RUMINANT NUTRITION SYMPOSIUM: Improving cell wall digestion and animal performance with fibrolytic enzymes1

Abstract

This paper aimed to summarize published responses to treatment of cattle diets with exogenous fibrolytic enzymes (EFE), to discuss reasons for variable EFE efficacy in animal trials, to recommend strategies for improving enzyme testing and EFE efficacy in ruminant diets, and to identify proteomic differences between effective and ineffective EFE. A meta-analysis of 20 dairy cow studies with 30 experiments revealed that only a few increased lactational performance and the response was inconsistent. This variability is attributable to several enzyme, feed, animal, and management factors that were discussed in this paper. The variability reflects our limited understanding of the synergistic and sequential interactions between exogenous glycosyl hydrolases, autochthonous ruminal microbes, and endogenous fibrolytic enzymes that are necessary to optimize ruminal fiber digestion. An added complication is that many of the standard methods of assaying EFE activities may over- or underestimate their potential effects because they are based on pure substrate saccharification and do not simulate ruminal conditions. Our recent evaluation of 18 commercial EFE showed that 78 and 83% of them exhibited optimal endoglucanase and xylanase activities, respectively, at 50 °C, and 77 and 61% had optimal activities at pH 4 to 5, respectively, indicating that most would likely act suboptimally in the rumen. Of the many fibrolytic activities that act synergistically to degrade forage fiber, the few usually assayed, typically endoglucanase and xylanase, cannot hydrolyze the recalcitrant phenolic acid-lignin linkages that are the main constraints to ruminal fiber degradation. These factors highlight the futility of random addition of EFE to diets. This paper discusses reasons for the variable animal responses to dietary addition of fibrolytic enzymes, advances explanations for the inconsistency, suggests a strategy to improve enzyme efficacy in ruminant diets, and describes differences among the proteomes of effective and ineffective EFE.

In vitro gas production kinetics and degradability of a diet for growing lambs: effect of fibrolytic enzyme products at different dose levels

“…This may create conditions in which supplementary fibrolytic exogenous enzymes can have beneficial effects on the degradation of the fibre Mendoza et al 2014). There is a renewed interest in the use of fibrolytic exogenous enzymes for ruminants due to the increase in feeding costs and access to high quality enzymes (Adesogan et al 2014;He et al 2014). However, the effectiveness of enzyme products is highly variable (Colombatto et al 2003a(Colombatto et al , 2003bMeale et al 2014;Mendoza et al 2014).…”

In vitro and in vivo ruminal fermentation of micronised wood powder for volatile fatty acid production in beef cattle

“…Ruminal anaerobic digestion (fermentation) of holocelluloses is dependent on the cellulase activity caused by bacteria and fungi [6]. Hence, cross-linkages of lignin with holocelluloses or phenolic acids possibly reduce the cellulolytic activity of rumen microorganisms [9]. Wood by-product will also make it difficult to contribute to volatile fatty acid production in ruminants as mentioned above.…”

Effects of micronised wood powder irradiated with ultraviolet light and exposed to ozone gas on in vitro ruminal fermentation in beef cattle

“…In plant cell walls, lignin is covalently bound to hemicelluloses and gradually develops the strength and rigidity of cell walls [6,7]. In ruminal fermentation, cellulase activity caused by bacteria and fungi [8] is affected by cross-linkages of lignin [9]. Thus, especially in woody feedstuffs, the cross-linkage of lignin will interfere with the ruminal anaerobic digestion (fermentation) of lignocelluloses for volatile fatty acid production.…”