New biochemical pathways for forming short-chain fatty acids during fermentation in rumen bacteria

Short-chain fatty acids (SCFA) are essential to cattle as a source of energy and for other roles in metabolism. These molecules are formed during fermentation by microbes in the rumen, but even after decades of study, the biochemical pathways responsible for forming them are not always clear. Here we review recent advances in this area and their importance for improving animal productivity. Studies of bacterial genomes have pointed to unusual biochemical pathways in rumen organisms. One study found that 8% of rumen organisms forming acetate, a major SCFA, had genes for a pathway previously unknown in bacteria. The existence of this pathway was subsequently confirmed biochemically in propionibacteria. The pathway was shown to involve 2 enzymes that convert acetyl-coenzyme A to acetate. Similar studies have revealed new enzymatic steps for forming propionate and butyrate, other major SCFA. These new steps and pathways are significant for controlling fermentation. With more precise control over SCFA, cows can be fed more precisely and potentially reach higher productivity.

Silibinin reduces in vitro methane production by regulating the rumen microbiome and metabolites

This study used Silibinin as an additive to conduct fermentation experiments, wherein its effects on rumen gas production, fermentation, metabolites, and microbiome were analyzed in vitro. The silibinin inclusion level were 0 g/L (control group), 0.075 g/L, 0.15 g/L, 0.30 g/L, and 0.60 g/L (experimental group). Fermentation parameters, total gas production, carbon dioxide (CO2), methane (CH4), hydrogen (H2), and their percentages were determined. Further analysis of the rumen microbiome's relative abundance and α/β diversity was performed on the Illumina NovaSeq sequencing platform. Qualitative and quantitative metabolomics analyses were performed to analyze the differential metabolites and metabolic pathways based on non-targeted metabolomics. The result indicated that with an increasing dose of silibinin, there was a linear reduction in total gas production, CO2, CH4, H2 and their respective percentages, and the acetic acid to propionic acid ratio. Concurrent with a linear increase in pH, when silibinin was added at 0.15 g/L and above, the total volatile fatty acid concentration decreased, the acetic acid molar ratio decreased, the propionic acid molar ratio increased, and dry matter digestibility decreased. At the same time, the relative abundance of Prevotella, Isotricha, Ophryoscolex, unclassified_Rotifera, Methanosphaera, Orpinomyces, and Neocallimastix in the rumen decreased after adding 0.60 g/L of silibinin. Simultaneously, the relative abundance of Succiniclasticum, NK4A214_group, Candidatus_Saccharimonas, and unclassified_Lachnospiraceae increased, altering the rumen species composition, community, and structure. Furthermore, it upregulated the ruminal metabolites, such as 2-Phenylacetamide, Phlorizin, Dalspinin, N6-(1,2-Dicarboxyethyl)-AMP, 5,6,7,8-Tetrahydromethanopterin, Flavin mononucleotide adenine dinucleotide reduced form (FMNH), Pyridoxine 5'-phosphate, Silibinin, and Beta-D-Fructose 6-phosphate, affecting phenylalanine metabolism, flavonoid biosynthesis, and folate biosynthesis pathways. In summary, adding silibinin can alter the rumen fermentation parameters and mitigate enteric methane production by regulating rumen microbiota and metabolites, which is important for developing novel rumen methane inhibitors.

Quantification of methane emitted by ruminants: A review of methods

The contribution of greenhouse gas (GHG) emissions from ruminant production systems varies between countries and between regions within individual countries. The appropriate quantification of GHG emissions, specifically methane (CH₄), has raised questions about the correct reporting of GHG inventories and, perhaps more importantly, how best to mitigate CH₄ emissions. This review documents existing methods and methodologies to measure and estimate CH₄ emissions from ruminant animals and the manure produced therein over various scales and conditions. Measurements of CH₄ have frequently been conducted in research settings using classical methodologies developed for bioenergetic purposes, such as gas exchange techniques (respiration chambers, headboxes). While very precise, these techniques are limited to research settings as they are expensive, labor-intensive, and applicable only to a few animals. Head-stalls, such as the GreenFeed system, have been used to measure expired CH₄ for individual animals housed alone or in groups in confinement or grazing. This technique requires frequent animal visitation over the diurnal measurement period and an adequate number of collection days. The tracer gas technique can be used to measure CH₄ from individual animals housed outdoors, as there is a need to ensure low background concentrations. Micrometeorological techniques (e.g., open-path lasers) can measure CH₄ emissions over larger areas and many animals, but limitations exist, including the need to measure over more extended periods. Measurement of CH₄ emissions from manure depends on the type of storage, animal housing, CH₄ concentration inside and outside the boundaries of the area of interest, and ventilation rate, which is likely the variable that contributes the greatest to measurement uncertainty. For large-scale areas, aircraft, drones, and satellites have been used in association with the tracer flux method, inverse modeling, imagery, and LiDAR (Light Detection and Ranging), but research is lagging in validating these methods. Bottom-up approaches to estimating CH₄ emissions rely on empirical or mechanistic modeling to quantify the contribution of individual sources (enteric and manure). In contrast, top-down approaches estimate the amount of CH₄ in the atmosphere using spatial and temporal models to account for transportation from an emitter to an observation point. While these two estimation approaches rarely agree, they help identify knowledge gaps and research requirements in practice.

Synchronization of rumen degradable protein with non-fiber carbohydrate on microbial protein synthesis and dairy ration digestibility

Background and Aim: Dairy ration formulations should consider the synchronization of the rumen degradable protein (RDP) to rumen undegradable protein (RUP) ratio (RDPR) with non-fiber carbohydrate (NFC) to achieve optimum microbial protein synthesis (MPS), reduce feed costs, and reduce N excretion to the environment. This study aimed to investigate the effect of RDPR and NFC synchronization on in vitro digestibility, fermentability, and MPS. Materials and Methods: The experiment used a 3×3 factorial randomized block design with four replications. The first factor was RDPR (RDPR1=50:50; RDPR2=55:45; RDPR3=60:40) and the second factor was NFC levels (NFC1=30%, NFC2=35%, NFC3=40%). The experimental diets were evaluated using a two-stage in vitro method. The examined parameters included rumen pH, NH3 concentration, total volatile fatty acid (VFA) concentration, the molar proportion of VFAs, rumen microbes (protozoa and total bacteria population), and MPS. Data were analyzed using ANOVA, followed by the Duncan test. Results: The results show that neither RDPR nor NFC affected rumen pH, NH3, total VFA, and the rumen microbe population. The interaction between RDPR and NFC affected the molar proportion of acetate, iso-butyrate, and n-valerate. The combination of RDPR1 and NFC1 produced a lower molar proportion of acetate (49.73%) than the other treatment combinations (>54%). The acetate to propionate ratio was influenced by the NFC levels, in which NFC2 and NFC3 produced the highest ratio (p<0.05). MPS was affected by RDPR and NFC, but not by their interaction. Treatments NFC2 and RDPR3 produced the highest MPS. NFC affected the dry matter and organic matter digestibility (DMD and OMD), with treatment NFC3 resulting in the highest DMD and OMD. Conclusion: The combination of a 60:40 RDPR with 35% NFC resulted in the best synchronization of protein and energy available for MPS and digestion activity in the rumen.

Cyberlindnera jadinii yeast as a protein source in early- to mid-lactation dairy cow diets: Effects on feed intake, ruminal fermentation, and milk production

We examined the effects of substituting soybean meal with either yeast protein from Cyberlindnera jadinii or barley in concentrate feeds on feed intake, ruminal fermentation products, milk production, and milk composition in Norwegian Red (NRF) dairy cows. The concentrate feeds were prepared in pellet form as soy-based (SBM; where soybean meal is included as a protein ingredient), yeast-based (YEA; soybean meal replaced with yeast protein), or barley-based (BAR; soybean meal replaced with barley). The SBM contained 7.0% soybean meal on a dry matter (DM) basis. This was replaced with yeast protein and barley in the YEA and BAR concentrate feeds, respectively. A total of 48 early- to mid-lactation [days in milk ± standard deviation (SD): 103 ± 33.5 d] NRF cows in their first to fourth parity and with initial milk yield of 32.6 kg (SD = 7.7) were allocated into 3 groups, using a randomized block design, after feeding a common diet [SBM and good-quality grass silage: crude protein (CP) and neutral detergent fiber (NDF) content of 181 and 532 g/kg of DM, respectively] for 14 d (i.e., covariate period). The groups (n = 16) were then fed one of the dietary treatments (SBM, YEA, or BAR) for a period of 56 d (i.e., experimental period). The concentrate feeds were offered in split portions from 3 automatic feeders using electronic identification, with ad libitum access to the same grass silage. Dietary treatments had no effect on daily silage intake, total DM intake, or total NDF intake. Dietary CP intake was lower and starch intake was higher in the BAR group compared with the other groups. Ruminal fluid pH, short-chain volatile fatty acid (VFA) concentrations, acetate-to-propionate ratio, and non-glucogenic to glucogenic VFA ratio were not affected by dietary treatments. No effects of the dietary treatments were observed on body weight change, body condition score change, milk yield, energy-corrected milk yield, milk lactose and fat percentages, or their yields. In conclusion, yeast protein can substitute conventional soybean meal in dairy cow diets without adverse effect on milk production and milk composition, given free access to good-quality grass silage.

Near-infrared calibration models for estimating volatile fatty acids and methane production from in vitro rumen fermentation of different total mixed rations

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Near-infrared (NIR) prediction models accurately predicted volatile fatty acids, methane, and gas production.

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Outputs of models could provide useful information for calibrating rumen mechanistic models.

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Calibrations of valeric and isovaleric acids need to be improved.

Volatile fatty acids (VFA) and methane (CH₄) are the major products of rumen fermentation. The VFA are considered an energy source for the animal and rumen microbiota, and CH₄ (which is released by eructation) is considered an energy loss. Quantification of these fermentation products is fundamental for the evaluation of feeds and diets, and provides important information regarding the use of nutrients by ruminants. Near-infrared (NIR) spectroscopy is increasingly used for the evaluation of animal feeds because it is rapid, nondestructive, noninvasive, and inexpensive; does not require reagents; and the results are reproducible. The aim of this study was to develop NIR calibration models for estimating the production of VFA (acetic, propionic, butyric, valeric, isovaleric, and isobutyric acids), total gas, and CH₄ using in vitro gas production tests with buffered rumen inoculum throughout fermentation. Fifty-four total mixed rations (TMRs) were examined, and rumen fluid was manually collected from 2 dry Holstein dairy cows that had ruminal fistulas and were fed at maintenance energy levels. Then, 30 mL of buffered rumen fluid was incubated in bottles with ~220 mg of TMR. The total gas, VFA, and CH₄ were measured after 2, 5, 9, 24, 30, 48, and 72 h of rumen incubation for each TMR. The VFA were measured on 32 randomly selected TMR. In particular, 7 bottles were used for each TMR, one for each incubation time. Methane was measured in the headspace and VFA were measured in the buffered rumen fluid. The bottles were considered experimental units for calibration purposes. The production of CH₄ was quantified from the bottle headspaces by gas chromatography, and total gas production was measured using a pressure transducer at each incubation time. Two aliquots of the fermented liquids were sampled by opening the bottles at each incubation time, and (1) the concentrations of VFA were determined by gas chromatography or (2) spectra were obtained from Fourier-transform NIR spectroscopy. The data were randomly divided into calibration and validation data sets. The average concentrations of acetic acid (45.30 ± 11.92 and 43.86 ± 11.93 mmol/L), propionic acid (14.97 ± 6.08 and 14.38 ± 6.56 mmol/L), butyric acid (8.47 ± 3.47 and 8.65 ± 3.79 mmol/L), total gas (111.34 ± 81.90 and 116.46 ± 82.44 mL/g of organic matter), and CH₄ (9.65 ± 9.45 and 10.35 ± 9.33 mmol/L) were similar in the 2 data sets. The best calibration models were retained based on the coefficient of determination (R²) and the ratio of prediction to deviation (RPD). The R² values for prediction of VFA ranged from 0.69 (RPD = 3.28) for valeric acid to 0.94 (RPD = 4.20) for acetic acid. The models also provided good predictions of CH₄ (R² = 0.89, RPD = 3.05) and cumulative gas production (R² = 0.91, RPD = 3.30). The models described here precisely and accurately estimated the production of CH₄ and VFA during in vitro rumen fermentation tests. Validations at additional laboratories may provide more robust calibrations.

Effect of dietary inclusion of winter brassica crops on milk production, feeding behavior, rumen fermentation, and plasma fatty acid profile in dairy cows

This study determined feeding behavior, dry matter (DM) intake (DMI), rumen fermentation, and milk production responses of lactating dairy cows fed with kale (Brassica oleracea) or swede (Brassica napus ssp. napobrassica). Twelve multiparous lactating dairy cows (560 ± 22 kg of body weight, 30 ± 4 kg of milk/d, and 60 ± 11 d in milk at the beginning of the experiment; mean ± standard deviation) were randomly allocated to 3 dietary treatments in a replicated 3 × 3 Latin square design. The control diet comprised 10 kg of grass silage DM/d, 4 kg of ryegrass herbage DM/d, and 8.8 kg of concentrate DM/d. Then, 25% of herbage, silage, and concentrate (DM basis) was replaced with either kale or swede. Cows offered kale had decreased total DMI compared with cows fed the control and swede diets, whereas inclusion of swede increased eating time. Milk production, composition, and energy-corrected milk:DMI ratio were not affected. Cows fed with kale had a greater rumen acetate:propionate ratio, whereas swede inclusion increased the relative percentage of butyrate. Estimated microbial N was not affected by dietary treatments, but N excretion was reduced with inclusion of kale, improving N utilization. Cows fed kale tended to have increased nonesterified fatty acids and showed presence of Heinz-Ehrlich bodies, whereas hepatic enzymes such as aspartate aminotransferase, γ-glutamyl transferase, and glutamate dehydrogenase were not affected by dietary treatments. In plasma, compared with the control, swede and kale reduced total saturated fatty acids and increased total polyunsaturated fatty acids and total n-3 fatty acids. Overall, feeding cows with winter brassicas had no negative effect on production responses. However, mechanisms to maintain milk production were different. Inclusion of swede increased the time spent eating and maintained DMI with a greater relative rumen percentage of butyrate and propionate, whereas kale reduced DMI but increased triacylglycerides mobilization, which can negatively affect reproductive performance. Thus, the inclusion of swede may be more suitable for feeding early-lactating dairy cows during winter.

Evaluation of Molly model predictions of ruminal fermentation, nutrient digestion, and performance by dairy cows consuming ryegrass-based diets

Several studies have been conducted to improve grazing management and supplementation in pasture-based systems. However, it is necessary to develop tools that integrate the available information linking the representation of biological processes with animal performance for use in decision making. The objective of this study was to evaluate the precision and accuracy of the Molly cow model predictions of ruminal fermentation, nutrient digestion, and animal performance by cows consuming pasture-based diets to identify model strengths and weaknesses, and to derive new digestive parameters when relevant. Model modifications for adipose tissue, protein synthesis in lean body mass and viscera representation were included. Data used for model evaluations were collected from 25 publications containing 115 treatment means sourced from studies conducted with lactating dairy cattle. The inclusion criteria were that diets contained ≥45% perennial ryegrass (Lolium perenne L.), and that dry matter intake, dietary ingredient composition, and nutrient digestion observations were reported. Animal performance and N excretion variables were also included if they were reported. Model performance was assessed before and after model reparameterization of selected digestive parameters, global sensitivity analysis was conducted after reparameterization, and a 5-fold cross evaluation was performed. Although rumen fermentation predictions were not significantly improved, rumen volatile fatty acids absorption rates were recalculated, which improved the concordance correlation coefficient (CCC) for rumen propionate and ammonia concentration predictions but decreased CCC for acetate predictions. Similar degradation rates of crude protein were observed for grass and total mixed ration diets, but rumen-undegradable protein predictions seemed to be affected by the solubility of the protein source as was the intestinal digestibility coefficient. Ruminal fiber degradation was greater after reparameterization, driven primarily by hemicellulose degradation. Predictions of ruminal and fecal outflow of neutral detergent fiber and acid detergent fiber, as well as total fecal output predictions, improved significantly after reparameterization. Blood urea N and urinary N excretion predictions resulted in similar accuracy using both sets of model parameters, whereas fecal N excretion predictions were significantly improved after reparameterization. Body weight and body condition score predictions were greatly improved after model modifications and reparameterization. Before reparameterization, yield predictions for daily milk, milk fat, milk protein, and milk lactose were greatly overestimated (mean bias of 61.0, 58.7, 73.7, and 64.6% of mean squared error, respectively). Although this problem was partially addressed by model modifications and reparameterization (mean bias of 3.2, 1.1, 1.7, and 0.4% of mean squared error, respectively), CCC values were still small. The ability of the model to predict grass digestion and animal performance in dairy cows consuming pasture-based diets was improved, demonstrating the applicability of this model to these productive systems. However, the failure to predict grass digestion based on standard model inputs without reparameterization indicates there are still fundamental challenges in characterizing feeds for this model.

Effect of Dried Distillers Grains With Solubles and Red Osier Dogwood Extract on Fermentation Pattern and Microbial Profiles of a High-Grain Diet in an Artificial Rumen System

The objective of this study was to evaluate the effect of dried distillers grains with solubles (DDGS) and red-osier dogwood (ROD) extract on in vitro fermentation characteristics, nutrient disappearance, and microbial profiles using the rumen simulation technique. The experiment was a completely randomized design with a 2 × 2 factorial arrangement of treatments and four replicates per treatment. A basal diet [10% barley silage, 87% dry-rolled barley grain, and 3% vitamin and mineral supplement, dry matter (DM) basis] and a DDGS diet (as per basal diet with 25% of wheat DDGS replacing an equal portion of barley grain) were supplemented with ROD extract at 0 and 1% (DM basis), respectively. The experimental period was 17 d, consisting 10 days of adaptation and 7 days of data and sample collection. The substitution of wheat DDGS for barley grain did not affect gas production; disappearances of DM, organic matter, and crude protein; total volatile fatty acid (VFA) production; and microbial protein production. However, replacing barley grain with wheat DDGS increased (P = 0.01) fermenter pH and molar proportion of branched-chain VFA, switched (P = 0.06) the fermentation pattern to higher acetate production due to increased (P = 0.01) disappearance of neutral detergent fiber (NDF), and decreased (P = 0.08) methane (CH4) production. In the basal barley diet, the ROD extract increased the acetate to propionate (A:P) ratio (P = 0.08) and reduced the disappearance of starch (P = 0.06) with no effect on any other variables. No effects of ROD in the DDGS diet were observed. The number of operational taxonomic unit (OTUs) and the Shannon diversity index of the microbial community had little variation among treatments. Taxonomic analysis revealed no effect of adding the ROD extract on the relative abundance of bacteria at the phylum level with either the basal diet or DDGS diet, while at the genus level, the microbial community was affected by the addition of both DDGS and the ROD extract. Prevotella and Fibrobacter were the most abundant genera in the basal diet; however, Treponema became the most abundant genus with the addition of the ROD extract. These results indicated that the substitution of wheat DDGS for barley grain may mitigate enteric CH4 emissions. The trend of reduced starch fermentability and increased NDF disappearance with the addition of ROD extract suggests a reduced risk of rumen acidosis and an improvement in the utilization of fiber for cattle-fed high-grain diet.

The effects of pelleted dried distillers grains and solubles fed with different forage concentrations on rumen fermentation, feeding behavior, and milk production of lactating dairy cows

The physical form of feeds can influence dairy cow chewing behavior, rumen characteristics, and ruminal passage rate. Changing particle size of feeds is usually done through grinding or chopping forages, but pelleting feed ingredients also changes particle size. Our objective was to determine if pelleted dried distillers grains and solubles (DDGS) affected the feeding value for lactating dairy cattle. Seven lactating Jersey cows that were each fitted with a ruminal cannula averaging (± standard deviation) 56 ± 10.3 d in milk and 462 ± 75.3 kg were used in a crossover design. The treatments contained 15% DDGS in either meal or pelleted form with 45% or 55% forage on a dry matter basis. The forages were alfalfa hay, corn silage, and wheat straw. The factorial treatment arrangement was meal DDGS and low forage (mDDGS-LF), pelleted DDGS and low forage (pDDGS-LF), meal DDGS and high forage (mDDGS-HF), and pelleted DDGS and high forage (pDDGS-HF). Dry matter intake and energy-corrected milk were both unaffected by treatment averaging 19.8 ± 2.10 kg/d and 33.9 ± 1.02 kg/d, respectively. Fat yield was unaffected averaging 1.7 ± 0.13 kg/d, but protein yield was affected by the interaction of forage and DDGS. Protein yield was similar for both low forage treatments but was increased by when pDDGS was fed in the high forage treatment (1.05 vs. 0.99 ± 0.035 kg/d). When forage concentration was increased, starch digestibility increased by 1.9 percentage units, crude protein digestibility tended to increase 1.1 percentage units, and residual organic matter digestibility decreased 3.4 percentage units. Pelleting DDGS increased digestibility of neutral detergent fiber (NDF) digestibility (49.2 vs. 47.5 ± 1.85%) and gross energy (68.2 vs. 67.1 ± 1.18%). Increasing forage increased ruminal pH (5.85 to 5.94 ± 0.052). Passage rate slowed from 2.84 to 2.65 ± 0.205 %/h when feeding HF compared with LF. Rumination time increased from 417 to 454 ± 49.4 min with increasing forage concentration but was unaffected by the form of DDGS or the interaction of forage and DDGS. Eating time increased with pDDGS (235 vs. 209 ± 19.8 min), which may be a result of increased feed sorting behavior. Pelleting DDGS increased preference for particles retained on the 8-mm sieve and decreased preference for particles on the 1.18-mm sieve and in the pan (<1.18 mm). Results confirm that increasing forage concentration increases ruminal pH, rumination time, and slows passage rate, but contrary to our hypothesis increasing forage concentration did not increase NDF digestibility. Results also suggest that pelleted DDGS do not appear to affect milk production, ruminal characteristics, or passage rate, but pelleted DDGS may increase sorting behavior of lactating Jersey cows and increase NDF and gross energy digestibility.

Effects of feeding frequency and oil supplementation on feeding behavior, ruminal fermentation, digestibility, blood metabolites, and milk performance in late-lactation cows fed a high-forage diet

Many dairy producers are keen to feed low-producing late-lactation cows only once per day (1×) to reduce production costs. This study examined effects of feeding frequency (FF: thrice versus once daily) on behavioral patterns, ruminal fermentation, and milk production performance of cows and supplementation of yellow grease oil (YO) rich in 18:2n-6 as a potential strategy to alleviate the possible negative effects of 1× daily feeding. Twenty-four late-lactation Holstein cows (215 ± 53.8 DIM) housed in tiestalls were assigned to 4 treatments according to a 2 × 2 factorial arrangement with 2 FF [3 times daily (3×) at 0800, 1400, and 2000 h; or 1× at 0800 h] and 2 high-forage total mixed rations (TMR), without (CON) or with 25 g/kg of dry matter of YO (YGO), in a randomized complete block design. Treatments were applied for 21 d. Feeding behavior was recorded every 5 min over a 24-h period on d 19. Fresh TMR and orts were sampled (d 15 to 21) and separated using a 3-screen (19, 8, and 1.18 mm) Penn State Particle Separator for sorting activity. Ruminal fluid samples were collected using oral stomach tubing on d 21. Cows on 1×-CON spent more time eating during the first 6 h after feeding at 0800 h than did cows on 3×-CON or 1×-YGO. Decreasing FF increased meal length and tended to increase meal size for CON cows, but supplementing YO increased meal bouts and reduced meal length and size for cows fed 1×. Cows on 1×-CON had the greatest ruminating time between 2000 and 0800 h compared with other treatments. Total and daytime distribution of lying time did not vary by treatments. Sorting activity was higher for cows fed frequently, and the extent of sorting was increased by oil supplementation. In the morning ruminal fluid samples, pH was not different among treatments, but in the evening samples 1× daily feeding reduced ruminal pH compared with 3×. In the morning and evening samples, ratios of acetate to propionate were the lowest for 1×-CON cows compared with other treatments. Dry matter intake and milk yield were similar among the groups. Milk fat content and yield decreased with 1×-CON treatment, but supplementing YO numerically increased milk fat for cows fed 1×. These results suggest that decreasing FF from 3× to 1× daily increases meal length, particularly after feed delivery, in cows fed high-forage diets; but supplementation of plant oil changes feeding patterns and may improve ruminal pH and milk fat in cows fed once a day.

Effects of rumen-protected methionine or methionine analogs in starter on plasma metabolites, growth, and efficiency of Holstein calves from 14 to 91 d of age

During weaning, methionine (Met) supply decreases as liquid feed intake is reduced and ruminal function is developing. During this transition, the calf starter should both promote ruminal development and provide adequate nutrients post-ruminally. In mature ruminants, rumen-protected Met (RPM) and the Met analogs, 2-hydroxy-4-(methylthio)-butanoic acid (HMTBa) and HMTBa isopropyl ester (HMBi), are used to increase Met supply, stimulate ruminal fermentation, or exert both effects, respectively. To evaluate the effects of these forms of Met on calf performance during development of ruminal function, 74 Holstein calves were raised until 91 d of age, in 2 enrollment periods. Calves were individually housed from birth and, at 14 d of age, balanced for sex and randomly assigned to receive a starter with no added Met (CTRL, n = 20) or one supplemented with RPM (Smartamine M, Adisseo USA Inc., Alpharetta, GA; n = 16), HMTBa (RumenSmart, Adisseo; n = 19), or HMBi (MetaSmart, Adisseo; n = 19). Milk replacer [28% crude protein (CP), 15% fat] was offered up to 1.6 kg of dry matter (DM)/d and fed 3 times daily. Weaning was facilitated from d 49 to 63. The 4 starters (25% CP, 2.5 Mcal of metabolizable energy/kg of DM) were offered ad libitum, and supplement inclusion was set to provide an additional 0.16% DM of Met equivalents, and equal amounts of HMTBa within the analogs. Body weight and stature were measured, and blood was collected and analyzed for plasma urea nitrogen, β-hydroxybutyrate, and free AA on a weekly basis. Supplementation of RPM and HMBi increased free plasma Met, but no differences in growth or feed efficiency compared with calves fed the CTRL starter could be attributed to the additional Met supply alone. The addition of HMBi in the starter increased feed intake and body weight during the last weeks of the experiment. On the contrary, HMTBa failed to increase plasma Met and depressed intake and growth after weaning, likely because the level included in the diet was too high and intake was greater than previous studies, exacerbating the level of HMTBa ingested. No differences were observed in stature, feed efficiency, or non-AA plasma measurements among groups. These results demonstrate that RPM and HMBi are effective sources of metabolizable Met; however, Met was apparently not limiting calves fed the basal diet in this study. The increased feed intake observed with the inclusion of HMBi in the starter during the weaning and early postweaning period might be mediated by its metabolism in the rumen, and further research is needed to determine the mechanisms involved.

Broccoli byproduct-wheat straw silage as a feed resource for fattening lambs

The effect of feeding broccoli byproduct-wheat straw silage [BBWS; 69:31 ratio, dry matter (DM) basis] on performance, microbial N synthesis (MNS), rumen, and blood parameters in Fashandy lambs were evaluated. Three diets, with equal metabolizable energy and crude protein (CP) with a forage to concentrate ratio of 27:73 (DM basis), were formulated in which forage (lucerne and wheat straw) was replaced by BBWS (0, 100, or 200 g/kg of diet DM). These were assigned to three groups (n = 15/group) in a completely randomized block design for a 70-d period in which diets were offered as a total mixed ration. For each animal, dry matter intake (DMI), average daily gain (ADG), in vivo apparent digestibility, MNS, N retention, rumen, and blood parameters were measured. The BBWS diets had no influence on DMI, ADG, feed conversion efficiency, in vivo apparent digestibility coefficients of DM, organic matter, CP, and ash-free neutral detergent fiber. Neither MNS and N retention nor serum concentrations of glucose, triglycerides, creatinine, cholesterol, urea N, triiodothyronine, thyroxine, total protein, albumin, and globulin were affected. Rumen pH, NH₃-N, short-chain fatty acid concentrations, the ratio of acetic to propionic acid, and protozoa numbers were, also, not influenced. In summary, BBWS may be fed to Fashandy lambs up to 200 g/kg of diet DM without any adverse impacts on growth performance.

Interaction between feed use efficiency and level of dietary crude protein on enteric methane emission and apparent nitrogen use efficiency with Norwegian Red dairy cows1

We assessed the interactive effects of gross feed use efficiency (FUE, milk yield/kg DMI) background (“high” = HEFF vs. “low” = LEFF) and graded levels of dietary CP (130, 145, 160, and 175 g/kg DM) on milk production, enteric methane (CH₄) emission, and apparent nitrogen use efficiency (NUE, g milk protein nitrogen/g nitrogen intake) with Norwegian Red (NRF) dairy cows. Eight early- to mid-lactation cows were used in a 4 × 4 Latin square design experiment (2 efficiency backgrounds, 4 dietary treatments, and 4 periods each lasting 28 d). The diets were designed to be identical in physical nature and energy density, except for the planned changes in CP, which was a contribution of slight changes in other dietary constituents. We hypothesized that HEFF cows would partition more dietary energy and nitrogen into milk components and, as such, partition less energy in the form of methane and excrete less nitrogen in urine and feces compared with their LEFF contemporaries. We observed no interactions between dietary CP level and efficiency background on DMI, other nutrient intake, NUE, CH₄ emission, and its intensity (g CH₄/kg milk). Gradually decreasing dietary CP from 175 to 130 g/kg DM did not affect DMI, milk and energy-corrected milk yield, and milk component yields and daily CH₄ emission. However, decreasing dietary CP increased NUE and reduced urinary nitrogen (UN) excretion both in quantitative terms and as proportion of nitrogen intake. The HEFF cows showed improved NUE and decreased CH₄ emission intensity compared with the LEFF cows. In the absence of interaction effects between efficiency background and dietary CP level, our results suggest that CH₄ emission intensity and UN excretions can be reduced by selecting dairy cows with higher FUE and reducing dietary CP level, respectively, independent of one another. Furthermore, UN excretion predictions based on milk urea nitrogen (MUN) and cow BW for NRF cows produced very close estimates to recorded values promising an inexpensive and useful tool for estimating UN excretion under the Nordic conditions where ordinary milk analysis comes with MUN estimates.

Negative Energy Balance Influences Nutritional Quality of Milk from Czech Fleckvieh Cows due Changes in Proportion of Fatty Acids

The objective of this study was to evaluate the influence of negative energy balance on fatty acids proportion in the milk of Czech Fleckvieh cows after calving. Milk quality was determined based on fatty acid group proportion. Milk quality was evaluated in relation to selected negative energy balance (NEB) traits: body condition change (DEC) and milk citric acid content (CAC) after calving. Milk samples (n = 992) were collected once per week from 248 Czech Fleckvieh cows during the first month of lactation. Fatty acid content (%) in milk samples was determined and results were grouped as saturated (SFA) (hypercholesterolemic or volatile fatty acids) or unsaturated (UFA) (monounsaturated or polyunsaturated). Our results showed that cows with a deep NEB produce milk that is healthier for human consumption. Cows with a more significant DEC or the highest level of CAC in milk had the lowest proportion of SFA and the highest proportion of UFA (p < 0.01). These cows experienced higher physiological stress after calving; however, they produced milk of higher nutritional quality. Nowadays, we can see preventive efforts to mitigate NEB periods as a result of modern breeding trends regarding vitality, robustness, or longevity.

Characterization of variations within the rumen metaproteome of Holstein dairy cattle relative to morning feed offering

Few studies have utilized proteomic techniques to progress our knowledge of protein-mediated pathways within the rumen microbial community, and no previous research has used these techniques to investigate the patterns or variations of these proteins within this community. It was hypothesized that there would be fluctuations of rumen microbial protein abundances due to feed intake-mediated nutrient availability and that these could be identified using non gel-based proteomic techniques. This study investigated the fluctuations of bovine rumen metaproteome utilizing three mid to late-lactation Holsteins. Rumen fluid was collected at three timepoints on three days relative to their first morning feed offering (0 h, 4 h, and 6 h). Samples were pooled within timepoint within cow across day, analyzed using LC-MS/MS techniques, and analyzed for variations across hour of sampling using PROC MIXED of SAS with orthogonal contrasts to determine linear and quadratic effects. A total of 658 proteins were characterized across 19 microbial species, with 68 proteins identified from a variety of 15 species affected by time of collection. Translation-related proteins such as 50S and 30S ribosomal protein subunit variants and elongation factors were positively correlated with hour of sampling. Results suggest that as nutrients become more readily available, microbes shift from conversion-focused biosynthetic routes to more encompassing DNA-driven pathways.

Rumen In Vitro Fermentation and In Situ Degradation Kinetics of Winter Forage Brassicas Crops

The aim of the present study was to evaluate the nutritional value, the rumen in vitro fermentation, and the in situ degradation of Brassica oleracea (L.) ssp. acephala (kales) and Brassica napus (L.) ssp. napobrassica (swedes) for winter use. Five varieties of each brassica were used in three field replicates and were randomized in a complete block nested design. All forage varieties were harvested at 210 days post-sowing to analyze the chemical composition, in vitro gas production, volatile fatty acid (VFA) production and in situ dry matter (DM) and crude protein (CP) degradability. Kales presented higher DM and neutral detergent fiber (NDF) content (p < 0.01), whereas swedes showed higher CP, metabolizable energy (ME), glucose, fructose, total sugars, NFC, and nonstructural carbohydrate (NSC) content (p < 0.01). The kale and swede varieties differed in their CP and sugar concentrations, whereas the kale varieties differed in their DM and raffinose content. The rates of gas production were higher for swedes than for kales (p < 0.01). No differences between the brassica species (p > 0.05) were observed in the total VFA production, whereas kales had a higher proportion of acetate and swedes had higher proportions of butyrate (p < 0.05). Only the swede varieties showed differences in VFA production (p < 0.05). The soluble fraction "a", potential and effective in situ DM degradability were higher in swedes (p < 0.01), but kales presented greater DM and CP degradation rates. Differences were observed between brassica species in the chemical composition, degradation kinetics, and ruminal fermentation products, whereas differences among varieties within species were less frequent but need to be considered.

Feed utilization and lactational performance of Friesian cows fed beet tops silage treated with lactic acid bacteria as a replacement for corn silage

Thirty multiparous lactating Friesian cows were used to study the effect of partial or complete replacement of corn silage with lactic acid bacteria (LAB), molasses and calcium carbonate ensiled sugar beet tops for 3 months in a complete randomized experimental design with repeated measures. A week after parturition, cows were grouped into three treatments of 10 cows each and fed a control treatment containing corn silage at 300 g/kg DM. In the other treated diets, 50% or 100% of the control corn silage was substituted with beet tops silage treated with LAB included at 150 g or 300 g per kg diet. Ensiling of beet tops with LAB decreased its contents of oxalic acid and neutral detergent and acid detergent fibers but increased its contents of non-structural carbohydrate and calcium. Without affecting daily milk production and feed efficiency, beet tops silage treated with LAB diets decreased (p < 0.05) feed intake, total ruminal volatile fatty acids, acetate and propionate concentrations, energy-corrected milk yield and concentrations of milk total solids, fat, protein and energy. In conclusion, beet tops silage treated with LAB can replace corn silage in diets of lactating cows. An inclusion rate of 15% of beet tops silage treated with LAB (replacing 50% of corn silage) in the diet was the most suitable level for lactating cows under the current experimental conditions.

Effect of supplementation of saponin containing herbs on in vitro methane production under different feeding systems

This study was taken up to assess the effect of herbal feed additives [HFAs; kulthi (Dohichos biflorus), patha (Cissampelos pareria), aritha (Sapindus trifoliatus)] supplemented at 0–3% on DM basis of total mixed rations (TMR) on the in vitro methane production and nutrient fermentation in a 3 × 4 factorial design. TMR with different roughage to concentrate ratio (R:C) of 80:20, 75:25, 70:30 and 65:35 on DM basis were formulated. The roughage portion was made up of wheat straw and maize green fodder in 70:30 ratio. The chemical analysis of HFAs revealed that aritha had the highest concentration of both water and methanol soluble saponins; and condensed tannins (Leucocyanidin). Patha followed by kulthi had the highest concentration of vitamin C, flavonoids, total phenols and true tannins. The digestion kinetic parameters revealed that with the increase in level of concentrate in the diet, irrespective of type and level of supplementation of HFAs, the lag phase for fermentation of diet decreased linearly. The data conclusively revealed that the best response with respect to net gas production (NGP), digestibility of nutrients, methane production, volatile fatty acid (VFA) production, ME availability and other fermentation parameters from TMRs with different R:C ratios was observed in kulthi and patha supplemented at the rate of 2% of TMR with R:C ratio of 65:35 on DM basis.

Evaluation of a sheep rumen model with fresh forages of diverse chemical composition

The sheep rumen submodel MollyRum14 was evaluated on its methane and VFA predictions against data from respiration-chamber trials conducted with sheep fed perennial ryegrass, white clover, chicory, forage rape, turnip (leafy and bulb varieties), swedes, kale, or forage radish. We assessed the model's response to substrate degradation rate (settings that affect the rate of cellulose and hemicellulose digestion) and to fermentation stoichiometry (settings that alter nonglucogenic to glucogenic short-chain fatty acid ratios). Model predictions were evaluated against data for methane production (pCH4: g/d), methane yield (yCH4: g/kg DMI), and acetate to propionate ratio (A:P). The predictive ability of the model for both pCH4 and yCH4 was superior for perennial ryegrass than for other forages. Except for swedes and chicory, predictions for yCH4 were correctly ranked across the forages evaluated. Except for forage rape, robust predictions were obtained for all forages using fast degradation kinetics and a predominantly acetogenic stoichiometry. Model predictions for forage rape were enhanced using slow degradation kinetics and a predominantly propionic stoichiometry. These results indicate that MollyRum14 is suitable to predict methane emissions from sheep fed a variety of fresh forages including annual fodder crops. However, a clear understanding of degradation rates and stoichiometries is needed to enhance the utility of the model as a predictive tool. This would allow continuous adjustment of digestion rates and stoichiometries to be potentially tailored to individual forage species.

Effect of individual SCFA on the epithelial barrier of sheep rumen under physiological and acidotic luminal pH conditions

The objective of this study was to investigate whether individual short-chain fatty acids (SCFA) have a different potential to either regulate the formation of the ruminal epithelial barrier (REB) at physiological pH or to damage the REB at acidotic ruminal pH. Ruminal epithelia of sheep were incubated in Ussing chambers on their mucosal side in buffered solutions (pH 6.1 or 5.1) containing no SCFA (control), 30 mM of either acetate, propionate or butyrate, or 100 mM acetate. Epithelial conductance (Gt), short-circuit current (Isc), and fluorescein flux rates were measured over 7 h. Thereafter, mRNA and protein abundance, as well as localization of the tight junction proteins claudin (Cldn)-1, -4, -7, and occludin were analyzed. At pH 6.1, butyrate increased Gt and decreased Isc, with additional decreases in claudin-7 mRNA and protein abundance (each P < 0.05) and disappearance of Cldn-7 immunosignals from the stratum corneum. By contrast, the mRNA abundance of Cldn-1 and/or Cldn-4 were upregulated by 30 mM propionate, 30 mM butyrate, or 100 mM acetate (P < 0.05), however, without coordinated changes in protein abundance. At luminal pH 5.1, neither Gt, Isc, nor TJ protein abundance was altered in the absence of SCFA; only fluorescein flux rates were slightly increased (P < 0.05) and fluorescein signals were no longer restricted to the stratum corneum. The presence of acetate, propionate, or butyrate at pH 5.1 increased fluorescein flux rates and Gt, and decreased Isc (each P < 0.05). Protein abundance of Cldn-1 was decreased in all SCFA treatments but 30 mM butyrate; abundance of Cldn -4 and -7 was decreased in all SCFA treatments but 30 mM acetate; and abundance of occludin was decreased in all SCFA treatments but 30 mM propionate (each P < 0.05). Immunofluorescence staining of SCFA-treated tissues at pH 5.1 showed disappearance of Cldn-7, discontinuous pattern for Cldn-4 and blurring of occludin and Cldn-1 signals in tight junction complexes. The fluorescein dye appeared to freely diffuse into deeper cell layers. The strongest increase in Gt and consistent decreases in the abundance and immunosignals of tight junction proteins were observed with 100 mM acetate at pH 5.1. We conclude that SCFA may contribute differently to the REB formation at luminal pH 6.1 with possible detrimental effects of butyrate at 30 mM concentration. At luminal pH 5.1, all SCFA elicited REB damage with concentration appearing more critical than SCFA species.

Dairy system, parity, and lactation stage affect enteric methane production, yield, and intensity per kilogram of milk and cheese predicted from gas chromatography fatty acids

Ruminants (and milk production) contribute to global climate change through enteric methane emissions (EME), and any attempt to reduce them is complicated by the fact that they are difficult and expensive to measure directly. In the case of dairy cows, a promising indirect method of estimating EME is to use the milk fatty acid profile as a proxy, as a relationship exists between microbial activity in the rumen and the molecules available for milk synthesis in the mammary gland. In the present study, we analyzed the detailed fatty acid profiles (through gas chromatography) of a large number of milk samples from 1,158 Brown Swiss cows reared on 85 farms with the aim of testing in the field 2 equations for estimating EME taken from a published meta-analysis. The average estimated methane yield (CH₄ emission per kg of dry matter intake, 21.34 ± 1.60 g/kg) and methane intensity (per kg of corrected milk, 14.17 ± 1.78 g/kg), and the derived methane production (CH₄ emissions per day per cow, 357 ± 109 g/d) were similar to those previously published. Using data from model cheese makings from individual cows, we also calculated estimated methane intensity per kilogram of fresh cheese (99.7 ± 16.4 g/kg) and cheese solids (207.5 ± 30.9 g/kg). Dairy system affected all EME estimates. Traditional dairy farms, and modern farms including corn silage in the TMR exhibited greater estimated methane intensities. We found very wide variability in estimated EME traits among different farms within dairy system (0.33 to 0.61 of total variance), suggesting the need to modify the farms' feeding regimens and management practices to mitigate emissions. Among the individual factors, parity order affected all estimated EME traits excepted methane yield, with an increase from first lactation to the following ones. Lactation stage exhibited more favorable estimated EME traits during early lactation, concomitant with the availability of nutrients from body tissue mobilization for mammary synthesis of milk. Our results showed a coherence between the EME traits estimated from the analysis of milk fatty acids and the expectations according to current knowledge. Further research is needed to validate the results obtained in this study in other breeds and populations, to assess the magnitude of the genetic variation and the potential of these phenotypes to be exploited in breeding programs with the aim to mitigate emissions.

Modeling Microbial Communities: A Call for Collaboration between Experimentalists and Theorists

With our growing understanding of the impact of microbial communities, understanding how such communities function has become a priority. The influence of microbial communities is widespread. Human-associated microbiota impacts health, environmental microbes determine ecosystem sustainability, and microbe-driven industrial processes are expanding. This broad range of applications has led to a wide range of approaches to analyze and describe microbial communities. In particular, theoretical work based on mathematical modeling has been a steady source of inspiration for explaining and predicting microbial community processes. Here, we survey some of the modeling approaches used in different contexts. We promote classifying different approaches using a unified platform, and encourage cataloging the findings in a database. We believe that the synergy emerging from a coherent collection facilitates a better understanding of important processes that determine microbial community functions. We emphasize the importance of close collaboration between theoreticians and experimentalists in formulating, classifying, and improving models of microbial communities.

The Contribution of Mathematical Modeling to Understanding Dynamic Aspects of Rumen Metabolism

All mechanistic rumen models cover the main drivers of variation in rumen function, which are feed intake, the differences between feedstuffs and feeds in their intrinsic rumen degradation characteristics, and fractional outflow rate of fluid and particulate matter. Dynamic modeling approaches are best suited to the prediction of more nuanced responses in rumen metabolism, and represent the dynamics of the interactions between substrates and micro-organisms and inter-microbial interactions. The concepts of dynamics are discussed for the case of rumen starch digestion as influenced by starch intake rate and frequency of feed intake, and for the case of fermentation of fiber in the large intestine. Adding representations of new functional classes of micro-organisms (i.e., with new characteristics from the perspective of whole rumen function) in rumen models only delivers new insights if complemented by the dynamics of their interactions with other functional classes. Rumen fermentation conditions have to be represented due to their profound impact on the dynamics of substrate degradation and microbial metabolism. Although the importance of rumen pH is generally acknowledged, more emphasis is needed on predicting its variation as well as variation in the processes that underlie rumen fluid dynamics. The rumen wall has an important role in adapting to rapid changes in the rumen environment, clearing of volatile fatty acids (VFA), and maintaining rumen pH within limits. Dynamics of rumen wall epithelia and their role in VFA absorption needs to be better represented in models that aim to predict rumen responses across nutritional or physiological states. For a detailed prediction of rumen N balance there is merit in a dynamic modeling approach compared to the static approaches adopted in current protein evaluation systems. Improvement is needed on previous attempts to predict rumen VFA profiles, and this should be pursued by introducing factors that relate more to microbial metabolism. For rumen model construction, data on rumen microbiomes are preferably coupled with knowledge consolidated in rumen models instead of relying on correlations with rather general aspects of treatment or animal. This helps to prevent the disregard of basic principles and underlying mechanisms of whole rumen function.

Thermodynamic Driving Force of Hydrogen on Rumen Microbial Metabolism: A Theoretical Investigation

Hydrogen is a key product of rumen fermentation and has been suggested to thermodynamically control the production of the various volatile fatty acids (VFA). Previous studies, however, have not accounted for the fact that only thermodynamic near-equilibrium conditions control the magnitude of reaction rate. Furthermore, the role of NAD, which is affected by hydrogen partial pressure (P_H2), has often not been considered. The aim of this study was to quantify the control of P_H2 on reaction rates of specific fermentation pathways, methanogenesis and NADH oxidation in rumen microbes. The control of P_H2 was quantified using the thermodynamic potential factor (F_T), which is a dimensionless factor that corrects a predicted kinetic reaction rate for the thermodynamic control exerted. Unity F_T was calculated for all glucose fermentation pathways considered, indicating no inhibition of P_H2 on the production of a specific type of VFA (e.g., acetate, propionate and butyrate) in the rumen. For NADH oxidation without ferredoxin oxidation, increasing P_H2 within the rumen physiological range decreased F_T from unity to zero for different NAD⁺ to NADH ratios and pH of 6.2 and 7.0, which indicates thermodynamic control of P_H2. For NADH oxidation with ferredoxin oxidation, increasing P_H2 within the rumen physiological range decreased F_T from unity at pH of 7.0 only. For the acetate to propionate conversion, F_T increased from 0.65 to unity with increasing P_H2, which indicates thermodynamic control. For propionate to acetate and butyrate to acetate conversions, F_T decreased to zero below the rumen range of P_H2, indicating full thermodynamic suppression. For methanogenesis by archaea without cytochromes, F_T differed from unity only below the rumen range of P_H2, indicating no thermodynamic control. This theoretical investigation shows that thermodynamic control of P_H2 on individual VFA produced and associated yield of hydrogen and methane cannot be explained without considering NADH oxidation.

Effect of dietary replacement of alfalfa with urea-treated almond hulls on intake, growth, digestibility, microbial nitrogen, nitrogen retention, ruminal fermentation, and blood parameters in fattening lambs

The objective of this study was to assess the effect of dietary replacement of alfalfa with urea-treated almond hulls (UAH) on DM and nutrients intakes, growth performance, diet digestibility, microbial N supply (MNS), N retention, rumen fermentation parameters, and blood metabolites in fattening male Shall lambs (29.9 ± 1.9 kg initial BW). Three diets, with equal ME and CP concentrations and a forage-to-concentrate ratio of 40 to 60, were formulated in which alfalfa was replaced by different levels (0, 200, or 400 g/kg of diet DM) of UAH. Experimental diets were randomly assigned to the 3 groups ( = 8/group) in a completely randomized design for a 74-d period (14 d for adaptation and 60 d for data collection). Diets were offered as a total mixed ration to ensure 10% orts. Dry matter and nutrients intakes, animal growth, diet digestibility, MNS, N retention, rumen fermentation parameters, and plasma metabolites were determined. The dietary substitution of UAH for alfalfa had no effects on DMI (linear, = 0.96; quadratic, = 0.86), ADG (linear, = 0.35; quadratic, = 0.19), and G:F (linear, = 0.66; quadratic, = 0.13). In vivo digestibility coefficients of DM (linear, = 0.82; quadratic, = 0.42), OM (linear, = 0.73; quadratic, = 0.95), CP (linear, = 0.24; quadratic, = 0.66), and ash-free NDF (linear, = 0.69; quadratic, = 0.74) were not affected by the dietary treatment. Feeding lambs on diets containing UAH instead of alfalfa had no effects on MNS (linear, = 0.63; quadratic, = 0.68) and N retention (linear, = 0.44; quadratic, = 0.17). Rumen pH (linear, = 0.26; quadratic, = 0.071), ammonia N (linear, = 0.39; quadratic, = 0.13), and VFA (linear, = 0.091; quadratic, = 0.86) concentrations, acetic acid-to-propionic acid ratio (linear, = 0.93; quadratic, = 0.62), and protozoa population (linear, = 0.62; quadratic, = 0.22) were not influenced by the experimental diets. Substituting alfalfa with UAH had no effects on the plasma concentrations of glucose (linear, = 0.55; quadratic, = 0.91), triglycerides (linear, = 0.97; quadratic, = 0.44), cholesterol (linear, = 0.71; quadratic, = 0.70), urea N (linear, = 0.084; quadratic, = 0.12), total protein (linear, = 0.53; quadratic, = 0.96), albumin (linear, = 0.43; quadratic, = 0.39), and globulin (linear, = 0.39; quadratic, = 0.25). It is concluded that UAH can be fed to fattening Shall lambs as a total replacement (400 g/kg of diet DM) for alfalfa without negative effects on animal performance. This byproduct can be a safe feedstuff to use in sheep diets and could help to reduce environmental pollution.

Ruminal pH predictions for beef cattle: Comparative evaluation of current models

This study evaluated 8 empirical models for their ability to accurately predict mean ruminal pH in beef cattle fed a wide range of diets. Models tested that use physically effective fiber (peNDF) as a dependent variable were Pitt et al. (1996, PIT), Mertens (1997, MER), Fox et al. (2004, FOX), Zebeli et al. (2006, ZB6), and Zebeli et al. (2008, ZB8), and those that use rumen VFA were Tamminga and Van Vuuren (1988, TAM), Lescoat and Sauvant (1995, LES), and Allen (1997, ALL). A data set of 65 published papers (231 treatment means) for beef cattle was assembled that included information on animal characteristics, diet composition, and ruminal fermentation and mean pH. Model evaluations were based on mean square prediction error (MSPE), concordance correlation coefficient (CCC), and regression analysis. The prediction potential of the models varied with low root MSPE (RMSPE) values of 4.94% and 5.37% for PIT and FOX, RMSPE values of 9.66% and 12.55% for ZB6 and MER, and intermediate RMSPE values of 5.66% to 6.26% for the other models. For PIT and FOX, with the lowest RMSPE, approximately 96% of MSPE was due to random error, whereas for ZB6 and MER, with the highest RMSPE, 15.85% and 23.42% of MSPE, respectively, was due to linear bias, and 37.19% and 60.12% of the error, respectively, was due to deviation of the regression slope from unity. The CCC was greatest for PIT (0.67) and FOX (0.62), followed by 0.60 for LES and TAM, 0.52 for ZB8, 0.39 for MER, 0.34 for ALL, and 0.22 for ZB6. Residuals plotted against model-predicted values showed linear bias (P < 0.001) for all models except PIT (P = 0.976) and FOX (P = 0.054) and mean bias (P < 0.001) except for FOX (P = 0.293), LES (P = 0.215), and TAM (P = 0.119). The study showed that the empirical models PIT and FOX, based on peNDF, and LES and TAM, based on VFA, are preferred over the others for prediction of mean ruminal pH in beef cattle fed a wide range of diets. Several animal (BW and intake), diet (forage and OM contents), and ruminal (ammonia and acetate concentrations) factors were (P < 0.001) related to the residuals for each model. We conclude that the accuracy of prediction of mean ruminal pH was relatively low for all extant models. Consideration of factors in addition to peNDF and total VFA, as well as the use of data from studies with continuous measurement of ruminal pH over 24 h or more, would be useful in the development of improved models for predicting ruminal pH in beef cattle.

In vitro study of the effect of corn dried distillers grains with solubles on rumen fermentation in sheep

The aim of the in vitro study was to determine the effect of corn dried distillers grains with solubles (corn DDGS), used as a replacement for the concentrate ingredients of sheep diet, on rumen fermentation. The material for the study was the ruminal fluid of Polish Merino sheep which was incubated during 4-, 8- or 24-hour periods. Five groups of samples were prepared for in vitro fermentation: C - control, incubated with the substrate consisting of the concentrate ingredients; D1, D2 and D3, where DDGS was used as a substrate added in proportions of 10, 20 and 30% of dry matter of the concentrate; and D4, where 100% DDGS was used as a substrate. After fermentation, the gas and short chain fatty acids (SCFAs) analyses were performed using gas chromatography. The ammonia concentration and pH were also determined, and the SCFA utilization index (NGR), the fermentation efficiency (FE) and the index of cell yield of ruminal microorganisms (CY) were calculated. This research showed no effect of DDGS on the methane emission. The positive correlations between the amount of methane and ammonia concentrations in the 8- and 24-hour fermentation periods were found. DDGS addition increased propionate proportion, but decreased production of acetate (p<0.01). Additionally, D1, D2, D3 and D4 substrates lowered isobutyrate (p<0.05) and isovalerate (p<0.01) production. Based on the results obtained, it can be stated that partial substitution of the concentrate ingredients with DDGS did not have deleterious effect on sheep rumen fermentation processes.

Yeast hydrolysate product enhances ruminal fermentation in vitro

The present study examined the mode of action of a patented Saccharomyces cerevisiae yeast hydrolysate product (YHP) on the fermentation of bovine rumen in vitro. Three experiments were conducted. Fresh fluid from rumen-cannulated dairy cows was used as an inoculum to ferment a mixture of grass silage and concentrate feed with or without YHP. The first two experiments were batch fermentations of 12–24 h duration while the third experiment was a semi-continuous fermentation of six days. Production of gas, concentration of short chain fatty acids (SCFAs), microbial cell density and pH were measured from the fermentation medium as a function of time. In experiment 1, YHP dose-dependently stimulated the production of gas, and increased the density of microbial cells and concentration of SCFAs. Experiment 2 studied the effect of YHP on the ruminal fermentation using three ratios of concentrate feed to grass silage (25:75, 50:50, and 75:25). Both YHP and the elevated proportion of concentrate in the feed mixture significantly increased the production of gas, microbial populations and SCFAs, including propionic acid, by the ruminal microbiota. In experiment 3, YHP increased the concentration and relative proportion of propionic acid in the fermentation medium. YHP stimulated the rate of microbial fermentation of bovine ruminal microbiota, indicated by the effects on gas and SCFA production and microbial mass in these experiments. In particular, YHP increased the production of propionic acid. These results, which were likely due to modulation of microbial community by YHP, suggest that YHP enhances bovine ruminal fermentation and may thus improve the performance of these animals.

Quantifying effects of grassland management on enteric methane emission

Data on the effect of grassland management on the nutritional characteristics of fresh and conserved grass, and on enteric methane (CH4) emission in dairy cattle, are sparse. In the present study, an extant mechanistic model of enteric fermentation was evaluated against observations on the effect of grassland management on CH4 emission in three trials conducted in climate-controlled respiration chambers. Treatments were nitrogen fertilisation rate, stage of maturity of grass and level of feed intake, and mean data of a total of 18 treatments were used (4 grass herbage treatments and 14 grass silage treatments). There was a wide range of observed organic matter (OM) digestibility (from 68% to 84%) and CH4 emission intensity (from 5.6% to 7.3% of gross energy intake; from 27.4 to 36.9 g CH4/kg digested OM; from 19.7 to 24.6 g CH4/kg dry matter) among treatment means. The model predicted crude protein, fibre and OM digestibility with reasonable accuracy (root of mean square prediction errors as % of observed mean, RMSPE, 6.8%, 7.5% and 3.9%, respectively). For grass silages only, the model-predicted CH4 correlated well (Pearson correlation coefficient 0.73) with the observed CH4 (which varied from 5.7% to 7.2% of gross energy intake), after predicted CH4 was corrected for nitrate consumed with grass silage, acting as hydrogen sink in the rumen. After nitrate correction, there was a systematic under-prediction of 18%, which reduced to 9% when correcting the erroneously predicted rumen volatile fatty acid (VFA) profile (RMSPE 15%). Although a small over-prediction of 3% was obtained for the grass herbages, this increased to 14% when correcting VFA profile. The model predictions showed a systematic difference in CH4 emission from grass herbages and grass silages, which was not supported by the observed data. This is possibly related to the very high content of soluble carbohydrates in grass herbage (an extra 170 g/kg dry matter compared with grass silages) and an erroneous prediction of its fate and contribution to CH4 in the rumen. Erroneous prediction of the VFA profile is likely to be due to different types of diets included in the empirical database used to parameterise VFA yield in the model from those evaluated here. Model representations of feed digestion and VFA profile are key elements to predict enteric CH4 accurately, and with further evaluations, the latter aspect should be emphasised in particular.

Effect of glycerol in combination with alfalfa on in vitro gas production and microbial protein synthesis

Alfonso-Ávila, Á. R., Charbonneau, E., Lafrenière, C. and Berthiaume, R. 2015. Effect of glycerol in combination with alfalfa on in vitro gas production and microbial protein synthesis. Can. J. Anim. Sci. 95: 577–588. This study sought to determine the effect of added glycerol on microbial protein synthesis, ruminal degradation and utilization of alfalfa at different concentrations of nonstructural carbohydrates (NSC), using in vitro gas production. The 2×3 factorial plus one treatment consisted of oven-dried alfalfa with two NSC levels [high: 17.9 (HNSC) or low: 7.4% dry matter (DM) (LNSC)] and three glycerol treatments [control without glycerol, 15% crude glycerol (CG) and 15% pure glycerol (PG)], the additional treatment was LNSC+exogenous sugars (LNSC+ES: LNSC with 5% sucrose+5% starch). Five pre-planned contrasts were evaluated from the seven treatments: (1) HNSC vs. LNSC alfalfa; (2) with glycerol vs. without; (3) interaction of alfalfa and glycerol; (4) CG vs. PG, and; (5) LNSC+ES vs. HNSC. Gas production over 24 h was higher for HNSC than LNSC (202 vs. 179 mL g−1 DM) and with glycerol than without glycerol (202.2 vs. 168 mL g−1 DM). A decrease in the acetate:propionate ratio was observed for HNSC compared with LNSC (2.87 vs. 3.27) and for the addition of glycerol vs. no glycerol (2.78 vs. 3.65). Reduced microbial mass (185.5 vs. 240.5 mg g−1 DM) was observed for CG compared with PG. The LNSC+ES treatment had lower microbial protein synthesis and propionic acid production in relation to HNSC. No significant interaction was observed between the effect of NSC content of alfalfa and glycerol utilization. When effects were studied separately, results indicate that increasing NSC in alfalfa stimulates the synthesis of microbial protein. Also, the addition of glycerol promotes the synthesis of glucose precursors. Finally, the type of glycerol has an impact on results obtained suggesting caution when extrapolating results for PG to CG.

Evaluation of predictions of volatile fatty acid production rates by the Molly cow model

Predicting ruminal volatile fatty acid (VFA) production is important, as VFA are an energy source to the animal, affect nutrient partitioning, and dictate methane production. The VFA production submodel in the Molly cow model was evaluated using data from 8 publications that reported VFA production rates for cattle. Evaluations were conducted with ruminal water balance predictions enabled and the ruminal VFA stoichiometry coefficients set to "mixed" for all diets, or "mixed" when forage represented between 20 and 80% of the diet, "concentrate" when <20% forage, or "forage" when >80% forage. Prediction errors were relatively insensitive to changes in VFA coefficients by diet type. Root mean square prediction errors (RMSPE) were 63, 63, and 49% for acetate, propionate, and butyrate production rates, respectively. A large proportion of the error was slope bias for acetate and butyrate, and a modest proportion for propionate. Because interconversions between acetate and propionate represent approximately 15% of the variation in net production rates, lack of such consideration in the model may contribute to the substantial model prediction errors. The potential of using thermodynamic equations to predict interconversions was assessed using observed ruminal pH and VFA concentrations from 2 studies and assuming constant hydrogen pressure and concentrations of CO₂, H₂O, adenosine diphosphate, ATP, and inorganic P. Rate constants for conversion of acetate to propionate and propionate to acetate were derived independently from the control treatments and used to predict the fluxes for the other treatment. The observed changes in VFA concentrations and pH explained the observed changes in conversion of acetate to propionate, but overpredicted the change in the propionate to acetate flux in one study. When applied to the other study, the equations predicted the increase in propionate to acetate flux, but failed to predict the observed reduction in acetate to propionate flux. The inability to predict responses accurately may be due to a lack of data for controlling factors other than pH and VFA concentrations.

Prediction of ruminal volatile fatty acid proportions of lactating dairy cows based on milk odd- and branched-chain fatty acid profiles: new models, better predictions

The volatile fatty acids (VFA) produced in the rumen and the proportions in which they are produced are important determinants of a ruminant's metabolism, but their monitoring requires rumen-fistulated animals, which is not feasible under practical conditions or in experimental setups at herd level. An alternative approach was suggested earlier, consisting of predicting the VFA proportions from measured odd- and branched-chain fatty acid concentrations in the milk with a linear model. Here, we have improved this strategy through the development and application of 2 new model structures: the quadratic model, containing quadratic terms and interactions, and the rational model, consisting of a ratio of linear expressions. Both were found to improve prediction accuracy significantly compared with the linear model. Although the quadratic model achieved the best prediction accuracy, the rational model has the interesting property that it takes the dependence of the 3 predicted VFA into account and guarantees that the 3 proportions add up to 1. Adding a study effect to correct for a possible study bias in the multi-study data improved prediction substantially for all 3 methods. Our results demonstrate the potential of using milk odd- and branched-chain fatty acid concentrations to predict rumen VFA proportions.

Microbial butyrate and its role for barrier function in the gastrointestinal tract

Butyrate production in the large intestine and ruminant forestomach depends on bacterial butyryl-CoA/acetate-CoA transferase activity and is highest when fermentable fiber and nonstructural carbohydrates are balanced. Gastrointestinal epithelia seem to use butyrate and butyrate-induced endocrine signals to adapt proliferation, apoptosis, and differentiation to the growth of the bacterial community. Butyrate has a potential clinical application in the treatment of inflammatory bowel disease (IBD; ulcerative colitis). Via inhibited release of tumor necrosis factor α and interleukin 13 and inhibition of histone deacetylase, butyrate may contribute to the restoration of the tight junction barrier in IBD by affecting the expression of claudin-2, occludin, cingulin, and zonula occludens poteins (ZO-1, ZO-2). Further evaluation of the molecular events that link butyrate to an improved tight junction structure will allow for the elucidation of the cofactors affecting the reliability of butyrate as a clinical treatment tool.