SUMMARY

This experiment has been conducted in PK "Beograd" on bullock fattening (total of 99 bullocks of the domestic pied breed of the Simental type) classified in three groups which had been using rations with 30, 50 and 70% of energy from corn silage and added concentrate mixtures.

Analyses of blood serum and liquid rumen fraction that has been done during the fattening period showed that in blood serum total nitrogen decreased when silage increased in the ration as well as urea. In liquid rumen fraction we found decreasing of propionic acid and increasing of butiric acid at the same time. Other parameters didn't show constant (permanent) trend.

          Key words: fattening, bullock fattening, silage, concentrate, blood serum, biochemistry, voiatile fatty acids.