The effect of ammoniation using urea on the intake and nutritive value of chopped barley straw

Chopped barley straw was sprayed with a 10% urea solution at the rate of 400 ml kg^-1 straw and stored in sealed containers. Two experiments were conducted with this straw.
In experiment 1 the effect of ensiling periods of 1, 15, 30, 45, 60, 75 and 90 d on the in vitro digestibility, total N and free NH3-N of straw were examined. In vitro digestibility reached a maximum 45 d post-treatment and remained constant thereafter; the overall increase in digestibility of treated over untreated straw was 0·21 units. Forty-four% of the added N was retained in the straw and free NH3-N accounted for 31% of the total N. In experiment 2 when straw was given alone the voluntary intake and crude fibre (CF) and DM digestibilities of urea-treated straw were increased by 47, 40 and 26% respectively over the untreated straw. The digestibilities of the diets were similar when either treated or untreated straw formed 20% of the diets. The CF digestibility of the two high-concentrate diets was similar to that of the untreated straw. Treatment of straw with urea increased the digestible energy value of straw by up to 20%. Feeding urea-treated straw resulted in a significant increase of ruminal NH₃-N concentration without any change of rumen pH.