Laboratory variation of 24 h in vitro gas production and estimated metabolizable energy values of ruminant feeds

Evaluation of ruminal methane and ammonia formation and microbiota composition as affected by supplements based on mixtures of tannins and essential oils using Rusitec

BACKGROUND

Dietary supplements based on tannin extracts or essential oil compounds (EOC) have been repeatedly reported as a promising feeding strategy to reduce the environmental impact of ruminant husbandry. A previous batch culture screening of various supplements identified selected mixtures with an enhanced potential to mitigate ruminal methane and ammonia formation. Among these, Q-2 (named after quebracho extract and EOC blend 2, composed of carvacrol, thymol, and eugenol) and C-10 (chestnut extract and EOC blend 10, consisting of oregano and thyme essential oils and limonene) have been investigated in detail in the present study with the semi-continuous rumen simulation technique (Rusitec) in three independent runs. For this purpose, Q-2 and C-10, dosed according to the previous study, were compared with a non-supplemented diet (negative control, NC) and with one supplemented with the commercial EOC-based Agolin® Ruminant (positive control, PC).

RESULTS

From d 5 to 10 of fermentation incubation liquid was collected and analysed for pH, ammonia, protozoa count, and gas composition. Feed residues were collected for the determination of ruminal degradability. On d 10, samples of incubation liquid were also characterised for bacterial, archaeal and fungal communities by high-throughput sequencing of 16S rRNA and 26S ribosomal large subunit gene amplicons. Regardless of the duration of the fermentation period, Q-2 and C-10 were similarly efficient as PC in mitigating either ammonia (-37% by Q-2, -34% by PC) or methane formation (-12% by C-10, -12% by PC). The PC was also responsible for lower feed degradability and bacterial and fungal richness, whereas Q-2 and C-10 effects, particularly on microbiome diversities, were limited compared to NC.

CONCLUSIONS

All additives showed the potential to mitigate methane or ammonia formation, or both, in vitro over a period of 10 d. However, several differences occurred between PC and Q-2/C-10, indicating different mechanisms of action. The pronounced defaunation caused by PC and its suggested consequences apparently determined at least part of the mitigant effects. Although the depressive effect on NDF degradability caused by Q-2 and C-10 might partially explain their mitigation properties, their mechanisms of action remain mostly to be elucidated.

Differences in Donor Animal Production Stage Affect Repeatability of In Vitro Rumen Fermentation Kinetics

In vitro gas production techniques (IVGPT) are widely used to screen feeds and feed additives to reduce the number of animals needed for experiments, which in turn, reduces costs and increases animal welfare. However, information about repeatability is scarce. The objective of this study was to evaluate the variation from in vitro gas production fermentations in the same laboratory using the same feed substrate. The source of rumen fluid used in the fermentations was from two different farms with either cannulated lactating dairy cows or cannulated fasting heifers, representing two distinct stages of production (donor types). Seventeen 24 h fermentations, undertaken during a year, were used to evaluate the variation between the following parameters: gas curve parameters, baseline-corrected total gas production (TGP (mL at Standard Temperature and Pressure (STP))/g incubated dry matter (DM)), methane concentration (%) and yield (mL gas at STP/g DM), pH and degraded dry matter (dDM). Significant differences between donor types were found for the pH of the rumen fluid from individual animals and pH of fermented fluid. However, no significant differences were observed within donor type. The means for methane concentration and yield, after 24 h of fermentation, were not significantly different between or within donor types. Rate of early gas production was significantly different between donor types, but baseline-corrected TGP was not significantly different at 24 h. No dDM differences after 24 h of fermentation between or within donor types were detected. Gas production curves were different between donor types, being either a monophasic version of the sigmoidal model or an exponential curve for the heifers and the production animals, respectively. No differences were observed within type. Repeatability of rumen fluid (CVRF), calculated as the coefficient of variation, and the associated parameters, which were investigated, was best for methane yield (CVRFALL = 0.3%) and least for TGP at 3 h (CVRFALL = 3%). Repeatability was dependent on donor type.

Effect of Paulownia Leaves Extract Levels on In Vitro Ruminal Fermentation, Microbial Population, Methane Production, and Fatty Acid Biohydrogenation

Paulownia is a fast-growing tree that produces a huge mass of leaves as waste that can be used as a feed source for ruminants. The previous study showed that phenolic compounds were the most active biological substances in Paulownia leaves, which affected the ruminal parameters and methane concentration. However, there are no scientific reports on the Paulownia leaves extract (PLE) containing phenolic compounds for their mode of action in the rumen. Phenolics constituted the main group of bioactive compounds in PLE (84.4 mg/g dry matter). PLE lowered the concentration of ammonia, modulated the VFA profile in the ruminal fluid, and decreased methane production. The PLE caused a significant reduction of in vitro dry matter degradability, reduced the number of methanogens and protozoa, and affected selected bacteria populations. PLE had a promising effect on the fatty acid profile in the ruminal fluid. Paulownia as a new dietary component or its extract as a feed additive may be used to mitigate ruminal methanogenesis, resulting in environmental protection and reducing ruminal biohydrogenation, improving milk and meat quality.

Potential of Tunisian carob pulp as feed for ruminants: chemical composition and in vitro assessment

The nutritive value of the carob fruits harvested from ten different geographic regions of the North and the Center of Tunisia was assessed on the basis of chemical composition and in vitro rumen fermentation kinetic. Results showed that the chemical composition (ash, crude protein, fat, and sugar) of carob pods was highly influenced by geographic origin. Neutral detergent fiber varied from 24.37 to 35.58 g/100 g DM, acid detergent fiber from 13.24 to 25.15 g/100 g DM, and acid detergent lignin from 4.72 to 11.09 g/100 g DM. Total phenol, flavonoids, and condensed tannin contents varied from 2.55 to 6.84 g gallic acid equivalents (GAE)/100 g DM, from 74.89 to 276.51, and from 0.23 to 1.63 mg catechin equivalents (CE)/100 g DM, respectively. The samples varied widely in asymptotic gas production (66.6-86.34 ml/300 mg DM). The calculated metabolizable energy and digestible organic matter contents of carob pods ranged from 65.09 to 84.65% and 9.84 to 12.82 MJ/kg DM, respectively.

Effect of dried distillers' grain with solubles as a replacer of peanut cake for sheep fed on low quality forage

Several concerns exist on the performance and health attributes of sheep fed on complete replacements of the traditional feed ingredients with dried distillers' grain solubles (DDGS). The study intended to know the effect of DDGS on replacing the peanut cake (PNC) at 0%, 50%, 75%, and 100% in sheep fed Jowar stover-based diet. Replacing PNC with DDGS increased (P < 0.05) the final body weight and concentrate intake. The weight gain and average daily gain tended to increase (P = 0.086), whereas the feed conversion ratio tended to decrease (P = 0.092) with increased DDGS inclusion levels. The CP intake increased linearly (P < 0.01) with an increase in DDGS levels. However, the intakes of DM, OM, NDF, and ADF increased quadratically (P < 0.01) and showed a quadratic maximum at 75% replacements group. The in vitro dry matter digestibility and 24 h-gas (ml) production linearly increased (P < 0.05) with increased DDGS inclusion levels, while the CH₄ (% total gas) and CH₄ (ml) showed a quadratic increase (P < 0.05). The metabolisable energy, ammonia nitrogen, and volatile fatty acid concentrations were higher for DDGS diets. Further, the Gompertz curve fitting of the gas production data revealed higher asymptotic volume with lower constant of integration (b) and rate of production (k) of the DDGS incubations. No significant differences were observed for any of the carcass characteristics, except for leg weight, which showed a linear increase (P < 0.05). Increased tendency was observed for EBW, loin eye area at 12th rib, and edible portion of the sheep fed DDGS groups. Further, the visceral organs and carcass composition did not show any significant differences, except for kidney weight (linear, P < 0.05). The income over feed cost (IOFC) was higher for 100% DDGS group with lower feed cost and higher income per Kg mutton. Replacing the traditional peanut cake with DDGS in the crop residue-based diets of growing lambs contributes to higher yields for producers.

Fitting of the In Vitro Gas Production Technique to the Study of High Concentrate Diets

Simple Summary

The in vitro gas production technique, either based on volume or pressure measurements, was initially set up for the evaluation of the rate and extent of fermentation of feeds for ruminants. Since it is carried out under pH conditions simulating a well-buffered medium (from pH 6.5 to 6.8), it has been generally focused to evaluation of forages and fibrous by-products, or by estimating fermentation of concentrate feeds (cereals, protein sources) for extrapolation of their use in mixed diets. However, it has also been used for determination of the nutritive value of feeds in all-concentrate diets, without taking into account that in such cases pH may range between 6.5 and 5.8, and often below this range, creating unfavourable conditions for bacterial fermentation. Modifying the concentration of bicarbonate ion in the incubation solution allows to adjust the incubation pH to conditions that simulate the in vitro fermentation conditions to those occurring under high-concentrate feeding. This highlights the importance of the incubation pH for the estimation of fermentation of feeds.

Abstract

In vitro rumen fermentation systems are often adapted to forage feeding conditions, with pH values ranging in a range close to neutrality (between 6.5 and 7.0). Several attempts using different buffers have been made to control incubation pH in order to evaluate microbial fermentation under conditions simulating high concentrate feeding, but results have not been completely successful because of rapid exhaustion of buffering capacity. Recently, a modification of bicarbonate ion concentration in the buffer of incubation solution has been proposed, which, together with using rumen inoculum from donor ruminants given high-concentrate diets, allows for mimicking such conditions in vitro. It is important to consider that the gas volume recorded is in part directly produced from microbial fermentation of substrates, but also indirectly from the buffering capacity of the medium. Thus, the contribution of each (direct and indirect) gas source to the overall production should be estimated. Another major factor affecting fermentation is the rate of passage, but closed batch systems cannot be adapted to its consideration. Therefore, a simple semicontinuous incubation system has been developed, which studies the rate and extent of fermentation by gas production at the time it allows for controlling medium pH and rate of passage by manual replacement of incubation medium by fresh saliva without including rumen inoculum. The application of this system to studies using high concentrate feeding conditions will also be reviewed here.

Nutritional potential, in vitro ruminal fermentation kinetics and methanogenesis of stover from newer cultivars of sorghum (Sorghum bicolor) in buffalo

Context In developing countries of south Asia and Africa, cereal crop residues provide important fodder resources for ruminants. Genetic improvement through plant breeding for high-quality crop residues as well as for grain yield is gaining in demand among mixed crop–livestock farmers. Aims The present study investigated the potential nutritional quality, in vitro ruminal fermentation kinetics, gas production, enzyme activities and methane production of stover of newly developed brown midrib cultivars of sorghum (Sorghum bicolor (L.) Moench) compared with other cultivars in buffalo (Bubalus bubalis). Methods Stover from seven sorghum cultivars – brown midrib sorghum (SPV-2017, SPV-2018), normal grain sorghum (CSV-27), forage sorghum (SSG-59-3, CSV-32F) and sweet sorghum (CSH 22SS, CSV 24SS) – was analysed for chemical composition. Stover samples (200 ± 5 mg dry matter) from each cultivar were incubated with buffered rumen fluid (30 mL) in 100-mL calibrated glass syringes at 39°C for 72 h following a standard in vitro gas-production protocol for gas production and fermentation kinetics. Key results Stover chemical composition varied significantly (P &lt; 0.05) among cultivars, with highest organic matter in forage sorghum SSG-59-3 and lowest in sweet sorghum CSV-24SS. Acid detergent lignin was lowest in stover of the brown midrib cultivars (1.27% in SPV-2018 and 1.67% in SPV-2017) and highest in forage sorghum SSG-59-3 (9.42%). The brown midrib cultivars showed highest (P &lt; 0.001) total gas production, truly degradable dry matter, organic matter digestibility and metabolisable energy content. The brown midrib cultivars and forage sorghum CSV-32F had highest (P &lt; 0.05) production of volatile fatty acids (acetate, propionate and butyrate) and activity of ruminal enzymes (carboxymethyl cellulase and xylanase) during fermentation. Conclusions This study demonstrates that stover from brown midrib sorghum cultivars (SPV-2017 and SPV-2018) and forage sorghum CSV-32F could be preferred over stover of other cultivars for animal feed owing to their potential for enhanced utilisation. Implications This study provides information on nutritional quality of stover from newly developed sorghum cultivars for large-scale utilisation as animal feed in smallholder production systems of developing countries.

Fitting of pH conditions for the study of concentrate feeds fermentation by the in vitro gas-production technique

Two experiments were conducted to simulate in vitro the fermentation conditions under high-concentrate feeding. The concentration of bicarbonate ion in the buffer of the incubation solution was assayed in Experiment 1, by adjusting medium pH to 6.50, 6.25, 6.00, 5.75 and 5.50, in two incubation series of 12 h, using barley as the reference substrate. The pH diminished linearly (P < 0001) by lowering the buffer, and remained constant throughout 12 h, except for treatments 5.75 and 5.50, where pH dropped to 5.51 and 5.31 at 12 h. Gas production decreased linearly with a decreasing medium pH (P < 0.001), with the total volume of gas produced after 12 h being highly dependent (P < 0.01) on pH at 12 h (R2 = 0.629), thus demonstrating the importance of the incubation pH for estimation of fermentation of concentrate feeds. In Experiment 2, the effect of pH on direct and indirect proportion of gas was studied by adding 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 mmol of acetic acid, either with or without (water added instead) rumen inoculum, to the media. Linear multiple regressions established between the volume of gas produced and the addition of acetic acid, and the bicarbonate ion concentration showed high determination coefficients for water (R2 = 0.929) and rumen inoculum (R2 = 0.851). Without inoculum, indirect gas production ranged from 9.4 to 12.4 mL/mmol of acid for medium pH of 5.50–6.50. With rumen inoculum, indirect gas was 20.8 mL/mmol acid, although this may have been biased by the contribution of inoculum itself to direct fermentation.

Effects of particle size of processed barley grain, enzyme addition and microwave treatment on in vitro disappearance and gas production for feedlot cattle

OBJECTIVE

The effects of particle size of processed barley grain, enzyme addition and microwave treatment on in vitro dry matter (DM) disappearance (DMD), gas production and fermentation pH were investigated for feedlot cattle.

METHODS

Rumen fluid from four fistulated feedlot cattle fed a diet of 860 dry-rolled barley grain, 90 maize silage and 50 supplement g/kg DM was used as inoculum in 3 batch culture in vitro studies. In Experiment 1, dry-rolled barley and barley ground through a 1-, 2-, or 4-mm screen were used to obtain four substrates differing in particle size. In Experiment 2, cellulase enzyme (ENZ) from Acremonium cellulolyticus Y-94 was added to dry-rolled and ground barley (2-mm) at 0, 0.1, 0.5, 1, and 2 mg/g, while Experiment 3 examined the interactions between microwaving (0, 30, and 60 s microwaving) and ENZ addition (0, 1, and 2 mg/g) using dry-rolled barley and 2-mm ground barley.

RESULTS

In Experiment 1, decreasing particle size increased DMD and gas production, and decreased fermentation pH (p<0.01). The DMD (g/kg DM) of the dry-rolled barley after 24 h incubation was considerably lower (p<0.05) than that of the ground barley (119.1 dry-rolled barley versus 284.8 for 4-mm, 341.7 for 2-mm; and 358.6 for 1-mm). In Experiment 2, addition of ENZ to dry-rolled barley increased DMD (p<0.01) and tended to increase (p = 0.09) gas production and decreased (p<0.01) fermentation pH, but these variables were not affected by ENZ addition to ground barley. In Experiment 3, there were no interactions between microwaving and ENZ addition after microwaving for any of the variables. Microwaving had minimal effects (except decreased fermentation pH), but consistent with Experiment 2, ENZ addition increased (p<0.01) DMD and gas production, and decreased (p<0.05) fermentation pH of dry-rolled barley, but not ground barley.

CONCLUSION

We conclude that cellulase enzymes can be used to increase the rumen disappearance of barley grain when it is coarsely processed as in the case of dry-rolled barley. However, microwaving of barley grain offered no further improvements in ruminal fermentation of barley grain.

A ring test of a wireless in vitro gas production system

The in vitro gas production (GP) technique has been widely used for feed evaluation. However, variability in results limits useful comparisons. Results from a ring test undertaken in four laboratories (Italy – IT, Spain – SP, Wales – WA and Denmark – DK) using the same wireless equipment (ANKOM Technology), same substrates and same laboratory protocol are presented, including calculation of repeatability and reproducibility according to ISO 5725-2. Hay, maize starch and straw samples and units without sample (blanks) were incubated in five repetitions using rumen inoculum from cows (DK, IT and WA) or sheep (SP). Curves, corrected for blanks, were fitted using an exponential regression model with a lag time. The following variables were considered: (i) GP24 and GP48: raw values at 24 and 48 h (mL/g DM), corrected for blanks; (ii) A: asymptotic GP (mL/g DM); (iii) T1/2: time when half A is produced (h); (iv) GPMR: maximum predicted GP rate (mL/h); (v) L: lag time (h). A mixed model including laboratories as random effect was used. A significant interaction between substrate and laboratories was found for all variables except A. The most repeatable and reproducible results were observed for A and GP48. The results from this ring test suggest the need for more standardisation, particularly in the procedures that occur outside the laboratory.

Metabolisable Energy, In situ Rumen Degradation and In vitro Fermentation Characteristics of Linted Cottonseed Hulls, Delinted Cottonseed Hulls and Cottonseed Linter Residue

Dietary supplementation with conventional linted cottonseed hulls (LCSH) is a common practice in livestock production all over the world. However, supplementation with mechanically delinted cottonseed hulls (DCSH) and cottonseed linter residue (CLR) is uncommon. Cottonseed by-products, including LCSH, DCSH and CLR, were assessed by chemical analysis, an in situ nylon bag technique, an in vitro cumulative gas production technique and in vitro enzyme procedure. The crude protein (CP) content of CLR (302 g/kg dry matter (DM)) was approximately 3 times that of LCSH and 5 times that of DCSH. The crude fat content was approximately 3 times higher in CLR (269 g/kg DM) than in LCSH and 4 times higher than in DCSH. Neutral detergent fibre (311 g/kg DM) and acid detergent fibre (243 g/kg DM) contents of CLR were less than half those of DCSH or LCSH. Metabolisable energy, estimated by in vitro gas production and chemical analyses, ranked as follows: CLR (12.69 kJ/kg DM)>LCSH (7.32 kJ/kg DM)>DCSH (5.82 kJ/kg DM). The in situ degradation trial showed that the highest values of effective degradability of DM and CP were obtained for CLR (p<0.05). The in vitro disappearance of ruminal DM ranked as follows: CLR>LCSH>DCSH (p<0.05). The lowest digestibility was observed for DCSH with a two-step in vitro digestion procedure (p<0.05). The potential gas production in the batch cultures did not differ for any of the three cottonseed by-product feeds. The highest concentration of total volatile fatty acids was observed in CLR after a 72 h incubation (p<0.05). The molar portions of methane were similar between all three treatments, with an average gas production of 22% (molar). The CLR contained a higher level of CP than did LCSH and DCSH, and CLR fermentation produced more propionate. The DCSH and LCSH had more NDF and ADF, which fermented into greater amounts of acetate.

Effect of tannin-binding agents (polyethylene glycol and polyvinylpyrrolidone) supplementation on in vitro gas production kinetics of some grape yield byproducts

The effects of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) on in vitro gas production characteristics, organic matter digestibility (OMD), and metabolizable energy (ME) contents of some grape yield byproducts were investigated. The gas production was recorded after 2, 4, 6, 8, 12, 16, 24, 36, and 48 h of incubation. The gas production profiles in triplicate fitted with equation Y = A (1 – e^−ct). The data was analyzed using completely randomized design. Total phenol (TP) and total tannin (TT) contents were highest for raisin waste (RW). The TP content (g/kg DM) ranged from 30.1 in grape pomace (GP) to 96.3 in RW, which also had the higher TT (72.1 g/kg DM). The potential gas production (a + b) of DGB, GP, and RW were 239.43, 263.49, and 208.22 mL/g DM, respectively. In the absence of PEG and PVP, rate constant of gas production (c) for GP was highest among the feedstuffs (0.1073 mL/h), but in presence of PEG or PVP, RW had highest fraction (c) among the feedstuffs. Addition of PEG and PVP inactivated effects of tannins and increased gas production, ME, NE₁, OMD, and VFA in grape yield byproducts. Addition of PEG and PVP could overcome adverse effects of tannins on nutrient availability as indicated by gas production parameters.