In vitro acidification potential and fermentation pattern of cereal grains incubated with inoculum of animals given forage or concentrate-based diets

Abstract

This work aimed to study the acidification and fermentation pattern of maize (M1, M2, M3), barley (B1, B2, B3) and sorghum (S1, S2, S3) varieties depending on the rumen environment (inoculum from forage or concentrate diets, FI or CI), in 10 h incubation series with a low buffered medium. With CI, gas volume from barley was similar to maize (P > 0.05) except at 4 and 6 h, when M2 and M1 were lower. Barley or maize varieties did not differ in gas production (P > 0.05). After 10 h, barley and maize produced on average 82.5 and 73.0 mL/g organic matter (OM), whereas S1, S2 and S3 rendered 68.4, 31.1 and 39.7 mL/g. With FI, differences between barley and maize were detected after 6 h (61.0, 35.3 and 14.1 mL/g OM at 10 h for barley, maize and sorghum). Among inocula, pH with CI was lower than with FI (P < 0.001). Incubation pH at 10 h was 5.51, 5.21 and 5.00 with CI, and 5.52, 5.85 and 5.91 with FI, for sorghum, maize and barley varieties. Gas production and total volatile fatty acid (VFA) concentration were higher (P < 0.001) with CI than FI (67.3 vs 36.8 mL/g and 31.0 vs 19.9 mmol/L at 10 and 8 h). Butyrate and valerate proportions were higher with CI (P < 0.001), whereas acetate and branched chain VFA were lower (P < 0.001). Fermentative activity against vitreous starch such as maize or sorghum was lower for forage than concentrate inoculum. Study of fermentation of starch-rich substrates in a low buffered medium gives a more realistic picture than conventionally buffered conditions.

Fermentation Pattern of Several Carbohydrate Sources Incubated in An in Vitro Semicontinuous System with Inocula From Ruminants Given Either Forage or Concentrate-Based Diets

“…Calsamiglia et al [43] justified similar results by the differences between rumen and in vitro microbial ecosystems, partly because the dilution of inoculum in the latter reduces the extent of the degradation. In contrast to DMd, the concentration of total VFA followed a similar trend than that of gas production, being higher for CI at both sampling times, as has been observed by others [15,32,43]. Calsamiglia et al [43] did not observe any inoculum effect on the acetate and butyrate proportions, and propionate proportion was higher with the concentrate inoculum, as observed in our study at 10 h incubation.…”

“…The source of rumen fluid has an important role in the pattern of in vitro fermentation [15,31,32], with an inoculum promoted by a concentrate diet having a higher fermentative potential than another from a forage diet. In our experiment, the lower buffering of the incubation medium during the first 6-8 hours allowed for a clear expression of the acidification potential of the incubated substrates, which was expressed at a higher extent with CI than FI (average pH along the 24 h incubation period ranging from 6.45 to 5.96 vs. 6.87 to 6.22) as pH dropped to values close to those considered as a threshold for microbial activity [33], whereas a higher pH was maintained with FI.…”

“…Despite this, substrates incubated with CI rendered almost two-fold gas volume more than with FI, irrespective of the chemical nature (starch-or fibre-rich) of those substrates. Despite the more pronounced drop of pH with CI, the incubation environment promoted by a concentrate diet given to the donor animals was more favourable for fermentation of non-fibrous carbohydrates than that induced by a fibrous diet [20,34], probably because of the lack of adaptation of microbiota to ferment starch and sugar substrates with a forage inoculum [15,35] and the inherent buffering capacity of forage legumes such as alfalfa. However, assuming that a part of the gas produced comes from the activity of bicarbonate ion in the buffering of fermentation acids produced, such differences in gas production could be partly associated with the lower pH promoted by CI inoculum, although the contribution of this indirect gas is hard to quantify [14].…”

“…However, most of these in vitro methods are designed to mimic the environment promoted by high forage diets, including the use of inoculum from forage-fed animals [12], and it is not easy to adapt the main physiological conditions, such as pH and rate of passage to conditions promoted by high-concentrate diets [13]. Amanzougarene and Fondevila [14] succeeded in maintaining a low incubation pH in an in vitro closed-batch system by reducing the bicarbonate concentration in the incubation solution, allowing to compare the fermentation of different carbohydrate sources under conditions simulating high-concentrate feeding [15,16]. However, this is not the real physiological situation in vivo, as pH changes across a wide range throughout the day [17] and, besides, rumen outflow rate cannot be assessed in this system.…”

Microbial fermentation of starch‑ or fibre‐rich feeds added with dry or pre‐activated Saccharomyces cerevisiae studied in vitro under conditions simulating high‐concentrate feeding for ruminants

“…36 Therefore, a clear positive effect on this rumen parameter could not be manifested. Observed total VFAs and lactate concentrations were in the range of previous in vitro studies 37 considering the inoculum dilution, but well below in vivo values with beef calves given concentrate diets, 38 and did not apparently reach challenging conditions for bacterial activity. Anyway, the higher VFAs concentration with AY with respect to CT agrees with results from others 4,7 and supports observed gas production results along the incubation period, although no treatment differences were recorded in molar VFAs proportions, suggesting that the effect of yeasts on fermentation is quantitative rather than qualitative.…”