Influence of manganese intake on body, wool and testicular growth of young rams and on the concentration of manganese and the activity of manganese enzymes in tissues

Abstract

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.