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

Abstract 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.