Abstract
A balance experiment was conducted on five ewes divided into two groups (young and old) which had been fed on two control and four low-magnesium diets of various levels of Mg. Decreased dietary Mg resulted in linear decreases in fecal, urinary and serum Mg in both groups (P<0.01 and <0.001). With regression equations, minimum dietary requirements, true absorption values of Mg and endogenous fecal Mg in these young and old groups were estimated at 11.78 and 14.50 mg/kg body wt/day, 41.7 and 39.8%, 3.11 and 3.46 mg/kg body wt/day, respectively. Exponential regressions were obtained between serum and urinary Mg in both groups (P<0.001). Significant positive correlations of Mg with Ca in Mg deficiency were found in urine and serum (P<0.05, <0.01 and <0.001), and acute lowering of serum Mg concentration was accompanied with hypocalcemia in both groups. Mobilization from body pools of Mg in deficiency was about 1.1 mg/kg body wt/day and there was observed no difference by age in Mg mobilization in both groups. The lowering of serum Mg concentration more remarkable in old group in Mg deficiency was presumedly due to the hypofunctional Mg absorption in intestines and Mg excretion in kidneys in old group. With Mg intake of 2.9 mg/kg body wt/day toward seventh day, an ewe in old group developed tetany, which was almost coincident with the increase in serum Ca/Mg ratio due to the relatively high rise of serum Ca concentration. At the tenth day serum Ca/Mg ratio increased up to 16.7.