G. O. Ribeiro

Inclusion of glycerol in forage diets increases methane production in a rumen simulation technique system.

We hypothesised that the inclusion of glycerol in the forage diets of ruminants would increase the proportion of propionate produced and thereby decrease in vitro CH₄ production. This hypothesis was examined in the present study using a semi-continuous fermentation system (rumen simulation technique) fed a brome hay (8·5 g) and maize silage (1·5 g) diet with increasing concentrations (0, 50, 100 and 150 g/kg DM) of glycerol substituted for maize silage. Glycerol linearly increased total volatile fatty acids production (P<0·001). Acetate production was quadratically affected (P=0·023) and propionate and butyrate production was linearly increased (P<0·001). Glycerol linearly increased (P=0·011) DM disappearance from hay and silage. Crude protein disappearance from hay was not affected (P=0·789), but that from silage was linearly increased (P<0·001) with increasing glycerol concentrations. Neutral-detergent fibre (P=0·040) and acid-detergent fibre (P=0·031) disappearance from hay and silage was linearly increased by glycerol. Total gas production tended to increase linearly (P=0·061) and CH₄ concentration in gas was linearly increased (P<0·001) by glycerol, resulting in a linear increase (P<0·001) in mg CH₄/g DM digested. Our hypothesis was rejected as increasing concentrations of glycerol in a forage diet linearly increased CH₄ production in semi-continuous fermenters, despite the increases in the concentrations of propionate. In conclusion, this apparent discrepancy is due to the more reduced state of glycerol when compared with carbohydrates, which implies that there is no net incorporation of electrons when glycerol is metabolised to propionate.

Repeated inoculation of cattle rumen with bison rumen contents alters the rumen microbiome and improves nitrogen digestibility in cattle

Future growth in demand for meat and milk, and the socioeconomic and environmental challenges that farmers face, represent a “grand challenge for humanity”. Improving the digestibility of crop residues such as straw could enhance the sustainability of ruminant production systems. Here, we investigated if transfer of rumen contents from bison to cattle could alter the rumen microbiome and enhance total tract digestibility of a barley straw-based diet. Beef heifers were adapted to the diet for 28 days prior to the experiment. After 46 days, ~70 percent of rumen contents were removed from each heifer and replaced with mixed rumen contents collected immediately after slaughter from 32 bison. This procedure was repeated 14 days later. Intake, chewing activity, total tract digestibility, ruminal passage rate, ruminal fermentation, and the bacterial and protozoal communities were examined before the first and after the second transfer. Overall, inoculation with bison rumen contents successfully altered the cattle rumen microbiome and metabolism, and increased protein digestibility and nitrogen retention, but did not alter fiber digestibility.

Effect of Propionibacterium freudenreichii in diets containing rapeseed or flaxseed oil on in vitro ruminal fermentation, methane production and fatty acid biohydrogenation

The objectives of the present study were to determine the effect of inoculating Propionibacterium freudenreichii subsp. shermanii ATCC 8262 (1 × 109 colony-forming units per vial) in a barley silage-based diet supplemented with flaxseed oil or rapeseed oil (60 g/kg DM), on in vitro proportions and yield of volatile fatty acids, methane production and fatty acid (FA) biohydrogenation. Total volatile fatty acid production (mM) and proportions of individual FAs were not affected (P ≥ 0.10) by P. freudenreichii. Similarly, propionibacteria had little impact on FA biohydrogenation, resulting only in an increased accumulation (P < 0.01) of C18:1 cis-15 (g/kg total FA) at 6 h of incubation, compared with the control (CON). Compared with the CON, an increased (P < 0.01) accumulation of vaccenic acid was observed at 48 h in all oil-containing treatments, regardless of the oil type. Similarly, the apparent biohydrogenation of flaxseed oil resulted in an increased (P ≤ 0.04) accumulation of conjugated linoleic acid cis-9, trans-11, compared with all other treatments. Additionally, flaxseed oil produced a greater (P ≤ 0.01) accumulation of beneficial biohydrogenation intermediates (C18:2 trans-11, cis-15; C18:1 cis-15 and vaccenic acid), reflecting its ability to produce a more desirable FA profile than that of rapeseed oil or CON. The inability of P. freudenreichii subsp. shermanii ATCC 8262 to alter ruminal fermentation in a manner that lowered methane production, along with only minor effects on FA profiles through biohydrogenation, suggests that the biological activity of this strain was not realised under in vitro batch-culture conditions.

Fermentation of Ammonia Fiber Expansion Treated and Untreated Barley Straw in a Rumen Simulation Technique Using Rumen Inoculum from Cattle with Slow versus Fast Rate of Fiber Disappearance

The purpose of this study was to determine the effect of rumen inoculum from heifers with fast vs. slow rate of in situ fiber digestion on the fermentation of complex versus easily digested fiber sources in the forms of untreated and Ammonia Fiber Expansion (AFEX) treated barley straw, respectively, using an artificial rumen simulation technique (Rusitec). In situ fiber digestion was measured in a previous study by incubating untreated barley straw in the rumen of 16 heifers fed a diet consisting of 700 g/kg barley straw and 300 g/kg concentrate. The two heifers with fastest rate of digestion (Fast ≥ 4.18% h-1) and the two heifers with the slowest rate of digestion (Slow ≤ 3.17% h-1) were chosen as inoculum donors for this study. Two Rusitec apparatuses each equipped with eight fermenters were used in a completely randomized block design with two blocks (apparatus) and four treatments in a 2 × 2 factorial arrangement of treatments (Fast or Slow rumen inoculum and untreated or AFEX treated straw). Fast rumen inoculum and AFEX straw both increased (P < 0.05) disappearance of dry matter (DMD), organic matter, true DMD, neutral detergent fiber, acid detergent fiber, and nitrogen (N) with an interactive effect between the two (P < 0.05). Fast rumen inoculum increased (P > 0.05) methane production per gram of digested material for both untreated and AFEX straw, and reduced (interaction, P < 0.05) acetate: propionate ratio for untreated straw. Greater relative populations of Ruminococcus albus (P < 0.05) and increased microbial N production (P = 0.045) were observed in Fast rumen inoculum. AFEX straw in Fast inoculum had greater total bacterial populations than Slow, but for untreated straw this result was reversed (interaction, P = 0.013). These findings indicate that differences in microbial populations in rumen fluid contribute to differences in the capacity of rumen inoculum to digest fiber.

Synergism of cattle and bison inoculum on ruminal fermentation and select bacterial communities in an artificial rumen (Rusitec) fed a barley straw based diet

This study evaluated the effect of increasing the proportion of bison relative to cattle inoculum on fermentation and microbial populations within an artificial rumen (Rusitec). The experiment was a completely randomized design with a factorial treatment structure (proportion cattle:bison inoculum; 0:100, 33:67, 67:33, and 100:0) replicated in two Rusitec apparatuses (n = 8 fermenters). The experiment was 15 d with 8 d of adaptation and 7 d of sampling. Fermenters were fed a diet of 70:30 barley straw:concentrate (DM basis). True digestibility of DM was determined after 48 h of incubation from d 13 to 15, and daily ammonia (NH3) and volatile fatty acid (VFA) production were measured on d 9–12. Protozoa counts were determined at d 9, 11, 13, and 15 and particle-associated bacteria (PAB) from d 13 to 15. Select bacterial populations in the PAB were measured using RT-qPCR. Fermenter was considered the experimental unit and day of sampling as a repeated measure. Increasing the proportion of bison inoculum resulted in a quadratic effect (P < 0.05) on straw, concentrate and total true DM disappearance and on straw and total neutral detergent fiber (aNDF) disappearance, with greater disappearances observed with mixed inoculum. There were no effect of source or proportion of inoculum on ADF disappearance (P > 0.05). Increasing bison inoculum linearly increased (P < 0.05) concentrate aNDF disappearance, total and concentrate N disappearance as well as total daily VFA and acetate production. A positive quadratic response (P < 0.05) was observed for daily NH3-N, propionate, butyrate, valerate, isovalerate and isobutyrate production, as well as the acetate:propionate ratio. Increasing the proportion of bison inoculum linearly increased (P < 0.05) total protozoa numbers. No effects were observed on pH, total gas and methane production, microbial N synthesis, or copies of 16S rRNA associated with total bacteria, Selenomonas ruminantium or Prevotella bryantii. Increasing bison inoculum had a quadratic effect (P < 0.05) on Fibrobacter succinogenes, and tended to linearly (P < 0.10) increase Ruminococcus flavefaciens and decrease (P < 0.05) Ruminococcus albus copy numbers. In conclusion, bison inoculum increased the degradation of feed protein and fiber. A mixture of cattle and bison rumen inoculum acted synergistically, increasing the DM and aNDF disappearance of barley straw.

Effect of engineered biocarbon on rumen fermentation, microbial protein synthesis, and methane production in an artificial rumen (RUSITEC) fed a high forage diet1

The objective of this study was to investigate the effects of adding engineered biocarbon to a high-forage diet on ruminal fermentation, nutrient digestion, and enteric methane (CH4) production in a semi-continuous culture artificial rumen system (RUSITEC). The experiment was a completely randomized block design with four treatments assigned to sixteen fermentation vessels (four/treatment) in two RUSITEC apparatuses. The basal diet consisted of 60% barley silage, 27% barley grain, 10% canola meal, and 3% supplement (DM basis) with biocarbon added at 0, 0.5, 1, and 2% of substrate DM. The study period was 17 d, with a 10-d adaptation and 7-d sample collection period. Increasing biocarbon linearly increased (P < 0.05) disappearance of DM, OM, CP, ADF and NDF. Compared to control, increasing biocarbon enhanced (P < 0.01) production of total VFA, acetate, propionate, branch-chained VFAs, and tended to increase (P = 0.06) NH3-N. Microbial protein synthesis linearly increased (P = 0.01) with increasing biocarbon. Addition of biocarbon reduced overall CH4 production compared with the control (P ≤ 0.05). There were no differences (P > 0.05) in production of total gas, large or small peptides, or in the number of protozoa as a result of addition of biocarbon to the diet. Addition of biocarbon to a forage diet increased DM digestibility by up to 2%, while lowering enteric CH4 production and enhancing microbial protein synthesis in in vitro semi- continuous culture fermenters.