Evaluation of straw treatment with ammonia sources on growing bulls

Energetical and ecological aspects of straw ammoniation were calculated based on five feeding trials with growing bulls consuming untreated, ammonia or urea treated wheat straw. Dry straw was gased with ammonia (3.0-3.2%) and wet straw (38.1-56.3% dry matter, DM) was treated with urea (2.5-5% on DM base). In digestibility experiments with sheep and feeding trials with 104 growing bulls fed treated and untreated straw was compared. Bulls consumed 2 kg concentrate per day and untreated or treated straw ad libitum. In two experiments ammonia or urea treated straw was given in adequate amounts to untreated straw (pair feeding). Based on the results of feeding trials energetic input (60 or 80 MJ per kg N from ammonia or urea) and ecological output (NH3, CO2) were calculated, Ammoniation increased apparent digestibility of organic matter of wheat straw from 43.9 to 52.7%, urea treatment enhanced it from 46.5 to 53.0% on average. Pair feeding of ammonia or urea treated wheat straw resulted in an increase of daily liveweight gain amounting 69 and 55 g day(-1). Ad libitum intake of treated straw increased daily weight gain with range of 75 to 290 g. Animal growth rate was used to evaluate the different straw treatments with regard to the ammonia sources. Between 0.8 and 7.0 kg body weight were produced per kg N added to the straw due to higher digestibility and increased straw intake. Assuming a conversion rate of 5 kg grains for 1 kg beef, one kg N used as fertilizer has at least to increase the yield of cereals in the range of 3.8 and 35 kg, otherwise the N-utilization on the field would be less efficient. Low animal response to ammoniation of straw resulted in high fossil energy needs per animal and high environmental pollution. More dose-response trials are necessary to allow a better evaluation of N-efficiency in straw treatment.