Simple Rumen Research Articles

Repeated Inoculation of Young Calves With Rumen Microbiota Does Not Significantly Modulate the Rumen Prokaryotic Microbiota Consistently but Decreases Diarrhea.

The complex rumen microbiota exhibits some degree of host specificity. The undeveloped simple rumen microbiota is hypothetically more amendable. The objective of this study was to investigate if the rumen prokaryotic microbial assemblage of young calves can be reprogrammed by oral inoculation with rumen microbiota of adult cows. Twenty newborn male calves were randomly assigned to four groups (n = 5 per group), with two groups being orally inoculated with rumen microbiota (fresh rumen fluid) collected from two lactating dairy cows, while the other two groups receiving autoclaved rumen fluid collected from another two donor cows. Each calf was orally drenched with 100, 200, 300, 400, and 500 mL of the rumen fluid at d3, d7, d21, d42, and d50, respectively, after birth. The inoculation with rumen microbiota did not affect (P > 0.05) feed intake, average daily gain (ADG), heart girth, or feed conversion ratio but significantly (P < 0.01) lowered instance of diarrhea. At the age of 77 days (27 days post-weaning), all the calves were slaughtered for the sampling of rumen content and determination of empty rumen weight. Rumen fermentation characteristics were not affected (P > 0.05) by the inoculation. Rumen prokaryotic microbiota analysis using metataxonomics (targeting the V4 region of the 16S rRNA genes) showed that the calf rumen prokaryotic microbiota differed from that of the donors. Two Succinivibrionaceae OTUs, two Prevotella OTUs, and one Succiniclasticum OTU were predominant (relative abundance > 2%) in the donors, but only one Succinivibrionaceae OTU was found in the calves. On the other hand, five other Prevotella OTUs were predominant (>3%) in the calves, but none of them was a major OTU in the donors. No correlation was observed in relative abundance of major OTUs or genera between the donor and the calves. Principal coordinates analysis (PCoA) based on weighted UniFrac distance showed no significant (P > 0.05) difference in the overall rumen prokaryotic microbiota profiles among the four calf groups, and principal component analysis (PCA) based on Bray-Curtis dissimilarity showed no significant (P > 0.05) difference in functional features predicted from the detected taxa. Nor the calf rumen microbiota showed any clustering with their donor’s. Repeated oral inoculation with rumen microbiota probably has a limited effect on the development of rumen microbiota, and the rumen microbiota seems to develop following a program determined by the host and other factors.

Effect of different levels of rapidly degradable carbohydrates calculated by a simple rumen model on performance of lactating dairy cows

Aggregating rumen degradation characteristics of different carbohydrate components into the term modeled rapidly degradable carbohydrates (mRDC) can simplify diet formulation by accounting for differences in rate and extent of carbohydrate degradation within and between feedstuffs. This study sought to evaluate responses of lactating dairy cows to diets formulated with increasing levels of mRDC, keeping the supply of other nutrients as constant as possible. The mRDC content of feedstuffs was calculated based on a simple rumen model including soluble, washable, and nonwashable but potentially degradable fractions, as well as the fractional degradation and passage rates, of sugar, starch, neutral detergent fiber, and other carbohydrates. The mRDC term effectively represents the total amount of carbohydrates degraded in the rumen within 2 h after ingestion. Fifty-two lactating Holstein cows (of which 4 were rumen fistulated) were assigned to 4 treatments in a 4 × 4 Latin square design. Treatments were fed as a total mixed ration consisting of 25.4% corn silage, 23.1% grass silage, 11.6% grass hay, and 39.9% concentrate on a dry matter basis. Differences in mRDC were created by exchanging nonforage neutral detergent fiber-rich ingredients (mainly sugar beet pulp) with starch-rich ingredients (mainly wheat) and by exchanging corn (slowly degradable starch) with wheat (rapidly degradable starch) in the concentrate, resulting in 4 treatments that varied in dietary mRDC level of 167, 181, 194, or 208 g/kg of dry matter. Level of mRDC did not affect dry matter intake. Fat- and protein-corrected milk production and milk fat and lactose yield were greatest at 181 mRDC and decreased with further increases in mRDC. Milk protein yield and concentration increased with increasing mRDC level. Mean rumen pH and diurnal variation in ruminal pH did not differ between treatments. Total daily meal time and number of visits per meal were smaller at 181 and 194 mRDC. Despite milk production responses, increasing dietary mRDC levels, while maintaining net energy and intestinal digestible protein as well as other nutrients at similar levels, did not influence rumen pH parameter estimates and had minor effects on feeding behavior. These results indicate that aggregating rapidly degradable carbohydrate content into one term may be a simple way to further improve predictability of production responses in practical diet formulation for lactating dairy cows.

Effect of ammoniation or protein supplementation of barley straw on digestion and purine derivative excretion in sheep

AbstractAn experiment was conducted to examine the effect of ammonia treatment or soya-bean meal supplementation on rumen and lower tract digestion and urinary purine-derivative excretion in sheep given barley straw-based diets. Four wethers each fitted with simple rumen and duodenal cannulae were randomly allocated to four diets in a 4×4 Latin-square design. The diets were, untreated barley straw + molasses meal (diet 1), ammonia-treated barley straw + molasses meal (diet 2), untreated barley straw + soya-bean meal + molasses meal (diet 3) and ammonia-treated barley straw + soya-bean meal + molasses meal (diet 4). Dry-matter (DM) intake, total tract neutral- and acid-detergent fibre apparent digestibility and faecal nitrogen (N) output were higher for diets 2 and 4. Microbial protein yield, determined from total urinary purine-derivative excretion, was also high in sheep on diets 2 and 4. However, supplementation with soya-bean meal in diet 4 reduced DM and fibre digestion but increased intake and microbial synthesis. Despite the lower microbial protein synthesis for diet 3, total tract N digestion was high for the diet, an indication of higher nutrient absorption in the lower tract. The above results indicated that there was a substantial increase in rumen microbial N yield from ammoniated straw-based diets. However, not all the N was made available to the animals. Some of the microbial N absorbed in the lower tract may have been overestimated by the use of the purine derivative-microbial N evaluation method. On the other hand, when protein supplements were given the amount of microbial protein available to the ruminant through absorption in the lower tract may have been underestimated by urinary purine derivatives.

Ruminal plant cell wall digestibility estimated from digestion and passage kinetics utilizing mathematical models

Methods to describe the digestion and passage kinetics for estimating ruminal neutral detergent fibre digestibility (RNDFD) with simple mathematical models were evaluated in cattle fed a diet of hay, barley and urea (600, 396 and 4 g dry matter (DM) kg −1 total DM) at two levels of intake. The parameters of digestion kinetics were determined by in situ incubation and rumen evacuation technique. Digesta passage kinetics was estimated from duodenal and faecal Cr and Yb concentrations either from exponential decline in marker concentration or by using two-compartmental models with gamma age dependency in the first compartment. Increasing the feeding level from 40 to 80 g DM kg −1 live weight 0.75 decreased ( P < 0.05) the digestibility of DM (0.775 vs. 0.749), DNF (0.758 vs. 0.707) and cell solubles (0.838 vs. 0.824). The amount of total digesta, digesta DM content and the amount of DM in the rumen increased as feed intake increased. The relative increase in rumen pool size of digestible NDF was greater than in that of indigestible NDF (0.72 vs. 0.34). Using in situ digestion kinetics data and the exponential decline in marker concentration in a simple rumen digestion model yielded RNDFD estimates which were much lower than those based on rumen evacuation data, and only about 0.70 of the total in vivo NDF digestibility. This was partly because of the slower ( P < 0.01) rate of digestion observed with the in situ method than estimated from rumen evacuation (0.0458 vs. 0.0607), and partly because of an underestimation of rumen residence time by the passage model. Incorporation of the selective retention of feed particles in the digestion model yielded RNDFD estimates which were 0.13 units higher than those based on exponential marker concentration decline curves. The kinetics parameters for this model were calculated from duodenal marker concentrations using two-compartmental passage models. The RNDFD estimates were 0.94–0.96 of the total in vivo NDF digestibility when the passage kinetics parameters, estimated with the two-compartmental model, were used in combination with the rumen evacuation derived rate of digestion. The values for RNDFD were higher when Cr and faecal sampling were used rather than Yb and duodenal sampling to estimate passage kinetics.

The degradation of different protein supplements in the rumen of steers and the effects of these supplements on carbohydrate digestion.

1. Four steers with simple rumen and abomasal cannulas were given diets consisting of ground and pelleted alkali-treated straw, rolled barley and tapioca supplemented with urea (diet U) or containing single-cell protein (diet SCP), maize-gluten meal (diet MGM) or rapeseed meal (diet RSM) in place of some of the tapioca. The isoenergetic diets were given in a 4 x 4 Latin square design in eight feeds/d at 3-h intervals and provided sufficient metabolizable energy to support a growth rate of approximately 0.5 kg/d. Chromic oxide and polyethylene glycol were given as markers and appropriate samples taken from the rumen and abomasum. Flows (g/d) at the abomasum of organic matter and nitrogenous and carbohydrate constituents were calculated. 2. Rumen ammonia levels were similar with all three protein supplements at about 9 mmol/l, which was significantly lower (P less than 0.05) than that in animals on diet U (16 mmol/l). Rumen liquid outflow rates (/h) were 0.099, 0.139, 0.125 and 0.160 for diets U, SCP, MGM and RSM respectively; the difference between diet U and diet RSM was significant (P less than 0.05). Corresponding values for Cr2O3 outflow rates were 0.027, 0.032, 0.027 and 0.030/h respectively, which did not differ significantly from each other. 3. RNA, 35S and diaminopimelic acid (DAP) were used as microbial markers. Efficiencies of microbial-N (MN) synthesis, expressed as g MN/kg apparently digestible organic matter, truly digestible organic matter or carbohydrate fermented, were generally not significantly affected by the diet and averaged 29, 22 and 29 respectively based on mean RNA and 35S markers. Corresponding values derived from DAP of 22, 16 and 21 g MN/kg respectively were all significantly (P less than 0.001) lower. Using 35S as microbial marker, MN flows at the abomasum as a proportion of non-ammonia-nitrogen flow were 0.78, 0.64, 0.51 and 0.78 for diets U, SCP, MGM and RSM respectively. Derived true rumen degradability values (g/g intake) of the total dietary N were 0.91, 0.79, 0.69 and 0.90 for diets U, SCP, MGM and RSM respectively. Protein supplement degradabilities for single-cell protein, maize-gluten meal and rapeseed meal were 0.73, 0.51 and 0.98 respectively. 4. Mouth-to-abomasum digestibility coefficients of the main neutral-sugar components of dietary polysaccharides were 0.68, 0.63 and 0.61 for arabinose, xylose and cellulose-glucose on diet U.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of frequency of feeding on some quantitative aspects of digestion in the rumens of growing steers.

Three steers with simple rumen and abomasal cannulas were given ground and pelleted diets containing predominantly dried grass meal (DG) or rolled barley (RB). Diets were given at frequencies of two or eight feeds/d in a simple changeover design. Chromic oxide and polyethylene glycol were given as flow markers and flows (g/24 h) of organic matter (OM), nitrogenous and carbohydrate compounds were calculated. Ribonucleic acid and 35S were used as microbial markers and diaminopimelic acid (DAP) as a bacterial marker. Frequency of feeding had no significant effect on mean rumen pH, ammonia levels or liquid outflow rates with either diet. Rumen volume was decreased and abomasal digesta flow increased on Diet DG with more feeds but these parameters were unaffected with Diet RB. Increased feeding frequency with both feeds resulted in increased numbers of protozoa. There were no significant effects of feeding frequency of Diet DG on the abomasal flows of any of the nitrogenous constituents measured. However, there was a significant increase in microbial-N flow from 33 to 43 g/d with more frequent feeding of diet RB which was not reflected in bacterial-N flow as measured by DAP. The apparent digestion of OM in the rumen, expressed as g/g intake with diet DG was 0.41 and 0.31 for two feeds and eight feeds/d respectively. Corresponding values for diet RB were 0.56 and 0.63 respectively. The reduction in OM digestion with frequent feeding of diet DG was reflected in similarly reduced rumen digestibilities of all dietary carbohydrate components whereas the increase in OM digestion with diet RB was reflected only by the component sugars of the dietary fibre. The efficiencies of microbial protein synthesis (expressed as gMN/kg ADOM) increased from 36 to 46 when the feeding frequency of diet DG was increased from two to eight times/d. No significant effect of frequency of feeding was found for diet RB. Mouth to abomasum degradation of feed-N (expressed as g/g intake) of 0.64 was unaffected by the number of feeds of diet DG but was significantly increased from 0.55 to 0.82 when eight rather than two feeds/d of diet RB were given.

Evaluation of detergent extraction procedures for characterising carbohydrate components in ruminant feeds and digesta

AbstractSteers fitted with simple rumen and abomasal cannulas were given isoenergetic diets of approximately equal amounts of untreated (UT) barley straw and concentrates (flaked maize + tapioca) alone (BS) or with urea (BSU) or fishmeal (BSF). Similar diets were also given in which the barley straw had been treated (AT) with NaOH (BSA, BSAU and BSAF respectively). The diets were given in a 6 × 6 Latin square design. Feed components and abomasal digesta samples were analysed for neutral (NDF) and acid (ADF) detergent fibres and for monosaccharide constituents of structural polysaccharides. Hemicellulose contents were estimated as the sum of xylose + arabinose (X + A) and by the difference between ash‐free NDF and ash‐free ADF (NDF‐ADF). Cellulose was estimated as β‐linked glucose (C) and by the difference between ash‐free ADF and lignin (ADF–L).103 Ruthenium and PEG were given as flow markers and flows (g24h−1) at the abomasum of carbohydrate components estimated in these ways were calculated. Approximately 98% (by wt.) of the cellulose (C) found in original feed and digesta samples was recovered in both NDF and ADF. Recoveries of hemicellulose (X + A) in NDF from UT straw, AT straw and abomasal digesta were approximately 92, 48 and 50%, respectively. The ADF fraction of feeds and digesta contained 3–6 and 10–17% of the nitrogen and xylose, respectively, present in the original samples. Mouth to abomasum digestibilities of hemicellulose (NDF– ADF) for diets BS, BSU, BSF, BSA, BSAU and BSAF were 39, 62, 67, 29, 61 and 76%, respectively. Corresponding values for cellulose (ADF–L) were 37, 34, 50, 45, 48, and 63%, respectively. The use of NDF–ADF and ADF–L as measures of hemicellulose and cellulose contents, respectively, of feeds and digesta, and the digestibility of these carbohydrate fractions between mouth and abomasum of steers are discussed.

The efficiency of microbial protein synthesis in the rumen and the degradability of feed nitrogen between the mouth and abomasum in steers given different diets.

Protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with barley straw (BS) or alkali-treated barley straw (BSA). Other diets were supplemented with urea (BSU and BSAU respectively) or with fish meal replacing the tapioca (BSF and BSAF respectively). The diets were isoenergetic and calculated to provide sufficient metabolizable energy (ME) to support a growth rate of 0.5 kg/d. Rumen-degradable nitrogen (RDN):ME values (g/MJ) were estimated to be 0.50, 1.20 and 0.80 for the basal diet, urea- and fish-meal-supplemented diets respectively. RNA and alpha,epsilon-diaminopimelic acid (DAP) were used as microbial markers. 103Ruthenium and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Samples of mixed bacteria separated from rumen digesta from animals receiving N-supplemented diets contained significantly more N than those from animals receiving basal diets (approximately 74 and 62 mg/g dry matter (DM) respectively) but there were no other significant differences in total-N contents between treatments. RNA-N:total-N values were similar for all diets (approximately 0.13). DAP-N:total-N values were significantly lower in bacteria from animals receiving alkali-treated (AT) rather than untreated (UT) straw (approximately 0.008 and 0.011 respectively). The proportion of OM intake digested in the rumen (ADOM) was significantly higher for animals receiving AT straw rather than UT straw (approximately 0.54 and 0.43 respectively). N supplementation had no effect on OM digestibility.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the chemical composition of mixed bacteria harvested from the liquid and solid fractions of rumen digesta

Steers, equipped with simple rumen cannulas, were given diets of approximately equal parts of rolled barley and straw supplemented with urea. The diets provided sufficient estimated rumen degradable nitrogen (RDN; RDN:metabolizable energy values of 1:3) to maintain maximum microbial synthesis. In some experiments Na235SO4 was introduced into the rumen to label microbial protein. Rumen digesta samples were taken before feeding and mixed rumen bacteria were separated from the solid (solid-associated bacteria; SAB) and liquid (liquid-associated bacteria; LAB) fractions of digesta. The most effective method of removing SAB from the fibre was a combination of homogenizing and pummelling. This process did not affect the physical form or chemical composition of the bacteria. Samples of SAB contained significantly (P less than or equal to at least 0.05) less ash, total N, RNA and diaminopimelic acid (DAP) and significantly (P less than or equal to 0.01) more lipid than samples of LAB. Concentrations (g/kg dry matter) of ash, total N, RNA, DAP and lipid in SAB were approximately 87, 70, 35, 2.2 and 245 respectively. Corresponding values for LAB were 157, 80, 50, 3.8 and 124 respectively. RNA-N:total N and DAP-N:total N values in SAB were significantly lower than those in LAB (P less than or equal to 0.05 and 0.02 respectively). 35S:total N values were similar in both groups of bacteria. The importance of differences in constituent:total N values in the two groups of bacteria in relation to their use as indices of microbial protein synthesis is discussed.

Factors influencing the digestion of dietary carbohydrates between the mouth and abomasum of steers.

Six protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with either barley straw (BS) or alkali-treated barley straw (BSA). Other diets used were supplemented with urea (BSU and BSAU respectively) or contained fish meal in place of tapioca BSF and BSAF respectively). The diets were given in a 6 X 6 Latin square design. Diets were isoenergetic and provided sufficient metabolizable energy (ME) to support a growth rate of approximately 0.5 kg/d. Basal diets, urea- and fish-meal-supplemented diets had estimated rumen-degradable nitrogen (RDN):ME values (g/MJ) of 0.5, 1.2 and 0.8 respectively. 103Ruthenium and polyethylene glycol were given as flow markers, and flows (g/24 h) at the abomasum of organic matter (OM) and carbohydrate components were calculated. True digestibility coefficients of OM between mouth and abomasum were significantly greater for diets containing alkali-treated straw (approximately 0.63) than for those containing untreated straw (approximately 0.55) but were not significantly affected by N supplementation. Digestibility coefficients of the neutral-sugar components of dietary polysaccharides between mouth and abomasum were 0.28, 0.34, 0.31, 0.23, 0.31 and 0.87 for mannose, galactose arabinose, xylose, cellulose-glucose and starch-glucose respectively for diet BS. Corresponding values were 0.37, 0.42, 0.56, 0.51, 0.40 and 0.88 for diet BSA. All but the mannose and starch-glucose values were significantly greater for the latter diet. N supplementation also led to increases in digestibility of all neutral sugars except mannose and starch-glucose. Fish meal produced a markedly greater effect than urea but only significantly so for cellulose-glucose. Thus, the highest digestibilities were seen for diet BSAF and were 0.68, 0.67, 0.74 and 0.64 for galactose, arabinose, xylose and cellulose-glucose respectively. Of all these sugars xylose consistently showed the greatest response in digestibility to sodium hydroxide treatment or N supplementation.

Effects of level of dietary intake and physical form of protein supplement on the digestibilities of different dietary carbohydrates between mouth and abomasum of young steers.

Steers fitted with simple rumen and abomasal cannulas were given isoenergetic diets of rolled barley and chopped straw, pelleted together with some tapioca alone (B) or with some tapioca replaced by coarse soyabean meal (M) or finely ground soyabean flour (F). The diets were given at two levels to support 0.5 (L) and 1.0 (H) kg/d live weight gain. Chromic oxide and PEG were given as digesta flow markers. Mouth to abomasum digestibilities of different dietary sugars at the low level of intake (LB) were 0.65, 0.68, 0.59, 0.56 and 0.94 for arabinose, galactose, xylose, cellulose-glucose and starch-glucose respectively. Corresponding values at the higher level of intake (HB) were 0.55, 0.66, 0.55, 0.44 and 0.93 respectively. Supplementation with either soya bean meal or flour had no significant effects on the mouth to abomasum of dietary carbohydrate digestibilities at either level of feeding.

Estimation of flows of organic matter and nitrogen components in postruminal digesta and effects of level of dietary intake and physical form of protein supplement on such estimates.

1. Steers fitted with simple rumen, abomasal and sometimes duodenal cannulas were given isonitrogenous and isoenergetic diets consisting of pellets containing equal amounts of rolled barley and chopped straw together with tapioca alone (B), or with some tapioca replaced by coarse soya-bean meal (M) or finely ground soya-bean flour (F). Diet B had an estimated rumen degradable nitrogen (RDN): metabolizable energy (ME) value of approximately 0·8 g/MJ. The corresponding value for each of the supplemented diets was 1·3–1·4. Diets were given at two levels of intake designed respectively to provide ME intakes to support weight gains of 0·5 kg/d (L) and 1·0 kg/d (H). Chromic oxide and polyethylene glycol were given as indigestible markers. Values were calculated for flows (g/24 h) at the abomasum of organic matter (OM), non-ammonia-N (NAN) and microbial (bacterial)-N (MN). Estimates of MN were based on RNA and α-ε;-diaminopimelic acid (DAP) measurements. The steers had low rumen protozoal counts throughout the whole experiment with fewer than 8000 ciliate protozoa/ml of rumen fluid.2. Proportions of OM apparently digested between the mouth and abomasum were significantly lower for H than for L intakes but showed no other significant differences. Mean estimated efficiency of microbial protein synthesis was approximately 17 g N/kg OM apparently digested in the rumen for the LB diet, but was significantly greater at approximately 26 g N/kg OM apparently digested for the HB diet. The protein-supplemented diets gave values of 31–32 which were significantly greater than the value for the LB but not the HB diet.3. Amounts of feed nitrogenous constituents surviving between the mouth and the abomasum were estimated from NAN minus MN corrected for endogenous N. Values for the proportions of feed N degraded, derived from these estimates, were 0·71, 0·66, 0·72, 0·69, 0·67 and 0·70 for diets LB, HB, LM, HM, LF and HF respectively. There were no significant differences due to level of feeding, supplementary protein or the physical form of that protein.4. Estimates of MN flows at the abomasum based on RNA determinations in fresh samples did not differ significantly from estimates based on DAP determinations. However, storage of aqueous suspensions of mixed rumen bacteria by deep-freezing or freeze-drying resulted in significant losses of RNA. No such losses were observed for abomasal digesta. This meant that if samples were stored by these means before analysis, the use of RNA as a microbial marker was vitiated.5. In some experiments digesta samples were taken from the duodenum as well as the abomasum. Estimates of total N flows did not differ significantly between these sites.

Effect of different levels of casein, with or without formaldehyde treatment, on carbohydrate metabolism between mouth and duodenum of steers.

AbstractSteers, fitted with simple rumen and duodenal cannulas, were given a basal diet of approximately equal parts of straw and flaked maize [containing 12 g N kg−1 dry matter (DM)] or similar diets in which part of the flaked maize was replaced by different amounts of untreated (UT) casein or formaldehyde‐treated (FT) casein to give low (L), medium (M) or high (H) intakes of nitrogen (19, 26 and 34 g N kg−1 DM, respectively). Rumen bacteria, separated from samples of rumen digesta taken about 4 h after giving a feed of the basal diet, contained approximately 160 g α‐dextran‐glucose (‘starch’) and 300 g crude protein (CP) kg−1 DM. Bacteria from steers receiving the highest level of FT or UT, contained approximately 140 and 70 g ‘starch’ and 320 and 580 g CP kg−1 DM, respectively. It was calculated that bacteria contributed approximately 65, 50 and 30 g ‘starch’ day−1 at the duodenum of steers receiving basal, FT casein and UT casein diets, respectively. Of the total carbohydrates entering the small intestine, all the rhamnose and ribose and approximately 50–65% of the mannose, galactose and ‘starch’ were contributed by the bacteria, the remainder being dietary in origin. Virtually all the xylose, arabinose and cellulose‐glucose were contributed by surviving dietary materials. For steers receiving the basal ration, mean coefficients of digestibility between mouth and duodenum (corrected for bacterial contribution) were 0.91, 0.97, 0.79, 0.43, 0.22 and 0.41 for mannose, starch‐glucose, galactose, arabinose, xylose and cellulose‐glucose, respectively. Coefficients of digestibility for diets supplemented with FT caseins were not appreciably different from those obtained with basal diets, but for diets supplemented with UT caseins those of arabinose, xylose and cellulose‐glucose were significantly increased to 0.66, 0.55 and 0.56, respectively.

Effect of dietary nitrogen source on carbohydrate metabolism in the rumen of the young steer

1. Steers, fitted with simple rumen and duodenal cannulas, were given diets of approximately equal parts of flaked maize and hay (A) (containing 16 g nitrogen/kg dry matter (DM) or diets of flaked maize and straw supplemented with decorticated groundnut meal (B), fish meal (C), or heated (D) or unheated (E) soya-bean meal (containing 24 g N/kg DM). Chromic oxide was given as a marker with the feeds, and flows of different combined sugars at the duodenum estimated from the values for sugars:marker at this site. Contributions of bacterial constituents to these flows were estimated from amounts of RNA present. 2. Rumen bacteria from steers receiving diet A contained approximately 110 g alpha-dextran-glucose/kg DM and contributed about 60 g alpha-dextran-glucose/d at the duodenum; bacteria from steers receiving diets B, C, D or E contained 25-40 g alpha-dextran-glucose/kg DM and contributed about 20-30 g alpha-dextran-glucose/d at the duodenum. There were no significant differences between different N supplements. About half the alpha-dextran-glucose, varying amounts of the mannose and galactose, and nearly all the rhamnose and ribose in duodenal digesta were contributed by the bacteria. Almost all the arabinose, xylose and cellulose-glucose was of dietary origin. 3. For steers receiving diet A, mean coefficients of digestibility between mouth and duodenum, corrected where necessary for bacterial contribution, were 0-96, 0-73, 0-58, 0-22 and 0-53 for starch-glucose, galactose, arabinose, xylose and cellulose-glucose respectively. Corresponding mean values when diets B, C, D and E were given, which did not differ significantly amongst themselves, were 0-98, 0-79, 0-81, 0-59 and 0-58. Most values for galactose, arabinose and xylose were significantly higher than the diet A values.