Abstract
An experiment was carried out to determine the effects of age, milking and season on Mg, Ca and Pi metabolisms of cows in the northern part of Iwate Prefecture where cows often suffered from hypomagnesemia or hypocalcemia. Most of the old milking cows suffered from hypomagnesemia in June and October when the average diurnal variation in temperature was the largest. This group always showed a lower serum Mg concentration than the young milking cows. On the relationship between serum and urine concentration of Mg, significant exponential regressions were obtained by age, milking and season. Serum Pi concentration was significantly higher in the warm period than in the cold period in 4 of the 5 groups. Urine concentration ratios of Ca and Pi to creatinine were within a certain range in most of milking cows. In a part of the old milking cows, however, the urine Ca concentration ratio changed over the certain range. Exceptionally high urine Ca or Pi concentration was observed in the cows just after parturition. There was a significant positive correlation between average serum Mg and Ca concentrations in the young non-milking cows and the old milking cows and there was a significant negative correlation between average serum Ca and Pi concentrations in the young milking cows. These results suggest that the old milking cattles with their declined renal function might suffered from hypomagnesemia due to the deficiency of Mg intake, and that a sudden increase in the diurnal variation of the environmental temperature might enhance the urine Mg excretion rate.
