An exogenous protease increases enzymic activities, microbial numbers and fiber degraation by mixed ruminal microorganisms in continuous culture

Contributed to: Conference on Gastrointestinal Function (Chicago, Illinois, Mar 10-12, 2003).The effects of pH and addition of a protease mixture on the fermentation characteristics of a total mixed ration (TMR) were investigated in a dual-flow continuous culture apparatus, using a 4 x 4 Latin Square design with a 2 x 2 factorial arrangement of treatments. The diet (DM basis) consisted of 30% alfalfa hay, 30% corn silage and 40% rolled corn. The silage and the grain were milled fresh, mixed with the alfalfa and treated with the enzyme (1.5 μL/g feed) daily. Ruminal fluid was collected 2 h post-feeding from 3 lactating dairy cows fed a TMR. Fermenters were fed 80 g DM/d in equal portions every 12 h. Treatments were control (C) and enzymetreated (T) TMR at either high pH (HC and HT) or low pH (LC and LT). The pH was altered by diluting the artificial saliva to 60% of its original composition. Enzymic activities and total and cellulolytic bacterial numbers were determined on the liquid phase of the fermenter contents, 6 h post-feeding. Fiber degradation was determined from the outflow residues. Enzyme addition increased (P < 0.05) xylanase, xylosidase, endoglucanase, and protease activities (608 vs. 750; 0.48 vs. 0.80; 82 vs. 112; and 1.2 vs. 7.5 units for C and T, respectively), whereas it tended (P < 0.12) to increase exoglucanase and glucosidase activities (0.8 vs. 1.4; and 4.7 vs. 5.9 units). However, enzyme did not affect (P = 0.18) arabinofuranosidase activity (5.2 vs. 6.8). Total microbial numbers (expressed as Log10) were increased (P < 0.05) at low pH (9.13 vs. 9.36) but enzyme had no effect (P = 0.13). Cellulolytic bacteria were reduced (P < 0.02) at low pH (3.91 vs. 2.79), with no effect (P = 0.88) of enzyme. Low pH reduced (P < 0.001) NDF, ADF, and cellulose degradation. NDF degradation was increased (P < 0.01) by enzyme addition (20% vs. 27%) but ADF was unaffected (P < 0.20), resulting in an increase (P < 0.001) in hemicellulose degradation. It is speculated that the enzyme removed structural barriers present in the feed, allowing a more rapid colonization of the fiber by ruminal microorganisms.Peer reviewe

Agent-Based Modeling of Host-Pathogen Systems: The Successes and Challenges

Agent-based models have been employed to describe numerous processes in immunology. Simulations based on these types of models have been used to enhance our understanding of immunology and disease pathology. We review various agent-based models relevant to host-pathogen systems and discuss their contributions to our understanding of biological processes. We then point out some limitations and challenges of agent-based models and encourage efforts towards reproducibility and model validation.Comment: LaTeX, 12 pages, 1 EPS figure, uses document class REVTeX 4, and packages hyperref, xspace, graphics, amsmath, verbatim, and SIunit