Fresh and dried brewers' grains as protein supplements to barley straw diets given to pregnant beef cows

Abstract

Two experiments were conducted to compare the rumen degradability of the dry matter (DM) and nitrogen (N) in fresh (FBG) and dried brewers' grains (DBG) and their effects with or without urea on the voluntary intake of straw by pregnant beef cows. In Experiment 1, degradability values of DM and N, calculated from both exponential and linear equations, were similar for the two forms of brewers' grains. In Experiment 2, when pregnant beef cows were given 2.2 kg DM of either FBG or DBG, either unsupplemented or supplemented with 0.1 kg urea to increase the rumen degradable protein from ∼ 300 to ∼ 600 g, the two forms of grains promoted similar intakes of straw. Urea addition did not improve the voluntary intake of straw, but it increased blood ammonia concentrations. Significant increases in rumen ammonia nitrogen ( P < 0.05) and plasma urea ( P < 0.01) were associated with increases in RDP intake. Plasma urea concentrations also increased significantly ( P < 0.001) with increasing rumen ammonia nitrogen concentrations.