Effects Of Non-fiber Carbohydrates On Ruminal Fermentation, Microbial Synthesis, And Populations Of Ruminal Cellulolytic Bacteria Using The Rumen Simulation Technique (Rusitec)

Dietary non-fibre carbohydrates (NFC) are the major source of energy forhigh-producing dairy cattle. They are a very diverse group of carbohydrates, which includestarch, sugars, and neutral detergent soluble fiber (NDSF, largely pectic substances). Differentfeed sources vary greatly in the major components of NFC, although NFC has beenrepresented as a single value for feeds or diets. The NFC in corn grain is mostly starch, citruspulp provides sugars and NDSF, and sugars are predominant in molasses. However,fermentation of different NFC sources varies in digestion characteristics and the profiles oforganic acids produced. For example, pectins differ from starch and sugars producing little orno lactate, and they also elicit a higher acetate-to-propionate ratio compared with starch. Inaddition, the fermentation of pectin can be repressed or be ceased by lower ruminal pH.Sugars produce more butyrate compared with starch and pectin. Therefore, it is notappropriate for NFC as a whole. Effects of replacing cereal with molasses or sugar beet pulpon ruminal fermentation and animal production were not consistent among studies in pastyears. We investigate the effects of NFC on nutrients digestion, ruminal fermentation,microbial synthesis, and populations of ruminal cellulolytic bacteria using four artificialrumen (RUSITEC) experiments in order to determine the appropriate supply methods amongstarch, sugars, and NDSF and to provide theoretical basis for rational use of molasses andsugar beet pulp in the production and practice.Trial1The objective of this study was to investigate the effects of rumen degradableprotein (RDP) and non-fibre carbohydrates (NFC) on ruminal fermentation, microbialsynthesis, and populations of ruminal cellulolytic bacteria using the rumen simulationtechnique (RUSITEC). Treatments consisted of four NFC types (corn starch, sucrose, pectin,and inulin) supplemented with0g/d (low RDP) or1.56g/d (high RDP) sodium caseinate.Apparent disappearance of dry matter (DM) and organic matter (OM) was greater (P <0.01)for the main effect means of sucrose and pectin than for other treatments, when averaged over both RDP supplementation rates. A NFC×RDP interaction (P <0.01) was observed forapparent neutral detergent fibre (NDF) disappearance, which tended to be lower for sucrose (P=0.10) and pectin (P=0.09) than for starch treatment under low RDP conditions, but did notdiffer among treatments under high RDP conditions. The16S ribosomal deoxyribonucleicacid (rDNA) copies of Ruminococcus albus were greater (P <0.01) and tended to be greater(P=0.10) for the main effect means of pectin than for starch treatment in liquid and solidfraction, respectively. There were NFC×RDP interactions for16S rDNA copy numbers ofRuminococcus flavefaciens, which in solid fraction tended to be lower (P=0.06) for sucrosethan for starch treatment under low RDP conditions. Increasing dietary RDP increased totalvolatile fatty acids production (P <0.01) and total microbial nitrogen (N) flow (P <0.01) inall treatments. The molar proportion of acetate and the ratio between acetate and propionatewere both greatest (P <0.05and P <0.01, respectively) for the main effect means of pectinamong treatments. Butyrate molar proportions were greater (P <0.01) for sucrose and inulintreatments than for other treatments regardless of RDP level. Total microbial N (MN) flow didnot differ among treatments under low RDP conditions, but sucrose (P <0.01) and pectin (P=0.10) produced greater MN than starch with increased RDP. Results showed NFC type, RDPlevel, and their interaction affected ruminal fermentation, microbial synthesis, and cellulolyticbacteria populations, and under sufficient ruminal available N sucrose and pectin had greateradvantage in microbial N synthesis than starch.Trial2The objective of this study was to investigate the effects of neutral detergentsoluble fiber (NDSF) and sucrose supplementation on ruminal fermentation, microbialsynthesis, and populations of ruminal cellulolytic bacteria in Rusitec fermenters. Theexperiment had a2×2factorial design with two dosages of sucrose, low (ca.0.26g/d,low-sucrose) and high (ca.1.01g/d, high-sucrose), and two dosages of supplied NDSF, low(1.95g/d, low-NDSF) and high (2.70g/d, high-NDSF). Numerical or significant interactionsbetween NDSF and sucrose were detected for apparent disappearance of DM (P=0.08), OM(P=0.04), NDF (P=0.01), and hemicellulose (P=0.09), and xylanase from solid phase (P=0.04), which were reduced by supplemental NDSF only in high-sucrose diets. Althoughinteractions between NDSF and sucrose were detected for the molar proportions of butyrate(P=0.05), on the whole, high-NDSF diets increased the molar proportion of acetate andreduced that of butyrate compared with low-NDSF diets; however, the effects of supplementalsucrose on VFA profiles depended upon NDSF amount. A NDSF×sucrose interaction wasobserved for the production of methane (P <0.01) where supplementation with NDSF only increased the production of methane in low-sucrose diets. Supplementation with NDSF andsucrose both reduced the net production of ammonia-N (P <0.01and P=0.03, respectively).High-NDSF fermenters had greater daily flow of total non-ammonia N (NAN)(P=0.01),total MN (P=0.01), and solid-associated microbial pellets (SAM)(P <0.01) and greaterefficiency of microbial synthesis (EMS)(P=0.02), expressed as g microbial N/kg OMfermented compared with low-NDSF fermenters. Supplementation with NDSF resulted in anincrease in16S rDNA copies of Ruminococcus flavefaciens (P <0.02) and a reduction incopies of Ruminococcus albus (P <0.01). Supplementation with sucrose increased the16SrDNA copies of Ruminococcus albus (P=0.01) from liquid fraction, but did not affect dailytotal MN flow and cellulolytic bacterium populations from solid fraction. These data indicatethat the effects of the interaction between NDSF and sugars on ruminal fermentation and fiberdigestion should be taken into account in diet formulation. Ruminal fermentation andmetabolism of sugars warrant further investigation.Trial3The objective of this study was to investigate the effects of replacing dietarystarch with neutral detergent soluble fiber (NDSF) on ruminal fermentation, microbialsynthesis, and populations of ruminal cellulolytic bacteria using the rumen simulationtechnique (RUSITEC). Experimental diets contained12.7,16.4,20.1, and23.8%NDSFsubstituted for dietary starch on a dry matter basis. With the increasing dietary NDSF,apparent disappearance of DM (P=0.05), OM (P=0.08) and NDF (P=0.06) had afluctuation change, increasing first and decreasing afterwards, with the maximum valueobserved in the16.4%NDSF diet. Increasing dietary NDSF caused an increase in apparentdisappearance of acid detergent fiber (ADF)(P=0.03) and fibrolytic enzyme activity and areduction in the number of ruminal cellulolytic bacteria (i.e., R. albus and R. flavefaciens) andapparent disappearance of dietary nitrogen (P <0.01). Substituting NDSF for starch appearedto increase the molar proportion of acetate (P <0.01), acetate: propionate (P <0.01), theproduction of methane (P=0.03), and methane: VFA (P <0.01). Increasing dietary NDSFreduced the daily production of ammonia-N (P <0.01) and increased the daily flow of NAN(P <0.01) and SAM (P <0.01), and EMS (P=0.07), but total microorganisms flow did notfurther increase as dietary NDSF exceeded20.1%of diet DM (P=0.07). Results suggest thatsubstituting NDSF for starch up to16.4%of diet DM increased digestion of nutrients (exceptfor N) and microbial synthesis, and further increase (from16.4to23.8%) in dietary NDSF didnot repress microbial synthesis but significantly reduced digestion of dietary N. Replacingdietary starch with NDSF may be beneficial for ruminants production due to increased flow of microbial protein and ruminally undegradable feed protein.Trial4The objective of this study was to investigate the effects of replacing dietarystarch with neutral detergent soluble fiber (NDSF) in high sucrose diets on ruminalfermentation, microbial synthesis, and populations of ruminal cellulolytic bacteria using therumen simulation technique (RUSITEC). Experimental diets contained12.9,16.6, and20.3%NDSF substituted for dietary starch on a dry matter basis. Increasing dietary NDSF reducedor tended to reduce the apparent disappearance of DM (P=0.03), OM (P=0.05), N (P <0.01), and NDF (P=0.09), but increased that of NFC (P=0.03). Substituting NDSF forstarch appeared to increase the molar proportion of butyrate (P <0.01), acetate: propionate(P=0.06), and methane: VFA (P=0.04), and reduced the molar proportion of propionate (P=0.04). Increasing dietary NDSF reduced the daily production of ammonia-N (P=0.04) andincreased the daily flow of NAN (P=0.02) and SAM (P <0.01), and EMS (P=0.06). Totalmicroorganisms flow did not further increase as dietary NDSF exceeded16.6%of diet DM (P=0.13). Increasing dietary NDSF caused a reduction in xylanase activity from liquid fraction(P=0.02) and carboxymethylcellulase activity from solid fraction (P=0.02), but did notaffect typical cellulolytic bacteria population. Results suggest that substituting NDSF forstarch reduced digestion of nutrients especially dietary N, but improved the microbialsynthesis under high sugar conditon. Replacing dietary starch with NDSF may be beneficialfor ruminant production due to increased flow of microbial protein and ruminallyundegradable feed protein, but its repression on fiber digestion should be taken into account indiet formulation.