Ethanol microbially produced in continuously operated aerated bioreactors is partly discharged with the liquid flow and is partly stripped off with the gas phase. The calculation of ethanol formation rates – as required, for example, in data evaluation by Metabolic Flux Analysis – solely based on the liquid‐borne ethanol, while neglecting the ethanol stripping, inevitably results in defective data interpretation. The proportion of stripped ethanol can be measured or, alternatively, calculated. The developed structured model describes the ethanol stripping as a two‐step process while differentiating between the phase transition from the liquid into the gas and the discharge of the evaporated ethanol with the off‐gas. As shown by model analysis as well as stripping experiments, the stripping rate is mainly determined by the ethanol discharge rather than by the phase transition. Consequently, the ethanol‐stripping rate depends on the specific gas flow rate and the partition coefficient for ethanol (at 30 °C, KL/G = 3125 L/L), but not on the mass transfer coefficient. As shown by model simulations, the lower the dilution rate and the larger the gas flow rate of an aerated chemostat with a microbial ethanol formation, the higher the proportion of stripped ethanol. Under practically relevant conditions, more than 30 % of the produced ethanol may be stripped off. Exhaust‐gas coolers, actually used to reduce water losses by evaporation, do not prevent but slightly affect ethanol stripping.

The objective of this study was to improve knowledge regarding the amino acid profile of the insoluble portion of ingested forage escaping rumen degradation. Six forage categories were analyzed. Categories varied in botanical composition and each contained 2 samples. Samples within categories were derived from the same parent material but differed in harvest, maturity, or conservation type. The rumen-undegradable protein of all forages was measured by incubation for 16h in the rumen of 3 nonlactating cows. All residues were corrected for microbial colonization. The AA profile of the residue was different to the original profile. Degradation trends of individual AA, in terms of increase or decrease relative to the original concentration, were similar between all forages. The AA profiles of forage residues, both within and between categories, were more similar to each other than to their respective original profile. This information may aid in improving the accuracy of estimating postruminal AA supply from forages while decreasing the number of samples required to be analyzed.

Using ruminally cannulated steers, we investigated how urinary allantoin excretion was related to variations in feed intake and stage of forage maturity. Further, different approaches were compared for predicting ruminal microbial crude protein (MCP) synthesis and its efficiency. Experimental diets were arranged in a replicated 3 x 3 Latin square design (experiment 1) and a 4 x 4 Latin square design (experiment 2). In experiment 1, a mixed diet [forage to concentrate, 68:32 on a dry matter (DM) basis] was fed at three intake levels corresponding to 1, 1.5 and 2 times maintenance energy requirements. In experiment 2, four silage-based diets were fed based on perennial ryegrass (Lolium perenneL.), which was harvested at four maturity stages. Both experiments demonstrated the influence of diet on microbial growth rate and by this on efficiency of MCP synthesis, although the magnitude of the effects differed between approaches used for estimating MCP. Linear functions satisfactorily characterised the relationship between urinary allantoin excretion (y) and digestible organic matter (OM) intake (x, kg/day; experiment 1: y = 7.94 + 17.34 x; R(2) = 0.785) or intake of OM effectively degraded in the rumen (x, kg/day; experiment 2; y = 22.32 + 5.93 x; R(2) = 0.695). Urinary excretion of allantoin permitted a semi-quantitative prediction of MCP synthesis: ranking of diets and magnitude of changes in MCP synthesis were reflected.

This contribution is meant to obtain basic data for feeding chinchillas (ingestion behaviour, feed and water intake) kept as companion animals. The chinchillas ingested more than 70% of their total feed intake during the dark phase (highest level of activity between 9:00 pm and 7:00 am). Daily amounts of feed intake varied between 2.5 (fresh grass) or 2.6 (hay) and 5.5 (pelleted complete diet) g of dry matter per 100 g of body weight. An offered mixed feed based on native components led to a selection of individual ingredients (high palatability: carob, beet pulp, sunflower seeds). The chinchillas' daily water intake varied between 30 (mixed feed in briquette form) and 40 ml (alfalfa cubes) and amounted on average between 1.5 and 3 ml/g of dry matter. Compared with rabbits or guinea-pigs, the chinchillas generally showed noticeable differences (rhythm of feed intake, palatability of individual ingredients, capacity for digestion, etc.) which must be considered in order to optimize the nutrition of this species.

The achievement of maximum ruminal feed conversion into microbial biomass is a widely accepted concept of ruminant nutrition because high microbial efficiency improves microbial protein supply to the small intestine and, proportionally, reduces fermentative gaseous carbon losses (Beever 1993; Leng 1993). It has recently been demonstrated that differences between forages in in vitro microbial efficiencies, i.e. differences in the proportion of fermented substrate incorporated into microbial biomass, could be determined by a combination of in vitro gas volume measurements with a concomitant evaluation of the amount of substrate truly degraded during 24 h of incubation (for review see Blümmel et al. 1997a). It has been pointed out that these two measurements are not synonymous but complementary. The measurement of degradability is a modification by Goering and van Soest (1970) of the Tilley and Terry (1963) method to remove any residual microbial biomass from the undegraded substrate, thus allowing the calculation of the total amount of substrate dissimilated into all fermentation products, i.e. microbial biomass, short chain fatty acids (SCFA) and gases. In contrast, the gas volume measurement indicates how much of the fermented substrate was used for the formation of SCFA and gases since these two fermentation products are stoichiometrically very closely associated (Blümmel et al. 1997a). The measurements described above were performed after 24 h of incubation because the analytical approach used required all substrate solubles to already be fermented at the time of the residue determination; they would otherwise be removed by the treatment, leading to an overestimation of substrate degradability. On the other hand the determination should not be conducted too far beyond the microbial peak yield in order to minimize the possible contribution of microbial lysis to gas production. The ratio of truly degraded substrate to the gas volume thereby produced in 24 h was termed partitioning factor (PF). This factor denotes the substrate specific variation of in vitro microbial efficiency. The concept of the PF value was derived from, and applied to, crop residues of temperate and tropical origin (Blümmel et al. 1997b) and to Mediterranean grass and legume hays (Blümmel and Bullerdieck 1997). Forages with a high PF value, i.e. proportionally low gas production per unit of substrate degraded, were related to higher voluntary feed intakes than those with a low PF value. High in vitro PF values were also associated with high excretion of renal purine derivatives in Malawian goats fed maize stover leaves with different PF values but similar digestibilities (Mgomezulu and Blümmel 1996). For 61 straws and hays examined, the production of 1 ml of gas was associated with the concomitant in vitro true degradability of 2.74 to 4.65 mg of substrate i.e. PF values ranged from 2.74 to 4.65 mg/ml of which a minimum of 2.20 mg (Blümmel et al. 1997a) were required for the formation of acetate, propionate, butyrate and fermentative CO2, CH4...