Nine hybrids (three maturity groups, dry matter 343 ± 5.6 g/kg) of whole‐crop maize were ensiled in eight replicates in laboratory‐scale silos. Each hybrid was sampled at harvest and after 30, 60, 90 and 120 days (d) of ensiling. Samples were analysed for chemical composition (proximate constituents, fermentation products and pH), starch, non‐protein N (NPN) and NH3‐N. Each sample and its neutral detergent fibre (NDF) fraction were incubated in the Hohenheim gas test system. In vitro gas production was measured after 0, 2, 4, 8, 12, 16, 24, 36, 48, 72 and 96 hr of incubation. Gas production of the neutral detergent soluble (NDS) fraction (mainly starch) was calculated using a curve subtraction method. Gas production dynamics over time were estimated using a nonlinear regression equation; afterwards, a two‐factorial analysis of variance (storage length, maturity group and their interaction) using the general linear models procedure was conducted. After 30 d, all silages were well fermented. Most fermentation products and proximate constituents only changed until 30 or maximum 60 d of ensiling. Only few changes in in vitro nutrient degradability were detected after the first 30 d or as influenced by maturity group. Ensiling per se increased the ruminal degradability of the NDS, but there was no further increase caused by a prolonged duration of storage. However, extensive changes in crude protein fractions occurred with a linear increase in NPN and NH3‐N compounds from 0 to 120 d of storage, indicating continual protein and amino acid degradation.

This study investigated the impact of carbohydrate source and fluid passage rate (dilution rate) on ruminal fermentation characteristics and microbial crude protein (MCP) formation. Three commonly used feeds (barley grain [BG], beet pulp [BP], and soybean hulls [SBH]), which differ considerably in their carbohydrate composition, were incubated together with a mixture of grass hay and rapeseed meal in two identical Rusitec apparatuses (each 6 vessels). Differences in fluid passage rate were simulated by infusing artificial saliva at two different rates (1.5% [low] and 3.0% [high] of fermenter volume per h). This resulted in six treatments (tested in 3 runs): BGhigh, BGlow, BPhigh, BPlow, SBHhigh and SBHlow. The system was adapted for 7 d, followed by 4 d of sampling. Production of MCP (mg/g degraded organic matter [dOM]; estimated by 15N analysis) was greater with high dilution rate (DL; p < 0.001) and was higher for SBH compared to both BG and BP (p < 0.001). High DL reduced OM degradability (OMD) compared to low DL (p < 0.001), whereas incubation of BG resulted in higher OMD compared to SBH (p < 0.002). Acetate:propionate ratio decreased in response to high DL (p < 0.001). Total gas and methane production (both /d and /g dOM) were lower with high DL (p < 0.001). In our study increasing liquid passage rate showed the potential to increase MCP and decrease methane production simultaneously. Results encourage further studies investigating these effects on the rumen microbial population.

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The aim of this study was to investigate the microbial protein yield of different pure carbohydrates to contribute to a more precise prediction of the microbial protein formed in the rumen. In a first experiment, sucrose, wheat starch, microcrystalline cellulose and citrus pectin were incubated for 8 and 24 hr in the modified Hohenheim gas test (HGT) system (3 runs × 2 syringes) including gas production, ammonia and short‐chain fatty acid concentration measurements. Ammonia values were used for estimation of the microbial protein formation. In a second experiment, the same substrates were incubated for 96 hr in the HGT system (2 runs × 3 syringes) and gas production was measured after 2, 4, 6, 8, 12, 16, 24, 30, 36, 48, 60, 72 and 96 hr of incubation to obtain the fermentation kinetics and the time of half‐maximal gas production (t1/2) of the substrates. The substrates differed considerably in their fermentation kinetics, and therefore, comparison on the basis of t1/2 was chosen as the most meaningful. At t1/2, microbial protein yield [g/kg dry matter] was higher for cellulose than for sucrose and pectin and higher for starch than for sucrose. The microbial protein expressed in g/L gas production was higher for starch and cellulose than for sucrose and pectin at t1/2. Effects of carbohydrates related to ruminal pH may remain undetected in in vitro trials.