Purkinje cells of the cerebellum. Spheroids were common throughout the brain and there was also consistent severe foamy cytoplasmic vacuolation of renal tubular epithelial cells and hepatocytes. The activities of alpha-mannosidase, the lysosomal enzyme whose activity is deficient in mannosidosis, and activities of five other lysosomal enzymes were compared in brain, liver, and kidney tissues of three mannosidosis-affected calves and normal calf tissues. Tissues from the affected calves had a marked deficiency of alpha-mannosidase activity compared with the normal tissues; the greatest deficiency was in the liver (99%) and brain (98%). Activities of the other lysosomal enzymes were elevated in the affected tissues compared with normal. Mannosidosis is a lysosomal storage disease that results from a defect in glycoprotein metabolism and affects man, Angus and Angus-related breeds of cattle, such as Murray greys, and the cat. The congenital disease is caused by an inherited deficiency of the lysosomal enzyme alpha-mannosidase, and is inherited in an autosomal recessive manner. Mannosidosis was recently reported in a number of aborted and stillborn Australian Galloway calves from an experimental breeding trial. This is more detailed account of the histological and biochemical results obtained during the trial.

Absence of a role for selenium deficiency in the runting syndrome of broiler chickens in Australia.

The role of selenium deficiency in the etiology of the runting-stunting syndrome (RSS) of broiler chickens in Australia was investigated. Commercial broiler chickens maintained on selenium-deficient developed signs consistent with selenium deficiency of exudative diathesis and markedly reduced plasma glutathione peroxidase activity, but they did not develop pancreatic atrophy and fibrosis or elevated plasma amylase activity, which are the other lesions associated with RSS. Supplementation of the diets of birds from a RSS-susceptible flock with a mixture of selenium, vitamin E, cysteine, and sulfate had no effect on the incidence of runting in the treated birds. In field outbreaks of RSS there were no observable differences between affected and unaffected birds in the concentration of selenium in tissue samples. Furthermore, evidence is presented which suggests that in cases of RSS, pancreatic atrophy and elevations in plasma amylase precede reductions in plasma glutathione peroxidase activity.

Pancreatic degeneration in broilers with runting and stunting syndrome.

A number of plasma biochemical parameters were examined in five outbreaks of runting in broiler chickens. In four of the five outbreaks, runts showed consistent elevations in plasma amylase activity and reductions in glutathione peroxidase activity. In two of the five outbreaks the plasma vitamin E concentration was reduced, as was the activity of plasma alkaline phosphatase. A highly significant number of runted chickens were found to have pancreatic degeneration, elevated plasma amylase activity and reduced plasma glutathione peroxidase activity, compared with non-runted chickens. The implications of these changes are discussed in relation to the aetiology of runting and stunting syndrome and, in particular, the possible involvement of selenium.

Serum biochemical changes in calves with Johne's disease.

Calves clinically affected with experimentally induced Johne's disease exhibited elevation of caeruloplasmin oxidase activity, and marked depression of alpha-mannosidase activity during the period when clinical signs of the disease were most prominent. Changes in serum copper levels and alkaline phosphatase activity were closely correlated with the elevation of caeruloplasmin oxidase activity, and depression of alpha-mannosidase activity. The pattern of these changes was similar to nutritional and metabolic changes described previously in acute infectious conditions in man and animals.

Control of alpha-mannosidosis in Angus cattle.

Tests for the detection of animals heterozygous for alpha-mannosidosis were undertaken on samples taken from 34,203 cattle registered with the Angus Society of Australia. Results indicates 1,836 (5.4%) of the animals were heterozygotes. Heterozygotes were detected in 214 (51%) of the herds examined.

A comparison of fluorimetric and colorimetric methods for the determination of alpha-mannosidase activity in bovine plasma.

This paper compares both manual colorimetric and fluorimetric methods for the assay of acidic alpha-mannosidase activity in bovine EDTA plasma. The effect of variable blood volumes per 10 ml blood collecting tube has been investigated, and the colorimetric assay conditions adjusted (for example, zinc concentration in pre-incubation buffer) to cope with low blood volumes resulting in high EDTA/plasma ratios. We have shown that with non-haemolysed EDTA plasma samples, the two methods give similar results, but for haemolysed samples, the colorimetric method yields significantly lower results than those obtained fluorimetrically. Using the manual fluorimetric method, samples can be assayed more rapidly and simply than by using the colorimetric method. This provides definite advantages in a laboratory receiving variable numbers of samples, or which cannot afford the high cost of automated equipment.

An improved fluorimetric determination of alpha-mannosidase activity in bovine plasma.

This paper describes a manual fluorimetric method for the assay of acidic alpha-mannosidase activity in bovine plasma. The optimum conditions for the assay of this enzyme were studied. The assay method devised includes the addition of zinc to the substrate, which stimulates activity by approximately twofold, and reduces the optimum substrate concentration. This latter feature affords considerable cost saving in each test. We have also shown that the alpha-mannosidase activity in lithium heparin plasma, EDTA plasma and blood serum is the same whether the plasma/serum is separated from the cells/clot at 6, 20 or 25 hours after sample collection. This has eliminated the previous necessity of having to deliver whole blood samples to the laboratory within 6 hours of collection. Furthermore samples for the supplementary neutrophil assay can now be taken at the same time as those for the plasma test, and both samples forwarded together. The plasma alpha-mannosidase assay is a rapid and reliable screening test for the mannosidosis genotype and for detecting carrier animals. Carrying out this plasma assay in conjunction with the more definitive neutrophil assay provides a reliable method of distinguishing homozygotes and heterozygotes from normal animals.