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

¹ Departamento de Producción Animal. Universidad de León, 24071 León, Spain; Universidad Nacional de Colombia, Sede Medellín, Facultad de Ciencias Agropecuarias, Colombia
² Departamento de Producción Animal. Universidad de León, 24071 León, Spain

^* To whom correspondence should be addressed. E-mail: mdcart{at}unileon.es.

	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. Substrate was sprayed with buffer (CON; 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 fed to 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 methane:VFA ratio (P = 0.70). There were no differences (P = 0.80) among treatments in the daily flow of solid-associated microorganisms measured using ¹⁵N as microbial marker. Whereas 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 ASP treatment. The results show that 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 substrate with a mixture of both cellulases did not further improve the effects of TRI treatment.

Key Words: cellulases, ruminal fermentation, microbial protein synthesis, Rusitec

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