Effect of ammonia and urea treatments on digestibility and nitrogen content of dehydrated lucerne

Dehydrated lucerne of low (L: 0.53), normal (N: 0.55) and high (H: 0.73) in vivo dry matter (DM) digestibility were treated with ammonia or urea to study the effects on in situ and pepsin-cellulase DM digestibilities, water solubility and nitrogen content (Experiments 1, 2, 4) and on cell wall composition and degradability (Experiment 3). (1)N lucerne was treated with 30 g NH3 kg(-1) DM for 1 to 12 weeks at 30 degrees C and 2 to 6 days at 80 degrees C; (2) L, N and H lucerne were treated with increasing ammonia levels: 15 to 100 g kg(-1) DM for 3 weeks at 30 degrees C and 4 days at 80 degrees C; (3) L, N and H lucerne were treated with 60 g NH3 kg(-1) DM for 3 weeks at 30 degrees C and 4 days at 80 degrees C; (4) L, N and H lucerne were treated with 60 g urea kg(-1) DM without addition of urease for 3 and 6 weeks at 30 degrees C. All treatments were carried out at 40% humidity. In situ and pepsin-cellulase DM digestibilities increased significantly (P < 0.05) with the duration of treatment (up to 3 weeks at 30 degrees C and 4 days at 80 degrees C) and with the level of ammonia (P < 0.01) (up to 30 g kg(-1) DM). The greatest improvements (similar at both temperatures) were for L, N and H of 7.3, 7.2 and 3.9 points for in situ and of 10.6, 11.3 and 6.3 points for cellulase digestibilities, respectively. Water solubility also increased with duration of treatment and level of ammonia (P < 0.01) and was greater at 80 degrees C than at 30 degrees C. Urea treatment significantly improved (P < 0.01) digestibilities and water solubility but the doubling of treatment duration had no influence. The degree of ureolysis was only 50 to 60%. Ammonia and urea treatments considerably increased (P < 0.01) nitrogen content. Treatment with 60 g NH3 kg(-1) DM induced a decrease in ethanol insoluble residue content, which was significant(P < 0.01 for L and N, P < 0.05 for H) at 80 degrees C but not at 30 degrees C, and was greater far L and N than for H (about 12 and 5 points, respectively). This decrease was essentially due to solubilisation of hemicelluloses (-15%) and uronic acids (-26%). Thus, at 30 degrees C, the chemical solubility of the cell wall was lower than at 80 degrees C for the same total increase in microbial degradation. This result indicates that other phenomena are involved, such as an increase in cell wall porosity and consequently improved accessibility of cell wall polysaccharides to glycolytic enzymes. (C) 1997 Elsevier Science B.V.