Short Communication: Amino Acids Antagonistic to the Amino Acids Inhibitory for Growth Rate of Mixed Ruminal Bacteria

Supplementing branched-chain volatile fatty acids in dual-flow cultures varying in dietary forage and corn oil concentrations. III: Protein metabolism and incorporation into bacterial protein

Some cellulolytic bacteria cannot transport branched-chain AA (BCAA) and do not express complete synthesis pathways, thus depending on cross-feeding for branched-chain volatile fatty acid (BCVFA) precursors for membrane lipids or for reductive carboxylation to BCAA. Our objective was to assess BCVFA uptake for BCAA synthesis in continuous cultures administered high forage (HF) and low forage (LF) diets without or with corn oil (CO). We hypothesized that BCVFA would be used for BCAA synthesis more in the HF than in LF diets. To help overcome bacterial inhibition by polyunsaturated fatty acids in CO, BCVFA usage for bacterial BCAA synthesis was hypothesized to decrease when CO was added to HF diets. The study was an incomplete block design with 8 dual-flow fermenters used in 4 periods with 8 treatments (n = 4) arranged as a 2 × 2 × 2 factorial. The factors were: HF or LF (67 or 33% forage, 33:67 alfalfa:orchardgrass pellets), without or with supplemental CO (3% of dry matter), and without or with 2.15 mmol/d (5 mg/d 13C) each of isovalerate, isobutyrate, and 2-methylbutyrate for one combined BCVFA treatment. The flow of bacterial BCAA increased by 10.7% by supplementing BCVFA and 9.14% with LF versus HF; similarly, dosing BCVFA versus without BCVFA increased BCAA by 1.98% in total bacterial AA, whereas LF increased BCAA by 1.92% versus HF. Additionally, BCVFA supplementation increased bacterial AA flow by 16.6% when supplemented in HF - CO and 12.4% in LF + CO diets, but not in the HF + CO (-1.5%) or LF - CO (+6.7%) diets (Diet × CO × BCVFA interaction). The recovery of 13C in bacterial AA flow was 31% lower with LF than with HF. Of the total 13C recovered in bacteria, 13.8, 17.3, and 30.2% were recovered in Val, Ile, and Leu, respectively; negligible 13C was recovered in other AA. When fermenters were dosed with BCVFA, nonbacterial and total effluent flows of AA, particularly of alanine and proline, suggest decreased peptidolysis. Increased ruminal outflow of bacterial AA, especially BCAA, but also nonbacterial AA could potentially support postabsorptive responses from BCVFA supplementation to dairy cattle.

Regulating mechanism of denitrifier Comamonas sp. YSF15 in response to carbon deficiency: Based on carbon/nitrogen functions and bioaggregation

There is an urgent demand to investigate mechanisms for the improvement of denitrification in carbon-deficient environment, which will effectively reduce the eutrophication in water bodies polluted by nitrate. In this study, denitrifying bacterium Comamonas sp. YSF15 was used to explore the differences in different carbon source concentrations, with the complete genome, metabolomics, and other detecting methods. Results showed that strain YSF15 was able to achieve efficient denitrification, with complete pathways for denitrification and central carbon metabolism. The carbon deficiency prompted the bacteria to use extracellular amino acid-like metabolites initially, to alleviate inhibition and maintain bioactivity, which also facilitated glycogen storage. The biogenic inhibitors (tautomycin, navitoclax, and glufosinate) at extremely low level potentially favored the competitiveness and intraspecific utilization of extracellular polysaccharides (PS). Optimal solutions for bioaggregation in carbon-deficient condition are achieved by regulating the hydrophobicity, and hydrogen bond in extracellular metabolites. The strategy contributes to the maintenance of bioactivity and adaptation to carbon deficiency. Overall, this study provides a new perspective on understanding the denitrification strategies in carbon-deficient environment, and helps to improve the nitrate removal in low-carbon wastewater treatment.

Assessing milk response to different combinations of branched-chain volatile fatty acids and valerate in Jersey cows

Some cellulolytic bacteria require 1 or more branched-chain volatile fatty acids (BCVFA) for the synthesis of branched-chain AA and branched-chain long-chain fatty acids because they are not able to uptake branched-chain AA or lack 1 or more enzymes to synthesize branched-chain AA de novo. Supplemental BCVFA and valerate were included previously as a feed additive that was later removed from the market; these older studies and more current studies have noted improvements in neutral detergent fiber digestibility and milk efficiency. However, most studies provided a single BCVFA or else isobutyrate (IB), 2-methylbutyrate (MB), isovalerate, and valerate altogether without exploring optimal combinations. Our objective was to determine a combination of isoacids that is optimal for milk production. Sixty (28 primiparous and 32 multiparous) lactating Jersey cows (106 ± 54 days in milk) were blocked and assigned randomly to either a control (CON) treatment without any isoacids, MB [12.3 mmol/kg dry matter (DM)], MB + IB (7.7 and 12.6 mmol/kg DM of MB and IB, respectively), or all 4 isoacids (6.2, 7.3, 4.2, and 5.1 mmol/kg DM of MB, IB, isovalerate, and valerate, respectively). Cattle were fed the CON treatment for a 2-wk period, then were assigned randomly within a block to treatments for 8 wk (n = 15). There was a trend for an interaction of supplement and parity for milk components. There were no differences in components for primiparous cows, whereas MB + IB tended to increase protein concentration by 0.04 and 0.08 percentage units in multiparous cows compared with the CON and MB treatments, respectively. Feeding MB + IB increased fat concentration by 0.23 to 0.31 percentage units compared with all other treatments in multiparous cows. Milk yield and dry matter intake (DMI) did not change with treatment. Treatment interacted with week for milk net energy for lactation/DMI; MB + IB tended to increase milk net energy of lactation/DMI by 0.10 Mcal/kg compared with MB and approached a trend for CON, mainly during the early weeks of the treatment period, whereas differences decreased during the last 2 wk of the treatment period. Cows fed MB had the highest 15:0 anteiso fatty acids in the total milk fatty acid profile, which was greater than that for CON or MB + IB cows, but not cows supplemented with isoacids. Cows fed MB alone had the numerically lowest milk net energy for lactation/DMI. The combination of MB + IB appeared optimal for increasing feed efficiency in our study and was not at the expense of average daily gain. Further research is needed for evaluating how potential changes in supplemental isoacid dosage should vary under differing dietary conditions.

Glutamate Supplementation Improves Growth Performance, Rumen Fermentation, and Serum Metabolites in Heat-Stressed Hu Sheep

This study evaluated the effect of glutamate supplementation on the physiological parameters of heat-stressed Hu sheep. Forty-eight male Hu sheep with an average initial body weight of 17.74 ± 0.17 kg were randomly divided into two groups: The control group (CON) was fed a basal diet and a treatment group (GLU) was fed a basal diet + 3 g/head/day of L-glutamate. There were six replications in each group with four sheep in each replication for a 90 days feeding test. Growth performance, serum biochemistry, and serum hormones were measured during phase 1 (1–30 days), phase 2 (31–60 days), and phase 3 (61–90 days) of the experiment; rumen fermentation characteristics, nutrient digestibility, and slaughter performance were measured at the end of the experimental periods. There were no differences in growth performance, serum biochemical indices, and immune indices between CON and GLU during phases 1 and 2. However, a higher average daily gain (ADG), a lower average daily feed intake (ADFI), and a lower F:G ratio (ADFI/ADG) were observed in GLU during phase 3 (p < 0.05). Serum levels of glutamate, globulin, immunoglobulin A, immunoglobulin G, immunoglobulin M, and growth hormone in GLU were higher than those in CON only on day 90 (p < 0.05). Serum levels of heat shock protein 70, adrenocorticotrophic hormone, corticosterone, triiodothyronine, and tetraiodothyronine in GLU were lower than those in CON on day 90 (p < 0.05). At the end of the experiment, ruminal pH, microbial crude protein, ammonia nitrogen, and isovalerate concentrations in GLU were higher than those in CON (p < 0.05). The apparent digestibility of dry matter, organic matter, and crude protein in GLU was higher than those in CON (p < 0.05). There were no differences in carcass traits and organ indices but spleen weight and spleen index tended to be higher in GLU. In conclusion, dietary glutamate supplementation improved rumen fermentation, increased nutrition digestibility and metabolism, enhanced immunity, and promoted growth performance of heat-stressed Hu sheep. This suggests that a longer period of glutamate supplementation (not less than 60 days) at a level of 3 g/head/day is beneficial to Hu sheep under heat stress.

Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. III: Relation with solid passage rate and pH on prokaryotic fatty acid profile and community in continuous culture

Our objectives were to evaluate potential interactions in culture conditions that influence how exogenously dosed branched-chain VFA (BCVFA) would be recovered as elongated fatty acids (FA) or would affect bacterial populations. A 2 × 2 × 2 factorial arrangement of treatments evaluated 3 factors: (1) without versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate; each dose was partially substituted with ¹³C-enriched tracers before and during the collection period); (2) high versus low pH (ranging diurnally from 6.3 to 6.8 vs. 5.7 to 6.2); and (3) low versus high particulate-phase passage rate (k_p; 2.5 vs. 5.0%/h) in continuous cultures administered a 50:50 forage:concentrate diet twice daily. Samples of effluent were collected and composited before harvesting bacteria from which FA and DNA were extracted. Profiles and enrichments of FA in bacteria were evaluated by gas chromatography and isotope-ratio mass spectrometry. The ¹³C enrichment in bacterial FA was calculated as percentage recovery of dosed ¹³C-labeled BCVFA. Dosing BCVFA increased the even-chain iso-FA, preventing the reduced concentration at higher k_p and potentially as a physiological response to decreased pH. However, decreasing pH decreased recovery of ¹³C in these even-chain FA, suggesting greater reliance on isobutyrate produced from degradation of dietary valine. The iso-FA were decreased, whereas anteiso-FA and 16:0 increased with decreasing pH. Thus, 2-methylbutyrate still appeared to be important as a precursor for anteiso-FA to counter the increased rigidity of bacterial membranes that had more saturated straight-chain FA when pH decreased. Provision of BCVFA stimulated the relative sequence abundance of Fibrobacter and Treponema, both of which require isobutyrate and 2-methylbutyrate. Numerous bacterial community members were shifted by low pH, including increased Prevotella and genera within the phylum Proteobacteria, at the expense of members within phylum Firmicutes. Because of relatively few interactions with pH and k_p, supplementation of BCVFA can stimulate neutral detergent fiber degradability via key fibrolytic bacteria across a range of conditions. Decreasing pH shifted bacterial populations and their FA composition, suggesting that further research is needed to distinguish pH from dietary changes.

Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. II: Relation with solid passage rate and pH on neutral detergent fiber degradation and microbial function in continuous culture

To support improving genetic potential for increased milk production, intake of digestible carbohydrate must also increase to provide digestible energy and microbial protein synthesis. We hypothesized that the provision of exogenous branched-chain volatile fatty acids (BCVFA) would improve both neutral detergent fiber (NDF) degradability and efficiency of microbial protein synthesis. However, BCVFA should be more beneficial with increasing efficiency of bacterial protein synthesis associated with increasing passage rate (k_p). We also hypothesized that decreasing pH would increase the need for isobutyrate over 2-methylbutyrate. To study these effects independent from other sources of variation in vivo, we evaluated continuous cultures without (control) versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate), low versus high k_p of the particulate phase (2.5 vs. 5.0%/h), and high versus low pH (ranging from 6.3 to 6.8 diurnally vs. 5.7 to 6.2) in a 2 × 2 × 2 factorial arrangement of treatments. Diets were 50% forage pellets and 50% grain pellets administered twice daily. Without an interaction, NDF degradability tended to increase from 29.7 to 35.0% for main effects of control compared with BCVFA treatments. Provision of BCVFA increased methanogenesis, presumably resulting from improved NDF degradability. Decreasing pH decreased methane production. Total volatile fatty acid (VFA) and acetate production were decreased with increasing k_p, even though true organic matter degradability and bacterial nitrogen flow were not affected by treatments. Decreasing pH decreased acetate but increased propionate and valerate production, probably resulting from a shift in bacterial taxa and associated VFA stoichiometry. Decreasing pH decreased isobutyrate and isovalerate production while increasing 2-methylbutyrate production on a net basis (subtracting doses). Supplementing BCVFA improved NDF degradability in continuous cultures administered moderate (15.4%) crude protein diets (excluding urea in buffer) without major interactions with culture pH and k_p.

Use of monosodium glutamate by-product in cow diet on performance of lactating dairy cows

Eight multiparous lactating Holstein cows were randomly assigned in a 4 × 4 replicated Latin square design to receive four dietary treatments. The dietary treatments were monosodium glutamate by-product (MSGB) replacement for soybean meal in concentrate at four levels: MSGB replacement at 0, 20, 40 and 60%, respectively. Pangola hay was given on an ad libitum basis. It was found that total dry matter intake, concentrate intake, pangola hay intake and all apparent digestibilities were not different among treatments. Ammonia nitrogen concentration in the rumen at 4 h post-feeding was significantly different, in which the 0% treatment had the highest (P < 0.05) while the 20% treatment had the lowest. Milk fat percentage was the highest (P < 0.05) in the 0% treatment. MSGB replacement at 40% and 60% were shown to be the lowest (P < 0.05) feed cost for milk production, and profitability of milk production was the highest (P < 0.05) for the 60% treatment. Based on this experiment, it could be concluded that MSGB replacement for soybean meal at 20-60% in the feed for dairy cows presented no negative effects on their performances. In addition, it could decrease feed cost 2.9-17.3% and increase milk production profit up to 33.3% in the 60% treatment.

Kinetics of microbial methionine metabolism in continuous cultures administered different methionine sources

The Met precursor 2-hydroxy-4-(methylthio) butanoic acid (HMB) is expected to be more extensively degraded in the rumen than its isopropyl ester (HMBi). A control and 3 isomolar treatments-0.097% dl-methionine, 0.11% HMBi (HMBi), and 0.055% HMBi plus 0.048% Met (Met + HMBi)-were dosed every 8h simultaneously with 3-times-daily feeding into continuous cultures. Starting on d 9, for 6 consecutive doses, both [1-(13)C]-l-Met and [methyl-(2)H3]-l-Met replaced part of the unlabeled dl-Met, [(13)C5]-dl-HMBi replaced a portion of the unlabeled dl-HMBi, and [1-(13)C]-l-Met plus [(13)C5]-dl-HMBi replaced a portion of the respective unlabeled doses for the Met + HMBi treatment. After the sixth dose (d 11), unlabeled Met or HMBi provided 100% of the doses to follow elimination kinetics of the labels in HMBi, free Met, and bacterial Met compartments. The free [1-(13)C]-l-Met recycled more and was recovered in bacterial Met to a lesser extent than was the free [methyl-(2)H3]-l-Met recycling and that was recovered in bacterial Met. Increasing HMBi inclusion (0, 50, and 100% substitution of the exogenously dosed Met on a molar equivalent basis) tended to increase HMBi escape from 54.7 to 71.3% for the 50 and 100% HMBi treatments, respectively. Despite HMBi substituting for and decreasing the dosage of Met, increasing HMBi increased accumulation of free Met in fermenter fluid. The HMBi (after de-esterification of the isopropyl group) presumably produces Met through the intermediate α-ketomethylthyiobutyrate with an aminotransferase that also has high affinity for branched-chain AA. We provide evidence that the HMBi-derived Met is likely released from bacterial cells and accumulates rather than being degraded, potentially as a result of lagging d-stereoisomer metabolism. More research is needed to evaluate racemization and metabolism of stereoisomers of HMBi, Met, and other AA in ruminal microbes.

Ruminal Nitrogen Metabolism: Perspectives for Integration of Microbiology and Nutrition for Dairy

Our objectives are to integrate current knowledge with a future perspective regarding how metagenomics can be used to integrate rumen microbiology and nutrition. Ruminal NH3-N concentration is a crude predictor of efficiency of dietary N conversion into microbial N, but as this concentration decreases below approximately 5 mg/dL (the value most often suggested to be the requirement for optimal microbial protein synthesis), blood urea N transfer into the rumen provides an increasing buffer against excessively low NH3-N concentrations, and the supply of amino N might become increasingly important to improve microbial function in dairy diets. Defaunation typically decreases NH3-N concentration, which should increase the efficiency of blood urea N and protein-derived NH3-N conversion into microbial protein in the rumen. Thus, we explain why more emphasis should be given toward characterization of protozoal interactions with proteolytic and deaminating bacterial populations. In contrast with research evaluating effects of protozoa on N metabolism, which has primarily been done with sheep and cattle with low dry matter intake, dairy cattle have greater intakes of readily available carbohydrate combined with increased ruminal passage rates. We argue that these conditions decrease protozoal biomass relative to bacterial biomass and increase the efficiency of protozoal growth, thus reducing the negative effects of bacterial predation compared with the beneficial effects that protozoa have on stabilizing the entire microbial ecosystem. A better understanding of mechanistic processes altering the production and uptake of amino N will help us to improve the overall conversion of dietary N into microbial protein and provide key information needed to further improve mechanistic models describing rumen function and evaluating dietary conditions that influence the efficiency of conversion of dietary N into milk protein.