Browsing by Subject "Futterwert"

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Investigations on nutritional characteristics of microalgae with emphasis on ruminants
(2019) Wild, Katharina Judith; Rodehutscord, Markus
The main objective of the present thesis was to systematically determine nutritional characteristics of microalgae and evaluate the suitability of microalgae as feedstuffs, particularly for ruminants. The experiments comprised a comprehensive characterisation of microalgae nutrient profiles with chemical-analytical methods and the determination of extent and dynamics of nutrient utilization using in vitro methods. In order to generate a comprehensive database on nutrient composition of microalgae, 16 commercial microalgae biomasses of four genera (Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum) were analysed utilizing established methods for food and feed evaluation (Manuscript 1). These investigations included determination of the in vitro crude protein (CP) digestibility for pigs. Nutrient analyses showed a considerable variation particularly in concentrations of proximate nutrients, minerals, and fatty acids, both among and within genera. This variation presumably resulted from varying cultivation conditions and it was concluded that general mean values are not appropriate to characterize microalgae in terms nutrient composition. Manuscript 2 aimed to determine characteristics of the nutritional value of microalgae for ruminants utilizing different in vitro methods. The commercial biomasses included in Manuscript 1 were investigated using the Hohenheim Gas Test method. The investigations comprised the determination of several ruminal fermentation characteristics, of the energy value, and of the protein value. A three-step enzymatic in vitro system was used to estimate intestinal digestibility of ruminally undegraded CP (IDP). Ruminal fermentation of the investigated microalgae biomasses was overall low, which was indicated by an overall low level of production of gas and volatile fatty acids, and a low ruminal CP degradation. As a result of low ruminal fermentation, microalgae biomasses were characterized by high concentrations of ruminally undegradable CP (RUP; 386, 399, 315, and 263 g RUP/kg DM at passage rate of 8 %/h for Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum, respectively). Thus, microalgae appear to be potential alternative protein sources for high performing animals. However, this was contradicted by low IDP, which was determined for microalgae in the present thesis for the first time (mean values for Arthrospira, Chlorella, Nannochloropsis, and Phaeodactylum were 27, 43, 43, and 40 % of RUP respectively). The variation observed in nutrient profiles was reflected in several nutritional characteristics. A common objective of Manuscript 1 and Manuscript 2 was to investigate whether cell disruption affects nutritional characteristics of microalgae. In Manuscript 1, effects of cell disruption on in vitro CP digestibility for pigs were investigated and in Manuscript 2 several in vitro methods were utilized to investigate effects of cell disruption on the nutritional value of microalgae for ruminants. Mechanical cell disruption with a ball mill enhanced in vitro CP digestibility and ruminal fermentation in most of the samples, presumably by the destruction of cells and hence an increase in nutrient accessibility. Nevertheless, concerning the protein value of microalgae in ruminants, application of mechanical cell disruption cannot not be recommended because it decreased RUP but did not increase IDP so that intestinal digestible RUP was overall decreased by cell disruption. The aim of the third manuscript was to investigate the effects of variable cultivation conditions on nutrient composition and nutritional characteristics for ruminants of the microalgae Chlorella vulgaris. Chlorella vulgaris was cultivated under varying conditions (saturation, nitrogen and CO2 depletion, outdoor cultivation). The obtained biomasses were analysed for their nutrient composition and their nutritional value for ruminants using different in vitro methods. Both, nutrient composition and characteristics of the nutritional value for ruminants were affected by the cultivation process. Nutrient deficient conditions had rather adverse effects in terms of digestibility, protein value, and nutrient productivity. It can be concluded that microalgae have potential as alternative protein source for ruminants. Nevertheless, this potential is contradicted by low IDP, but the findings obtained herein have to be verified in future studies. Furthermore, the results of the present thesis show that nutrient composition and ruminal fermentation characteristics of microalgae vary considerably between and in many cases even within microalgae genera. Thus, to the extent possible, it should be strived for a standardisation of cultivation conditions, in order allow better predictions of nutritional characteristics of microalgae.
Investigations on the effects of forage source and feed particle size on ruminal fermentation and microbial protein synthesis in vitro
(2012) Hildebrand, Bastian; Rodehutscord, Markus
The synthesis of microbial protein in the rumen has a major impact on protein- and amino acid supply in ruminants. The amount and amino acid composition of the protein that enters the small intestine primarily depends on diet formulation. In the present studies the effects of maize silage (MS) and grass silage (GS) on ruminal fermentation and microbial protein synthesis were investigated, considering methodical aspects of in vitro studies, particularly grinding of feed samples. In the first experimental series five mixed diets with different proportions of MS and GS (100:0, 79:21, 52:48, 24:76 and 0:100) and a constant proportion of soybean meal (11%) were used. The content of crude protein (CP) and fibre fractions increased, whereas the content of organic matter (OM) and starch decreased with increasing proportion of GS in the diet. It was hypothesised that a combination of MS and GS can benefit microbial growth and thus fermentation of nutrient fractions to a higher extent than using only one forage source separately. It was also to be investigated how changes in diet composition affect the amino acid profile of microbial protein. A well standardised semi-continuous rumen simulation technique (RUSITEC) was used, which is a commonly accepted experimental model in investigations on ruminal fermentation. Changes in fermentation characteristics, as a result of changing the MS-to-GS ratio, were tested for linear and quadratic effects in order to identify possible associative effects. Prior to the in vitro incubation, feedstuffs were dried and ground. It was aimed to investigate in which way fermentation in the RUSITEC system is influenced by mean feed particle size. Therefore two milling screen sizes (MSS; 1 vs. 4 mm) were used in all diets and results on fermentation characteristic were tested for possible interactions of forage source and MSS. One incubation period lasted for 13 days (6 days adaption period, 7 days sampling period), and each treatment was tested in at least three replicates. Ruminal digesta, obtained from rumen-fistulated wether sheep, was used as the inoculum for starting the incubation. Diets were fed once daily to the RUSITEC system, and nylon feed bags remained for 48 h inside the fermentation vessel. A buffer solution, containing 15NH4Cl, was infused continuously into the vessel and the respective effluent was analysed for short chain fatty acids (SCFA) and NH3-N. Solid- and liquid- associated microbial fractions were isolated from the feed residues, the liquid inside the vessel and the effluent by differential centrifugation. The flow of microbial CP was quantified on the basis of N and 15N balances. The feed residues were analysed for crude nutrients and detergent fibre fractions and the respective degradation rates were calculated. OS and CP in the feed residues were corrected for the contribution of solid-associated microbes. The degradation of OM and fibre fractions, as well as amounts of NH3-N increased linearly with stepwise replacement of MS by GS. Degradation of CP was unaffected by diet composition, as well as total SCFA production. The degradation of OM and CP was higher in coarse milled (4 mm-MSS) than in fine milled (1 mm-MSS) treatments, accompanied by higher amounts of NH3-N and total SCFA. An improvement of growth conditions for some microbial groups, e.g. anaerobe fungi, was discussed. The amount of microbial CP increased linearly by the stepwise replacement of MS by GS, and was higher at 4 mm-MSS than at 1 mm-MSS. The amount of available N was assumed to advance microbial growth in the RUSITEC system. Efficiency of microbial CP synthesis was improved from 29 to 43 mg microbial N per g degraded OM by increasing the proportion of GS in the diet, but was unaffected by MSS. The N content and the profiles of amino acids of the three microbial fractions, as well as the ratio of solid- to liquid-associated microbes were affected by diet composition and MSS. Interactions of forage source and MSS were rare. However, the results indicated interactions between dietary factors and origin of microbial isolate on characteristics of microbial protein synthesis. In order to provide additional information on the nutritional value, the mixed diets were evaluated by two further methods. The total tract digestibility of crude nutrients was determined in wether sheep. The content of metabolisable energy was similar between diets and averaged 11.5 MJ per kg dry matter. The in vitro gas production was measured within 93 h by using a modified Hohenheim gas production test, providing information on kinetics and extent of ruminal fermentation. Cumulative gas production decreased with increasing proportion of GS in the diet. A negative effect of coarse milling on fermentation in the Hohenheim gas production test was confirmed. Across all diets gas production was delayed at 4 mm-MSS compared to 1 mm-MSS. The results from both approaches supported the findings of the RUSITEC study that a stepwise replacement of MS by GS led to a linear response in degradation of nutrients. As indicated by the gas production data, positive associative effects might only occur in the first hours after starting an incubation. When mixed diets are used effects cannot be clearly related to individual diet ingredients. Moreover, in the mixed diets interactions between soybean meal inclusion and forage source or feed particle size cannot be excluded. Therefore pure silages were incubated separately in the RUSITEC system in the second experimental series and three milling screens of different size were used (1, 4 and 9 mm). In accordance with the first experimental series, degradation of OM, fibre fractions and non-structural carbohydrates, production of NH3-N, as well as microbial CP flow and efficiency of microbial CP synthesis were higher in GS than in MS. A higher degradation of CP was found for MS than for GS, indicating interactions between forage source and soybean meal inclusion. An increase in MSS from 1 mm to 9 mm led to an improvement in the degradation of OM, CP and non-structural carbohydrates, particularly of starch in MS, as well as in the microbial CP flow for both silages. But the efficiency of microbial CP synthesis and microbial amino acid profile were less affected by MSS. In the second experimental series additionally the effect of available N on fermentation of MS was investigated. The supplementation of urea-N improved the degradation of non-structural carbohydrates, especially starch, but not that of fibre fractions in MS. The efficiency of microbial CP synthesis was increased from 26 to 35 mg microbial N per g degraded OM by urea-N supplementation to MS. The way of urea administration, either supplied together with the feed once daily or infused continuously by buffer solution, had only marginal effects on fermentation characteristics. It was concluded that microbial growth is improved by degradation of OM from GS compared to MS and by an increasing availability of N in the RUSITEC system. Meaningful associative effects of mixtures of MS and GS on ruminal fermentation characteristics are not likely to occur. However, transferability of results to other batches of MS and GS is limited, as high variations in chemical composition are known for both types of silage. Fermentation of MS- and GS-based diets in the RUSITEC system benefits more by coarse milling at MSS up to 9 mm than by fine milling at 1 mm-MSS. Consequently, variations in MSS and feed particle size distribution have to be taken into account when evaluating feeds by rumen simulation systems. The changes in composition and contribution of microbial fractions give indications to a shift in the microbial community as a result of variation of silage type and feed particle size, but further research on this aspect is needed. Moreover, the present results stated that the origin of the microbial samples is very important for measurements on microbial protein synthesis.