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The purpose of the thesis was to compare the bioavailability of various race elements dependent on their dose and source and to examine the previous requirement recommendations by means of investigations in an extensive management cattle farm. Furthermore, to show ways of optimising the mineral provision in the first three months of life by varying the ration arrangements of die calves.For this purpose two investigations were carried out with pregnant suckling cows in the winter stable period. Every trial involved 240 suckling cows and their new born calves. The mineral food used for the first trial contained sodium selenite and copper sulphate (group A), and selenium yeast in various concentrations and copper methionine (groups B, C and D), respectively. To investigate the effect of high doses of inorganic trace elements sources on the milk content and to compare the bioavailability of these compounds with the bioavailability of organic sources, mineral feed with a high zinc (12.000 mg/ kg DM, group B), copper (1.800 mg/ kg DM, group C) and selenium content (80 mg/ kg DM, group D) were used. Group A was comprised the control group.A third feeding trial was carried out with 60 calves, which were on average 13 days old at the start of the trial. One group was provided with only milk and hay (group A), another with customary supplementary food (group B) and group C with mineralised supplementary food. All three trials included an analysis of the nutrients, minerals and trace elements of the basic food offered as well as of the mineral and supplementary food, which was used. An analysis also of the milk contents was carried out in the suckling cow trials in order to estimate the bioavailability. Blood samples and subsequent serum analyses followed in the second suckling cow and in the calves trial.The provision of the suckling cows of all groups covered the requirements. The partially high trace element intakes of the cows in trial 2 did not necessarily lead to physiological serum zinc, copper and selenium values in the cows and calves.The different selenium intakes in the first trial and the different zinc, copper and selenium intakes in the second trial were reflected in the milk only in the case of selenium. When using sodium selenite (selenium intake 4,7 mg/ cow and day) the milk content amounted to 0,03 mg/ 1, with selenium yeast (selenium intake 4,4 mg/ cow and day) values of 0,07 mg/ 1 were reached. An intake of 8,6 mg selenium/ cow and day as sodium selenite lead to the highest milk content (0,10 mg selenium/ 1). With organic and high doses of inorganic zinc and copper compounds o increase in milk contents of the corresponding trace elements could be reached.
Organic sources of zinc, copper and selenium appeared to be partially superior to inorganic compounds. In the area of necessary requirement intakes there was o difference between the bioavailabilities of zinc sulphate and zinc methionine. Zinc intakes from 600 mg/ cow and day occasionally lead to an increase of the serum contents of cows, when zinc methionine was used. Such an increase could not be reached with zinc sulphate.
With intakes of 175 mg copper/ cow and day copper methionine is about 33 to 95% superior to copper sulphate in its effect on the serum copper concentrations of the cows and their new-born calves.
Among the selenium sources the bioavailability of selenium yeast was around 112% higher and that of selenium methionine was about 18% higher than the bioavailability of sodium selenite (selenium intake 3,5 mg/ cow and day). Relating to the serum contents of the cows, increases in the values of around 24% with selenium methionine and around 71% with selenium yeast were reached (selenium intake 2,3 mg/ cow and day). Concerning the serum contents of the calves selenium methionine was around 1 % superior to sodium selenite in its effect and selenium yeast was around 21% superior. Because of the different bioavailabilities particular requirements for each trace element source must be recommended.The investigations enabled the following recommendations for suckling cows with 500 kg weight in the final three weeks of gestation. The basis was the milk and serum contents on the corresponding trace elements. The intake from the basic food is put in parentheses.? Zinc: 500 (237) mg/ cow and day as zinc sulphate or zinc methionine (GfE 500 mg/ cow and day)? Copper: 220 (69) mg/ cow and day as copper methionine or more than 300 (69) mg/ cow and day as copper sulphate (GfE 100 mg/ cow and day)? Selenium: 4,9 (0,45) mg/ cow and day as selenium yeast (GfE 2,0 mg/ cow and day)The deficient provision for the calves in the first months of life could also be confirmed here. With the exception of selenium and zinc intake in the first month of life and zinc intake of group C in the second month of life the trace element provision of all groups did not cover the requirements. Although the serum iron content reached physiological values in the third month of life, altogether the blood investigations resulted in an underprovision of iron, copper and selenium. By means of results of the calves trial it became clear, that without limiting the daily supplementary food intake to 100 g/ calf and day the animals are in danger of developing a rumen acidosis. This leads to an increasing underproviding due to decreasing food intakes. To secure a sufficient trace element provision the mineral content of the supplementary food should be either increased or the mineral food should be offered separately from the supplementary food. The calves, which received supplementary food in addition to the basic food, showed a higher hay intake in the third month of life than calves, which had been fed only with milk and hay.