Differences in nutritional characteristics of three varieties of sorghum grain determine their in vitro rumen fermentation

Abstract

The effect of phenolic compounds and protein matrix on microbial fermentation of three sorghum grains (S1, S2 and S3) were studied in vitro. Total phenolics and total tannins concentration (g/kg dry matter, DM) were 1.5 and 0.2 for S1, 19.3 and 8.1 for S2 and 2.6 and 1.3 for S3. Protein enzymatic digestibility was 0.614, 0.226 and 0.454, respectively. Trial 1 was conducted for 24 h, without or with polyethylene glycol (PEG) to determine the effect of phenolic compounds on fermentation. Without PEG, gas production for S1 was the highest after 24 h (257, 237 and 238 mL/g organic matter, for S1, S2 and S3; p<0.05), and higher proportion of propionate at the expense of acetate was recorded with S3 after 6 h. Gas produced with S1 and S3 remained unaffected (p>0.10), but increased in S2 by 0.21 to 0.30 with vs. without PEG. No differences in gas production between S1 and S2 were observed with PEG, S3 recording the lowest (p<0.05) values from 8 h onwards. Addition of PEG reduced proportion of butyrate (p<0.05) and increased three-fold lactate (1.62 vs. 4.98 mM; p<0.001). In Trial 2 (12 h) gas production followed a similar pattern. Without PEG, starch disappearance was the highest in S1 (0.356, 0.231 and 0.216, respectively), but no differences were recorded with PEG. Considering differences in protein digestibility and the effect of phenolic compounds, the effect of starch nature and structure on fermentation is apparently minor. Colour of grain is not necessarily related to phenolic compounds proportion or rumen utilization.

Fitting of the In Vitro Gas Production Technique to the Study of High Concentrate Diets

“…Maintaining a low incubation pH in an in vitro closed-batch system by reducing the bicarbonate concentration in the buffering solution according to the calculations by Kohn and Dunlap [ 32 ] allowed to compare the fermentation of different carbohydrate sources under conditions simulating high concentrate feeding [ 26 , 46 ]. In this sense, the concentration of bicarbonate ion in the incubation solution can be theoretically adjusted to approach the desired pH values ( Table 1 ).…”

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

“…In addition, WB have a considerable amount of NDSF and highly fermentable NDF ( Table 1). The structure of the starch endosperm of maize and sorghum, together with their different proportions of amylose [4], as well as the protein matrix in the endosperm in these cereal species [56] and the presence of phenolic compounds in the brown sorghum [16] explain why the fermentation of starch of barley and wheat bran by ruminal bacteria was higher [4,57,58]. Consequently, the differences in the starch characteristics and fermentation rate promote the response in a medium pH [15].…”

“…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.…”