title: The effect of the feed-to-buffer ratio on bacterial diversity and ruminal fermentation in single-flow continuous-culture fermenters.
abstract: 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.
authors.affiliation: Estación Experimental del Zaidín (Consejo Superior de Investigaciones Científicas), Profesor Albareda, 1, 18008 Granada, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Cantalapiedra-Hijar
authors.forename: D R
authors.initials: DR
authors.lastname: Yáñez-Ruiz
authors.forename: C J
authors.initials: CJ
authors.lastname: Newbold
authors.forename: E
authors.initials: E
authors.lastname: Molina-Alcaide
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D019149:Bioreactors; D002021:Buffers; D004032:Diet / Q000662:veterinary; D005285:Fermentation / Q000502:physiology*; D006041:Goats; D006863:Hydrogen-Ion Concentration; D012417:Rumen / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology*
chemical_list: D002021:Buffers