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: 0.7 3) in vivo dry matter (DM) digestibility were treated with ammonia or urea to study the effects on in situ and pepsin-cellulase DM digestibi lities, water solubility and nitrogen content (Experiments 1, 2, 4) an d on cell wall composition and degradability (Experiment 3). (1)N luce rne was treated with 30 g NH3 kg(-1) DM for 1 to 12 weeks at 30 degree s C and 2 to 6 days at 80 degrees C; (2) L, N and H lucerne were treat ed with increasing ammonia levels: 15 to 100 g kg(-1) DM for 3 weeks a t 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 day s 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 t he 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 s olubility also increased with duration of treatment and level of ammon ia (P < 0.01) and was greater at 80 degrees C than at 30 degrees C. Ur ea treatment significantly improved (P < 0.01) digestibilities and wat er solubility but the doubling of treatment duration had no influence. The degree of ureolysis was only 50 to 60%. Ammonia and urea treatmen ts considerably increased (P < 0.01) nitrogen content. Treatment with 60 g NH3 kg(-1) DM induced a decrease in ethanol insoluble residue con tent, which was significant(P < 0.01 for L and N, P < 0.05 for H) at 8 0 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 essenti ally 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 microbi al degradation. This result indicates that other phenomena are involve d, 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.