In vitro fermentation pattern and acidification potential of different sources of carbohydrates for ruminants given high concentrate diets

Abstract

The in vitro fermentation pattern of five sources of carbohydrates of differing nature (maize grain, MZ; sucrose, SU; wheat bran, WB; sugarbeet pulp, BP; and citrus pulp, CT) under conditions of high concentrate diets for ruminants was studied. A first 8 h incubation trial was performed under optimal pH using inoculum from ewes given a fibrous diet, to compare fermentative characteristics of substrates. As planned, incubation pH ranged within 6.3 to 6.6. The gas produced from CT was higher than MZ, SU and BP from 4 and 6 h onwards, and at 8 h, respectively (p<0.05). There were no differences (p>0.05) on total volatile fatty acid (VFA) concentration, nor on acetate or propionate proportions, but butyrate was lowest (p<0.05) with CT and BP. The second incubation trial was performed in a poorly-buffered medium, with inoculum from ewes given a concentrate diet. All substrates showed a gradual drop of pH, being lowest with SU after 4 h (p<0.05). Throughout the incubation, gas production was highest with CT and lowest with MZ and BP (p<0.05). Total 8 h VFA concentration was higher with CT than BP, SU and MZ (p<0.05). Acetate proportion was higher, and that of propionate lower, with BP than WB (p<0.05), butyrate proportion being higher with MZ and WB than with BP and CT (p<0.05). Lactic acid concentration was higher (p<0.05) with SU than WB and BP. Fermentation characteristics and acidification potential of feeds depend on the nature of their carbohydrate fraction, and must be considered for practical applications.Additional key words: incubation pH; gas production; sugarbeet pulp; sucrose; citrus pulp; wheat bran.

Effects of Replacing Extruded Maize by Dried Citrus Pulp in a Mixed Diet on Ruminal Fermentation, Methane Production, and Microbial Populations in Rusitec Fermenters

“…In agreement with previous in vitro [ 14 , 21 ] and in vivo [ 10 , 20 , 23 ] studies, the total VFA daily production was unaffected by the inclusion of DCP in the diet, but the VFA profile was markedly affected. Studies investigating the influence of DCP on the rumen VFA profile have produced contrasting results, but some of them reported shifts to greater acetate and lower propionate proportions, resulting in greater acetate/propionate ratios [ 10 , 21 , 22 ].…”

“…Due to the great content of highly-degradable NDF and readily fermentable carbohydrates, DCP has a high nutritional value and it has been proposed as a possible substitute of cereals in ruminant diets [ 10 , 11 ]. Several in vitro [ 12 , 13 , 14 ] and in vivo [ 15 , 16 , 17 ] studies evaluated the inclusion of DCP in the diet of small ruminants, mainly in sheep. These studies showed that replacing barley or other cereals by DCP can increase rumen pH [ 18 , 19 ], fiber digestibility [ 15 , 20 ], and acetate proportion [ 10 , 21 , 22 ], with no effects on either total volatile fatty acid (VFA) production [ 10 , 21 ] or microbial protein synthesis (MPS) [ 21 ].…”

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

“…Despite the high concentration of lactic acid with CP at 6 h ( Table 2), it did not achieve the range considered as a risk of acidosis in vivo [30] and, in fact, did not promote the values of incubation pH below 5.5 that are considered as a threshold for the onset of subacute acidosis [49]. These results were in agreement with those found by Amanzougarene et al [42] in a batch culture with a minimum buffer concentration, and could be associated with its richness in soluble sugars [50,51], estimated as 0.24 g/kg DM (Table 1), which are fermented at a very fast rate. Although CP also has a high proportion of soluble fibre (0.42, Table 1), this response cannot be directly associated with the fast fermentation of pectin [37,52], since BP includes a similar NDSF proportion (0.46) and it was fermented at a slower rate and magnitude.…”

“…This parameter was especially low compared to the extent of the rumen degradation of starch-rich sources (around 0.70-0.80 [40]) or fibrous sources (ranging from 0.40 to 0.70 [41]). This is difficult to explain, but we have also observed this low response in previous in vitro experiments [42], partly associated with a low pH [13]. 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.…”

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

“…The adjustment of the buffering capacity of the medium to fit the incubation pH has also been applied to the study of the acidification potential of cereal grains and carbohydrates of different characteristics [ 26 , 49 ], by allowing to ferment substrates in a low buffered medium (calculated for adjusting to pH 5.50). In these studies, the incubation period was shortened to 10 h to avoid biased results in the fermentation profile because of extreme low pH (around pH 5.0 or below) after buffer exhaustion.…”