| Abstrakt: |
Studies were conducted to determine whether the utilization of certain forage minerals by ruminants was altered when the animals consumed forages grown with liberal versus conservative quantities of nitrogenous fertilizers. In addition, the effect of vitamin D supplements upon the utilization of the forage minerals was studied.Nitrogen content in the dry matter of the forages grown with low levels of nitrogen ranged from 2.11 to 2.62%, while those of the forages grown with high levels of nitrogen ranged from 3.74 to 4.38%. These latter forages also contained greater quantities of magnesium, potassium, and nitrate.The overall utilization of magnesium, as evaluated in balance trials, was less for the high nitrogen-containing forages. For all experiments the average apparent availability of magnesium in the low nitrogen-containing forages ranged from 18 to 24%, while values for the high nitrogen-containing forages ranged from 11 to 16%. The decreased apparent availability of magnesium in the high nitrogen-containing forages was reflected by decreased urinary magnesium excretions and in most cases by decreased magnesium balances. Calcium tended to be retained in greater amounts by animals consuming the high nitrogen-containing forages, and a general inverse relationship was found between the retention of calcium and magnesium. Supplemental vitamin D increased the apparent availability and retention of calcium and magnesium in animals consuming low nitrogen-containing forage, but had no effect when given to animals consuming high nitrogen-containing forage. The presence of an anti-vitamin factor in the high nitrogen-containing forage is suggested.The apparent availability and retention of phosphorus was greater for the high nitrogen-fed animals in only one experiment, and the apparent availability of potassium was higher for these animals in all experiments.Blood sera from animals consuming the high nitrogen-containing forages contained higher nonprotein nitrogen, slightly higher phosphorus, and slightly lower calcium concentrations, while no differences were found in the magnesium, potassium, and sodium concentrations. |
