Two series of balance experiments were carried out by the end of the 2nd and 4th month with a total of 18 weaned lambs divided into three test groups. In the course of 150 days first group animals were offered daily 1200-1500 g of concentrate pellets for the first and second experiment. The lambs of the second group were given 1200-1500 g of concentrate pellets and 300 g chopped wheat straw, and those of the third group were given 800 and 1050 g each of concentrate pellets, and 540 g and 720 g of pellets of whole maize plant containing 40 per cent. Determined is the digestibility of feedstuffs at the end of the 2nd and 4th month. Studied were the values of pH and the content of ammonia gas and volatile fatty acids, the total acidity, and the count of Infusoria in the rumen content. It was found that continuous feeding of high amounts of concentrates produced a negative effect on the fermentative processes in the rumen, reliably lowering the values of pH, ammonia gas, and the total count of Infusoria and reliably raising the amount of volatile fatty acids and the total acidity of the rumen content. Affected was also the digestibility of crude fibers and mineral nutrients. Lowest digestibility of nutrient matter was shown by lambs fed on rations that included concentrate pellets of whole maize plants. It was demonstrated that the continuous intake of high-concentrate rations in which roughage was chopped to 2 mm particles and the amount of crude fibers was lowered to 5.29; 9.6; and 10.8 per cent of the dry matter led to latent metabolic acidosis. The latter could not prevented by the inclusion of 300 g chopped wheat straw and 540 and 720 g of pellets of whole maize plant.