Calves were surgically supplied with double fistular anastomoses (duodenal and ileal) to study the dynamic of digestive processes. The experiment was carried out in three periods: sucking, transitive (milk and vegetative feed), and fully vegetative. It was found that both the duodenal and the ileal chyme of sucking calves is by its physical and chemical properties substantially different from the chyme of adult cattle. With the transition from the milk type on to the vegetative type of feeding the composition of chyme of calves changes in colour, consistency, dry matter, organic matter, and crude fibers. With the vegetative type of feeding the digestion organs of calves were found to work more actively than with the feeding with milk with added plant feed. In the transition period 10 to 20 per cent of the dry and organic matter was digested and utilized before coming to the duodenal anastomosis. In this period beside the abomasum the forestomach with its three compartments was also shown to be involved in the digestion processes. With the increase in the amount of course feed in the diet of calves the amount of dry matter, organic matter, and crude fibers digested in the forestomach reached 45-52 per cent.