Concentration of indoles and other rumen metabolites in sheep after a meal of fresh white clover,perennial ryegrass or Lotus corniculatus and the appearance of indoles in the blood

The objective of this study was to determine the effect of feeding three fresh forage diets, white clover (WC), perennial ryegrass (PRG) and Lotus corniculatus (LC), on the formation of indole and skatole in the rumen of sheep. The formation of indole and skatole in the rumen and their appearance in the blood were also compared. Peak rumen indole and skatole concentrations per kg crude protein intake (CPI) were significantly higher when feeding WC compared with PRG and LC (P < 0.05) and this was associated with a significantly higher rumen concentration per kg CPI of ammonia, branched chain volatile fatty acids, total nitrogen and soluble nitrogen (P < 0.05). Greater indole and skatole concentrations when feeding WC can be attributed to high solubility and rapid degradation of the forage protein. LC had a similar nutrient composition to WC, but the condensed tannins in LC slowed protein degradation and reduced indole and skatole formation. Indole and skatole concentrations peaked in the plasma 1–2 h after the end of feeding, indicating that skatole and indole are rapidly absorbed from the rumen into the blood. High indole and skatole formation with low intakes of WC indicates that the WC component of traditional New Zealand pastures may be the primary cause of undesirable pastoral flavours that result from the presence of indoles in meat. To ameliorate undesirable flavours, producers reliant on pastoral systems will need to consider using alternative forages such as LC to reduce protein solubility and degradation rate. Copyright © 2007 Society of Chemical Industry     

The effect of supplementation of a white clover or perennial ryegrass diet with grape seed extract on indole and skatole metabolism and the sensory characteristics of lamb

Condensed tannin in the form of a grape seed extract (GSE) was dosed to weaned wether lambs fed white clover (WC) or perennial ryegrass (PRG) over a 9‐week period to determine whether the ‘pastoral’ flavour and odour of meat could be altered. The concentrations of the pastoral flavour compounds indole and skatole were determined in the rumen fluid, blood plasma and intermuscular fat. The odour and flavour of fat and meat from the slaughtered lambs was assessed by a trained panel. The rumen fluid and blood plasma concentrations of indole and skatole were higher in those lambs fed WC compared to PRG (P < 0.05) and the overall meat flavour intensity was greater when feeding WC (P < 0.01). The observed concentration of indole and skatole in the fat between WC and PRG feeding treatments was not statistically different. Power analysis indicated that increasing the number of lambs per treatment group from 20 to 65 would result in a higher fat skatole concentration (P < 0.05) being detected in lambs fed WC compared to PRG. Dosing with GSE gave a small reduction in skatole concentration in the rumen fluid and reduced plasma concentration of indole and skatole (P < 0.001). Odour and flavour scores of the fat and meat samples were not particularly high however, dosing with GSE lowered the overall and sweet odour and the sheepy, camphor, faecal and barnyard flavour (P < 0.05). Although the plasma concentration of indole and skatole suggests that GSE reduced indole and skatole formation, the intermittent supply of the GSE to the rumen environment was not sufficient to reduce their concentration in the fat. Hence, the small difference in the scores for pastoral odour and flavour attributes associated with GSE treatment may arise from other unknown factors. From a primary investigation, there was no difference in the concentration of indole and skatole in fat samples collected from carcasses before and after chilling. Further investigations into meat pastoral flavour are warranted through feeding condensed tannin‐containing forages. Copyright © 2007 Society of Chemical Industry     

Effect of different condensed tannin‐containing forages,forage maturity and nitrogen fertiliser application on the formation of indole and skatole in in vitro rumen fermentations

The objectives of this work were to establish the effect of seven different forages with a varied condensed tannin (CT) content, plant maturity and nitrogen fertiliser application on the ruminal formation of skatole and indole using an in vitro method designed to mimic rumen fermentation conditions. After 10 h of incubation, the concentration of indole and skatole was highest when incubating white clover (P < 0.05). Polyethylene glycol addition, to inhibit CT, showed that CT significantly reduced the formation of indole and skatole when incubating Lotus corniculatus, sulla, Dorynium rectum and Lotus pedunculatus (P < 0.01). Mature forage growth resulted in a significantly lower concentration of indole and skatole being formed in vitro compared to the incubation of new spring growth (P < 0.001). A higher application of nitrogen fertiliser to perennial ryegrass‐based pasture resulted in a higher crude protein concentration in the plant and a significantly higher concentration of skatole formed in vitro (P < 0.001). Forages containing CT reduced the conversion of endogenous protein to indole and skatole and plants containing a higher CT concentration tended to be more effective, but compositional differences of CT between forages may also have had an influence. New forage growth or swards that had a high application of nitrogen fertiliser promoted the formation of indole and skatole. Copyright © 2007 Society of Chemical Industry     

Condensed tannins from Lotus corniculatus and Lotus pedunculatus exert different effects on the in vitro rumen degradation of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) protein

Condensed tannins (CT) or proanthocyanidins (PA), which occur in a restricted range of forages, have the ability to interact with proteins and enzymes and can influence the digestion of plant protein in the rumen. We compared the effects of CT extracts from Lotus corniculatus and pedunculatus on degradation of the principal leaf protein, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), by rumen microorganisms. Total soluble leaf protein extracted from white clover (Trifolium repens ) was incubated with fresh rumen fluid from sheep and a range of concentrations of each CT extract. The rate of degradation of the large (LSU) and small subunit (SSU) of Rubisco was quantified by fractionating the proteins in samples taken from in vitro rumen incubations using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS‐PAGE) and imaging densitometry. To deduce the effects of the CT extracts, experiments were performed in the presence (CT inactive) and absence (CT active) of polyethylene glycol (PEG; MW 3350). The two CT extracts differed markedly in their effects on the degradation of the LSU and SSU of Rubisco. At concentrations of 0.89 and 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extract from L pedunculatus was more effective at preventing the degradation of the LSU and SSU by rumen microorganisms than the CT extract from L corniculatus. At a concentration of 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extracts from L corniculatus and pedunculatus prevented about 0.75 and 0.83 of the LSU and about 0.69 and 0.86 of the SSU, respectively, from being degraded. Addition of PEG removed the inhibition and almost complete degradation of these proteins occurred, as was the case in incubations without CT extracts. The results of this study suggest that the concentration of CT in the diet and the chemical structure which affects the activity of the CT needs to be considered when assessing the effects of CT on protein metabolism in ruminants. © 1999 Society of Chemical Industry     

Effect of feeding complete feed block containing Prosopis cineraria leaves and polyethylene glycol (PEG)‐6000 on nutrient intake,its utilization,rumen fermentation pattern and rumen enzyme profile in kids

A study was carried out to determine the effect of replacing the cake portion of concentrate mixture with 5 parts polyethylene glycol (PEG)‐6000 in a complete feed block (CFB) containing Prosopis cineraria leaves on the performance, rumen fermentation pattern and rumen enzyme profile of kids under an intensive system of rearing. Eighteen weaners of Sirohi goat of similar body weight (16.0 ± 0.5 kg) and age (90 ± 5 days) were divided into three equal groups. They were housed in individual cages in a side open asbestos roof shed with mud floor. All the kids received CFBs containing 50 parts P cineraria leaves and 50 parts concentrate mixture. CFB offered to the first group had high protein (183.8 g kg^?1; HP), that offered to the second group had low protein (131.3 g kg^?1; LP) and that offered to the third group had low protein (124.7 g kg^?1) but contained PEG‐6000 (LP‐PEG). The concentrate mixtures in LP and LP‐PEG were without groundnut cake, whereas in LP‐PEG, groundnut cake was replaced by barley and 5 parts PEG‐6000 were incorporated. CFBs were similar in their nutritive value except for crude protein (CP). Prosopis leaves utilized in the CFB contained (g kg^?1 dry matter) 129.1 CP, 535.5 neutral detergent fibre, 395.8 acid detergent fibre and 222.8 acid detergent lignin. There were significant differences in dry matter intake (g day^?1) between HP (1102), LP (1108) and LP‐PEG (1194); the trend in Metabolizable energy intake was similar. During the growth trial, LP kids consumed maximum amount of feed (76.91 kg) followed by HP (75.73 kg) and LP‐PEG (73.12 kg). However, maximum feed efficiency (feed consumed kg^?1 live weight gain) was recorded in LP‐PEG kids (9.59) followed by HP (10.64) and LP (11.60). These differences were statistically significant (p < 0.05). Although there was no significant difference in the digestibility of dry matter among the groups, there was significant difference in the digestibility of CP, neutral detergent fibre and acid detergent fibre. The digestibility of CP was 0.591, 0.484 and 0.645, that of neutral detergent fibre was 0.397, 0.308 and 0.499 and that of acid detergent fibre was 0.168, 0.154 and 0.282 in HP, LP and LP‐PEG, respectively. Rumen metabolites studied 6 h after feeding revealed that there were significant (p < 0.05) differences in the concentrations of ammonia N, tri‐chloro acetic acid precipitable N and total volatile fatty acids among the three groups, but not pH. The rumen enzyme concentrations showed significant (p < 0.05) differences for α‐amylase, whereas the differences were non‐significant for CMcase and protease. After 90 days of feeding trial, the maximum weight gain was recorded in LP‐PEG (7.62 kg) followed by HP (7.23 kg) and LP (6.53 kg). It can be concluded that, when kids are reared under an intensive system on complete feed blocks containing Prosopis leaves, high protein concentrate can be replaced with a low protein concentrate containing 5 parts PEG, which would not only alleviate the negative effects of tannin but would also spare expensive groundnut protein. Copyright © 2005 Society of Chemical Industry     

Fermentation characteristics,aerobic stability and ruminal degradation of ensiled pea/wheat bi‐crop forages treated with two microbial inoculants,formic acid or quebracho tannins

This study evaluated the effects of two commonly used microbial inoculants (Lactobacillus buchneri (LB) and Lactobacillus plantarum (LP)), formic acid (FA) and quebracho tannins (QT) on the fermentation quality, aerobic stability and in situ rumen degradation of pea/wheat bi‐crop forages. Precision‐chopped spring pea (Pisum sativum, var Magnus) and wheat (Triticum aestivum, var Axona) bi‐crops (3:1 pea/wheat ratio) harvested at a combined dry matter (DM) content of 301 g kg^?1 were used for the study. The bi‐crops were conserved without (Control) or with inoculants based on lactic acid bacteria (LB (10⁵ CFU g^?1 fresh weight (FW)) or LP (10⁶ CFU g^?1 FW)), QT (16 g kg^?1 FW) or FA (2.5 g kg^?1 FW) in laboratory silos of 1.5 kg capacity, with each treatment being replicated six times. The pH, chemical composition, aerobic stability and in situ rumen degradation of DM, nitrogen (N) and neutral detergent fibre (NDF) after 112 days of ensilage were measured. The average pH at silo opening was 4.0, suggesting that the silages were well fermented. There were no significant effects of additive treatment on water‐soluble carbohydrate, total N, soluble N, ammonia N and NDF. Lactic acid and acetic acid were the main fermentation products. High concentrations of acetic acid were found in all the treatments, indicating a heterofermentative pathway. Although FA treatment gave the most aerobically stable silage, the Control and QT‐treated silages did not heat up by more than 1 °C until after 6 days of exposure to air. There were no effects of additives on DM degradation characteristics. However, the inoculants increased the rate of N and NDF degradation in the rumen, and both FA and QT reduced the effective and potential degradation of N. © 2001 Society of Chemical Industry     

Spatial variation of intestinal skatole production and microbial community in Jinhua and Landrace pigs

BACKGROUND: An excessive accumulation of skatole in pigs is a major contributor to boar taint. Intestinal skatole concentrations may vary among different pig segments and breeds. The objective of this study was to evaluate the spatial variation of intestinal skatole production and the microbial community in local Jinhua and exotic Landrace pigs. RESULTS: For both breeds, skatole concentration increased towards the rectum and segment had a significant effect on skatole (P < 0.001). The caecal skatole concentration in Landrace was significantly lower than proximal, distal colonic and rectal skatole levels (P < 0.05). Compared with Jinhua pigs, the rectal skatole and proximal and distal colonic indole levels were significantly higher in Landrace pigs (P < 0.05). Volatile fatty acids were significantly affected by breed except for isobutyrate and isovalerate (P < 0.05), with higher butyrate level and lower pH in Landrace pigs (P < 0.05). There were no significant differences in mitosis and apoptosis for the two breeds. The denaturing gradient gel electrophoresis profile showed differences between breeds and segments within one breed, though some bands were common to all samples. CONCLUSION: The higher skatole levels in Landrace pigs may be not associated with higher intestinal apoptosis. The results suggested that pig genotype plays a role in the establishment of the host‐specific microbiota and that the variations in fermentation patterns are more likely to explain differences in intestinal skatole production. Copyright © 2009 Society of Chemical Industry     

Comparison of biological and chemical methods,and internal and external standards,for assaying tannins in Spanish shrub species

Tannin contents of stems, flowers and leaves of four shrub species (Erica arborea, Erica australis, Cytisus cantabricus and Genista occidentalis) were chemically assessed using two colorimetric assays (butanol–HCl and Folin–Ciocalteu) and several standards (tannic acid, purified quebracho condensed tannins (CT) and purified CT extracted from each species). A method based on the biological activity of tannins in the rumen was also used for assaying tannins. Depending on the species, the use of quebracho tannin as standard over‐ or underestimated CT contents, in comparison to the use of the respective internal standard. However, the high correlationship observed between in vitro gas production in the presence or absence of polyethylene glycol (PEG) and CT contents estimated from quebracho suggests that this standard could be used for a quicker estimate of the nutritive value of tannin‐containing plants. Tannin contents obtained by the Folin–Ciocalteu method, using tannic acid as standard, were also related to their activity on rumen fermentation. The use of the in vitro gas production technique, in the absence or presence of PEG, may provide more useful information than the chemical assays when the final aim of tannin analysis is to assess the nutritive value of feedstuffs for ruminants. Copyright © 2004 Society of Chemical Industry     

Simple phenols and indoles in anaerobically stored piggery wastes

Phenol, p-cresol, 4-ethylphenol, indole and skatole, which contribute to a large extent to the bad smell of piggeries, were estimated in anaerobically stored piggery wastes. p-Cresol, indole and skatole were also found in freshly voided faeces. Phenol, p-cresol and 4-ethylphenol are present in the urine as their glucuronides. It was shown that upon contact of urine and faeces, the urinary glucuronides are hydrolysed almost instantly liberating phenols. This hydrolysis is caused by the high β-glucuronidase activity of faeces. Protein degradation followed by transformation of tyrosine and tryptophane were found to be additional processes contributing to the accumulation of phenol, p-cresol, indole and skatole during the anaerobic storage of piggery wastes.     

Effects of intraruminal administration of polyol to sheep

In-vitro incubations were used to study the effect of intraruminal administration of a mixture of the polyhydric alcohols, arabinitol, xylitol, galactitiol, mannitol and sorbitol, on fermentation pattern and the fate of the polyhydric alcohols. Incubations were carried out with rumen fluid taken from sheep before receiving polyol and after 2 and 3 weeks of intraruminal administration of 2.12 g polyol DM/kg live wt.^0.75 per day to observe effects of adaptation. Inclusion of polyol in incubations with unadapted rumen fluid had little effect on the volatile fatty acid pattern. However, with adaptation there was a shift in the fermentation pattern in the presence of polyol towards a higher acetate: propionate ratio. The hexitols rapidly disappeared in all the incubations, while the pentitols were more resistant to fermentation. Significantly faster fermentation of arabinitol by rumen fluid from sheep which had received polyol indicated that adaptation had taken place. In the incubations with adapted microbes, xylitol was significantly more resistant to fermentation than arabinitol; after 6 h incubation, approximately half the xylitol and only one fifth of the arabinitol remained unfermented. Analysis of duodenal digesta from adapted sheep which were receiving polyol showed that most of the small amount of pentitol which entered the small intestine did so within 2–3 h of dosing. Despite the apparent resistance of pentitols to rumen fermentation, only 1.0% of the arabinitol and 1.8% of the xylitol in the daily dose entered the small intestine.     

Production of indole by wine-associated microorganisms under oenological conditions

A high concentration of indole has been linked to ‘plastic-like’ off-flavour in wines, predominantly in wines produced under sluggish fermentation conditions. The purpose of this study was to determine the ability of yeast and bacteria to form indole and whether tryptophan was required for indole accumulation during winemaking. Wine-associated yeast and bacteria species (Saccharomyces cerevisiae, Saccharomyces bayanus, Candida stellata, Hanseniaspora uvarum, Kluyveromyces thermoloterans, Oenococcus oeni, Lactobacillus lindneri, Pediococcus cerevisiae and Pediococcus parvulus) were screened for their potential to generate indole during alcoholic or malolactic fermentation. Tryptophan was required for the accumulation of indole in chemically defined medium, and all yeast and bacteria fermentations were able to accumulate indole. C. stellata showed the greatest potential for indole formation (1033 μg/L) and among the bacteria, the highest concentration was generated by L. lindneri (370 μg/L). Whether primary fermentation is the principle cause of indole formation remains to be determined. We hypothesise that during an efficient fermentation, indole is removed through catabolic metabolism, but, when a sluggish fermentation arises, non-Saccharomyces species might produce excess indole that is still present by end of fermentation.     

Screening of indoles in cheese

 Indole and skatole (3-methylindole) are formed from tryptophan by microbial activity. Depending on their concentration, they may either contribute to an unpleasant odour, as described for pig meat, or alternatively to a positive aroma profile, as during ripening of cheese. In a screening study, the two indoles in various types of cheese were determined, by both HPLC and GC. It was found that the two compounds mainly occur in mould cheese, such as Camembert and are even more pronounced in blue-veined cheese. The concentrations in unripened cheese were up to 700 ng/g fat for indole and 50 ng/g fat for skatole. The formation of the two indoles increases when proteolysis during ripening provides more tryptophan. Skatole formation appears to be specifically favoured by a low pH and anaerobic conditions. Received: 14 May 1997     

Screening of indoles in cheese

 Indole and skatole (3-methylindole) are formed from tryptophan by microbial activity. Depending on their concentration, they may either contribute to an unpleasant odour, as described for pig meat, or alternatively to a positive aroma profile, as during ripening of cheese. In a screening study, the two indoles in various types of cheese were determined, by both HPLC and GC. It was found that the two compounds mainly occur in mould cheese, such as Camembert and are even more pronounced in blue-veined cheese. The concentrations in unripened cheese were up to 700 ng/g fat for indole and 50 ng/g fat for skatole. The formation of the two indoles increases when proteolysis during ripening provides more tryptophan. Skatole formation appears to be specifically favoured by a low pH and anaerobic conditions. Received: 14 May 1997     

Potential nutritive value and tannin bioassay of selected Acacia species from Kenya

Six Acacia forage species–A. brevispica, A. elatior, A. mellifera, A. nilotica, A. senegal and A. seyal—were analysed for their chemical composition, including phenolics and rumen fermentation characteristics. In vitro gas production technique was used to study the rumen fermentation characteristics and the effect of tannins present in the browse forages on in vitro fermentation by including polyethylene glycol (PEG‐6000) in the incubation. The forages had high crude protein content (145.7–270.1 g kg^?1 DM) and low to moderate content of neutral detergent fibre (220.2–442.8 g kg^?1 DM). The forages had variable content of total extractable phenolics ranging from 18.4 to 384.2 g kg^?1 DM and total extractable tannins ranging from 7.1 to 364.8 g kg^?1 DM (tannic acid equivalent). Fractionation of the condensed tannin flavonoids showed that the delphinidin/cyanidin ratio ranged from not detected:100 to 71:29. The gas production potential ranged from 28.4 to 40.8 mL gas 0.2 g^?1 DM. The rate of gas production was highest in A. elatior and lowest in A. nilotica. Addition of PEG‐6000 increased gas production significantly (P < 0.05) in all species except A. mellifera. PEG‐6000 addition did not have any significant effect on in vitro true dry matter and organic matter degradability but decreased the partitioning factor in all the species. Gas production and degradability parameters correlated positively with the CP content and negatively with the fibre and phenolics contents. Based on chemical composition, gas production and degradability, the forages have high potential nutritive value, especially as supplements to low‐quality feeds in the tropics and particularly during the dry season. However, the presence of tannins in terms of high levels and biological antinutritive activity may limit the nutritive potential of some of the forages, such as A. seyal and A. nilotica. Copyright © 2007 Society of Chemical Industry     

Are Jatropha curcas phorbol esters degraded by rumen microbes?

BACKGROUND: Jatropha curcas, a non‐edible oil plant, is being promoted as a biofuel plant in a number of countries in tropical and subtropical regions. The kernel meal left after extraction of the oil is a potentially protein‐rich feed ingredient. However, the presence of highly toxic phorbol esters limits its use. Degradation of J. curcas phorbol esters by rumen microbes, using an in vitro rumen fermentation system, has been investigated in this study. RESULTS: The difference between phorbol ester contents in the residues obtained with and without substrates at 0, 24, 48 or 72 h of the incubations was statistically similar. Phorbol esters did not affect either the gas or short chain production in the in vitro rumen fermentation system. CONCLUSIONS: Rumen microbes can not degrade phorbol esters. In addition, the phorbol esters do not adversely affect rumen fermentation. Ruminants are expected to be as prone as monogastric animals to the toxicity of Jatropha seeds. Copyright © 2010 Society of Chemical Industry     

Method for the determination of indole and skatole in pig fat

A quantitative method was developed to determine by gas-liquid chromatography the concentrations of indole and skatole in pig fat. Methanolic extracts of subcutaneous adipose tissue were de-fatted by cooling, concentrated using solid-phase extraction columns, and analysed in a gas chromatograph fitted with a polar capillary column and a flame ionisation detector. The method detects indole and skatole to below 0-002 mg kg^?1 fat.     

Effect of Heat Treatment Upon the Chemical Composition of Cottonseed Meal and Upon the Reactivity of Cottonseed Condensed Tannins

The effects of heat treatment on the chemical composition of cottonseed meal (CSM), with or without the addition of cottonseed hulls (containing condensed tannins; CT), and upon reactivity of the CT were studied. Heat was applied in a forced draught oven at 100°C for 2 h. Fluorodinitrobenzene (FDNB)-available lysine, free gossypol, extractable- and bound-CT concentrations, in vitro total nitrogen (N) solubility and the in vitro rumen degradation of the two major seed proteins (52 and 48 kDa) present in cottonseed kernel (which does not contain CT) were determined. The reactivity of CT was assessed by determining N solubility and rumen degradation of cottonseed kernel proteins in the presence or absence of polyethylene glycol (PEG; molecular weight (MW) 3500), which binds and inactivates CT. Heat treatment reduced the concentrations of free gossypol and FDNB-available lysine by small amounts, reduced measurable total CT content by 13%, reduced the solubility of total N, and reduced potential degradability of the 52 and 48 kDa cottonseed storage proteins by mixed rumen microorganisms. Addition of hulls further depressed solubility of total N and ruminal degradation of the two major storage proteins in cottonseed kernel. The action of PEG in vitro indicated that only part of the depression caused by hull addition could be explained by the presence of CT in the hulls, and that the effects of CT upon N solubility and potential degradability in heated CSM were similar to that in unheated CSM. Addition of hulls also substantially reduced FDNB-available lysine. In commercially produced materials, CSM from the Brisbane mill had a lower total CT content, lower N solubility and lower ruminal protein degradation rate than CSM from the Narrabri mill, but a similar level of FDNB-available lysine. Although application of heat inactivated 13% of the total CT, such that it could no longer be extracted and detected with butanol/HCl, it did not seem to change the overall effects produced by CT in reducing N solubility and protein degradation. The effect of hull addition in reducing available lysine has considerable relevance for feeding CSM to monogastric livestock. Interactions involving heat, hulls and CT need to be further studied.     

Interrelationships between the concentrations of total condensed tannin,free condensed tannin and lignin in Lotus sp. and their possible consequences in ruminant nutrition

Interrelationships between the concentrations of total condensed tannin (TCT), free condensed tannin (FCT) and lignin were studied to gain knowledge of how to manipulate nutritive value of fresh herbages containing condensed tannins fed to ruminants. FCT was defined as condensed tannin not bound by macerates of fresh plants, with both FCT and TCT being determined with vanillin HCl. Effects of spraying lotus with polyethylene glycol (mol. wt 3350; PEG) upon the relationship between FCT and TCT was also studied. Increasing soil nutrient and climatic stress caused large and similar increases in the concentrations of TCT and of lignin. Over the range 0–90 g kg^?1 DM, 10% of TCT in Lotus sp. was detected as FCT, with increments in TCT above 90 g kg^?1 DM being released almost entirely as FCT. PEG formed much stronger chemical bonds with condensed tannins than did plant proteins, and did not release FCT; consequently PEG application reduced the concentration of condensed tannin that was detectable with vanillin HCl. After disintegration of plant material, it is proposed that most condensed tannin is bound and co-precipitated as an insoluble complex with protein, that FCT is in equilibrium with this complex, and that bound and free tannin are indices of nutritionally beneficial and detrimental effects produced by condensed tannins in fresh forages eaten by ruminants. It was concluded that growing Lotus pedunculatus under conditions of stress leads to depressions in nutritive value through simultaneously increasing concentrations of lignin and FCT, both of which depress rumen carbohydrate digestion and voluntary intake, and that treatment with PEG offers a convenient method of separating effects due to condensed tannins from other factors influencing nutritive value.     

Difference in the nature of tannins on in vitro ruminal methane and volatile fatty acid production and on methanogenic archaea and protozoal populations

Six plant sources of hydrolyzable tannins (HT) or HT and condensed tannins (CT; designated as HT1, HT2, HT3, HT + CT1, HT + CT2, and HT + CT3) were evaluated to determine their effects in vitro on CH₄ production and on ruminal archaeal and protozoa populations, and to assess potential differences in biological activities between sources containing HT only or HT and CT. Samples HT1, HT2, and HT3 contained only HT, whereas samples HT + CT1, HT + CT2, and HT + CT3 contained HT and CT. In experiment 1, in vitro incubations with samples containing HT or HT + CT resulted in a decrease in CH₄ production of 0.6 and 5.5%, respectively, compared with that produced by incubations containing the added tannin binder polyethylene glycol-6000. Tannin also suppressed the population of methanogenic archaea in all incubations except those with HT2, with an average decrease of 11.6% in HT incubations (15.8, 7.09, and 12.0 in HT1, HT2, and HT3) and 28.6% in incubations containing HT + CT (35.0, 40.1, and 10.8 in HT + CT1, HT + CT2, and HT + CT3) when compared with incubations containing added polyethylene glycol-6000. The mean decrease in protozoal counts was 12.3% in HT and 36.2% in HT + CT incubations. Tannins increased in vitro pH, reduced total VFA concentrations, increased propionate concentrations, and decreased concentrations of iso-acids. In experiment 2, when a basal diet was incubated with graded levels of HT + CT1, HT + CT2, and HT + CT3, the total gas and CH₄ production and archaeal and protozoal populations decreased as the concentration of tannins increased. Our results confirm that tannins suppress methanogenesis by reducing methanogenic populations in the rumen either directly or by reducing the protozoal population, thereby reducing methanogens symbiotically associated with the protozoal population. In addition, tannin sources containing both HT and CT were more potent in suppressing methanogenesis than those containing only HT.     

Oven drying improves the nutritional value of Calliandra calothyrsus and Gliricidia sepium as supplements for sheep given low-quality straw

Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n=3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F=fresh) or after drying at 60°C in a forced draught oven (D=dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg⁻¹ DM). Total phenolics (TP) were significantly decreased when Gliricidia was dried (F 39, D 21 g TP kg⁻¹ DM), and CT content was reduced from 20 g CT kg⁻¹ DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73–85 mg N litre⁻¹) than did sheep given Calliandra (37–40 mg N litre⁻¹). For both species, drying significantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0·40 to 0·28 g N g⁻¹ N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0·20 to 0·52 g N absorbed g⁻¹ N flowing into the small intestines. For Gliricidia, DNR decreased from 0·64 to 0·51 and ADN increased from 0·41 to 0·56. There were no significant effects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of protein–tannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation. ©1997 SCI