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

A pilot investigation on the effect of induced saliva flow on digestive parameters in sheep, and a comparison with cattle

Sheep with a relatively low methane yield were observed to have shorter fluid and particle mean retention times (MRT). Because the application of pilocarpine, a saliva stimulant, was successful in reducing retention times in ruminants in previous studies, we applied this substance to sheep, expecting a reduction in MRT and methane yield. Three non-pregnant sheep (74 ± 10 kg) were fed a hay-only diet in a 3 × 3 Latin square design with oral doses of 0, 2.5 and 5 mg pilocarpine/kg body weight and day. Measurements included feed and water intake, MRT of liquid and particulate phases in the reticulorumen (RR) and total gastrointestinal tract (GIT), ruminal microbial yield (via urinary purine bases and metabolic faecal nitrogen), total tract methane emission, apparent nutrient digestibility and rumen fluid parameters. Data were investigated for linear and quadratic effects using orthogonal polynomial contrasts. The MRT of liquid and small particles in the RR and total GIT, and the short-chain fatty acid concentration in rumen fluid, linearly declined with increasing pilocarpine dosage, while no quadratic relationship was detected. Intake of feed DM and water, apparent nutrient digestibility, methane yield and microbial yield were not affected by pilocarpine. When combining the sheep data with that of a similar experiment in cattle, we found that the MRT of the liquid phase was positively associated with estimated NDF digestibility and with methane production per digested NDF, but was not associated with microbial yield or the ratio of acetate to propionate. The ratio between MRT of the particulate and the liquid phase was smaller for sheep than that for cattle, and was not affected by treatment. Differences in this ratio might explain why species reacted differently to the saliva-inducing agent, which might help to explain the discrepancy between species in the effect of induced saliva flow on digestive parameters.

Diet Supplementation With Sulfur Amino Acids Modulated Fermentation Metabolome and Gut Microbiome in Goats

Dietary amino acids shift hydrogen metabolism to an alternative hydrogen sink consisting of dissolved hydrogen sulfur (dH2S) rather than methanogenesis; and influences the fermentation metabolome and microbiome associated with particles and liquid fractions in gut regions (foregut, small intestine, and hindgut) of goats. A completely randomized block design with a total of 20 goats (5 goats per treatment) was used to conduct the trial. The goats were fed on a diet that consisted of a concentrated mixture with maize stover roughage (50:50, on a dry matter basis) and randomly assigned to one of the four treatments: without amino acid supplementation (a basal diet), a basal diet supplemented with methionine (Met), a basal diet supplemented with lysine (Lys), and a basal diet supplemented with methionine and lysine (ML). Goats fed Met alone or in combination had less acetate, acetate to propionate ratio, and greater propionate (p < 0.05) in the foregut and hindgut than those fed control or Lys. Nonetheless, the goats fed on the amino acid supplements had higher levels of branched-chain VFA (p < 0.05) in the foregut and hindgut than the control goats. Goats fed on ML had the highest ammonia (p < 0.01), followed by Met or Lys, both in the foregut and hindgut, compared with the control. Those fed on Met alone or in combination, had lower dH2, dCH4 (p < 0.01), and higher dH2S (p < 0.01) in the foregut and hindgut than the control or Lys. The goats that were fed on Met alone or in combination, had higher 16S rRNA gene copies of total bacteria, methanogens, and 18S rRNA gene copies of protozoa, fungi, and fiber-utilizing bacterial species (p < 0.01) associated with particles vs. liquid, both in the foregut and hindgut than the control goats. This study gives insights into the use of sulfur-containing amino acids, as an alternative dietary mitigation strategy of methanogenesis in ruminants and highlights the need for further research in this direction.

Comparison of pH and bacterial communities in the rumen and reticulum during fattening of Japanese Black beef cattle

We used castrated and fistulated Japanese Black beef cattle (n = 9) to measure the pH and bacterial communities in the rumen liquid, rumen solid, and reticulum liquid during early, middle, and late fattening stages (10-14, 15-22, and 23-30 months of age, respectively). The pH was measured in the rumen and reticulum during the last 13 days of each fattening stage and was significantly lower in the rumen at the early and middle fattening stage and in the reticulum during the late stage. Sequencing analysis indicated similar bacterial compositions in the rumen and reticulum liquid fractions and stability of bacterial diversity in the rumen and reticulum liquid fractions and rumen solid fraction. By contrast, major operational taxonomic units (OTUs), such as Ruminococcus bromii strain ATCC 27255 (OTU1, OTU10, and OTU15), were differently correlated to the fermentation parameters among the rumen and reticulum liquid fractions. Therefore, the long-term feeding of Japanese Black beef cattle with a high-concentrate diet might reverse the trend of pH in the rumen and reticulum during the late fattening stage, and the bacterial communities adapted to changes in fermentation by preserving their diversity throughout fattening.

Ruminal use of undegraded-feed soluble protein and accuracy of the estimations of the nutrient content in ruminal bacteria

BACKGROUND

The possible escape from the rumen of undegraded-feed soluble proteins (SP) was investigated using nitrogen-15 (¹⁵ N) infusions (25 mg) in three rumen and duodenum cannulated wethers. Animals were fed three isoproteic diets differing in SP content and including protein concentrates either untreated (control) or treated with solutions of either malic acid (MHT) or orthophosphoric acid (OHT) and heat.

RESULTS

Compared with control, MHT and OHT diets reduced ruminal concentrations of ammonia-nitrogen (NH₃ -N) by 35.9% (P = 0.007), non-ammonia nitrogen (NAN) by 36.8% (P = 0.007), and SP-nitrogen (SP-N) by 45.2% (P = 0.072) over the post-feeding period. Both NAN and SP-N were lower (P ≤ 0.040) for OHT than for MHT diet. The ¹⁵ N enrichment of NAN and SP-N did not vary either among diets or with time, and both values were closely related (R² = 0.965; P < 0.001). Estimations, either using solid-associated bacteria (SAB) or liquid-associated bacteria (LAB) as a reference, indicated that 0.983 and 0.894 of SP-N (values averaged across diets) was of microbial origin, respectively, which would indicate a practically negligible ruminal escape of feed SP-N. Values of ¹⁵ N-enrichment in SAB and LAB fitted well to previously published SAB-LAB relationships, indicating a 22% underevaluation of the N supply from SAB when only LAB is used as a reference.

CONCLUSION

Both the negligible ruminal escape of feed SP and the underevaluation of the bacterial nutrient supply as a consequence of the use of LAB as the only bacterial reference should be considered to improve ruminant protein feeding systems. © 2019 Society of Chemical Industry.

Comparison of automated ribosomal intergenic spacer analysis (ARISA) and denaturing gradient gel electrophoresis (DGGE) techniques for analysing the influence of diet on ruminal bacterial diversity

The objective of this study was to compare the automated ribosomal intergenic spacer analysis (ARISA) and the denaturing gradient gel electrophoresis (DGGE) techniques for analysing the effects of diet on diversity in bacterial pellets isolated from the liquid (liquid-associated bacteria (LAB)) and solid (solid-associated bacteria (SAB)) phase of the rumen. The four experimental diets contained forage to concentrate ratios of 70:30 or 30:70 and had either alfalfa hay or grass hay as forage. Four rumen-fistulated animals (two sheep and two goats) received the diets in a Latin square design. Bacterial pellets (LAB and SAB) were isolated at 2 h post-feeding for DNA extraction and analysed by ARISA and DGGE. The number of peaks in individual samples ranged from 48 to 99 for LAB and from 41 to 95 for SAB with ARISA, and values of DGGE-bands ranged from 27 to 50 for LAB and from 18 to 45 for SAB. The LAB samples from high concentrate-fed animals tended (p < 0.10) to show greater peak numbers and Shannon index values than those isolated from high forage-fed animals with ARISA, but no differences were identified with DGGE. The SAB samples from high concentrate-fed animals had lower (p < 0.05) peak numbers and Shannon index values than those from animals fed high-forage diets with ARISA, but only a trend was noticed for these parameters with DGGE (p < 0.10). The ARISA detected that animals fed alfalfa hay diets showed lower (p < 0.05) SAB diversity than those fed grass hay diets, but no differences were observed with DGGE. No effect of forage type on LAB diversity was detected by any technique. In this study, ARISA detected some changes in ruminal bacterial communities that were not detected by DGGE, and therefore ARISA was considered more appropriate for assessing bacterial diversity of ruminal bacterial pellets. The results highlight the impact of the fingerprinting technique used to draw conclusions on dietary factors affecting bacterial diversity in ruminal bacterial pellets.

The fatty acid composition of solid- and liquid-associated rumen bacteria isolated from cows

The distinctive (phospholipid or total) fatty acid profiles of the major classes of micro-organism have been used in microbial taxonomy as well as to act as microbial markers in soils. Our studies seek to identify the potential of this approach in rumen studies. One of the main distinctions is between solid- and liquid-associated bacteria (SAB and LAB) in the rumen, though it is not clear what relative contributions these make to microbial yield from the rumen. The objective of this work was to determine whether SAB and LAB have distinctive fatty acid profiles and if differences are affected by dietary fat supplementation.

The relationship between odd- and branched-chain fatty acids and microbial nucleic acid bases in rumen

Objective

This study aims to identify the relationship between odd- and branched-chain fatty acids (OBCFAs) and microbial nucleic acid bases in the rumen, and to establish a model to accurately predict microbial protein flow by using OBCFA.

Methods

To develop the regression equations, data on the rumen contents of individual cows were obtained from 2 feeding experiments. In the first experiment, 3 rumen-fistulated dry dairy cows arranged in a 3×3 Latin square were fed diets of differing forage to concentration ratios (F:C). The second experiment consisted of 9 lactating Holstein dairy cows of similar body weights at the same stage of pregnancy. For each lactation stage, 3 cows with similar milk production were selected. The rumen contents were sampled at 4 time points of every two hours after morning feeding 6 h, and then to analyse the concentrations of OBCFA and microbial nucleic acid bases in the rumen samples.

Results

The ruminal bacteria nucleic acid bases were significantly influenced by feeding diets of differing forge to concentration ratios and lactation stages of dairy cows (p<0.05). The concentrations of OBCFAs, especially odd-chain fatty acids and C15:0 isomers, strongly correlated with the microbial nucleic acid bases in the rumen (p<0.05). The equations of ruminal microbial nucleic acid bases established by ruminal OBCFAs contents showed a good predictive capacity, as indicated by reasonably low standard errors and high R-squared values.

Conclusion

This finding suggests that the rumen OBCFA composition could be used as an internal marker of rumen microbial matter.

β-Glucans and Resistant Starch Alter the Fermentation of Recalcitrant Fibers in Growing Pigs

Interactions among dietary ingredients are often assumed non-existent when evaluating the nutritive value and health effects of dietary fiber. Specific fibers can distinctly affect digestive processes; therefore, digestibility and fermentability of the complete diet may depend on fiber types present. This study aimed to evaluate the effects of readily fermentable fibers (β-glucans and resistant starch) on the degradation of feed ingredients containing more persistent, recalcitrant, fibers. Six semi-synthetic diets with recalcitrant fibers from rapeseed meal (pectic polysaccharides, xyloglucans, and cellulose) or corn distillers dried grain with solubles (DDGS; (glucurono)arabinoxylans and cellulose) with or without inclusion of β-glucans (6%) or retrograded tapioca (40%) substituted for corn starch were formulated. Six ileal-cannulated pigs (BW 28±1.4 kg) were assigned to the diets according to a 6×6 Latin square. β-glucan-extract increased apparent total tract digestibility (ATTD) of non-glucosyl polysaccharides (accounting for ~40% of the fiber-fraction) from rapeseed meal (6%-units, P<0.001), but did not affect non-glucosyl polysaccharides from DDGS. Retrograded tapioca reduced ATTD of non-glucosyl polysaccharides from rapeseed meal and DDGS (>10%-units, P<0.001), indicating that the large amount of resistant starch entering the hindgut was preferentially degraded over recalcitrant fibers from rapeseed meal and DDGS, possibly related to reduced hindgut-retention time following the increased intestinal bulk. Fermentation of fiber sources was not only dependent on fiber characteristics, but also on the presence of other fibers in the diet. Hence, interactions in the gastrointestinal tract among fibrous feed ingredients should be considered when evaluating their nutritive value.

Microbial contribution to duodenal purine flow in fattening cattle given concentrate diets, estimated by purine N labelling (15N) of different microbial fractions

The origin of duodenal purine bases (PB) was studied in a digestion experiment with four heifers, cannulated in the rumen and duodenum, which received a basal concentrate (152 g crude protein (CP) per kg dry matter (DM)) together with barley straw (85: 15 fresh weight basis) or the same concentrate supplemented with soya-bean meal, carbohydrate-treated soya-bean meal, maize gluten meal or fish meal to increase its protein content to 192 g/kg DM. Tr eatments were assigned to the four animals in five experimental periods according to an incomplete Latin-square design. Each 30-day period included 20 days of change-over adaptation and 10 days of experimental measurements. The flow of digesta entering the duodenum was estimated using Yb and acid-detergent insoluble ash as indigestible markers according to a double-marker system and microbial nitrogen (N) and PB were labelled with15N infused into the rumen. The proportion of duodenal PB of microbial origin estimated from15N enrichment of PB-N averaged 0·66 (s.e. 0·029) and did not differ between treatments nor when protozoa or bacteria associated with liquid (LAB) and solid (SAB) fractions were used as a reference sample. On average microbial contribution to duodenal non-ammonia N was higher when estimated from the PB/N ratio than from15N (0·67 v. 0·55 (s.e. 0·015)) although differences were small and not significant when LAB was the reference sample (0·58 v. 0·52 (s.e. 0·018)) reflecting the higher PB/N ratio of this fraction compared with SAB and protozoa (2·04 v. 1·65 and 1·60 (s.e. 0·04) mmol/g). Considering only the duodenal PB of microbial origin resulted in estimates of microbial N synthesis from the PB/N ratio of SAB similar to those derived from15N enrichment of both bacterial fractions (12·9 v. 13·5 and 13·3 (s.e. 0·83) g/kg of organic matter apparently digested in the rumen OMADR)) but underestimated the values derived from LAB (9·9 g/kg OMADR). Regardless of the estimation method, neither the duodenal flow of microbial N nor the efficiency of microbial synthesis differed between treatments. These results suggest that a significant proportion of duodenal PB have a non-microbial origin which may lead to overestimation of microbial yield when PB are used as a marker. Differences in PB/N ratio between microbial fractions is another important factor to be considered.

Comparison of microbial markers (15N and purine bases) and bacterial isolates for the estimation of rumen microbial protein synthesis

The first objective of this experiment was to investigate the effect of using different bacterial isolates on the estimation of microbial protein production in semi-continuous fermenters (RUSITEC) given four diets, and to test whether a ‘mixed’ bacterial pellet was representative of the whole bacterial population in the fermenters. A second objective was to compare two different microbial markers (nitrogen-fifteen (15N) and purine bases (PB)). Diets consisted of neutral-detergent fibre from grass hay (10 g/day) and sugar-beet pulp (2 g/day) and 280 mg/day of one of four N forms (isolated soya-bean protein, soya-bean peptides, amino acids blended to profile soya-bean protein and NH4Cl). Two 14-day incubation runs were carried out and in each run each of the four different diets were given to two vessels. On days 12 and 13, total digesta (effluent plus nylon bags residues) was collected for analyses of non-ammonia N,15N enrichment and PB concentration, and for isolation of total mixed bacterial pellets (TB). On the last day of each incubation run, the system was stopped for isolation of liquid- (LAB) and solid-associated (SAB) bacteria. Microbial N flow was estimated from the15N enrichment and PB concentration in both total digesta and in the three different bacterial pellets (TB, LAB, and SAB). For all diets, LAB presented a greater (P < 005)15N enrichment and PB: N ratio than SAB, with TB having an intermediate value. For both markers, the use of LAB produced the lowest (P < 005) estimates of microbial N flow and the use of SAB produced the greatest (P < 005) estimates. The use of TB produced intermediate values with all diets, suggesting that TB consisted of SAB and LAB. For all bacterial pellets, PB produced greater (P 005) values of microbial N flow than15N. However, there was a positive relationship (r = 0·883; P 0001; no. = 15) between the values of microbial N flow determined with the two markers when TB were used as reference.

The effect of clover silages on long chain fatty acid rumen transformations and digestion in beef steers

Ten Hereford ✕ Friesian steers prepared with rumen, duodenal and ileal cannulae were offered ad libitum access to either grass (G), white clover (W) or red clover (R) silage or mixtures of the grass silage with the clover silages (GW and GR; 60: 40 dry matter (DM) basis). The experiment was conducted as a two-period change-over design within each clover treatment, with grass silage as an experimental control. The clover silages had higher concentrations of DM, nitrogen (N), and total fatty acids and lower concentrations of fibre (P < 0·05) than the grass silage. Rumen fermentation characteristics were similar between treatments apart from a slight elevation of n-butyric acid levels with white clover silage diets (P < 0·05). Duodenal flows of DM, organic matter (OM), total and microbial nitrogen (MN) were significantly higher (P < 0·05) with the white clover silage treatments compared with the grass silage diet. However there were no significant differences in the efficiency of microbial protein synthesis with a mean value of 27·1 g MN per kg OM apparently digested in the rumen. Duodenal flows of total fatty acids per unit intake were not significantly different, although there was a trend (P < 0·1) for increased flows with the white clover silage diets. Duodenal flows of cis-vaccenic acid (P < 0·01), linoleic acid (P < 0·05), α-linolenic acid (P < 0·05) and cis-9 trans-11 conjugated linoleic acid (CLA) (P < 0·05) were higher for the clover silages, particularly white clover silage. The increased flows of α-linolenic and linoleic acids remained significant after correcting for differences in DM intake. Biohydrogenation of linoleic (mean = 0·83) and α-linolenic (mean = 0·86) acids was extensive for all diets but the latter was significantly lower (P < 0·01) for the diets based on red clover silage. These results suggest potential for modifying the fatty acid composition of ruminant products by feeding clover silages.

Effects of Saccharomyces cerevisiae fermentation products on dairy calves: Ruminal fermentation, gastrointestinal morphology, and microbial community

The aim of this study was to evaluate the effects of Saccharomyces cerevisiae fermentation products (SCFP) in the calf starter and milk on ruminal fermentation, gastrointestinal morphology, and microbial community in the first 56 d of life. Thirty Holstein bull calves were randomly assigned to 1 of 3 groups: a texturized calf starter containing 0 (CON), 0.5, or 1% SCFP (XPC, Diamond V, Cedar Rapids, IA) of dry matter from d 4 to 56. In addition, the XPC-supplemented calves were fed with 1 g/d SCFP (SmartCare, Diamond V, Cedar Rapids, IA) in milk from d 2 to 30. All calves were fed 4 L of colostrum within 1 h of birth and were subsequently fed milk twice daily until weaned on d 56. Rumen fluid was collected by an esophageal tube 4 h after the morning feeding on d 28 and 56 to determine ruminal pH, ammonia-N, and volatile fatty acids concentrations. On d 56, 15 (5 per treatment) calves were harvested and slaughter weight, gastrointestinal morphology parameters, and bacteria community were recorded. Papilla length, width, and surface area were measured from 5 locations within the rumen. Villus height, width, surface area, crypt depth, and villus height-to-crypt depth ratio were measured in the duodenum, jejunum, and ileum. Next-generation sequencing technology was used to test the microbial community of the rumen and duodenum samples on d 28 and 56. Data were analyzed by MIXED procedure in SAS (SAS Institute Inc., Cary, NC) with contrast statements to declare CON versus all SCFP and 0.5 versus 1% SCFP in starter grains. Ruminal pH, ammonia-N, and total volatile fatty acids were not altered by SCFP. However, the supplemented groups exhibited higher ruminal butyrate concentrations coinciding with higher Butyrivibrio and lower Prevotella richness than CON group. Supplementation of SCFP increased papilla length in the rumen. In the small intestine, SCFP reduced crypt depth of jejunum, and increased villus height-to-crypt depth ratio in all segments of the small intestine, especially when supplemented at a higher dosage in the starter. In conclusion, Saccharomyces cerevisiae fermentation products improved gastrointestinal morphology, possibly due to increased Butyrivibrio and decreased Prevotella richness of the rumen fluid, which resulted in an increase in butyrate production, and the effect was slightly greater with the higher dosage of SCFP in the starter.

Impact of subacute ruminal acidosis on the diversity of liquid and solid-associated bacteria in the rumen of goats

This study was aimed to investigate the impact of subacute ruminal acidosis (SARA) on the diversity of liquid (LAB) and solid-associated bacteria (SAB) following high-grain feeding. Six ruminally cannulated goats were divided into two groups: one group was fed a hay diet (COD), and the other group was fed a high grain diet (SAID). Rumen liquids and rumen solids were sampled after 2 weeks adaption. SARA was diagnosed with a pH below 5.8 for 8 h. SAID decreased ruminal pH (P < 0.001) and increased the acetate (P = 0.017), propionate (P = 0.001), butyrate (P < 0.001) and total volatile fatty acid (P < 0.001) concentration in rumen compared with the COD. Denaturing gradient gel electrophoresis fingerprints analysis revealed a clear separation between both the diet and the fraction of rumen digesta in bacterial communities. Pyrosequencing analysis showed that the proportion of phylum Bacteroidetes in the SAID-LAB and SAID-SAB communities was less than in the COD group, whereas the SAID group had a greater percentage of Firmicutes in both the LAB and SAB libraries. UniFrac analyses and a Venn diagram revealed a large difference between the two diets in the diversity of rumen bacterial communities. Overall, our findings revealed that SARA feeding did alter the community structure of rumen liquids and rumen solids. Thus, manipulation of dietary factors, such as ratio of forage to concentrate may have the potential to alter the microbial composition of rumen liquid and rumen solid.

Analysis of rumen microbial populations in lactating dairy cattle fed diets varying in carbohydrate profiles and Saccharomyces cerevisiae fermentation product

The rumen microbial ecosystem is a critical factor that links diets to bovine physiology and productivity; however, information about dietary effects on microbial populations has generally been limited to small numbers of samples and qualitative assessment. To assess whether consistent shifts in microbial populations occur in response to common dietary manipulations in dairy cattle, samples of rumen contents were collected from 2 studies for analysis by quantitative real-time PCR (qPCR). In one study, lactating Holstein cows (n=8) were fed diets in which a nonforage fiber source replaced an increasing proportion of forages and concentrates in a 4×4 Latin square design, and samples of ruminal digesta were collected at 9-h intervals over 3 d at the end of each period. In the second study, lactating Holstein cows (n=15) were fed diets with or without the inclusion of a Saccharomyces cerevisiae fermentation product (SCFP) in a crossover design. In this study, rumen liquid and solid samples were collected during total rumen evacuations before and after feeding in a 42-h period. In total, 146 samples of ruminal digesta were used for microbial DNA isolation and analysis by qPCR. Validated primer sets were used to quantify total bacterial and anaerobic fungal populations as well as 12 well-studied bacterial taxa. The relative abundance of the target populations was similar to those previously reported. No significant treatment effects were observed for any target population. A significant interaction of treatment and dry matter intake was observed, however, for the abundance of Eubacterium ruminantium. Increasing dry matter intake was associated with a quadratic decrease in E. ruminantium populations in control animals but with a quadratic increase in E.ruminantium populations in cows fed SCFP. Analysis of sample time effects revealed that Fibrobacter succinogenes and fungal populations were more abundant postfeeding, whereas Ruminococcus albus tended to be more abundant prefeeding. Seven of the target taxa were more abundant in either the liquid or solid fractions of ruminal digesta. By accounting for the total mass of liquid and solid fractions in the rumen and the relative abundance of total bacteria in each fraction, it was estimated that 92% of total bacteria were found in the solid digesta fraction.

Ruminal protozoal contribution to the duodenal flow of fatty acids following feeding of steers on forages differing in chloroplast content

Ruminant products are criticised for their SFA content relative to PUFA, although n-6:n-3 PUFA is desirable for human health ( < 4). Rumen protozoa are rich in unsaturated fatty acids due to engulfment of PUFA-rich chloroplasts. Increasing the chloroplast content of rumen protozoa offers a potentially novel approach to enhance PUFA flow to the duodenum and subsequent incorporation into meat and milk. We evaluated protozoal contribution to duodenal n-3 PUFA flow due to intracellular chloroplast content. A total of six Holstein × Friesian steers were fed, in a two-period changeover design, either straw:concentrate (S:C, 60:40; DM basis; S:C, low chloroplast) or fresh perennial ryegrass (PRG; high chloroplast). Following 12 d adaptation to diet, ruminal protozoal and whole duodenal samples were obtained. N and fatty acid content of whole duodenum and rumen protozoal samples were assessed and protozoal 18S rDNA quantitative PCR performed, enabling calculation of protozoal N flow. The ratio of individual fatty acids:N in rumen protozoal samples was calculated to obtain protozoal fatty acid flows. Based on total fatty acid flow, contribution (%) of protozoa to individual fatty acid flows was calculated. Protozoal fatty acid data and microscopical observations revealed that protozoa were enriched with 18 : 3n-3 following PRG feeding, compared with the S:C diet, due to increased intracellular chloroplast content. However, duodenal protozoal 18S rDNA concentration post PRG feeding was low, indicating rumen retention of the protozoa. Nutrition influences the 18 : 3n-3 content of protozoa; the challenge is to increase protozoal flow to the small intestine, while maintaining sustainable rumen densities.

Comparison of fermentation of diets of variable composition and microbial populations in the rumen of sheep and Rusitec fermenters. II. Protozoa population and diversity of bacterial communities

Four ruminally and duodenally cannulated sheep and 8 Rusitec fermenters were used to determine the effects of dietary characteristics on microbial populations and bacterial diversity. The purpose of the study was to assess how closely fermenters can mimic the differences between diets found in vivo. The 4 experimental diets contained forage to concentrate (F:C) ratios of 70:30 (high forage; HF) or 30:70 (high concentrate; HC) with either alfalfa hay (A) or grass hay (G) as the forage. Total bacterial numbers were greater in the rumen of sheep fed HF diets compared with those fed HC diets, whereas the opposite was found in fermenters. The numbers of cellulolytic bacteria were not affected by F:C ratio in any fermentation system, but cellulolytic numbers were 2.7 and 1.8 times greater in sheep than in fermenters for HF and HC diets, respectively. Neither total bacterial nor cellulolytic numbers were affected by the type of forage in sheep or fermenters. Decreasing F:C ratio increased total protozoa and Entodiniae numbers in sheep by about 29 and 25%, respectively, but it had no effect in fermenters. Isotrichidae and Ophryoscolecinae numbers in sheep were not affected by changing F:C ratio, but both disappeared completely from fermenters fed HC diets. Total protozoa and Entodiniae numbers were greater in sheep fed A diets than in those fed G diets, whereas the opposite was found in fermenters. Results indicate that under the conditions of the present study, protozoa population in Rusitec fermenters was not representative of that in the rumen of sheep fed the same diets. In addition, protozoa numbers in fermenters were 121 and 226 times lower than those in the sheep rumen for HF and HC diets, respectively. The automated ribosomal intergenic spacer analysis of the 16S ribosomal DNA was used to analyze the diversity of liquid- and solid-associated bacteria in both systems. A total of 170 peaks were detected in the automated ribosomal intergenic spacer analysis electropherograms of bacterial pellets across the full set of 64 samples, from which 160 were detected in at least 1 individual from each system (sheep or fermenter). Diversity of liquid-associated bacterial pellets was greater with G diets in fermenters but seemed to be unaffected by diet in sheep. Bacterial diversity in solid-associated bacteria pellets was greater for G diets compared with A diets in sheep and fermenters. Different conditions in the fermenters compared with sheep rumen might have caused a selection of some bacterial strains.

Evaluation of milk allantoin excretion as an index of microbial protein supply in lactating dairy cows

The potential of milk allantoin as an index ofmicrobial protein supply was evaluated in two experiments conducted with 12 multiparous Holstein-Friesian dairy cows that examined the effects of altering the supply of metabolizable energy (ME) and fermentable metabolizable energy (FME). In the first experiment, late lactation cows received a 14·3 kg dry matter (DM) per day basal diet consisting of (g/kg DM) chopped barley straw (415), soya-bean meal (322), molassed sugar-beet pulp (197), molasses (33), urea (17) and a vitamin and mineral supplement (17) for a 21-day co-variance period. During four 16-day periods, six treatments were allocated randomly to cows, consisting of potato starch (1, 2 or 3 kg DM per day) or fat supplements (0·64, 1·27 or 1·91 kg DM per day). In the second experiment, early lactation cows received 40 kg/day (fresh weight, (FW)) of silage (307 g/kg toluene-corrected dry matter, 149 g/kg DM crude protein and 11·6 MJ/kg ME). During three 21-day periods, four treatments were evaluated consisting of supplements of either 4·1 (LI) or 8·1 (12) kg fresh weight per day of a low fat concentrate (acid hydrolysis ether extract (AHEE) 45 g/kg DM) or 3·8 (HI) or 7·5 (H2) kg fresh weight per day of a high fat concentrate (AHEE 110 g/kg DM). Both experiments showed individual cow milk allantoin concentration or excretion to be poorly correlated with urinary purine derivative excretion or calculated microbial protein supply. Use of treatment mean (TM) values dramatically improved these relationships. For pooled TM (no. = 10) values from both experiments, close relationships existed between milk allantoin excretion and concentration with milk yield (r values 0·991 and 0·883, respectively). Auto-correlation with milk yield appeared to account for milk allantoin excretion and concentration being highly correlated with urinary purine derivative excretion (r values 0·908 and 0·934, respectively) and calculated microbial protein supply (r values 0·938 and 0·945, respectively). Current experimental data indicates that measurement of milk allantoin is not a reliable indicator of microbial protein supply for individual cows.

Rumen microbial production estimated either from urinary purine derivative excretion or from direct measurements of 15N and purine bases as microbial markers: effect of protein source and rumen bacteria isolates

Four ewes fitted with ruminal and duodenal T-piece cannulae were each given six diets in a 6 × 4 factorial design. Diets or experimental treatments consisted of two ratios of forage: concentrate (700:150 (LC) and 400: 600 (HO). Forage was ammonia-treated straw and the concentrate was formulated with barley supplemented with one of three protein sources: sunflower meal, soya-bean meal or fish meal. Duodenal flows ofdigesta were estimated by the dual-phase technique using Co-EDTA and Yb acetate as liquid and solid markers. Microbial nitrogen (N) was estimated from the digesta flow of purine bases and 15N enrichment using as reference samples, bacterial isolates from the liquid (LAB) or solid (SAB) phase of rumen digesta.

Duodenal flow of purine bases (mmol/day) was lower on LC (12·9) than HC (17·7) diets but in both treatments it was depressed by fish meal (12·3) compared with either soya-bean (17·3) or sunflower meal (16·3) as supplements (s.e. 1·13). Urinary excretion of purine derivatives showed a similar trend, 8·6 v. III mmol/day in LC and HC respectively and 8·8 v. 10·4 and 10·5 mmol/day in fish meal, soya-bean and sunflower meal diets (s.e. 0·56), respectively. Variation in excretion of urinary purine derivatives was mainly associated with digestible organic matter intake with an average ratio of 1·7 (s.e. 0·11) mmol per 100 g digestible organic matter intake. Irrespective of the microbial marker used, microbial yield was higher in animals offered HC than in those offered LC and with soya-bean or sunflower meal compared with fish meal supplemented diets. The microbial purine bases/N (mmol/g) ratio varied between LAB (1·99, s.e. 0·092) and SAB (1·69, s.e. 0·071) isolates leading to different estimates of microbial-N yield (g) from duodenal purine bases (7·76 (s.e. 2·84) v. 9·13 (s.e. 3·24)), urinary excretion of allantoin (5·57 (s.e. 2·0) v. 6·57 (s.e. 2·03)) or total purine derivatives (6·43 (s.e. 2·39) v. 7·56 (s.e. 2·77)). Urinary excretion of allantoin or total purine derivatives provided consistently lower estimates of duodenal microbial-N than duodenal purine bases or 15N, although it closely reflected the pattern observed in direct measurements.

Evaluation of procedures for detaching particle-associated microbes from forage and concentrate incubated in Rusitec fermenters: efficiency of recovery and representativeness of microbial isolates

Three detachment procedures (DP) were evaluated for their ability to remove particle-associated microbes from digesta in Rusitec fermenters fed a 30:70 alfalfa hay:concentrate diet. Forage and concentrate were incubated in separate nylon bags, and incubation residues were treated independently. Microbial biomass was labeled with (15)NH(4)Cl. Treatments were 1) MET: residues were incubated at 38 degrees C for 15 min with saline solution (0.9% NaCl) containing 0.1% methylcellulose with continuous shaking; 2) STO: residues were mixed with cold saline solution and homogenized with a stomacher for 5 min at 230 revolutions per min; and 3) FRE: residues were immediately frozen at -20 degrees C for 72 h, thawed at 4 degrees C, mixed with saline solution, and subjected to STO procedure. Common to all treatments was storing at 4 degrees C for 24 h after the treatment, homogenization, filtration, and resuspension of residues 2 times in the treatment solutions. Microbial pellets were obtained by centrifugation, and microbial removal was estimated indirectly by measuring removal of (15)N. The PCR-single-stranded conformation polymorphism analysis of the 16S ribosomal DNA was used to analyze the similarity between microbial communities attached to the substrate and those in the pellet obtained after each DP. There were no feed x DP interactions (P = 0.16 to 0.96) for any variable, except for N content in microbial pellets (P = 0.02). Detaching efficiency (P = 0.004) and total recovery (P = 0.01) were affected by DP, with STO showing the greatest values (mean values across substrates of 64.1% for detaching efficiency and 58.3% for total recovery) and MET the least values (57.0 and 51.8%). Similarity index between the microbes attached to substrates and those in the pellets were affected (P = 0.02) by DP, with MET showing greater (P < 0.02) values (84.0 and 86.4% for forage and concentrate, respectively) than FRE (72.5 and 67.8%) and STO having intermediate values (77.1 and 82.4%). There were no differences (P = 0.70) among particle-associated microbe pellets in their N content, but MET pellets had greater (P < 0.05) (15)N enrichments than those obtained by STO and FRE. Although STO was the most effective method to detach ruminal microbes from concentrate and forage, MET produced pellets with the greatest similarity to the microbial communities attached to the substrates and therefore could be considered the most appropriate DP method for treating digesta from Rusitec fermenters.

Effects of Fatty Acid Oxidation Products (Green Odor) on Rumen Bacterial Populations and Lipid Metabolism In Vitro

This study investigated the effects of green odor fatty acid oxidation products (FAOP) from cut grass on lipid metabolism and microbial ecology using in vitro incubations of rumen microorganisms. These compounds have antimicrobial roles in plant defense, and we hypothesized that they may influence rumen lipid metabolism. Further, they may partially explain the higher levels of conjugated linoleic acid cis-9, trans-11 in milk from cows grazing pasture. The first of 2 batch culture experiments screened 6 FAOP (1 hydroperoxide, 3 aldehydes, 1 ketone, and 1 alcohol) for effects on lipid profile, and in particular C(18) polyunsaturated fatty acid biohydrogenation. Experiment 2 used the most potent FAOP to determine effects of varying concentrations and identify relationships with effects on microbial ecology. Batch cultures contained anaerobic buffer, rumen liquor, and FAOP to a final concentration of 100 microM for experiment 1. Triplicates for each compound and controls (water addition) were incubated at 39 degrees C for 6 h. The hydroperoxide (1,2-dimethylethyl hydroperoxide, 1,2-DMEH) and the long chain aldehyde (trans-2 decenal) had the largest effects on lipid metabolism with significant increases in C(18:0) and C(18:1) trans and reductions in C(12:0), C(14:0), C(16:0), C(18:1) cis, C(18:2n-6), C(18:3n-3), C(20:0) and total branch and odd chain fatty acids compared with the control. This was associated with significantly higher biohydrogenation of C(18) polyunsaturated fatty acid. In experiment 2, 1,2-DMEH was incubated at 50, 100, and 200 microM for 2, 6, and 24 h. Increasing 1,2-DMEH concentration resulted in a significant linear increase in C(18:1) trans-10, trans-11, conjugated linoleic acid, and C(18:0) and a linear decrease in C(18:2n-6) and C(18:3n-3), although the scale of this response declined with time. Microbial profiling techniques showed that 1,2-DMEH at concentrations of 100 and 200 microM changed the microbial community from as early as 2 h after addition, though microbial biomass remained similar. These preliminary studies have shown that FAOP can alter fatty acid biohydrogenation in the rumen. This change was associated with changes in the microbial population that were detected through DNA and branched- and odd-chain fatty acid profiling approaches.

Mineral absorption in the black rhinoceros (Diceros bicornis) as compared with the domestic horse

To test whether mineral recommendations for horses are likely to guarantee adequate mineral provision for black rhinoceroses (Diceros bicornis), we investigated the apparent absorption (aA) of macro- and microminerals in eight black rhinoceroses from three zoological institutions in a total of 32 feeding trials with total faecal collection, with additional data from three unpublished studies (18 feeding trials). Feeds and faeces were analysed for Ca, P, Mg, Na, K, Fe, Mn, Cu, Zn and Co. The resulting aA coefficients, and the linear relationships of apparently absorbable dietary mineral content to total dietary mineral content [per 100 g dry matter (DM)], were compared with data for domestic horses. Rhinoceroses had significantly higher aA coefficients for Ca and Mg (because of a higher calculated 'true' absorption), and lower ones for Na and K (because of calculated higher endogenous faecal losses). High absorption efficiency for divalent cations is hypothesized to be an adaptation to a natural diet of particularly high Ca:P ratio (approximately 14:1); an effective removal of Ca from the ingesta guarantees sufficient P availability at the fermentation site in the hindgut. Higher faecal losses of Na and K are hypothesized to be linked to a higher faecal bulk per DM intake in black rhinoceroses as compared with horses because of a generally lower digestive efficiency. There were no relevant differences in the absorption patterns of microminerals. In particular, there were no discernable differences in Fe absorption within the rhinoceroses for diets with and without tannin supplementation. Several of the zoo diets assessed in this study were deficient in Cu, Mn or Zn, and most contained excessive levels of Fe when compared with horse requirements. The findings of this study indicate that differences in mineral absorption between occur even between species of similar digestive anatomy; that in particular, Ca absorption might vary between hindgut fermenters with Ca:P ratio in their natural diet; that Na might be a particularly limiting factor in the ecology of free-ranging rhinoceroses; that moderate doses of tannins do not seem to markedly influence mineral absorption; and that diets for captive animals should contain adequate, but not excessive mineral levels.

Composition of bacteria harvested from the liquid and solid fractions of the rumen of sheep as influenced by feed intake

A study was conducted to determine the effect of the feed intake on the chemical composition of bacteria associated with the solid (solid-associated bacteria; SAB) and liquid (liquid-associated bacteria; LAB) fractions of rumen digesta, the digestive passage kinetics and their relationships. Whole rumen contents were sampled after a period of continuous infusion of 15NH3 from four ruminally-cannulated wethers provided successively with a hay–concentrate diet (2: 1 w/w on a DM basis) at two rates of feed intake: 40 and 80 g DM/kg body weight0·75. SAB had a higher content of organic matter and total lipids (P < 0·001) and a similar N content as compared with LAB. The concentration of purines and 15N was lower (P = 0·011 and P < 0·001 respectively) in SAB than LAB, whereas the opposite was observed for the concentration of amino acids (mg/g DM; P = 0·031). An increase in feed intake produced an increase in the N (P = 0·034) and purine (P = 0·066) concentrations in bacteria and a decrease (P = 0·033) in their amino acid concentrations. Significant increases of rumen outflow rates of liquid and particles were also observed with increased feed intake. Rates of rumen outflow showed positive and negative linear relationships (P < 0·001) with the purine: N ratio and the proportion of amino acid on total N of bacteria respectively. SAB contained significantly higher proportions of leucine, isoleucine, lysine and phenylalanine and lower proportions of alanine, methionine and valine than LAB. The increase in feed intake also induced significant changes in the amino acid profile of bacteria, increasing arginine and methionine and decreasing alanine and glycine proportions. Results show that the outflow rate of rumen contents is a major factor in determining the proportion of nucleic acids and protein in rumen bacteria and explains some of the differences observed between LAB and SAB.

Comparative Evaluation of Alternative Forages to Grass Silage in the Diet of Early Lactation Dairy Cows

Fifty-six autumn-calving Holstein-Friesian cows, blocked on the basis of days in milk (27.6 +/- 10.65 d), lactation number (3.1 +/- 2.21), and preexperimental milk yield (28.4 +/- 6.69 kg) were used to examine the effects of replacing 330 g/kg of dry matter (DM) of first-cut perennial ryegrass silage with either fermented whole-crop wheat (WCW), urea-treated processed WCW, or corn silage on subsequent feed intake, milk production, and efficiency of nitrogen utilization. The DM (g/kg), crude protein (CP, g/kg of DM) and in vitro DM digestibility (g/kg) of the forages were 204, 179, and 762 for grass silage; 389, 90, and 711 for fermented WCW; 795, 141, and 768 for urea-treated processed WCW; and 346, 93, and 783 for corn silage, respectively. Four forage treatments were evaluated as follows: 1) grass silage as the sole forage (GS); 2) a mixture of grass silage and fermented WCW silage, (F-WCW); 3) a mixture of grass silage and urea-treated processed WCW, (UP-WCW); and 4) a mixture of grass silage and corn silage (CS). In all cases, the alternative forages comprised 67% of the forage mix on a DM basis. Isonitrogenous diets were formulated by offering all cows 8 kg of concentrate as fed, formulated to different CP concentrations. Cows were offered these diets from 28 to 104 d in milk. Total DM intake and milk yield were greater on UP-WCW (20.0 and 30.2 kg/d) and CS (18.3 and 33.2 kg/d) than on GS (13.5 and 26.5 kg/d). Although DM intake was greater on F-WCW (17.1 kg/d) than on GS, milk yield was not significantly greater (+2.7 kg/d). Milk protein concentration was greater on F-WCW (30.5 g/kg), UP-WCW (31.3 g/kg), and CS (30.7 g/kg) than on GS (28.5 g/kg). However, there was no difference between treatments in milk fat or lactose concentrations. Body weight change was greater for cows offered GS (-0.27 kg/d) than for those offered UP-WCW (-0.01 kg/d) and CS (+0.05 kg/d) but not compared with those offered F-WCW (-0.06 kg/d). There was no effect of treatment on plasma glucose, nonesterified fatty acids, beta-hydroxybutyrate, urea, or total protein at d 64 +/- 17.4 and d 92 +/- 17.4 postpartum. Efficiency of N utilization was greatest for CS with 0.36 of N intake being recovered in milk compared with 0.28, 0.32, and 0.26 for GS, F-WCW, and UP-WCW, respectively. There was no effect of treatment on milk urea N concentration or the urinary allantoin N to creatinine N ratio. The results of this experiment indicate that corn silage is a more suitable supplementary forage to grass silage than fermented or urea-treated processed WCW, with advantages realized in milk production and more efficient N utilization.

Effects of high-sugar ryegrass silage and mixtures with red clover silage on ruminant digestion. 2. Lipids1

The experiment investigated the digestion of lipids from different forage silages in beef steers. Six Hereford x Friesian steers prepared with rumen and duodenal cannulas were given ad libitum access to a high-sugar grass silage, control grass silage, red clover silage, or mixtures of the red clover and each of the grass silages (50:50, DM basis). The experiment was conducted as an incomplete 5 x 5 Latin square, with an additional randomly repeated sequence. Total fatty acid and C18:3n-3 concentrations were greater (P < 0.05) for the high-sugar grass silage than the control grass silage or the red clover silage. Dry matter and total fatty acid intake were less (P < 0.05) for steers fed the control grass silage than for steers fed the other diets. Duodenal flow of C18:3n-3 was greater (P < 0.05), and flows of C18:0 and total C18:1 trans were less (P < 0.05), for the red clover silage compared with the 2 grass silage diets, with the mixtures intermediate. These results were supported by a reduction (P < 0.05) in biohydrogenation of C18:3n-3 for the red clover silage, with the mixtures again being intermediate. Flows of total branched- and odd-chain fatty acids were greater (P < 0.05) for the high-sugar grass silage diet, possibly as a result of greater microbial flow, because these fatty acids are associated with bacterial lipid. Duodenal flows of the chlorophyll metabolite, phytanic acid, were greater (P < 0.05) for animals fed the high-sugar grass silage treatments compared with the other treatments. These results confirm the potential for modifying the fatty acid composition of ruminant products by feeding red clover silage.

In situ study of the relevance of bacterial adherence to feed particles for the contamination and accuracy of rumen degradability estimates for feeds of vegetable origin

An in situ study was conducted on four rumen-cannulated wethers to determine (using (15)N infusion techniques) the microbial contamination (mg bacterial DM or crude protein (CP)/100 mg DM or CP) and the associated error on the effective degradability of fourteen feeds: barley and maize grains, soyabean and sunflower meals, full-fat soyabean, maize gluten feed, soyabean hulls, brewers dried grains, sugarbeet pulp, wheat bran, lucerne and vetch-oat hays, and barley and lentil straws. The DM or CP contamination in residues (M) fitted to single exponential or sigmoid curves. A general model (M=m (1-e(-ft) ) (j)) was proposed to match this fit. Asymptotic values (m) varied from 2.84% to 13.3% and from 2.85% to 80.9% for DM and CP, respectively. Uncorrected results underestimated the effective degradability of both DM (P<0.05) and CP (P<0.01). For CP, this underestimation varied from 0.59 % to 13.1%, with a higher but unascertainable error for barley straw. Excluding maize grain, the microbial contamination of both DM and CP, and the associated underestimation of the effective degradability of CP, were positively related to the cellulose content of the feed. The error in the effective degradability of CP was also negatively related to the CP content and its apparent effective degradability (R(2) 0.867). This equation allows easier and more accurate estimates of effective degradability, needed to improve protein-rationing systems.

Effect of Forage:Concentrate Ratio on Fatty Acid Composition of Rumen Bacteria Isolated From Ruminal and Duodenal Digesta

Four dairy cows were used to examine the effect of the dietary forage:concentrate ratio [35:65, 50:50, 65:35, and 80:20 on a dry matter (DM) basis] on the fatty acid composition of rumen bacteria isolated from the liquid (LAB) and solid (SAB) phase of the rumen and duodenal digesta. Rumen contents were sampled 4 h after the morning feeding. Solid and liquid phases were separated from rumen contents and duodenal bacteria from a composite duodenal sample by differential centrifugation. Total fatty acid content in bacterial DM was 1.6 to 2.8 times higher in SAB compared with LAB, and increased with dietary concentrate. In combination with published reports, the data show that bacterial fatty acid content and composition is closely related to dietary fatty acids except for C18:2n-6 and C18:3n-3. A decrease in forage:concentrate ratio increased bacterial concentration of trans-10 C18:1, and this increase was 3.4 times higher in LAB compared with SAB. Analysis of odd- and branched-chain fatty acids showed large differences between SAB and LAB, which probably reflected a difference in species composition. The variation in odd- and branched-chain fatty acids between SAB and LAB was used to estimate their relative proportions in duodenal bacteria by means of linear programming, and showed an increased proportion of SAB from 64.7 to 74.8% with increasing forage:concentrate ratio. In addition, increasing the proportion of dietary forage was closely related to the proportion of anteiso C15:0 in total odd- and branched-chain fatty acids (r(pearson) = -0.771). The bacterial concentration of iso C17:0 closely reflected the bacterial growth rate as shown by the relation with cytosine:N (r(pearson) = -0.729). These strong relationships suggest that odd- and branched-chain fatty acids might be used as tool to evaluate nutrient supply to rumen bacteria.