Statistical research on the fate of dietary mineral elements in dry and lactating cows: II. Magnesium

Abstract

SUMMARY Statistical analyses were carried out on the data obtained under very strict conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows, and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2 to 6 months earlier and whose daily milk production ranged from 11 to 20 kg. The correlation between faecal and urinary losses of magnesium, magnesium in milk, digestible magnesium, and magnesium balance and the other nutritive factors of the 55 above-mentioned experimental diets have been calculated. The magnesium absorption is enhanced by increasing magnesium and calcium intake, while nitrogen and, to a lesser extent, fat, giving higher faecal losses, have an opposite effect. There is no influence at this level of lactating requirements. The urinary losses of magnesium are not related to the magnesium intake and digestibility, and the balance is thus directly proportional to the digestible amounts. But this balance is decreased when the diet contains more dry matter or energy, to the benefit of urine in dry cows. We were not able to determine whether this balance reduction also benefits the milk production in the lactating cows. Our results demonstrate that the faecal endogenous losses of magnesium can be highly variable. The balance of magnesium is frequently but not inevitably negative in cows with a daily milk production of 11–20 kg.