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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.

The fermentation pattern of several carbohydrate sources and their interaction with the nature of microbial inoculum was studied. Barley (B), maize (M), sorghum, (S), sugarbeet pulp (BP), citrus pulp (CP) and wheat bran (WB) were tested in an in vitro semicontinuous system maintaining poorly buffered conditions from 0 to 6 h, and being gradually buffered to 6.5 from 8 to 24 h to simulate the rumen pH pattern. Rumen fluid inoculum was obtained from lambs fed with either concentrate and barley straw (CI) or alfalfa hay (FI). The extent of fermentation was higher with CI than FI throughout the incubation (p < 0.05). Among the substrates, S, BP and M maintained the highest pH (p < 0.05), whereas CP recorded the lowest pH with both inocula. Similarly, CP recorded the highest gas volume throughout the incubation, followed by WB and B, and S recorded the lowest volume (p < 0.05). On average, the total volatile fatty acid (VFA), as well as lactic acid concentration, was higher with CP than in the other substrates (p < 0.05). The microbial structure was more affected by the animal donor of inoculum than by the substrate. The in vitro semicontinuous system allows for the study of the rumen environment acidification and substrate microbial fermentation under intensive feeding conditions.

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.

Context Good transition from suckling to high-concentrate diets is essential to avoid nutritional disorders during the fattening period of beef calves. Aims Assessing the optimal feeding strategies during the preweaning period of beef calves for an adequate adaptation to high-concentrate diets. Methods A total of 30 female beef calves (15 Parda de Montaña and 15 Pirenaica), managed under restricted suckling, were assigned to three preweaning diets (milk only [MO], milk plus hay [MH], milk plus concentrate [MC]), fed from the third month until weaning at 5 months. During the subsequent transition period (1 month), all animals received a fattening concentrate plus wheat straw ad libitum. Key results Milk intake did not differ among diets; solids intake was similar for MH and MC calves. Preweaning supplementation improved performance at the end of the suckling period (MC &gt; MH &gt; MO). During transition, concentrate intake was lower for MO calves; MH calves showed the lowest feed efficiency. At the end of transition, MC calves showed the highest liveweight and average daily gain (MC &gt; MH = MO). Rumen pH at weaning did not differ from that at the end of transition in MC calves, whereas MH and MO animals showed lower values at the latter. Supplemented calves showed higher volatile fatty acids concentration than MO calves at weaning; MC calves showed the lowest values at the end of the transition period. Ammonia and lactic acid concentration at weaning was the highest for MO and MC calves respectively, with no differences between diets at the end of transition. Glucose and non-esterified fatty acids concentrations were only affected by age; urea and β-hydroxybutyrate were affected by the interaction between diet and age. Economic profitability at weaning was higher for supplemented calves (MH = MC &gt; MO), and ranked MC &gt; MO &gt; MH at the end of the transition. Gains during the suckling period, and hence the economic margin, were higher for Parda de Montaña than for Pirenaica calves; during transition the economic margin was similar. Conclusions Preweaning supplementation with concentrates is the most interesting option in terms of performance and profitability. Implications Preweaning solid supplementation increases calf performance and provides better rumen development, essential for a smooth transition to fattening diets.

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.

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The potential use of tannin extracts from quebracho (QCT), grape (GCT), chestnut (CHT) and oak (OHT) included at 10, 20 or 30 mg/g to modulate rumen fermentation of concentrates was studied in three 24-h in vitro incubation runs, with barley grain as reference substrate and simulating high concentrate feeding conditions by adjusting pH at 6.2. Incubation pH at 8 and 24 h ranged from 6.14 to 6.18 and from 5.94 to 6.00, respectively. Gas production from barley alone (CTL) was linearly reduced with CHT (P &lt; 0.05 up to 6 h; P &lt; 0.10 from 8 to 18 h), OHT (P &lt; 0.05 up to 12 h; P &lt; 0.10 from 18 h), GCT (P &lt; 0.05 from 2 to 24 h) and QCT (P &lt; 0.10 up to 6 h), but a quadratic trend (P &lt; 0.10) was also detected on GCT. The effect of GCT was highest and that of CHT lowest. Similarly, dry matter disappearance after 24 h showed a linear decrease with all tannin sources (P &lt; 0.05), being lower with GCT than with QCT and CHT (P &lt; 0.05). All tannin sources linearly increased (P &lt; 0.05) molar butyrate proportion from CTL, at the expense of propionate proportion in GCT (P &lt; 0.01) and CHT (P &lt; 0.10). Except for the linear effect of chestnut on barley fermentation, all sources already reached their maximum level of response at their first level of inclusion (10 mg/g), especially with GCT. Qualitatively, tannins did not largely affect pH or other environmental parameters, except for an increase in butyrate proportion.