Recombinant fibrolytic feed enzymes and ammonia fibre expansion (AFEX) pretreatment of crop residues to improve fibre degradability in cattle

摘要

Low digestibility of crop residues limits their use as animal feeds. The study examined the potential of Ammonia Fibre Expansion (AFEX) technology and dietary supplementation of a pre-selected recombinant xylanase to improve the in situ degradability of four crop residues for ruminants. AFEX pretreatment uses anhydrous ammonia, moisture, moderate temperature, and a short period of high pressure and results in partial lignin solubilization and hemicellulose hydrolysis, and increased surface area of substrate for microbial attachment. In situ neutral detergent fibre degradabilities of untreated (control) and AFEX pretreated crop residues (barley straw, corn stover, rice straw, and wheat straw) were determined in 8 heifers using a 2-period cross-over design with two dietary treatments (without and with XYL10C; 1,4-beta-xylanase; recombinant enzyme from glycoside hydrolase family 10 produced by Aspergillus niger). The enzyme was diluted in water and applied to the barley straw (6.6 x 10(4) IU enzyme/kg straw dry matter) component of the basal diet (30 g/100 g diet dry matter) and to the control and AFEX crop residues incubated in situ. There were no interactions between enzyme and crop residues for A, B, or A + B fractions, indicating no enzyme x substrate specificity. Averaged across crop residues, enzyme slightly decreased the A fraction (P 0.001) and slightly increased the B fraction (P = 0.02), such that there was no overall effect on A + B (P = 0.21). However, there were significant interactions between enzyme and AFEX for kd (P = 0.026); enzyme had no effect on control crop residues but it increased kd of AFEX residues by 12% (0.0323 vs. 0.0361 /h). As a result, xylanase supplementation increased the effective rumen degradability of crop residues by about 3%, but only when they were pretreated with AFEX (interaction, P = 0.098). AFEX greatly increased effective ruminal degradability (+ 28 to + 126% depending upon the crop residue; P 0.001), mainly by increasing the B fraction and decreasing the undigested fibre fraction, indicating increased accessibility of substrate to rumen microbial enzymes. The study demonstrates the tremendous potential of AFEX treatment to improve the feeding value of crop residues. Enzyme XYL10C was more effective for AFEX crop residues, possibly due to increased accessibility to substrate, suggesting that this enzyme may be more effective for less lignified and pretreated feeds.