The effect of the feed-to-buffer ratio on bacterial diversity and ruminal fermentation in single-flow continuous-culture fermenters

G Cantalapiedra-Hijar, D R Yáñez-Ruiz, C J Newbold, E Molina-Alcaide

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9 Citations (Scopus)


Eight single-flow continuous-culture fermenters were used in a completely randomized block design with a 2 × 4 factorial arrangement of treatments to investigate the effects of the feed-to-buffer ratio (F/B) on ruminal fermentation, the diversity and community structure of bacteria, nutrient digestibility, and N metabolism. Four diets with forage-to-concentrate ratios of 70:30 or 30:70 with alfalfa or grass hay as forage were supplied to fermenters twice per day at 2 different F/B (23.5 and 35 g of DM/L). The dilution rate was kept constant (5.3%) among all fermenters by infusing the same volume of buffer. An increase in the total volatile fatty acid (VFA) concentration and a decrease in the average pH were observed with an increased F/B. In addition, the molar proportions of all individual VFA found in fermenters differed, depending on the F/B. A terminal restriction fragment length polymorphism analysis showed that the community structure and diversity of bacteria were highly influenced by the F/B. Both diversity and the number of peaks in the electropherograms were lower in most fermenters receiving diets at a high F/B, whereas the similarity percentage of the bacterial communities across diets was higher as the F/B increased. Moreover, the high reduction of neutral detergent fiber digestibility (15.3% ± 3.65) in fermenters with high F/B suggested a pH-related decrease in the cellulolytic bacterial community as the F/B increased. The crude protein degradation found in fermenters receiving diets with a high F/B was lower compared with that from fermenters with a low F/B. The VFA concentration and purine bases flow response patterns to diets were similar to in vivo conditions only in the case of fermenters with a low F/B. The results suggested that the community structure and diversity of bacteria, as well as the in vitro fermentation parameters, may be affected by the F/B that is used, most likely through a pH effect. In addition, several fermentation parameters showed different response patterns to diets according to the F/B used. Therefore, the amount of feed supplied to single-flow continuous-culture fermenters in which pH is not under control should be carefully chosen according to the volume of buffer infused for the purpose of simulating ruminal fermentation.

Original languageEnglish
Pages (from-to)1374-84
Number of pages11
JournalJournal of Dairy Science
Issue number3
Publication statusPrint publication - Mar 2011
Externally publishedYes

Bibliographical note

Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.


  • Animal Feed
  • Animal Nutritional Physiological Phenomena
  • Animals
  • Bioreactors
  • Buffers
  • Diet/veterinary
  • Fermentation/physiology
  • Goats
  • Hydrogen-Ion Concentration
  • Rumen/chemistry


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