Effect of fibrolytic enzymes and incubation pH onin vitrodegradation of NDF extracts of alfalfa and orchardgrass

Abstract

Two in vitro assays (one with alfalfa and the other with orchardgrass) were conducted to evaluate the effects of a fibrolytic enzyme preparation (enzyme) and initial incubation pH (5.6, 6.2 and 6.8) on the degradation of NDF extracts. The enzyme increased (P≤0.05) degradation of alfalfa NDF: 1) at 6 h with pH 6.2 and 6.8; 2) at 9 and 12h with pH 5.6 and 6.2; 3) at 24h with all pH values; 4) at 48h with pH 5.6 and 6.8; 5) at 72h with pH 6.2 and 6.8. Alfalfa NDF degradation was changed (P≤0.05) by the enzyme with increasing pH, as follows: 1) a linear increase at 3h; 2) a linear decrease at 6 and 12h; 3) a quadratic effect at 24, 48, and 72h, and the highest value was observed with pH 6.2. Further effects (P≤0.05) of the enzyme on the alfalfa cell wall were the following: 1) with pH 5.6, the undegradable NDF fraction was reduced and the degradation rate was increased; 2) with pH 6.2, the lag phase was decreased; 3) as pH increased there was a quadratic effect on the lag phase, and the lowest value was found at pH 6.2. For orchardgrass the effects (P≤0.05) of the enzyme were as follows: 1) an increased NDF degradation at 24 and 48h; 2) a decreased linear degradation of NDF as pH increased, at 3, 6, and 9h. Scanning electron micrographs of the alfalfa cell wall showed that parenchyma cells appeared broken and the vascular bundles exposed after incubation with the enzyme mixture at pH 6.2 It may be concluded that a fibrolytic enzyme preparation at pH 6.2 enhanced in vitro degradation of alfalfa NDF.

Considerations on the Use of Exogenous Fibrolytic Enzymes to Improve Forage Utilization

“…We hypothesized that the addition of exogenous enzymes will have less of an effect than in higher quality forages with lower proportions of indigestible fractions. This would explain why experiments using higher quality forages result in a positive response in digestion to fibrolytic enzymes [ 9 ]. However these NDF fractions have been not well evaluated in studies investigating addition of enzymes to forage.…”

“…Xylanases and cellulases have been most commonly used for ruminants, although there have been assessments with ferulic acid esterase, proteases, phytases, and amylases to break ferulic acid bridges, attack cell wall nitrogen-containing compounds, increase phosphorus absorption, and improve starch digestion, respectively [ 5 , 6 ]. Responses vary with the type of forage; many researchers conclude that there is a forage-enzyme interaction but fail to present a biological explanation or hypotheses for the result [ 7 – 9 ]. As for any enzyme, activity depends on several factors: the type of enzyme, the species of animal to be used, pH, temperature and gastrointestinal conditions (e.g., the aqueous nature of the rumen is different from the chyme in intestine), dosage, substrate, degradation of the exogenous enzyme along the tract (rumen, stomach acid, and inhibitors), practical management conditions (stability and method of application), and other factors [ 10 ].…”