Effects of exogenous cellulase supplementation on microbial growth and ruminal fermentation of a high-forage diet in Rusitec fermenters1

Abstract

Two incubation runs were carried out with a Rusitec system to investigate the effects of 2 exogenous pure cellulases on ruminal microbial growth and fermentation of a 70:30 grass hay:concentrate (DM basis) substrate. The substrate was sprayed with buffer (control; pH = 6.5), a cellulase from Trichoderma longibrachiatum (TRI), a cellulase from Aspergillus niger (ASP), or a 1:1 mixture of both cellulases (MIX) 24 h before being placed in the fermenters. Enzymes were applied at a rate of 30 endoglucanase units/g of substrate DM. Treating the substrate with enzymes reduced substrate NDF and ADF content (P < 0.001 to P = 0.002) and increased DM, NDF, and ADF disappearance after 6 and 24 h of incubation (P < 0.001 to P = 0.004) but not after 48 h of incubation. Daily VFA production was increased (P = 0.004) by 15, 9, and 15% for TRI, ASP, and MIX, respectively, with half of the increase being due to production of acetate. All enzyme treatments augmented (P = 0.009) methane production, but none of them altered the methane:VFA ratio (P = 0.70). There were no differences (P = 0.80) among treatments in the daily flow of solid-associated microorganisms, as measured using 15N as a microbial marker. Although the TRI and MIX treatments increased (P < 0.05) the daily flow of liquid-associated microorganisms and the proportion of microbial N in the solid residue after 48 h of incubation, no effects were observed (P = 0.92 and P = 0.95, respectively) for the ASP treatment. The results show that the TRI and MIX treatments enhanced in vitro fermentation by increasing substrate fiber degradation, VFA production, and ruminal microbial growth. The lack of differences between TRI and MIX in most of the measured variables indicates that treating the substrate with a mixture of both cellulases did not further improve the effects of the TRI treatment.

Effect of fibrolytic enzymes added to a Andropogon gayanus grass silage-concentrate diet on rumen fermentation in batch cultures and the artificial rumen (Rusitec)

“…Wang et al (2001) reported that applying an enzyme preparation to the feed 24 h before feeding increased barley grain DM disappearance after 48 h of incubation, but had no effect when enzymes were directly infused into the fermenters. Although Giraldo et al (2007a) have shown an increase in 48 h DM, NDF and ADF disappearance in the Rusitec with enzyme application to a forage-based diet 24 h before feeding, additional work by this same group observed these responses after 6 and 24 h of incubation, but not after 48 h (Giraldo et al, 2007b). In addition, Wang et al (2001) did not observe higher DM or NDF disappearance of alfalfa hay after 48 h of incubation when enzymes were applied 24 h before feeding.…”

“…To determine daily volatile fatty acids (VFA) and NH 3 -N production, effluent was collected daily from day 9 to 11 in flasks containing 20 ml of 3.66 M H 2 SO 4 (20%, vol/vol; Giraldo et al, 2007b). Subsamples of the fermenter effluent (2.5 ml) were taken directly from the effluent flask at the time of feed-bag exchange and were placed in screw-capped vials containing 0.5 ml of 25% (wt/wt) metaphosphoric acid and stored at −20°C until VFA analysis.…”

Influence of the addition of exogenous xylanase with or without pre-incubation on the in vitro ruminal fermentation of three fibrous feeds

“…Mao et al (2013) found that the addition of cellulase and xylanase increased the numbers of total bacteria and Fibrobacter succinogenes in the incubation medium in vitro and thereby improved the substrate fermentation. Giraldo et al (2007) showed that treatment of poor quality forage or forage-based diets with exogenous enzymes stimulated the initial phases of microbial colonization in the rumen, and this is recognized as one mode of action of enzymatic products . The addition of fibrolytic enzymes facilitates the access of microorganisms to feed components enabling a faster microbial growth.…”

Rumen microorganisms and fermentation

“…Physical treatments include heating (Brandt and Klopfenstein 1986) and varying the particle sizes (Schadt et al 2012). On the other hand, chemical treatments are the best used methods, including the use of enzymes such as cellulases and xylanases (Giraldo et al 2007). The ruminant diet is based on forage consumption, in ruminant production systems, anything that improves the nutritional value of forage with a high fiber concentration and low digestibility can increase the productivity of ruminants (Giraldo et al 2007).…”

“…On the other hand, chemical treatments are the best used methods, including the use of enzymes such as cellulases and xylanases (Giraldo et al 2007). The ruminant diet is based on forage consumption, in ruminant production systems, anything that improves the nutritional value of forage with a high fiber concentration and low digestibility can increase the productivity of ruminants (Giraldo et al 2007). Researchers have shown that supplementing the cattle diet with fibrolytic enzymes significantly improves the use of nutrients and increases ruminant efficiency.…”