Effect of carbohydrate composition of the diet and ruminal fluid passage on microbial transformations in the rumen
Kumulative Dissertation
Datum der mündl. Prüfung:2023-11-30
Erschienen:2024-02-09
Betreuer:Prof. Dr. Jürgen Hummel
Gutachter:Prof. Dr. Jürgen Hummel
Gutachter:Prof. Dr. Karl-Heinz Südekum
Dateien
Name:Dissertation Friederike Pfau_eDiss.pdf
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Format:PDF
Zusammenfassung
Englisch
The aim of this study was to investigate certain effects on the microbial crude protein (MCP) production in the rumen and to investigate mechanisms which could promote the ruminal MCP yield to enhance the MCP supply to the ruminant. Due to the high protein requirements due to lactation, this is particularly important for high yielding dairy cows. First, the MCP yield of different pure carbohydrates and different feeds, which differ considerably in their carbohydrate composition, respectively, was investigated. Further, the impact of fluid passage rate (dilution rate [DL]) on MCP production was examined. The third question, which was explored, was if there is a different in mean retention time (MRT) of feed particles and fluid in the rumen of cattle and sheep and if relating thereto a difference in MCP production between the species could be obtained. For the first part of this study, fermentation characteristics and MCP production of four different pure carbohydrates (sucrose, starch, cellulose and pectin) were investigated in vitro by the modified Hohenheim gas test (HGT). After 8 and 24 h of incubation in the modified HGT (3 runs × 2 syringes) measurements of gas production (GP), short chain fatty acid and ammonia concentration were conducted. Ammonia values were used for estimation of the MCP formation. Additionally, the substrates were incubated for 96 h in the HGT system (2 runs × 3 syringes) and GP was measured after 2, 4, 6, 8, 12, 16, 24, 30, 36, 48, 60, 72 and 96 h of incubation to obtain the fermentation kinetics and the time of half‐maximal GP (t1/2) of the substrates. The pure carbohydrates differed considerably in their fermentation kinetics. At t1/2, MCP yield [g/kg dry matter] was higher for cellulose than for sucrose and pectin and higher for starch than for sucrose and MCP [g/L GP] was higher for starch and cellulose than for sucrose and pectin. These findings show, that different carbohydrates vary in their MCP yield, especially cellulose promotes higher MCP production. However, the slower fermentation rate of cellulose has to be kept in mind. In the second part of this study, three commonly used feeds (barley grain [BG], beet pulp [BP], and soybean hulls [SBH]) were incubated together with a mixture of grass hay and rapeseed meal in two identical Rumen simulation technique (Rusitec) apparatuses (each 6 vessels). Additionally, differences in DL 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. The system was adapted for 7 d, followed by 4 d of sampling. Production of MCP was estimated by 15N analysis. Production of MCP (mg/g degraded organic matter [dOM]) was higher for SBH compared to both BG and BP and greater with high DL. High DL reduced organic matter degradability (OMD) and methane production (both /d and /g dOM) compared to low DL. Feeds with different carbohydrate composition varied in their MCP yield, especially SBH containing mostly cellulose promoted a higher MCP production. However, the lower OMD of SBH have to be kept in mind. Additionally, increasing fluid passage rate showed the potential to increase MCP and decrease methane production at the same time. In the third part of this study, the hypothesis of a systematical difference between cattle and sheep in MRT of particle and fluid and its ratio (MRTparticle/MTRfluid = selectivity factor [SF]) as well as in the apparent digestibility of crude protein (aD CP) were investigated in a meta-analysis. Keeping the microorganism in a state of more intense growth due to a more pronounced digesta ‘washing’ by a higher SF should lead to an increase in MCP yield and therefore should increase the metabolic losses of fecal nitrogen of microbial origin and decrease the aD CP simultaneously (true digestibility of protein not being influenced). The datasets included 12 studies on MRT (of which 11 contained information on feed intake), yielding 102 (or 89) individual data; and 26 studies on protein digestibility (of which 18 contained information on intake), yielding 349 individual data. Only studies that investigated cattle and sheep simultaneously were used. Cattle had a higher SF than sheep, mainly due to longer MRTparticle. Only if body mass was included in the model, MRTfluid was significantly shorter in cattle in the larger MRT dataset. Cattle had a significantly lower aD CP than sheep, while there was no such difference in overall (dry or organic matter) digestibility. These findings indicate that cattle are especially good in maximizing the ruminal MCP yield. In conclusion, MCP production is affected by carbohydrate source or feedstuff composition, by DL and by SF. However, not all studies in the literature found the same effects and transferability from in vitro data into in vivo is challenging and not without limits. Also, optimizing diets for a maximal MCP yield is not easy as various other factors affecting MCP production in the rumen as well. Further research is needed for a more precise understanding of the complex relationships between diet, feedstuff and carbohydrate composition, MRT, animal individual factors and MCP production in the rumen.
Keywords: microbial protein; Hohenheim gas test; Rumen simulation technique (Rusitec); dilution rate; pectin; starch; cellulose; sucrose; barley grain; sugar beet pulp; soybean hulls; microbial growth; fermentation products; passage rate; retention time; cattle sheep comparison