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.

Association of aqueous hydrogen concentration with methane production in continuous cultures modulated to vary pH and solids passage rate

“…Continuous culture studies have demonstrated the decline of acetate-to-propionate ratio with decreasing pH (Cerrato-Sánchez et al, 2007a,b;Cantalapiedra-Hijar et al, 2011). A constant low pH (5.8) also decreased acetate-to-propionate ratio in our laboratory previously (Qiu et al, 2004); however, their low pH treatment was much lower than the diurnal average of the present study.…”

“…For the LpH treatment, we added H 3 PO 4 to a concentration of 12.5 mM to decrease buffer pH to 6.4. Both buffers allowed a parallel diurnal shift in pH (see Supplemental Figure S1; https://doi.org/10.3168/ jds.2016-12332) to better reflect normal rumen function in vivo postfeeding (Cantalapiedra-Hijar et al, 2011). The CpH treatment allowed fluctuation of fermentor pH from 6.9 prefeeding to 6.3 approximately 8 h postfeeding, with a gradual return over the remaining 16 h of each experimental day.…”

Microbial and chemical composition of liquid‐associated bacteria in goats' rumen and fermenters

“…Similar VFA values were found in animals and fermenters for each diet although pH values were different depending on diet in both. The lack of correlation between pH values and VFA concentration was also observed by other authors both in vitro and in vivo (Busquet et al., ; Molina‐Alcaide et al., ; Cantalapiedra‐Hijar et al., ; Romero‐Huelva et al., ). Differences in pH probably reflect non‐structural carbohydrate content (OM‐(EE+CP+NDF)) that was higher in concentrate than in feed blocks (524, 393 and 438 g/kg dry matter for concentrate, feed block I and feed block II respectively).…”

Changes in ruminal microbiota due to rumen content processing and incubation in single-flow continuous-culture fermenters

“…Some authors have reported that cellulolytic populations do not vary when pH changes are not sharp or pH values are physiological (Mackie et al 1978;Gordon and Phillips 1989;Khafipour et al 2009). Although total volatile fatty acids and pH were not measured over the adaptation period in fermenters, the results obtained in our laboratory using the same diets and in vitro system exhibited values within physiological range (pH 6.31-6.53 and total volatile fatty acids 120-125 mmol/L for diets HC and LC, respectively;Cantalapiedra-Hijar et al 2011). These results may indicate that although the pH values in the fermenter may play an important role in the in vitro fermentation profile, other in vitro-related factors such as the dilution rate (Crawford et al 1980), content stratification (Muetzel et al 2009), or the harvest and processing of fermenter inoculum (Ziemer et al 2000) are also involved in the in vivo-in vitro discrepancies.…”