Volatile Fatty Acids In Rumen Fluid Research Articles

Relationship between Rumen Microbial Differences and Phenotype Traits among Hu Sheep and Crossbred Offspring Sheep.

This experiment was conducted to investigate the effect of three-way hybrid sheep and Hu sheep on serum indicators, rumen fermentation, rumen enzyme activity, and microorganisms in sheep. Healthy and similar birth weights from three groups (Hu, n = 11; Charolais × Australian White × Hu, CAH, n = 11; Charolais × Dorper × Hu, CDH, n = 11) were selected to be fed by the ewes until 45 days of age. Subsequently, they were weaned intensively and underwent short-term fattening for 3 months along with selected male lambs fed intensively. During this period, they were fed and watered ad libitum. Blood and rumen fluid were collected and analyzed for serum indicators and rumen fluid microorganisms, enzyme activity, and VFA, respectively, at the end of the fattening period. Compared with Hu lamb, the offspring of the three-way hybrid lamb showed significant improvements in body weight, serum lactate dehydrogenase, and creatinine content. However, there was no significant effect on serum immunity and antioxidant indices. In addition, the rumen fluid volatile fatty acid (VFA) molar concentration and microcrystalline cellulose and lipase content were significantly lower in the three-way hybrid lamb compared to Hu lamb, but β-glucosidase, amylase, pepsin, and VFA molar ratio were not significantly affected. Subsequently, 16S rRNA sequencing diversity analysis revealed that three-way hybrid lamb significantly increased rumen microbial ACE and Chao1 indices compared to Hu lamb. Meanwhile, the abundance of Verrucomicrobiota and Synergistota significantly increased at the phylum level. Correlation analysis showed that Prevotella had the highest proportion, while Rikenellaceae_RC9_gut_group correlated most closely with others genus. The microbial communities isovaleric acid molar concentration and proportion were strongly correlated. In addition, there were significant differences in correlations between microbial communities and isobutyric acid, butyric acid and valeric acid content, and their molar proportion, but they were not significantly correlated with digestive enzymes. From the functional enrichment analysis, it was found that hybrid progeny were mainly enriched in the pyruvate metabolism, microbial metabolism in diverse environments, carbon metabolism, and quorum sensing pathways. In contrast, the Hu sheep were primarily enriched in the cysteine and methionine, amino sugar and nucleotide sugar, and biosynthesis of secondary metabolite pathways. These results suggest that hybridization can play a role in regulating organismal metabolism and improve animal production performance by influencing the structure and characteristics of microbial communities.

Nutrient Composition and Metabolic Energy of Different Fruit Tree Leaves as Feeding Sources for Ruminants

The need for roughage in the animal nutrition industry has led to the search for various alternative roughage. In this context, as a result of the research, tree leaves have the potential to be considered as a nutritious and balanced forage source for animals. In this study, it was aimed to investigate the usability of apple (Malus domestica), apricot (Prunus armeniaca), cherry (Prunus avium), grape (Vitis vinifera), and umber mulberry (Morus rubra) leaves in ruminant nutrition. As a result of the research, nutritional contents of tree leaves (dry matter, crude protein, crude ash, crude oil, neutral detergent fiber, acid detergent fiber, acid detergent lignin, tannin), in vitro gas, carbon dioxide and methane gas production, in vitro gas post-production rumen fluid volatile fatty acid contents were found to be different from each other (P

Effects of dietary concentrate level and feeding length on nutrient digestibility, rumen hydrolytic enzymes activity, intermediary metabolites, and feeding behavior in growing fat-tailed lambs: Iranian feedlot system

High concentrate diets (feedlot) are commonly used in the intensive lamb finishing systems. However, the use of high concentrate diets increases the cost of production especially when feeding length (FL) is prolonged. Both levels of concentrate and FL need to be adjusted in order to get the best economic profit in feedlot systems. This experiment aimed to evaluate the effects of dietary concentrate level (CL) and FL on nutrients digestibility, activity of rumen hydrolytic enzymes, circulating intermediary metabolites, and feeding behavior of growing fat-tailed lambs. Twenty-seven male Lori-Bakhtiari lambs (26.3 ± 3.3 kg body weight, age 90 ± 15 days) were maintained in individual pens and fed diets with 55% (CL55), 70% (CL70), and 85% (CL85) concentrate level and the remaining with alfalfa hay. The experiment lasted 105d including a 15d of adaptation period. Daily feed intakes, feed conversion ratio (FCR), average daily gain (ADG), dry matter digestibility (DMD), feeding behavior were measured three times during the 90d feeding period. Intermediary metabolites in blood and rumen fluid volatile fatty acid, ammonia, protozoa number, α-amylase, carboxymethyl cellulase (CMCase), microcrystalline cellulase (MCCase), and filter paper-degrading (FPD) activity were measured at 30, 60 and 90 d of feeding. At the end of feeding, final body weight (FBW), carcass weight and relative weight of offal were recorded. Lambs fed CL85 had higher (P < 0.05) ADG, DMD, activities of α-amylase, CMC, MCC, FDP and greater FBW, carcass weight and subcutaneous fat and lower acetate/propionate (AP) ratio, and less blood protein as compared to lambs fed CL55 or CL70. Lambs fed CL55 spent more (P < 0.05) time on eating and chewing than those fed CL70 and CL85. Overall, toward the end of feeding period, DMI, DMD, CPD and activity of α-amylase, CMC, MCC, FDP significantly increased (P < 0.05), while circulating glucose, cholesterol and total protein were decreased(P < 0.05) when compared with early feeding period. Extended feeding worsened FCR values and decreased the utilization efficiency of energy and protein for gain by 31% and 37% respectively. In conclusion, increased feeding length more than 60 days significantly reduces feed efficiency per unit of gain presumably through a shift towards elevated dietary energy usage for fat deposition in the body, evidenced by greater subcutaneous fat content and fat tail weight. The study indicates that the use of concentrate level more than 70% in the ration along with extended feeding length may not be profitable in finishing of fat-tailed lambs.

TECHNICAL NOTE: Analysis of volatile fatty acids in rumen fluid by gas chromatography mass spectrometry using a dimethyl carbonate extraction.

Analysis of rumen fluid volatile fatty acids (VFA) is typically conducted by injecting acidified aqueous rumen fluid into a gas chromatograph (GC) with a flame ionization detector (FID). Aqueous samples are highly problematic because of the large vapor volume that can lead to poor peak shape and contamination of inlets, potentially causing sample carryover. Methods using aqueous samples are not well suited for use in a mass spectrometer (MS) detector system. The objective of this project was to validate a dimethyl carbonate (DMC) extraction process and GCMS method for rumen VFA analysis. To perform the extraction, 100 µL of sample, KHSO4 (500 g/L), and 2-ethylbutyrate (internal standard; 8.5 mM) were added to a microcentrifuge tube (in order) followed by 1 mL of DMC. The mixture was thoroughly vortexed and centrifuged. The organic layer (top) was removed and placed in a GC vial. The DMC extract was injected (0.5 µL) into an Agilent 5977B GCMS (8:1 split injection) with a polar DB-FFAP column. The column was held at 105 °C for 5 min, increased at 10 °C/min to 150 °C, then 65 °C/min to 240 °C, and held constant for 10 min. The peak area of acetate relative to the internal standard is linear from approximately 2 mM to at least 130 mM and encompasses the expected values of rumen concentrations for the other VFA. Recovery of VFA from spiked rumen fluid was tested at three concentrations in rumen fluid from steers fed a finishing diet or grazing wheat pasture. Recovery was not affected by the diet of the animals (P > 0.10) or the amount of VFA spiked (P > 0.19) for acetate, propionate, isobutyrate, or butyrate. There was an interaction of amount of VFA spiked and the diet of the animal (P = 0.021) for valerate and a tendency for an interaction (P = 0.051) for isovalerate, due to the recovery of the VFA being lower in the medium spike amount in rumen fluid from cattle on wheat pasture. Overall, recovery was greatest for propionate (101.9 ± 1.67%) and lowest for valerate (95.7 ± 1.95%). Including the 10-min hold at 240 °C at the end of each run prevented carryover from sample to sample. This method appears to perform well in a GCMS system and accurately and precisely quantifies rumen fluid VFA.

PSVII-17 Use of a dimethyl carbonate extraction for rumen fluid volatile fatty acid quantification by gas chromatograph mass spectrometry

Abstract Analysis of rumen fluid volatile fatty acids (VFA) is typically conducted by injecting acidified aqueous rumen fluid into a gas chromatograph (GC) with a flame ignition detector (FID). Water in GC samples can lead to poor peak shape and to contamination of inlets, potentially causing sample carryover. Aqueous methods are not well suited for use in mass spectrometer (MS) detector systems. The objective of this project was to validate a dimethyl carbonate (DMC) extraction process and GCMS method for rumen VFA analysis. To perform the extraction, 100 µL of sample, KHSO4 (50 g/L), and 2-ethylbutyrate (internal standard; 0.86 mM) are added to a microcentrifuge tube (in order) followed by 1 mL of DMC. The mixture is thoroughly vortexed and centrifuged. The organic layer (top) is removed and placed in a GC vial. The DMC extract is injected (0.5 µL) into an Agilent 5977B GCMS (8:1 split injection) with a polar DB-FFAP column. The column was held at 105°C for 5 min, increased at 10°C/min to 150°C, then 65°C/min to 240°C, and held constant for 10 min. The assay is linear for acetate from approximately 2 mM to at least 130 mM and covers the expected values of rumen concentrations for the other VFA. Recovery of VFA from spiked rumen fluid was tested at three concentrations in rumen fluid from steers fed a finishing diet or grazing wheat pasture. Recovery was not affected by the diet of the animals (P &amp;gt; 0.19) or the amount of VFA spiked (P &amp;gt; 0.27) and averaged 99.9% for all VFA, with valerate being the lowest (95.9%). Including the 10 min hold at 240°C at the end of each run prevented carryover from sample to sample. This method appears to perform well in a GCMS system and accurately and precisely quantify rumen fluid VFA.

505 Late-Breaking: Ruminal Microbiota, Inflammation Cytokines, and Performance of High-yield Dairy Cows Supplemented with Saccharomyces Cerevisiae Culture

Abstract Dramatic increases in milk yields in recent decades have created challenges in terms of rumen pH and microbial health which ultimately impact dairy cow health. The objective of this study was to assess the effects on ruminal pH, Volatile Fatty Acid (VFA), microbiota, inflammation, and performance of high-yield dairy cows by supplementing Saccharomyces cerevisiae culture (SC). Forty Holstein cows were divided into two groups based on their milk yield, days of milk, and parity fed the same basal ration diet that did or did not contain 100 g of SC /cow per day. Individual dry matter intake (DMI) and milk yield were recorded each day. Rumen fluid and milk samples were collected after 2 hours of morning feeding at intervals of 15 days during the experiment period. The data showed that rumen pH was increased by 0.19 (P = 0.09) when SC was supplemented than no SC was provided. SC-supplemented cow consumed 0.28 kg (P &amp;lt; 0.05) extra DM/d. Those supplemented with SC produced 1.36 kg (P &amp;lt; 0.05) more milk/cow per day than did non-supplemented cows. Milk fat percentage was higher (4.11 vs. 3.96%) for cows receiving SC. There were no differences in milk protein percentage. Rumen fluid VFA concentration was not statistically affected by SC but was numerically higher acetic and lower propionic for supplemented cows. The blood of the SC group with lower inflammation cytokines and somatic cell count (SCC). SC-supplemented cows had a greater relative abundance of Prevotellaceae, Succinivibrionaceae, Fibrobacteraceae, Lactobacillaceae, and lower relative abundance of Spirochaetaceae, Methanobacteriaceae, Enterobacteriaceae than the unsupplemented cows. It had greater functions on xylanolysis, fermentation, cellulolysis in the rumen in terms of the KEGG function prediction analysis. This study demonstrated that high-yield lactation cows receiving supplemental SC produced more milk and potentially reduced the inflammation and enhanced rumen cellulolysis bacteria growth.

Small differences in biohydrogenation resulted from the similar retention times of fluid in the rumen of cattle grazing wet season C3 and C4 forage species

The effects of forage type and season on retention time (RT) and the fatty acid (FA) profile of the rumen fluid (RF) of steers grazing a range of grasses and a legume/grass mix were evaluated. Four rumen cannulated steers (790 ± 17 kg body weight (BW) grazed individual wet season pastures (herbage mass 2600-6200 kg DM/ha of C3 ryegrass Lolium perenne and C4 grasses pangola Digitaria eriantha, signal grass Brachiaria decumbens, star grass Cynodon dactylon, kikuyu Pennisetum clandestinum, and speargrass Heteropogon contortus in both seasons, and a mixture of leucaena Leucaena leucocephala and green panic Panicum maximum in the dry season. Each grazing period consisted of at least 21 d, followed by a 3 d collection period. On d 22 CrEDTA was used to estimate RT (182 mg Cr/100 kg BW via the cannula) and RF samples were collected at 0, 4, 8, 12, 16, 24, 28, 32 and 48 h after dosing for Cr analysis. Diet crude protein (CP) and dry matter digestibility (DMD) were estimated by faecal NIRS. Concentration of NH3N and volatile fatty acids (VFA) in RF was determined at 0, 8 and 16 h after dosing. Dry season speargrass had the lowest CP (18 and 39 g/kg DM in plucked sample (PS) and estimated by faecal NIRS, respectively) and DMD (49%), which was associated with a low NH3N (9 mg NH3N/L) and VFA concentration (70 mM) in RF, and much longer RT of Cr (20 h) than the other grasses. The RT of Cr of the other wet season grasses was similar across all forage species (8- to 11 hours). Total VFA in RF was lowest for steers grazing dry season grass, intermediate for grasses in the wet season and highest for steers grazing the legume/grass mix. Speargrass had the highest non-glucogenic:glucogenic VFA. Ryegrass had higher CP (190 g/kg DM) and DMD (68%), but steers grazing this pasture had similar NH3N concentration in RF to steers grazing kikuyu and leaucaena/grass mix (above 100 mg NH3N /L). Palmitic and stearic acid in RF were much higher than in plucked samples, but all grasses had similar total saturated FA in RF with a greater degree of saturation for ryegrass. A higher CLA c9,t11 in RF of steers grazing ryegrass most likely resulted from the linoleic content in the forage and the higher intake of ryegrass resulting in accumulation in RF. Total unsaturated FA (TUFA) content of RF was reduced markedly compared to forage samples with some small differences between species indicating an extensive biohydrogenation despite the grass type and season. It was concluded that RT of Cr in the rumen of cattle grazing wet season grasses was similar across all forage species (8 to 11 hours) and would not result in different times for biohydrogenation within the rumen.

The Concentrations of Rumen Fluid Volatile Fatty Acids and Ammonia, and Rumen Microbial Protein Production in Sheep Given Feed During the Day and Night Time

An experimental study was carried out to investigate the concentrations of volatile (VFA), ammonia and microbial protein production of rumen fluid in sheep given fedd during the day and at night. This study used 12 fat-tailed rams aged 12-18 months and weighed 24,12 ± 25 kg (CV = 10,51%). The rams were fed a complete feed containing 16.64% protein and 68,33% total digestible nutrients (TDN). The rams were allocated into a completely randomised design with 3 treatments and 4 replications. The treatments applied were: T1: day time feeding (6.00 hrs – 18.00 hrs); T2: night time feeding (18.00 hrs – 6.00 hrs); and T3: day and night time feedings (6.00 hrs – 6.00 hrs). The parameters observed were dry matter intake (DMI), rumen VFA concentration, rumen ammonia concentration, rumen rmicrobial protein production and the efficiency of rumen microbial protein production. The results showed that feeding time did not significantly affect (P>0.05) all the parameters observed. Dry matter intake, VFA concentration, ammonia concentration, the microbial protein production of rumen fluid and the efficiency of microbial protein production were 1,073g/d, 49.69 mmol; 4.77 mg N/100 ml, 12,111 g/d and 19.96 g per kg digestible organic matter intake (DOMI), respectively. It is concluded that feeding time did not affect DMI, condition of rumen fluid and rumen microbial protein production in sheep.

Effect of initial time of forage supply on growth and rumen development in preweaning calves

To determine the effects of the initial timing of forage supply on growth, ruminal fermentation parameters and rumen development in preweaning calves, 18 7-day-old Holstein calves of 42 ± 3 kg were randomly divided into three treatment groups. The dietary treatments were (1) milk and commercial starter diet (MS) control, (2) milk and starter diet supplemented with oat hay at 2 weeks (MSO2), and (3) milk and starter diet supplemented with oat hay at 6 weeks (MSO6). Starter feed and oat hay were provided ad libitum, and 2 L of milk was provided twice daily. Samples were collected at 64 days of age. Supplementing with hay increased the dry-matter intake; P &lt; 0.05). The height, body length, heart girth and cannon bone circumference were similar among the three treatments (P &gt; 0.05). The concentrations of serum glucose (P = 0.07) and β-hydroxybutyric acid; P &lt; 0.05) were lower in the MSO6 group than in the MS and MSO2 groups. Rumination time was longer, and time spent on non-nutritive oral behaviour (such as e.g. licking surfaces, tongue rolling, wood-shaving consumption) was lower for hay-supplemented calves than for the control (P &lt; 0.05). Although ruminal pH of hay-supplemented calves was significantly higher than that of the control, total rumen fluid volatile fatty acid concentrations were not significantly different among treatments. Calves in the MSO2 group had a smaller ratio of empty weight to slaughter weight (P &lt; 0.05) and a larger total digestive tract weight (P &lt; 0.05); the empty gastrointestinal tract weights were similar among the three treatments, suggesting that MSO2 calf weight gain may have resulted from intestinal chyme accumulation. Compared with the control, hay-supplemented calves had reduced rumen papilla width and epithelium thickness (P &lt; 0.05), and no discernable plaque formation. Hay supplementation in the diet of preweaning calves improved the overall dry-matter intake, improved rumination, reduced non-nutritive oral behaviours, improved rumen pH, and ensured healthy rumen development; furthermore, productivity and rumen development were better in calves supplemented with hay from the second week.

Associations of rumen parameters with feed efficiency and sampling routine in beef cattle

Characterizing ruminal parameters in the context of sampling routine and feed efficiency is fundamental to understand the efficiency of feed utilization in the bovine. Therefore, we evaluated microbial and volatile fatty acid (VFA) profiles, rumen papillae epithelial and stratum corneum thickness and rumen pH (RpH) and temperature (RT) in feedlot cattle. In all, 48 cattle (32 steers plus 16 bulls), fed a high moisture corn and haylage-based ration, underwent a productive performance test to determine residual feed intake (RFI) using feed intake, growth, BW and composition traits. Rumen fluid was collected, then RpH and RT logger were inserted 5.5±1 days before slaughter. At slaughter, the logger was recovered and rumen fluid and rumen tissue were sampled. The relative daily time spent in specific RpH and RT ranges were determined. Polynomial regression analysis was used to characterize RpH and RT circadian patterns. Animals were divided into efficient and inefficient groups based on RFI to compare productive performance and ruminal parameters. Efficient animals consumed 1.8 kg/day less dry matter than inefficient cattle (P⩽0.05) while achieving the same productive performance (P⩾0.10). Ruminal bacteria population was higher (P⩽0.05) (7.6×1011v. 4.3×1011 copy number of 16S rRNA gene/ml rumen fluid) and methanogen population was lower (P⩽0.05) (2.3×109v. 4.9×109 copy number of 16S rRNA gene/ml rumen fluid) in efficient compared with inefficient cattle at slaughter with no differences (P⩾0.10) between samples collected on-farm. No differences (P⩾0.10) in rumen fluid VFA were also observed between feed efficiency groups either on-farm or at slaughter. However, increased (P⩽0.05) acetate, and decreased (P⩽0.05) propionate, butyrate, valerate and caproate concentrations were observed at slaughter compared with on-farm. Efficient had increased (P⩽0.05) rumen epithelium thickness (136 v. 126 µm) compared with inefficient cattle. Efficient animals also spent 318% and 93.2% more time (P⩽0.05) in acidotic (4.14% v. 1.30%) (pH⩽5.6) and optimal (5.6<pH<6.0) (8.53% v. 4.42%) RpH range compared with inefficient cattle. The circadian patterns revealed lower (P⩽0.05) RpH and no differences (P⩾0.10) in RT pre-, during, and post-prandial periods in efficient compared with inefficient cattle. In essence, superior feed efficiency in cattle seems linked to rumen features consistent with improved efficiency of feed utilization. Microbial abundance, rumen epithelial histomorphology, and RpH, may serve as indicators for feed efficiency in cattle. The divergences of assessments made on-farm and at slaughter should be considered in the development of proxies for feed efficiency.

Feed intake and methane emissions from cattle grazing pasture sprayed with canola oil

Effects of canola oil spraying on feed intake, ruminal volatile fatty acids (VFA) concentrations and methane (CH4) emissions were investigated in cattle grazing a temperate pasture. Sixty 1-yr-old crossbred steers were allocated into two groups (n=30/group), balanced for body weight (293.8±14.0kg). Following acclimatisation the groups were randomly assigned to one of the two grazing treatments: daily grazing pasture strips (0.1ha) sprayed daily with canola oil (Oil-spray, 12L/strip) and no oil sprayed (Control). The experimental phase involved two periods (Period 1 and 2), for which a paddock of perennial ryegrass (Lolium perenne) was subdivided by electric fences into 0.1ha strips. Period 1 lasted 5 days, whereas Period 2 lasted 12 days. Treatments were applied only in Period 2. Methane emissions were measured using the SF6 tracer technique over 3 days in Period 1 (baseline emissions) and over 4 days in Period 2. Individual animals' feed dry matter intake (DMI) were estimated only in Period 2 using TiO2 as faecal output marker and in vitro digestibility of forage dry matter (IVDMD). Concentrations of VFA in rumen fluid were determined in samples collected at the end of the study by stomach-tubing. Baseline CH4 emissions did not differ between the cattle groups. In Period 2, the herbage eaten by cattle on Oil-spray treatment had higher fat content than on Control (8.9 vs. 3.9% of DM), with no apparent difference in other chemical entities. Cattle grazed on Oil-spray pasture had higher (P=0.02) DMI than those on Control pasture (8.29 vs. 7.51kg/d). Methane emissions from cattle on Oil-spray treatment were lower (P<0.01) than those on Control pasture both on gross (138.6 vs. 156.1g/d) and per unit of feed intake (17.2 vs. 20.9g/kg DMI) basis. Oil spraying of pasture resulted in lower (P<0.001) acetate/propionate ratio in rumen fluid compared to Control pasture (4.2 vs. 5.1). It is concluded that enhanced dietary lipids contents is an effective means of reducing CH4 emissions from grazed pasture. Longer term evaluation of oil supplementation effects on CH4 emission and feeding value of grazed herbages may aid in defining forage breeding avenues targeting lipid content of forage species.

Relationships between odd- and branched-chain fatty acid profiles in milk and calculated enteric methane proportion for lactating dairy cattle

The purpose of this study was to explore the relationships between odd- and branched-chain fatty acids (OBCFA) in milk with calculated enteric CH4 production for lactating dairy cows using multiple linear regression (MLR), partial least squares regression (PLS) and a genetic algorithm approach (GA). A dataset collected from 13 experiments containing 224 paired observations of measured acetate, propionate and butyrate proportions in rumen fluid VFA and 7 measured OBCFA was used. Methane proportion (mmol/mol VFA) was calculated from acetate, propionate and butyrate and expressed relative to the sum of these volatile fatty acids (VFA). Calculated CH4 production was related to milk OBCFA using MLR and PLS, resulting in a linear prediction model. The GA approach resulted in a model which predicted rumen VFA proportions of total VFA from milk OBCFA. Methane proportion was calculated from predicted acetate, propionate and butyrate proportions in total VFA based on rumen stoichiometry and compared with CH4 proportion calculated from measured VFA proportions. The prediction error was low (i.e., root mean square prediction error <5%), and models captured up to 66% of the variance in the data and the concordance correlation coefficient was close to 0.8. The variance of the prediction error was less than 40% of the variance of the calculated CH4 proportion. Seven milk OBCFA were initially considered as predictors, from which the branched-fatty acids iso C14:0, iso C15:0, iso C16:0 were positively related to calculated enteric CH4 production and the odd-fatty acids C15:0 and the sum of C17:0 and C17:1 cis–9 were negatively related to it. Relationships in this large data set identify the most relevant OBCFA in milk as potential predictors of rumen methanogenesis.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Rumen stoichiometric models and their contribution and challenges in predicting enteric methane production

Fermentation in the rumen is a complex process involving microbial activities and degradable dietary components. Therefore, representation of this process using mathematical models is also complex. Besides degradation of dietary components and microbial growth, fermentation stoichiometry needs to be known in order to evaluate specific dietary components for type of volatile fatty acid (VFA), H2 and CH4 produced during rumen fermentation. The objectives were to evaluate extant VFA stoichiometric models for their capacity to predict VFA molar proportion and CH4 using independent data sources. Two data sets were organized from the published literature. The first contained 141 treatments of rumen digestion studies with lactating dairy cows collected from 43 published experiments. The second data set contained 18 treatments from 8 studies. The experiments reported information on diet composition, true rumen substrate digestibility, molar proportion of VFA and enteric CH4 production (the latter only for data set 2). Model comparison was based on mean square prediction error (MSPE), concordance correlation coefficient and regression analysis. In general, models had different prediction performances with respect to the type of VFA in rumen fluid with root MSPE (RMSPE, % observed mean) values from 5.2 to 43.2. Among the 4 models evaluated, that of Murphy et al. (1982, MUR) had the highest RMSPE value for propionate (25.7%) with 19.6% MSPE being random error. The model of Bannink et al. (2006, BAN) had the lowest RMSPE (10.7%) for butyrate with 97.8% MSPE being random error. Similarly, the model of Nozière et al. (2010, NOZ) had the lowest RMSPE (5.2%) for acetate with 83.0% MSPE being random error. Variations among stoichiometric models in predicting VFA molar proportions affected estimated CH4 production. Comparison of predicted versus measured CH4 production showed that BAN had the lowest RMSPE (9.8%) with only 18.1% of MSPE error due to deviation of the regression slope from unity (ER). The RMSPE was 11.2 and 12.2% for NOZ and MUR, respectively, with ER being 44.3 and 21.4%, respectively. Prediction of CH4 production using Sveinbjörnsson et al. (2006) model had the highest RMSPE (16.7%) with 41.2% MSPE being ER. Results indicate that there were unexplained variations in model predicted VFA molar proportions versus observed values. The variation among stoichiometric models in predicting VFA production has a major influence on the accuracy of estimated enteric CH4 production. Currently, CH4 inventory is usually based on IPCC Tier 2 approach which, compared to BAN, NOZ and MUR had a higher prediction error in estimating CH4 emissions. The IPCC Tier 2 approach had an RMSPE of 16.4% of observed mean with 56.9% of the error due to ER indicating proportional bias due to inadequate representation of relationships. There may be a need for more mechanistic approaches that consider nutritional and microbial factors rather than empirical models that relate VFA molar proportions to nutritional factors. Based on our analysis, mechanistic models, particularly BAN, may be preferred for CH4 inventory or mitigation purposes. Although current mechanistic models have a higher prediction accuracy and a demonstrably more adequate representation of relationships compared with the widely used IPCC Tier 2 approach, the prediction accuracy of current models requires further improvement and they should be used with care for regulatory purposes either to create enteric CH4 mitigation strategies or document impacts of mitigation strategies.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture- Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Estimation of the stoichiometry of volatile fatty acid production in the rumen of lactating cows

The purpose of this study was to improve the prediction of the quantity and type of Volatile Fatty Acids (VFA) produced from fermented substrate in the rumen of lactating cows. A model was formulated that describes the conversion of substrate (soluble carbohydrates, starch, hemi-cellulose, cellulose, and protein) into VFA (acetate, propionate, butyrate, and other VFA). Inputs to the model were observed rates of true rumen digestion of substrates, whereas outputs were observed molar proportions of VFA in rumen fluid. A literature survey generated data of 182 diets (96 roughage and 86 concentrate diets). Coefficient values that define the conversion of a specific substrate into VFA were estimated meta-analytically by regression of the model against observed VFA molar proportions using non-linear regression techniques. Coefficient estimates significantly differed for acetate and propionate production in particular, between different types of substrate and between roughage and concentrate diets. Deviations of fitted from observed VFA molar proportions could be attributed to random error for 100%. In addition to regression against observed data, simulation studies were performed to investigate the potential of the estimation method. Fitted coefficient estimates from simulated data sets appeared accurate, as well as fitted rates of VFA production, although the model accounted for only a small fraction (maximally 45%) of the variation in VFA molar proportions. The simulation results showed that the latter result was merely a consequence of the statistical analysis chosen and should not be interpreted as an indication of inaccuracy of coefficient estimates. Deviations between fitted and observed values corresponded to those obtained in simulations.

Influence of Maturity of Grass Silage and Flaked Corn Starch on the Production and Metabolism of Volatile Fatty Acids in Dairy Cows

An experiment employing a Latin square design was used to quantify the effects of two stages of maturity of grass silage (early cut and late cut) and three concentrations of flaked corn starch (0, 2, and 4kg) on the molar proportion of rumen volatile fatty acids (VFA), the production of rumen VFA, and the net fluxes of VFA in the splanchnic tissue of cows. The molar proportions of VFA in rumen fluid were similar for cows fed both silages. When the silage diets were supplemented with starch, the proportion of propionic acid increased for cows fed diets containing early cut grass silage, but no effects were found for cows fed diets containing late cut grass silage. Estimated gastrointestinal production of acetate, propionate, butyrate, and branched-chain fatty acids plus valerate was related to intake of metabolizable energy and organic matter fermented into VFA. The portal release of acetate was approximately 14% lower than the estimated production of acetate by cows fed diets containing early cut grass silage, but cows fed diets containing late cut grass silage showed a variable difference between estimated production and portal release (31, 24, and 15%, respectively) as starch supplementation increased. The portal release of butyrate plus β-hydroxybutyrate and the release of branched-chain fatty acids plus valerate were approximately 70 and 25%, respectively, of the estimated gastrointestinal production. Propionate production was similar to the portal release of propionate.Net flux measurements in splanchnic tissue in combination with gastrointestinal digestion and kinetics provide information that increases the knowledge of pathways and metabolism and quantifies the availability of individual nutrients for milk production in dairy cows.

Production and absorption of volatile fatty acids in the rumen

Volatile fatty acids (VFA), produced by fermentation of organic matter in the rumen, can have a major effect on production and product composition in ruminants. The relative proportions in which VFA are produced, are influenced by a number of factors, including substrate composition, substrate availability and rate of depolymerization, and microbial species present. Interactions between these factors hamper conclusions with respect to the effect of one single factor. Molar proportions of VFA in rumen fluid are generally assumed to represent the proportions in which they are produced. Evidence is presented that individual VFA absorption rates vary with changes in pH or VFA concentration and hence, that this assumption need not be valid. Attempts to predict the supply of VFA based on substrate degradation in the rumen and stoichiometric parameters have not been satisfactory. Future attempts should include the differential VFA absorption rates, as well as provisions for the effect of amount and rate of degradation, pH and microbial species preferences on type of VFA produced. Such improvements, together with simplifications of the current detailed models of digestion and metabolism, and improved characterization of animals, should then allow better predictions of ruminant performance.

Rumen fermentation and digesta passage in ruminants fed cimaterol

In Experiment 1, rumen fluid samples were collected from 12 Finnish Landrace crossbred wether lambs following slaughter after a 64 day experimental period during which they were offered a pelleted concentrate ration ad libitum. Cimaterol was included in the concentrate ration at 0 or 10 mg kg −1. Neither ammonia and volatile fatty acid (VFA) concentrations, nor acetate, propionate or butyrate proportions of VFA were affected by dietary cimaterol inclusion. In Experiment 2, eight ruminally fistulated Friesian steers were fed either 0 or 0.09 mg cimaterol kg −1 body weight (BW) in a ration consisting of 340 g concentrate and 660 g hay kg −1 dry matter (DM). The allowance of 15.5 g DM kg −1 BW was fed in two equal portions daily for 35 days. Rumen fluid samples were collected immediately before the first feed and 2, 4, 8, 12, 16 and 24 h thereafter on two occasions. Rumen liquid and solid turnover were measured by ruminal pulse dosing with cobalt-EDTA and ytterbium-labelled hay, respectively. Dietary inclusion of cimaterol did not affect rumen fluid pH and concentrations of ammonia or VFA in rumen fluid, but increased the acetate and propionate proportions of VFA and decreased the butyrate proportion of VFA, particularly after the second daily feed. These effects resulted in significant alterations in the acetate to propionate and non-glucogenic ( acetate + 2- butyrate propionate ) ratio. Dietary inclusion of cimaterol did not affect rumen liquid or solid digesta turnover. It was concluded that cimaterol had a small but beneficial effect for growth on the concentration of measured end-products of ruminal metabolism, but had no effect on digesta passage from the rumen.

Comparative yield and feeding value of barley, oat and triticale silages

The yield and feeding value of barley (Hordeum vulgare 'Johnson'), oat (Avena sativa 'Calibre') and triticale(Triticosecale 'Carmen') silages were compared in a field study, a heifer growth trial (119 d in length, with four pens of eight Charolais cross heifers (average body weight 300 kg) per treatment), and a sheep digestibility trial (total fecal collection with eight sheep per treatment). The swathed and chopped plant material was ensiled in stack silos covered with plastic. Yields of dry matter (DM) and crude protein (CP) did not differ significantly (P &gt; 0.05) among species. At harvest, oat and triticale had greater acid detergent fiber (ADF) levels than barley. After ensiling, triticale alone had greater neutral detergent fiber, ADF and acid detergent insoluble nitrogen levels than the other silages. The three silages did not otherwise differ in chemical composition. Heifer intakes of barley (6.06 kg d−1) and oat (5.70 kg d−1) silage DM were similar, and greater than for triticale (4.86 kg d−1). Average daily gain was greatest with barley (0.65 kg d−1), intermediate with oat (0.57 kg d−1) and least with triticale (0.49 kg d−1). Intake of silage DM by the sheep was greatest with barley silage (741 g d−1), intermediate with oat (617 g d−1) and least with triticale (434 g d−1), which appeared less palatable than the other silages. Dry matter and CP digestibilities were greatest for barley silage (64.2 and 71.6%, versus 58.3. and 61.1% for oat, and 58.8 and 65.4% for triticale, respectively). Oat silage had the lowest fiber digestibility. Sheep given triticale silage had lower rumen fluid volatile fatty acid concentrations, apparently due to low DM intake. Oat silage gave a greater molar proportion of acetate, a lower proportion of propionate, and a higher acetate to propionate ratio than either barley or triticale. Triticale silage produced a greater molar proportion of acetate and a lower proportion of butyrate than barley silage. Based on animal performance, it was concluded that barley silage was the preferred of the three cereal silages for growing cattle. Triticale produced a less acceptable silage due to poor palatability and low DM intake. Key words: Cattle, sheep, cereal silage, forage quality, digestibility

Absorption of volatile fatty acids from the rumen of lactating dairy cows as influenced by volatile fatty acid concentration, pH and rumen liquid volume.

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 l), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, 50 or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4.5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) at an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.

The effects of hay and silage on growth and rumen function in young Holstein calves

Newborn calves were fed one of four different roughages (timothy hay, alfalfa hay, grass silage or two parts grass silage mixed with one part alfalfa hay) and a starter ration to a maximum of 2000 g d−1 beginning at 10 d of age along with whole milk to weaning at 28 d of age to measure the effect of forage type and method of conservation on voluntary intake and animal performance up to 112 d of age. Rumen fluid was sampled to determine whether the type of forage had a measureable effect on some gross parameters associated with rumen development. Forage dry matter became a larger proportion of total feed consumed as the animals became older. Overall alfalfa hay and silage:alfalfa mixture were consumed more than timothy hay (P &lt; 0.01). Calves fed silage:alfalfa grew more rapidly than those fed timothy (P &lt; 0.01). These differences were attributable to differences in forage protein and plant cell wall material. The differences in rumen fluid volatile fatty acid composition, pH, or in vitro gas production were found for treatments in only two sampling periods. In the 3rd period, gas production was more rapid from alfalfa hay than from silage (P &lt; 0.05) and in the 4th period, pH was greater for alfalfa hay than timothy hay (P &lt; 0.05). Rumen pH increased in the 3rd and 4th periods (P &lt; 0.01). The acetate:propionate ratio increased over time when the propionate values decreased from the 2nd to the 3rd period (P &lt; 0.01) and acetate values increased from the 3rd to the 4th period (P &lt; 0.01). Silage was equal to hay in terms of consumption, animal performance and those rumen fluid parameters examined and can be fed to young calves without any anticipated problems. Key words: Silage, hay, rumen, development, methane, calves