Effects of pH and pH Fluctuations on Microbial Fermentation and Nutrient Flow from a Dual-Flow Continuous Culture System

Abstract

Eight dual-flow continuous culture fermenters (1400 ml) were used in two consecutive periods to study the effects of pH and pH fluctuations on microbial fermentation and nutrient flow. Fermenters were maintained at 39 degrees C, with solid and liquid dilution rates of 5 and 10%/h, respectively, and fed continuously a 60% alfalfa hay and 40% concentrate diet (18.9% crude protein, 36.6% neutral detergent fiber, 17.6% acid detergent fiber). Treatments were high pH (constant at 6.4); low pH (constant at 5.7); cycles of 4 h at pH 6.4 and 4 h at pH 5.7; and pH constant at 6.4, except for two 30-min drops per day to pH 5.7, followed by a 3-h slow recovery to pH 6.4. The low pH (constant at 5.7) produced lower apparent dry matter, neutral detergent fiber and acid detergent fiber digestion, lower total and branch-chained volatile fatty acid concentrations, and lower acetate and higher propionate proportions than high pH (constant at 6.4). There were no differences in these estimates between constant high pH and the two treatments that alternated high pH and low pH. The constant low pH reduced protein degradation and increased nonammonia N and dietary N flow compared with constant high pH. The pH treatments had no effect on bacterial N flow or efficiency of microbial protein synthesis. Flow of essential amino acids was highest for constant low pH and lowest for constant high pH. Results indicate that constant low pH reduced fiber and protein digestion and increased the flow of total and some individual amino acids. However, the effects of transitory decreases of pH were either small or insignificant with the conditions tested in this study.

Supplementation with non-fibrous carbohydrates reduced fiber digestibility and did not improve microbial protein synthesis in sheep fed fresh forage of two nutritive values

“…It is unlikely that these changes affected the cellulolytic flora, as pH was below the critical value of 6.0 for less than 4 h (Calsamiglia et al, 2002). Another result, consistent with this idea, is that NDF digestibility was similarly reduced in both supplemented groups, meanwhile pH was only reduced in FG group.…”

Effect of subacute ruminal acidosis on in situ digestion of mixed hay in lactating dairy cows

“…Low rumen pH during control periods was likely due to the removal of sodium bicarbonate from the TMR, and low intake of the sodium bicarbonate offered separately. Average rumen pH during SARA was slightly higher than the constant pH of 5.7 in one of the treatments of Calsamiglia et al (1999), whereas the average rumen pH during the control periods was close to the average pH obtained by alternating pH 5.7 and pH 6.4 in Calsamiglia et al (1999). Average rumen pH during SARA periods was close to the lowest pH included in the in vitro experiments of Grant and Mertens (1992) and Grant (1994).…”

“…Calsamiglia et al (1999) found, using dual-flow continuous culture fermenters, that the NDF Abbreviations: ADF, acid detergent fibre; CP, crude protein; DM, dry matter; NDF, neutral etergent fibre; NE l , net energy for lactation; SARA, subacute ruminal acidosis; TMR, total mixed ration; VFA, volatile fatty acids digestion of a 60:40 alfalfa hay to concentrate diet was reduced from 53.8 to 46.1% as a result of alternating 4-h cycles of pH 6.4 and pH 5.7, compared with continuous pH of 6.4. When incubation pH was kept constant at pH 5.7, NDF digestion was reduced to 37.4%.…”

Comparison of microbial fermentation of high- and low-forage diets in Rusitec, single-flow continuous-culture fermenters and sheep rumen

“…Changes in molar proportions of individual VFA may reflect a shift in microbial species or alteration of microbial metabolism with changing culture conditions. The shifts in proportions of the major VFA could be due to differences in pH and solids retention time (Schadt et al, 1999;Calsamiglia et al, 2002). Solids retention time was higher for Rusitec fermenters (prefixed at 48 h for both diets) than for SFCCF (22.0 and 22.4 h for diet F80 and F20, respectively).…”

“…Although the composition of the saliva infused into the fermenters fed the diet F20 was modified to reduce its buffer capacity, the patterns of pH change observed in vivo were not reproduced in the fermenters. Some types of fermenters are equipped with an automatic system that controls and maintains rumen pH at programmed values by the infusion of HCl or NaOH (Calsamiglia et al, 2002), which would allow a precise simulation of patterns of change previously determined in vivo. Differences between in vivo and in vitro systems in the daily input of feed and saliva should also be taken into account when analyzing the reasons for the higher pH values observed in the fermenters.…”