Magnesium metabolism in the dairy cow. III. The intake and excretion of calcium, phosphorus, sodium, potassium, water and dry matter in relation to the development of hypomagnesaemia

1. Information, obtained in the metabolism experiments described previously (Rook et al. 1958; Rook & Balch, 1958), is given on the intake and oxcretion, of calcium, phosphorus, sodium, potassium, water and dry matter by milking cows receiving winter-stall diets or cut-grass in the stall.2. Grass diets cut from swards at an early stage of growth gave a lower intake of calcium, a lower Ca:P ratio and a lower intake of alkaline earth alkali (Ca + Mg – P in g. equiv./day) than did typical winter diets or a grass diet cut from a sward at a mature stage of growth.3. The intake of potassium was considerably higher with the grass diets (mean value, 327 g./day) than with the typical winter diets (mean value, 181 g./day). The intake of sodium, however, showed a similar range for cut-grass and winter stall diets, but the lowest average intake, of about 10 g./day, was with an early cut of a cocksfoot/rye-grass sward.4. The water ingested with the food was highest with the cut-grass diets but this was largely compensated for by a decrease in the water drunk. In a few individual animals, however, diuresis developed a few days after the feeding of grass was commenced and this was associated with a marked increase in the water drunk.5. No major difference in the metabolism of sodium, potassium or water was observed between the cut grass diets and the winter diets and the results obtained do not support the view that the fluidity of faeces of cattle at pasture in the spring is indicative of diarrhoea and is associated with an excessive loss of nutrients via athe faecal route.6. There was no evidence to suggest that the development of hypomagnesaemia was related to the amounts of calcium, phosphorus, sodium and potassium consumed and excreted with the cut grass diets.