Relationship between in vitro and in vivo methane production measured simultaneously with different dietary starch sources and starch levels in dairy cattle

Effect of buffer pH on methane production and fermentation characteristics of three forages tested in vitro

BACKGROUND

Low rumen pH is proposed to be a major mechanism for low methane (CH4) emissions from sheep fed forage rape. However, it is difficult to separate this from other in vivo factors, such as rumen passage rate. The objective of this study was to determine the effect of pH alone on CH4 production in vitro using different pH buffers. Ryegrass, white clover and forage rape were incubated in vitro using three different incubation buffers with starting pH values of 5.5, 6.2 and 6.8.

RESULTS

Decreasing pH reduced overall in vitro CH4 emission relative to fermented hexoses (CH4/FHex) by up to 54% and overall fermentation by 40%. pH also changed fermentation profiles where the acetate + butyrate to propionate + valerate ratio decreased when pH decreased. Within the three forages, forage rape led to the lowest CH4/FHex, but only in pH 5.5 and 6.2 buffer, and this was enhanced when the pH fell below 6.

CONCLUSION

Reducing pH in vitro decreased CH4 production and overall fermentation across all forages. The lower pH reached by forage rape compared to ryegrass and white clover appears to drive the lower CH4 production relative to the extent of fermentation from forage rape compared to the other forages. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A Review of Potential Feed Additives Intended for Carbon Footprint Reduction through Methane Abatement in Dairy Cattle

Eight rumen additives were chosen for an enteric methane-mitigating comparison study including garlic oil (GO), nitrate, Ascophyllum nodosum (AN), Asparagopsis (ASP), Lactobacillus plantarum (LAB), chitosan (CHI), essential oils (EOs) and 3-nitrooxypropanol (3-NOP). Dose-dependent analysis was carried out on selected feed additives using a meta-analysis approach to determine effectiveness in live subjects or potential efficacy in live animal trials with particular attention given to enteric gas, volatile fatty acid concentrations, and rumen microbial counts. All meta-analysis involving additives GO, nitrates, LAB, CHI, EOs, and 3-NOP revealed a reduction in methane production, while individual studies for AN and ASP displayed ruminal bacterial community improvement and a reduction in enteric CH4. Rumen protozoal depression was observed with GO and AN supplementation as well as an increase in propionate production with GO, LAB, ASP, CHI, and 3-NOP rumen fluid inoculation. GO, AN, ASP, and LAB demonstrated mechanisms in vitro as feed additives to improve rumen function and act as enteric methane mitigators. Enzyme inhibitor 3-NOP displays the greatest in vivo CH4 mitigating capabilities compared to essential oil commercial products. Furthermore, this meta-analysis study revealed that in vitro studies in general displayed a greater level of methane mitigation with these compounds than was seen in vivo, emphasising the importance of in vivo trials for final verification of use. While in vitro gas production systems predict in vivo methane production and fermentation trends with reasonable accuracy, it is necessary to confirm feed additive rumen influence in vivo before practical application.

A meta-analysis of methane-mitigation potential of feed additives evaluated in vitro

A systematic literature review of in vitro studies was performed to identify methane (CH4) mitigation interventions with a potential to reduce CH4 emission in vivo. Data from 277 peer-reviewed studies published between 1979 and 2018 were reviewed. Individual CH4 mitigation interventions were classified into 14 categories of feed additives based on their type, chemical composition, and mode of action. Response variables evaluated were absolute CH4 emission (number of treatment means comparisons = 1,325); total volatile fatty acids (n = 1,007), acetate (n = 783), propionate (n = 792), and butyrate (n = 776) concentrations; acetate to propionate ratio (n = 675); digestibility of dry matter (n = 489), organic matter (n = 277), and neutral detergent fiber (n = 177). Total gas production was used as an explanatory variable in the model for CH4 production. Relative mean difference between treatment and control means reported in the studies was calculated and used for statistical analysis. The robust variance estimation method was used to analyze the effects of CH4 mitigation interventions. In vitro CH4 production was decreased by antibodies (-38.9%), chemical inhibitors (-29.2%), electron sinks (-18.9%), essential oils (-18.2%), plant extracts (-14.5%), plant inclusion (-11.7%), saponins (-14.8%), and tannins (-14.5%). Overall effects of direct-fed microbials, enzymes, macroalgae, and organic acids supplementation did not affect CH4 production in the current meta-analysis. When considering the effects of individual mitigation interventions containing a minimum number of 4 degrees of freedom within feed additives categories, Enterococcus spp. (i.e., direct-fed microbial), nitrophenol (i.e., electron sink), and Leucaena spp. (i.e., tannins) decreased CH4 production by 20.3%, 27.1%, and 23.5%, respectively, without extensively, or only slightly, affecting ruminal fermentation and digestibility of nutrients. It should be noted, however, that although the total number of publications (n = 277) and treatment means comparisons (n = 1,325 for CH4 production) in the current analysis were high, data for most mitigation interventions were obtained from less than 5 observations (e.g., maximum number of observations was 4, 7, and 22 for nitrophenol, Enterococcus spp., and Leucaena spp., respectively), because of limited data available in the literature. These should be further evaluated in vitro and in vivo to determine their true potential to decrease enteric CH4 production, yield, and intensity. Some mitigation interventions (e.g., magnesium, Heracleum spp., nitroglycerin, β-cyclodextrin, Leptospermum pattersoni, Fructulus Ligustri, Salix caprea, and Sesbania grandiflora) decreased in vitro CH4 production by over 50% but did not have enough observations in the database. These should be more extensively investigated in vitro, and the dose effect must be considered before adoption of mitigation interventions in vivo.

A meta-analysis of methane mitigation potential of feed additives evaluated in vitro

A systematic literature review of in vitro studies was performed to identify methane (CH4) mitigation interventions with a potential to reduce CH4 emission in vivo. Data from 277 peer-reviewed studies published between 1979 and 2018 were reviewed. Individual CH4 mitigation interventions were classified into 14 categories of feed additives based on their type, chemical composition, and mode of action. Response variables evaluated were absolute CH4 emission (number of treatment means comparisons = 1,325); total volatile fatty acids (VFA; n = 1,007), acetate (n = 783), propionate (n = 792), and butyrate (n = 776) concentrations; acetate to propionate ratio (A:P; n = 675); digestibility of dry matter (DM; n = 489), organic matter (OM; n = 277), and neutral detergent fiber (NDF; n = 177). Total gas production was used as an explanatory variable in the model for CH4 production. Relative mean difference between treatment and control means reported in the studies were calculated and used for statistical analysis. Robust variance estimation method was used to analyze the effects of CH4 mitigation interventions. In vitro CH4 production was decreased by antibodies (-38.9%), chemical inhibitors (-29.2%), electron sinks (-18.9%), essential oils (-18.2%), plant extracts (-14.5%), plants inclusion (-11.7%), saponins (-14.8%), and tannins (-14.5%). Overall effects of direct fed microbials, enzymes, macroalgae, and organic acids supplementation did not affect CH4 production in the current meta-analysis. When considering the effects of individual mitigation interventions containing a minimum number of 4 degrees of freedom within feed additives categories, Enterococcus spp. (i.e., direct fed microbial), nitrophenol (i.e., electron sink), and Leucaena spp. (i.e., tannins) decreased CH4 production by 20.3, 27.1, and 23.5%, respectively, without extensively, or only slightly, affecting ruminal fermentation and digestibility of nutrients. It should be noted, however, that although the total number of publications (n = 277) and treatment means comparisons (n = 1,325 for CH4 production) in the current analysis were high, data for most mitigation interventions were obtained from less than 5 observations (e.g., maximum number of observations was 4, 7, and 22 for nitrophenol, Enterococcus spp., and Leucaena spp., respectively), because of limited data available in the literature. These should be further evaluated in vitro and in vivo to determine their true potential to decrease enteric CH4 production, yield, and intensity. Some mitigation interventions (e.g., magnesium, Heracleum spp., nitroglycerin, β-cyclodextrin, Leptospermum pattersoni, Fructulus Ligustri, Salix caprea, and Sesbania grandiflora) decreased in vitro CH4 production by over 50% but did not have enough observations in the database. These should be more extensively investigated in vitro, and the dose effect must be considered before adoption of mitigation interventions in vivo.

Effects of ensiling time on corn silage starch ruminal degradability evaluated in situ or in vitro

Accurate measurements of concentration and ruminal degradability of corn silage starch is necessary for formulation of diets that meet the energy requirements of dairy cows. Five corn silage hybrids ensiled for 0 (unfermented), 30, 60, 120, and 150 d were used to determine the effects of ensiling time on starch degradability of corn silage. In addition, the effects of grind size of silage samples on 7-h in vitro starch degradability and the relationship between in vitro, in situ and near-infrared reflectance spectroscopy (NIRS) starch degradability were studied. In situ disappearance of corn silage starch increased from 0 to 150 d of ensiling, primarily as a result of an increase in the washout or rapidly degraded fraction of starch, particularly during the first 60 d of ensiling. When analyzed in vitro and by NIRS, ensiling time increased corn silage starch degradability either linearly or to a greater extent during the first 2 mo of ensiling. Differences in in situ starch disappearance among corn silage hybrids were apparent during the first 2 mo of ensiling but were attenuated as silages aged. No differences among hybrids were detected using a 7-h in vitro starch digestibility approach. Results from the in vitro subexperiment indicate that 7-h in vitro starch degradability was increased by reducing grind size of corn silage from 4 to 1 mm, regardless of ensiling duration. Fine grinding corn silages samples (i.e., 1-mm sieve) allowed distinguishing low- from medium- and high-starch degradability rated hybrids. Correlations among in situ, in vitro and NIRS measurements for starch degradability were medium to high (r ≥0.57); however, agreement among methods was low (concordance correlation coefficient ≤0.15). In conclusion, ensiling time linearly increased degradation rate of corn silage resulting in greater in situ starch disappearance after 150 d of ensiling. Reductions in grind size from 4 to 1 mm resulted in greater in vitro starch degradability, regardless of ensiling duration. Strong correlation but low agreement between starch degradability methods suggest that absolute estimations of corn silage starch degradability will vary, but all methods can be used to assess the effect of ensiling time on starch degradability.

Impact of Co-Ensiling of Maize with Moringa oleifera on the Production of Greenhouse Gases and the Characteristics of Fermentation in Ruminants

The objective of this experiment was to evaluate the impact of maize co-ensiling with increasing percentages of MOL forage on the kinetics of biogas, methane (CH₄), carbon monoxide (CO) and hydrogen sulfide (H₂S) production, as well as the characteristics of ruminal fermentation and CH₄ conversion efficiency, using steers (STI) and sheep (SHI) as inoculum sources. With the STI, the inclusion of MOL reduced (linear: p ≤ 0.0199; quadratic: p ≤ 0.0267) biogas production (mL g^-1 DM incubated and degraded), CH₄ (mL g^-1 DM degraded), CO (mL g^-1 DM degraded), and H₂S (mL g^-1 DM incubated and degraded), without affecting (p > 0.05) the parameters (b = asymptotic gas, c = rate of gas production and Lag = initial delay time before gas production) of CH₄ and H₂S, and the proportion and production of CH₄ per kg of dry matter (DM). In addition, with this inoculum, pH, and dry matter degradation (DMD) increased (linear: p ≤ 0.0060), and although short-chain fatty acids (SCFA) and metabolizable energy (ME) decreased (linear: p < 0.0001; quadratic: p ≤ 0.0015), this did not affect (p > 0.05) the CH₄ conversion efficiency. Meanwhile, with the SHI, the inclusion of MOL only decreased (linear: p ≤ 0.0206; quadratic: p ≤ 0.0003) biogas per dry matter (DM) degraded and increased (linear: p ≤ 0.0293; quadratic: p ≤ 0.0325) biogas per DM incubated, as well as the production (mL g^-1 DM incubated and degraded and g^-1 kg DM) and proportion of CH₄, and CO per DM incubated and degraded. In addition, it did not impact (p > 0.05) on the CH₄ and H₂S parameters, and in the H₂S by DM incubated and degraded, and although it increased (linear: p ≤ 0.0292; quadratic: p ≤ 0.0325) the DMD, SCFA, and ME, it was inefficient (quadratic: p ≤ 0.0041) in CH₄ conversion. It is concluded that regardless of the percentage of MOL, the STI presented the highest values in the production of biogas, CH₄, H₂S, DMD, SCFA, and ME, and the lowest pH, so it turned out to be the most efficient in CH₄ conversion, while with the SHI only the highest production of CO and pH was obtained, and the lowest DMD, SCFA, and ME, so it was less efficient compared to STI.

Effects of the addition of non-fibre carbohydrates with different rumen degradation rates in dairy cow high-forage diets using the Rumen Simulation Technique

Nutrient synchronisation of protein and carbohydrates is a promising practice to improve ruminal nutrient utilisation. However, dietary sources supplying these nutrients can vary in ruminal nutrient availability due to differing degradation rates, therefore potentially affecting utilisation of nitrogen (N). The effects of the addition of non-fibre carbohydrates (NFCs) with different rumen degradation rates in high-forage diets on ruminal fermentation, efficiency and microbial flow were investigated in vitro using the Rumen Simulation Technique (RUSITEC). Four diets were tested: control with 100% ryegrass silage (GRS) and substitution of 20% on a DM basis of ryegrass silage with corn grain (CORN), processed corn (OZ) or sucrose (SUC). The four diets were assigned to 16 vessels in two sets of RUSITEC apparatuses in a randomised block design over a 17 d experimental trial; 10 d consisted of adaptation and 7 d for sample collection. Rumen fluid was collected from four rumen-cannulated dry Holstein-Friesian dairy cows and was treated without mixing. Then, rumen fluid from each cow was used to inoculate four vessels, and diet treatments were randomly allocated to each one. This was repeated for all cows resulting in 16 vessels. The inclusion of SUC in ryegrass silage diets improved DM and organic matter digestibility. The only diet to significantly lower ammonia-N concentration compared with GRS was SUC. The outflows of non-ammonia-N, microbial-N, and efficiency of microbial protein synthesis were not affected by diet type. However, the efficiency of nitrogen utilisation was improved by SUC compared with GRS. This indicates that the inclusion of an energy source with a high rumen degradation rate in high-forage diets improves rumen fermentation, digestibility, and N utilisation. Specifically, this effect was observed for the more readily available energy source, SUC, compared with the more slowly degradable NFC sources, CORN and OZ.

Technical note: Evaluation of sampling methods for methane concentration from in vitro fermentation

The objectives of this multipart study were 1) to assess the efficacy of sampling methods of methane concentration ([CH4]) of headspace gas produced during in vitro gas production (IVGP) fermentation, 2) to verify whether headspace [CH4] sampled from an exetainer has the same [CH4] as the headspace of IVGP bottles, 3) to measure relative humidity (RH) within an IVGP bottle, and 4) to compare [CH4] on a dry-gas (DG) basis when accounting for water vapor pressure (Pw). The original IVGP protocol recommends placing bottles on ice (0 °C) for 30 min to stop fermentation (ICE). A laboratory protocol recommends placing the bottles in the refrigerator (4 to 6 °C) to slow fermentation for 48 h and subsequently allowing the bottles to return to ambient temperature before sampling (FRIDGE). This study evaluated the previous methods against a direct sampling of the headspace gas after incubation (DIRECT). Rumen inoculum from four rumen-cannulated beef steers was combined and homogenized before incubating the fermentable substrate of ground alfalfa hay. After 48 h of IVGP incubation, each bottle was randomly assigned to a treatment protocol. The pressure (P), volume (V), and temperature (T) of headspace gas in each bottle were recorded. Headspace gas was then thoroughly mixed, and 12 mL gas was removed into an evacuated exetainer for [CH4] sampling via gas chromatography (EXET; Objective 1). Eight bottles from ICE and FRIDGE were randomly selected to follow EXET, whereas the remaining bottles had [CH4] directly measured from their headspace (BOTT; Objective 2). Five diets of differing feed composition and nutrient densities were used with a blank to test the RH of the IVGP slurry (Objective 3). Using RH, [CH4] was transformed to a DG basis to account for Pw (Objective 4). Statistical analysis was completed using a random coefficients model. There were no differences between EXET and BOTT (P = 0.28). The RH of the IVGP slurry was 100% (P = 1.00), confirming that IVGP gas is saturated with water vapor. The P, V, and T differed among treatments (P < 0.01). The [CH4] of DIRECT, ICE, and FRIDGE were different (P < 0.01). Dry-gas P, V, and [CH4] differed among treatments (P < 0.01). As the methods differ in their assessment of [CH4], there is no clear recommendation. Instead, to present a more accurate [CH4], P, V, and T should be measured when sampling headspace gas and equations presented should be used to remove volume inflation due to water vapor and present [CH4] on a DG basis.

Linking metabolites in eight bioactive forage species to their in vitro methane reduction potential across several cultivars and harvests

An in vitro Hohenheim gas test was conducted to analyze the fermentation end-products from 17 cultivars of eight polyphenol containing forage species. The polyphenol composition and proanthocyanidin (PA) structural features of all the cultivars were analyzed with UPLC-MS/MS in leaves of vegetative or generative plants. The samples were incubated with and without polyethylene glycol (PEG, a tannin-binding agent) to separate the tannin-effect on methane (CH4, ml/200 mg DM) production from that of forage quality. Sulla and big trefoil, two particularly PA rich species, were found to have the highest CH4 reduction potential of up to 47% when compared to the samples without PEG. However, concomitant reduction in gas production (GP, ml/200 mg DM) of up to 44% was also observed. An increase in both GP and CH4 production under PEG treatments, confirms the role of tannins in CH4 reduction. Moreover, PA structural features and concentration were found to be an important source of variation for CH4 production from PA containing species. Despite having low polyphenol concentrations, chicory and plantain were found to reduce CH4 production without reducing GP. Additionally, interspecies variability was found to be higher than intraspecies variability, and these results were consistent across growth stages, indicating the findings' representativeness.

Effects of Starch Level and a Mixture of Sunflower and Fish Oils on Nutrient Intake and Digestibility, Rumen Fermentation, and Ruminal Methane Emissions in Dairy Cows

Four multiparous dairy cows were used in a 4 × 4 Latin square to examine how starch level and oil mixture impact dry matter (DM) intake and digestibility, milk yield and composition, rumen fermentation, ruminal methane (CH4) emissions, and microbial diversity. Experimental treatments comprised high (HS) or low (LS) levels of starch containing 0 or 30 g of a mixture of sunflower and fish oils (2:1 w/w) per kg diet DM (LSO and HSO, respectively). Intake of DM did not differ between cows fed LS and HS diets while oil supplementation reduced DM intake. Dietary treatments did not affect milk and energy corrected milk yields. There was a tendency to have a lower milk fat concentration due to HSO compared with other treatments. Both high starch level and oil supplementation increased digestibility of gross energy. Cows receiving HS diets had higher levels of total rumen VFA while acetate was lower than LS without any differences in rumen pH, or ruminal CH4 emissions. Although dietary oil supplementation had no impact on rumen fermentation, decreased CH4 emissions (g/day and g/kg milk) were observed with a concomitant increase in Anoplodinium-Diplodinium sp. and Epidinium sp. but a decrease in Christensenellaceae, Ruminococcus sp., Methanobrevibacter ruminantium and Mbb. gottschalkii clades.

Chemical composition, ruminal degradation kinetics, and methane production (in vitro) of winter grass species

BACKGROUND

Information about the nutritive value, dry matter (DM) digestibility, and methane (CH₄ ) emission potential of grass species is required for their optimal utilization in ruminant rations. The present study was designed: (i) to quantify the nutrient profile, mineral composition and in vitro dry matter digestibility (IVDMD) of winter grass species commonly available in northern Pakistan; and (ii) to measure the in vitro gas production (IVGP) and CH₄ emission of the grass species during 72 h in vitro ruminal fermentation. Seven grass species, namely, Cenchrus ciliaris, Setaria anceps, Panicum antidotale, P. maximum, Pennisetum purpureum, Pennisetum orientale, and Atriplex lentiformis were assessed.

RESULTS

A high level of variability (P < 0.001) was observed among grass species for the content of all measured nutrients, IVDMD, IVGP, and CH₄ -production. Notably, the content (g kg^-1 DM) of crude protein varied from 59.8 to 143.3, neutral detergent fiber from 560.3 to 717.9, IVDMD from 375.1 to 576.2, and 72 h cumulative IVGP from 97.6 to 227.4 mL g^-1 organic matter (OM) and CH₄ from 48 to 67 mL g^-1 OM. Among the grasses, P. antidotale had greater content (g kg^-1 DM) of crude protein (CP) (143.3), IVDMD (576.2), and 72 h cumulative IVGP (227.4 mL g^-1 OM), and produced the smallest amount of total CH₄ (48 mL g^-1 OM) during 72 h fermentation. In contrast, A. lentiformis had the lowest content (g kg^-1 DM) of CP (59.8), IVDMD (375.1), 72 h cumulative IVGP (97.6 mL g^-1 OM), and produced a greater amount of total CH₄ (67 mL g^-1 OM) during 72 h fermentation.

CONCLUSION

The findings of the current study highlight that it is possible to select and further develop grass species with high nutritional value and lower CH₄ -production, which can improve livestock productivity, farm profitability, and long-term environment sustainability. © 2020 Society of Chemical Industry.

Methane emissions, feed intake, and total tract digestibility in lambs fed diets differing in fat content and fibre digestibility

This study determined enteric methane (CH4) emissions, intake, and apparent total tract digestibility of diets varying in fibre digestibility and fat content. A Latin square design with two levels of fat [2.0% and 6.0% dry matter (DM); low and high] and two levels of fibre digestibility [low fibre digestibility (LFbD) or high fibre digestibility (HFbD)] was used. Higher dry matter intake (DMI) was observed (P < 0.01) for LFbD versus HFbD diets (2.56 vs. 2.14 kg d−1, respectively), with no effect of fat. Fibre, DM, and organic matter digestibility were higher (P < 0.01) for HFbD than LFbD diets. Increasing fat did not affect intake or digestibility of DM or dietary constituents but there was a fibre digestibility × fat content interaction (P < 0.01) for fat digestibility. There was also a fat content × fibre digestibility interaction (P < 0.05) for CH4 (g kg−1 DMI, organic matter intake, neutral detergent fibre intake, and percent gross energy intake), with emissions being higher when fat was added to the HFbD than the LFbD diet. The CH4 emissions per kilogram of neutral detergent fibre (NDF) digested were higher (P < 0.01) for the HFbD than the LFbD diet. Methane emissions were increased by the HFbD diet, but inclusion of fat had a differential impact on CH4 emissions as a proportion of DMI or NDF intake in diets differing in fibre digestibility.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

Nitrogen is a component of essential nutrients critical for the productivity of ruminants. If excreted in excess, N is also an important environmental pollutant contributing to acid deposition, eutrophication, human respiratory problems, and climate change. The complex microbial metabolic activity in the rumen and the effect on subsequent processes in the intestines and body tissues make the study of N metabolism in ruminants challenging compared with nonruminants. Therefore, using accurate and precise measurement techniques is imperative for obtaining reliable experimental results on N utilization by ruminants and evaluating the environmental impacts of N emission mitigation techniques. Changeover design experiments are as suitable as continuous ones for studying protein metabolism in ruminant animals, except when changes in body weight or carryover effects due to treatment are expected. Adaptation following a dietary change should be allowed for at least 2 (preferably 3) wk, and extended adaptation periods may be required if body pools can temporarily supply the nutrients studied. Dietary protein degradability in the rumen and intestines are feed characteristics determining the primary AA available to the host animal. They can be estimated using in situ, in vitro, or in vivo techniques with each having inherent advantages and disadvantages. Accurate, precise, and inexpensive laboratory assays for feed protein availability are still needed. Techniques used for direct determination of rumen microbial protein synthesis are laborious and expensive, and data variability can be unacceptably large; indirect approaches have not shown the level of accuracy required for widespread adoption. Techniques for studying postruminal digestion and absorption of nitrogenous compounds, urea recycling, and mammary AA metabolism are also laborious, expensive (especially the methods that use isotopes), and results can be variable, especially the methods based on measurements of digesta or blood flow. Volatile loss of N from feces and particularly urine can be substantial during collection, processing, and analysis of excreta, compromising the accuracy of measurements of total-tract N digestion and body N balance. In studying ruminant N metabolism, nutritionists should consider the longer term fate of manure N as well. Various techniques used to determine the effects of animal nutrition on total N, ammonia- or nitrous oxide-emitting potentials, as well as plant fertilizer value, of manure are available. Overall, methods to study ruminant N metabolism have been developed over 150 yr of animal nutrition research, but many of them are laborious and impractical for application on a large number of animals. The increasing environmental concerns associated with livestock production systems necessitate more accurate and reliable methods to determine manure N emissions in the context of feed composition and ruminant N metabolism.

In vitro gas and methane production in rumen fluid from dairy cows fed grass silages differing in plant maturity, compared to in vivo data

The relationship between in vitro rumen CH₄ production of grass silages, using the gas production technique, and in vivo data obtained with the same cows and rations in respiration chambers was investigated. Silages were made from grass harvested in 2013 on May 6th, May 25th, July 1st and July 8th. The grass silages were used to formulate four different rations which were fed to 24 cows in early and late lactation, resulting in a slightly different dry matter intake (DMI; 16.5 kg/day vs. 15.4 kg/day). The experimental rations consisted of 70% grass silage, 10% maize silage, and 20% concentrates on a dry matter basis. Cows were adapted to the rations for 17 days before rumen fluid was collected via oesophageal tubing, and in vitro gas and CH₄ production were analysed. In vitro total gas and CH₄ production of the (ensiled) grass expressed as ml/g OM decreased with advancing maturity of the grass. The in vitro CH₄ production after 48 hr of incubation expressed in ml/g OM did not correlate with the in vivo CH₄ production expressed in g/kg organic matter intake or g/kg DMI (R²  = .00-.18, p ≥ .287). The differences in CH₄ emission per unit of intake observed in vivo were rather small between the different rations, which also contributed to the observed poor relationship. Utilizing stepwise multiple regression improved the correlation only slightly. In vitro gas and CH₄ production varied based on whether donor cows were previously adapted to the respective ration or not, suggesting that careful adaption to the experimental diet should be envisaged in in vitro gas and CH₄ production experiments.

Changes in in vitro gas and methane production from rumen fluid from dairy cows during adaptation to feed additives in vivo

The adaptation of dairy cows to methane (CH4)-mitigating feed additives was evaluated using the in vitro gas production (GP) technique. Nine rumen-fistulated lactating Holstein cows were grouped into three blocks and within blocks randomly assigned to one of three experimental diets: Control (CON; no feed additive), Agolin Ruminant® (AR; 0.05 g/kg dry matter (DM)) or lauric acid (LA; 30 g/kg DM). Total mixed rations composed of maize silage, grass silage and concentrate were fed in a 40 : 30 : 30 ratio on DM basis. Rumen fluid was collected from each cow at days -4, 1, 4, 8, 15 and 22 relative to the introduction of the additives in the diets. On each of these days, a 48-h GP experiment was performed in which rumen fluid from each individual donor cow was incubated with each of the three substrates that reflected the treatment diets offered to the cows. DM intake was on average 19.8, 20.1 and 16.2 kg/day with an average fat- and protein-corrected milk production of 30.7, 31.7 and 26.2 kg/day with diet CON, AR and LA, respectively. In general, feed additives in the donor cow diet had a larger effect on gas and CH4 production than the same additives in the incubation substrate. Incubation substrate affected asymptotic GP, half-time of asymptotic CH4 production, total volatile fatty acid (VFA) concentration, molar proportions of propionate and butyrate and degradation of organic matter (OMD), but did not affect CH4 production. No substrate×day interactions were observed. A significant diet×day interaction was observed for in vitro gas and CH4 production, total VFA concentration, molar proportions of VFA and OMD. From day 4 onwards, the LA diet persistently reduced gas and CH4 production, total VFA concentration, acetate molar proportion and OMD, and increased propionate molar proportion. In vitro CH4 production was reduced by the AR diet on day 8, but not on days 15 and 22. In line with these findings, the molar proportion of propionate in fermentation fluid was greater, and that of acetate smaller, for the AR diet than for the CON diet on day 8, but not on days 15 and 22. Overall, the data indicate a short-term effect of AR on CH4 production, whereas the CH4-mitigating effect of LA persisted.

Influence of main dietary chemical constituents on the in vitro gas and methane production in diets for dairy cows

BACKGROUND

Modification of chemical composition of diets fed to dairy cows might be a good strategy to reduce methane (CH4) production in the rumen. Notable reductions of CH4 production compared to conventional high-roughages rations were more frequently observed for very concentrated diets or when fat supplements were used. In these cases, the reduction in the gas emission was mainly a consequence of an overall impairment of rumen function with a reduction of fiber digestibility. These strategies do not always comply with feeding standards used in intensive dairy farms and they are usually not applied owing to the risks of negative health and economic consequences. Thus, the present study evaluated the effects of seven commercial diets with contents of neutral detergent fiber (NDF), protein and lipids ranging 325 to 435 g/kg DM, 115 to 194 g/kg DM, and 26 to 61 g/kg DM, respectively, on in vitro degradability, gas (GP), and CH4 production.

RESULTS

In this experiment, changes in the dietary content of NDF, crude protein (CP) and lipids were always obtained at the expense or in favor of starch. A decreased of the dietary NDF content increased NDF (NDFd) and true DM (TDMd) degradability, and increased CH4 production per g of incubated DM (P < 0.001), but not that per g of TDMd. An increase of the dietary CP level did not change in vitro NDFd and TDMd, decreased GP per g of incubated DM (P < 0.001), but CH4 production per g of TDMd was not affected. An increased dietary lipid content reduced NDFd, TDMd, and GP per g of incubated DM, but it had no consequence on CH4 production per g of TDMd.

CONCLUSIONS

It was concluded that, under commercial conditions, changes in dietary composition would produce small or negligible alterations of CH4 production per unit of TDMd, but greater differences in GP and CH4 production would be expected when these amounts are expressed per unit of DM intake. The use of TDMd as a standardizing parameter is proposed to account for possible difference in DM intake and productivity.