Effects of high concentrations of sodium and potassium in milk replacers on intestinal processes and faeces composition in young calves

In two feeding experiments with 15 calves (age: 5-12 days at trials' start) the effects of high ash and mineral contents in che diet on faeces composi tion (dry matter, mineral contents) and digestibility rates of organic matt er, nutrients and minerals were tested in both feeding experiments a change -over-design was used, during 10 days each calf was fed the control and exp erimental diet, respectively. In the first trial high ash and mineral conte nts in the milk replacer were caused by use of a special whey powder produc t (25% in the diet). In the second experiment comparable ash and macrominer al concentrations were achieved by adding minerals to the basic diet. Ash c oncentrations in diet (g/kg dry matter): 68 versus 138 (trial), 75 versus 1 35 (trial 2). The differences in the ash contents mere based mainly on diff erences in the sodium and potassium concentrations. The most significant effect in calves fed the experimental diet in trial 1 was the reduction of dry matter content in faeces (similar to 111 g dm/kg f aeces compared to similar to 186 g dm/kg during the control period). In exp eriment 2 there was the same trend (lower dry matter in faeces of calves fe d the experimental diet), but here the reduction was nor significant (152 v ersus 158 dry matter/kg faeces). The digestibility of organic matter (prote in, fat, NfE) mas nor influenced negatively by the higher ash contents in t he diet, whereas the apparent absorption of macrominerals (Ca, Mg, P, Na, K ) decreased when diets with higher contents of those elements were fed. It seems that the slightly reduced absorption rate of sodium and potassium dur ing the period of high intake of these electrolytes is followed secondarily by a forced excretion of water resulting in changes of faeces composition.