1983 Volume 45 Issue 4 Pages 435-442
In order to elucidate the relationship between hypomagnesemic tetany and Ca metabolism in ruminants, experiments were carried out on four 2-year-old lactating ewes divided into two groups (A and B) according to the order of feeding of two low-Mg diets (8.4mg/kg of body weight/day) with varying Ca contents (normal-Ca: 154.5 and low-Ca: 26.1mg/kg of body weight/day). Serum Mg and Ca concentrations as well as heart rate (HR) as an indicator for signs of hypomagnesemic tetany were determined every day throughout the experimental periods. On feeding either the low-Mg and normal-Ca diet or the low-Mg and low-Ca diet the decreased dietary levels of Mg resulted in a significant fall of serum Mg concentration (0.5-0.7mg/100ml). Serum Ca concentration gradually fell on feeding the low-Mg and low-Ca diet. On feeding the low-Mg and normal-Ca diet it temporarily fell and then returned nearly to the control level. Consequently, serum Ca/Mg ratio rised more remarkably on feeding the low-Mg and normal-Ca diet than the low-Mg and low-Ca diet. The significant increase in HR, or the onset of hypomagnesemic tetany was always preceded by remarkable rise in serum Ca/Mg ratio on feeding the low-Mg and normal-Ca diet. It is suggested that the imbalance in dietary Ca/Mg ratio might enlarge the imbalance of Ca/Mg ratio in extracellular and intracellular fluid resulting in the hypomagnesemic tetany in lactating ewes.
