The goal of the research is to provide a basis of decision making methods in the choice of the best corn hybrid and optimal harvest time and for the methods of nutritive quality testing of silages in agricultural practices and laboratories. In corn hybrids, the starch and fibre contents and fibre digestibility were evaluated. The significant effect of harvesting time on changes of monitored parameters was detected explaining 24 % of their variability. With increasing dry matter content, the fibre content and digestibility decreased representing about 38 % of the variability.