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

Abstract

Eight Rusitec and eight single-flow continuous-culture fermenters (SFCCF) were used to compare the ruminal fermentation of two diets composed of alfalfa hay and concentrate in proportions of 80 : 20 (F80) and 20 : 80 (F20). Results were validated with those obtained previously in sheep fed the same diets. Rusitec fermenters were fed once daily and SFCCF twice, but liquid dilution rates were similar in both types of fermenters. Mean values of pH over the 12 h postfeeding were higher ( P , 0.001) in Rusitec than in SFCCF, with diet F80 showing higher values ( P , 0.001) in both types of fermenters. Concentrations of total volatile fatty acids (VFA) were higher ( P , 0.001) in SFCCF than in Rusitec, and in both systems were higher ( P 5 0.002) for diet F20 than for diet F80. There were significant differences between systems in the proportions of the main VFA, and a fermentation system 3 diet interaction ( P , 0.001) was detected for all VFA with the exception of valerate. No differences ( P 5 0.145) between the two types of fermenters were detected in dry matter (DM) digestibility, but NDF, microbial N flow and its efficiency were higher ( P 5 0.001) in SFCCF compared to Rusitec. Whereas pH values and VFA concentrations remained fairly stable through the day in both in vitro systems, pH dropped and VFA increased shortly after feeding in sheep rumen reaching the minimum and maximal values, respectively, about 4 h after feeding. Both in vitro systems detected differences between diets similar to those found in sheep for liquid dilution rate, pH values, DM digestibility, microbial N flow and growth efficiency. In contrast, acetate/propionate ratios were lower for diet F20 than for F80 in sheep rumen (2.73 and 3.97) and SFCCF (3.07 and 4.80), but were higher for diet F20 compared to F80 (4.29 and 3.40) in Rusitec, with values considered to be unphysiological for high-concentrate diets. In vivo NDF digestibility was affected ( P 5 0.017) by diet, but no differences between diets ( P . 0.05) were found in any in vitro system. A more precise control of pH in both types of fermenters and a reduction of concentrate retention time in Rusitec could probably improve the simulation of in vivo fermentation.

Ruminal fermentation, microbial growth and amino acid flow in single-flow continuous culture fermenters fed a diet containing olive leaves

“…(2004a,b), who reported greater pH values and lower VFA concentrations in the rumen of goats and sheep fed diets composed either of AH or of OLSUP. Differences between in vivo and continuous‐culture fermenters in pH and VFA concentrations can be due to the relative amounts of daily input of feed and saliva produced (Carro et al., 2008). As in this study, the amount of saliva infused was the same in all fermenters, the lower pH values found in AH‐fed fermenters in comparison with OLSUP were probably due to increased VFA production, which was 1.41 times greater for AH.…”

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

“…In particular, studies with CCF have recently shown that the average pH (Calsamiglia et al, 2002), the time during which pH values are suboptimal (Cerrato-Sánchez et al, 2008), and the extent of pH variation (Wales et al, 2004) are important factors influencing ruminal fermentation. In addition, the pH in the fermenters has been thought to be responsible for shifts in the rumen bacterial population (Yang et al, 2002;Calsamiglia et al, 2008;Carro et al, 2009). These findings underline the need to maintain in vitro pH values across time that are as close as possible to those in the rumen of animals consuming similar diets to sustain similar compositions and structures of microbial community and, thus, to accurately simulate ruminal fermentation (Devant et al, 2001;Colombatto et al, 2003).…”

“…The results of some studies (Hoover et al, 1976;Crawford et al, 1980;Carro et al, 2009;Muetzel et al, 2009) seem to indicate an effect of the feed-tobuffer ratio (F/B; g of DM feed/L of buffer) on the pH reached in CCF, and although this ratio has been proposed as being responsible for pH changes , to our knowledge, no studies have analyzed the effect of different F/B. Because many discrepancies in fermentation between rumens and CCF have been clearly attributed to differences in pH values (Mansfield et al, 1995;Molina-Alcaide et al, 2009), the F/B should be carefully chosen in fermenters in which pH is not under control.…”

Preliminary study of the effects of condensed barley distillers soluble on rumen fermentation and plasma metabolites in Japanese Black cows

“…Okamoto () reported that when sheep were fed hay and barley, the concentration of total VFA in the rumen was reached a maximum 3 h after feeding and it decreased slowly until 12 h after feeding. In other studies, in ruminant fed a forage‐based diet, the total VFA reached a maximum value after 1.5–4 h (Sutoh et al ; Carro et al ; Zhang et al ). The BHBA, which is converted from butyrate in the rumen epithelium, was higher between 2 and 3 h after feeding, or between 2 and 4 h in multiparous dairy cows (Blum et al ; Nikkhah et al ).…”