Intake and apparent absorption of calcium, phosphorus, sodium, potassium and magnesium of calves fed diets with different levels of roughage

The effects of different levels of roughage on intake and apparent absorption of calcium (Ca), phosphorus (P), sodium (Na), potassium (K) and magnesium (Mg) were studied. Forty Holstein x Zebu calves, with initial average live weight of 60 kg, allotted to a completely randomized design, were fed concentrate and chopped coastcross (Cynodon dactylon) grass hay ad libitum in the following levels: 10; 25; 40;. 55 e 90%, on a DM basis. The coefficients of apparent absorption were obtained by one experiment with two experimental periods of digestibility, accomplished at 120 and 180 clays of age of the animals. The fecal dry matter excretion was estimated with chromium oxide. The intakes of Ca, P, Ma, Na and K in (g/day) showed a quadratic effect and the respective maximum intakes were estimated for 47.0, 30.0, 45.3, 41.0 and 51.8 % of roughage in the diet. The apparent absorption coefficients of Ca, P and K were affected by the level of roughage, showing a quadratic effect, with the respective maximum absorptions of 58.7, 56.1 and 78.3% for the levels of 20.3, 23.1 and 45.2 % of hay in the diet.