Four groups of 10-month-old Merino rams of similar liveweights were fed identical diets, except that the manganese contents were either 13, 19, 30 or 45 pg/g of dry matter. The basal diet (13 8g Mn/g) was fed to all rams for 14 days, then the treatment diets were fed for a further 84 days. All rams were slaughtered at the end of the experiment and tissues were collected. The intake of manganese had no affect on liveweight gain, dry matter intake, apparent digestibility of the diet or clean wool production. Although the size of testicles at slaughter was not related to manganese intake, testicular gain as a ratio to liveweight gain was higher in the rams fed 19 and 30 pg Mn/g, but not 45 8g Mn/g, than those fed 13 8g Mn/g. Also in rams fed the basal diet, the large rumen bacteria (12.90 to 16.24 pm in diameter) made up less of the bacterial biomass than in other groups. The treatments did not affect the total number of rumen bacteria or the size structure of bacteria population in the rumen. Rams fed the least amount of manganese had low concentrations of manganese in heart and lung and a lower activity of manganese superoxide dismutase in heart than rams fed 45 8g Mn/g. The concentration of manganese in these tissues, and the activity of manganese superoxide dismutase in the heart increased linearly as the concentration of manganese in the diet increased. An intake of 13 8g Mn/g of dry matter therefore caused some biochemical changes in rams, but was adequate for growth and wool production under the conditions of this experiment.
Two groups of sheep, both on a diet deficient in selenium, were either treated with intraruminal selenium pellets (containing 5% elemental selenium, 95% iron) or remained as untreated controls. At 23 weeks after pellet administration, activities of the selenium-containing enzyme glutathione peroxidase were greatly increased in many of the tissues of treated animals compared with the untreated controls. Maximum activity of erythrocyte glutathione peroxidase was reached 20 weeks after pellet administration. The maximum activity was considerably greater than the activity at which selenium-responsive diseases, in particular selenium-responsive unthriftiness, occur. This, together with the greatly increased enzyme activities in other tissues several months after pellet administration, suggests that selenium status can be adequately maintained for long periods by treatment with these pellets. In contrast to monogastric species, it appears that in the ruminant the biological availability of elemental selenium released from pellets, as determined by tissue glutathione peroxidase activities, is similar to that reported previously for selenite.
Low erythrocyte activities of the selenium-containing enzyme glutathione peroxidase were found in Merino lambs in an area of the Strathbogie Ranges in central Victoria where selenium-responsive conditions have previously been reported. Body weight gain trials conducted over 10 properties in the above area demonstrated that the severity of selenium-responsive unthriftiness was significantly correlated with the erythrocyte glutathione peroxidase activity (r = – 0.95, P <: 0.001). Positive body weight responses to selenium treatment were only observed in lambs with erythrocyte glutathione peroxidase activities less than 30 U/g Hb prior to selenium treatment. These findings indicate that measurement of erythrocyte glutathione peroxidase activity provides a convenient index of the selenium status in sheep. ________________ *Part I, Aust. J. Agric. Res., 30: 695 (1979).
Lupinosis in grazing sheep is often associated with a potentially deleterious increase in the concentration of copper in the liver. Siromin�, a mineral mix developed by CSIRO for sheep on dry herbage and containing Cu at 116 mg/kg, was tested for its suitability for use with sheep consuming toxic lupin stubble, taking particular regard for dangers of Cu toxicity. There were three dietary treatments applied at two levels (either present or absent) to 40 Merino wethers for 8 weeks. Treatments consisted of adding Cu (10 mg Cu as CuS04/kg), minerals (25 g/kg as Siromin�) and toxic lupin stubble (50 g/kg) to a basal diet consisting of oaten hay and lupin seed and containing 3 mg/kg of Cu. Toxic lupin stubble decreased feed intake and growth, increased plasma activities of liver enzymes and increased plasma concentrations of protein, globulin, bilirubin, Cu and Zn. It also decreased concentrations of Zn and Fe in liver, but had no effect on Cu. The mineral mix had no adverse effects on any signs of lupinosis, and it did not increase liver Cu concentration at either level of dietary Cu. The mineral mix prevented the inappetence caused by lupinosis in sheep fed the low Cu basal diet. Cu treatment resulted in increased concentrations of Cu and Fe in liver, and exacerbated some signs of lupinosis. The results show that the mineral mix is safe to feed to sheep grazing toxic lupin stubble, and it may provide a practical means of supplying additional Zn. The exacerbation of signs of lupinosis by the addition of only 10 mg Cu/kg as CuS04 suggests that under field conditions the supply of Cu in the absence of suitable amounts of molybdenum and sulfur should be kept to a minimum.
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