The definitive version is available at: http://jas.fass.org/cgi/content/full/81/10/2617
Previously published as proceeding at the XXXV Jornadas de Estudio (X Jornadas sobre Producción Animal AIDA (Zaragoza, Spain, May 14-16, 2003). https://digital.csic.es/handle/10261/5103
A dual-flow continuous culture system
was used to investigate the effects of pH and addition
of an enzyme mixture to a total mixed ration (TMR) on
fermentation, nutrient digestion, and microbial protein
synthesis. A 4 × 4 Latin square design with a factorial
arrangement of treatments was used, with four 9-d periods
consisting of 6 d for adaptation and 3 d for measurements.
Treatments were as follows: 1) high pH with
control TMR, 2) high pH with TMR treated with enzyme,
3) low pH with control TMR, and 4) low pH with
TMR treated with enzyme. Ranges of pH were 6.0 to 6.6
and 5.4 to 6.0 for high and low, respectively. Fermenters
were fed twice daily a TMR consisting of 30% alfalfa
hay, 30% corn silage, and 40% rolled corn (DM basis).
The silage was milled fresh and the TMR was fed to
the fermenters in fresh form (64% DM). The enzyme
mixture was a commercial product of almost exclusive
protease activity; it was applied daily to the fresh TMR
and stored at 4°C for at least 12 h before feeding.
Degradability of OM, NDF, ADF, and cellulose was decreased
(P < 0.05) by low pH. Hemicellulose and protein
degradation were not affected by pH. Enzyme addition
increased (P < 0.01) NDF degradability (by 43% and 25% at high and low pH, respectively), largely as a
result of an increase in hemicellulose degradation (by
79% and 51% at high and low pH, respectively). This
improvement was supported by an increase (P < 0.05)
in the xylanase and cellulase activities in the liquid
phase of the fermenter contents. Total VFA were decreased
(P < 0.05) by low pH, but were not affected by
enzyme addition. Total bacterial numbers were increased
(P < 0.03) at low pH and tended (P < 0.13) to
increase with enzyme addition. Cellulolytic bacteria in
effluent fluid were decreased (P < 0.02) at low pH but
were unaffected by enzyme addition. Despite a large
increase (P < 0.001) in protease activity, protein degradation
was only numerically increased by enzyme addition.
Microbial protein synthesis was higher (P < 0.10)
at high pH but was not affected by enzyme addition.
Methane production, expressed as a proportion of total
gases, was decreased (P < 0.001) at low pH but was not
affected by enzyme addition. It is concluded that it is
possible to adapt the continuous culture system to use
fresh feeds instead of dried feeds. Overall, the results
indicate that the enzyme product used in this study
has a potential to increase fiber degradability without
increasing methane production.
Lethbridge Research Centre contribution No. 387 03003. We
thank A. F. Furtado, D. D. Vedres, and G. R. Bowman for skilled
technical assistance; K. Koenig for helpful suggestions; and T. Entz
for help with statistical analysis. Herva´s acknowledges receipt of a
fellowship from the Spanish Ministry of Science and Technology
(MCyT).
Peer reviewed