The hydrogenation of some cis- and trans-octadecenoic acids to stearic acid by a rumen Fusocillus sp

INVITED REVIEW: Research on ruminal biohydrogenation: Achievements, gaps in knowledge, and future approaches from the perspective of dairy science

Scientific knowledge about ruminal biohydrogenation (BH) has improved greatly since this metabolic process was empirically confirmed in 1951. For years, BH had mostly been perceived as a process to be avoided to increase the post-ruminal flow of UFA from the diet. Two milestones changed this perception and stimulated great interest in BH intermediates themselves: In 1987, the in vitro anticarcinogenic properties of CLA were described, and in 2000, the inhibition of milk fat synthesis by trans-10 cis-12 CLA was confirmed. Since then, numerous BH metabolites have been described in small and large ruminants, and the major deviation from the common BH pathway (i.e., the trans-10 shift) has been reasonably well established. However, there are some less well-characterized alterations, and the comprehensive description of new BH intermediates (e.g., using isotopic tracers) has not been coupled with research on their biological effects. In this regard, the low quality of some published fatty acid profiles may also be limiting the advance of knowledge in BH. Furthermore, although BH seems to no longer be considered a metabolic niche inhabited by a few bacterial species with a highly specific metabolic capability, researchers have failed to elucidate which specific microbial groups are involved in the process and the basis for alterations in BH pathways (i.e., changes in microbial populations or their activity). Unraveling both issues may be beneficial for the description of new microbial enzymes involved in ruminal lipid metabolism that have industrial interest. From the perspective of diary science, other knowledge gaps that require additional research in the coming years are evaluation of the relationship between BH and feed efficiency and enteric methane emissions, as well as improving our understanding of how alterations in BH are involved in milk fat depression. Addressing these issues will have relevant practical implications in dairy science.

Alfalfa hay substitution for wheat straw improves beef quality via rumen microflora alteration

The use of high-quality roughage to improve beef quality has become an important issue in China, as the country has become the world's largest beef consumer. This study aimed to evaluate the effects of different forage qualities (wheat straw vs alfalfa hay) on Simmental crossbreed cattle's meat quality, rumen fermentation and microbiota. AHG (Alfalfa hay group) improved the ADFI (Average daily feed intake) and ADG (Average daily gain) of the beef cattle, meat-to-bone ratio and EE (Ether extract). The C18:3n3 and C20:3n3 composition of LD in AHG was significantly higher than WSG. An increase in the relative abundance of Firmicutes and a decrease in Bacteroidetes was observed. AHG resulted in higher relative abundance of Saccharomonospora, Streptomyces. A negative correlation between Treponema and muscle PUFA was noticed. Prevotella was negatively correlated with starch and sucrose metabolism. In conclusion, current study demonstrates that feeding alfalfa hay can raise meat quality by altering the rumen microbiota, providing valuable information for the application of alfalfa hay in beef cattle breeding.

Producing natural functional and low-carbon milk by regulating the diet of the cattle-The fatty acid associated rumen fermentation, biohydrogenation, and microorganism response

Conjugated linoleic acid (CLA) has drawn significant attention in the last two decades for its various potent beneficial effects on human health, such as anticarcinogenic and antidiabetic properties. CLA could be generally found in ruminant products, such as milk. The amount of CLA in ruminant products mainly depends on the diet of the animals. In general, the fat content in the ruminant diet is low, and dietary fat supplementation can be provided to improve rumen activity and the fatty acid (FA) profile of meat and milk. Especially, dietary 18-carbon polyunsaturated FA (C18 PUFA), the dominant fat source for ruminants, can modify the milk FA profile and other components by regulating the ruminal microbial ecosystem. In particular, it can improve the CLA in milk, intensify the competition for metabolic hydrogen for propionate producing pathways and decrease methane formation in the rumen. Therefore, lipid supplementation appears to be a promising strategy to naturally increase the additional nutritional value of milk and contribute to lower methane emissions. Meanwhile, it is equally important to reveal the effects of dietary fat supplementation on rumen fermentation, biohydrogenation (BH) process, feed digestion, and microorganisms. Moreover, several bacterial species and strains have been considered to be affected by C18 PUFA or being involved in the process of lipolysis, BH, CLA, or methane emissions. However, no review so far has thoroughly summarized the effects of C18 PUFA supplementation on milk CLA concentration and methane emission from dairy cows and meanwhile taken into consideration the processes such as the microorganisms, digestibility, rumen fermentation, and BH of dairy cattle. Therefore, this review aims to provide an overview of existing knowledge of how dietary fat affects rumen microbiota and several metabolic processes, such as fermentation and BH, and therefore contributes to functional and low-carbon milk production.

Microbiome and fermentation parameters in the rumen of dairy buffalo in response to ingestion associated with a diet supplemented with cysteamine and hemp seed oil

In this study, high-throughput gene amplicon sequencing was used to investigate the effects of 6 treatments [2 levels of hemp seed oil (HSO) × 3 levels of cysteamine (CS)] on bacterial and fungal communities in the rumen of 30 crossbred dairy buffalo. Our results indicate that the total numbers of bacterial and fungal taxa were unaffected regardless of diet (p > 0.05), while the total number of archaea was affected (p < 0.05) by the interaction of HSO and CS. Compared with control treatment, microbial composition of archaea was strongly influenced by CS (p < 0.05), while the addition of HSO, CS or both had a weak effect on fungus and bacteria. In addition, there was a significant increase in the lactic acid content with the addition of HSO, and the addition of CS to the feed caused a significant decrease in the ratio of acetic acid to propionic acid, compared with control treatment (p < 0.05). Correlation analysis showed that Acetobacter was significantly positively correlated with the genera Pichia, Klebsiella and Acinetobacter. pH was found to have a significant effect on the methanogens, and total volatile fatty acids (VFA) had a strong correlation with Butyrivibrio. The strong influence of CS on some methanogens shows that it may have potential in the development of methane reduction interventions.

Bioactivity and health effects of ruminant meat lipids. Invited Review

Ruminant meat (RM) is an excellent source of high-quality protein, B vitamins and trace minerals and plays an important role in global food and nutrition security. However, nutritional guidelines commonly recommend reduced intake of RM mainly because of its high saturated fatty acid (SFA) content, and more recently because of its perceived negative environmental impacts. RM is, however, rich in heart healthy cis-monounsaturated fatty acids and can be an important source of long-chain omega-3 (n-3) fatty acids in populations with low fish consumption. In addition, RM is a source of bioactive phospholipids, as well as rumen-derived bioactive fatty acids including branched-chain, vaccenic and rumenic acids, which have been associated with several health benefits. However, the role of bioactive RM lipids in maintaining and improving consumers' health have been generally ignored in nutritional guidelines. The present review examines RM lipids in relation to human health, and evaluates the effectiveness of different feeding strategies and possibilities for future profile and content improvement.

Prepartum fatty acid supplementation in sheep. IV. Effect of calcium salts with eicosapentaenoic acid and docosahexaenoic acid in the maternal and finishing diet on lamb liver and adipose tissue during the lamb finishing period1

The objective of this study was to evaluate the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplementation to ewes during late gestation on finishing lamb liver and adipose tissue fatty acid (FA) profile and gene expression. Lambs born from ewes supplemented with Ca salts of EPA + DHA, or palm FA distillate (PFAD) high in palmitic and oleic acid at 0.39% DM during the last 50 d of gestation were used. Lambs were weaned at 61 d of age and adapted to a high concentrate diet for 1.5 mo. After adaptation, 74 lambs (28 pens) were blocked by sex and BW and used in a 2 × 2 factorial arrangement of treatments using the factors of dam supplementation (DS) and lamb supplementation (LS) of Ca salts of EPA + DHA or PFAD at 1.48% DM. Lambs were slaughtered after 42 d and liver and adipose tissue collected for FA and gene expression analysis. Liver concentrations of EPA and DHA were greater (P < 0.01) with LS of EPA + DHA vs. PFAD during the finishing period. In adipose tissue, a lamb × dam interaction was observed for EPA (P = 0.02) and DHA (P = 0.04); LS of EPA + DHA increased EPA and DHA, but the increase was greatest in lambs born from ewes supplemented with PFAD. No lamb × dam treatment interactions were observed for gene expression in liver tissue (P > 0.10). Hepatic mRNA abundance of hormone-sensitive lipase (HSL; P = 0.01) was greater in lambs born from EPA + DHA ewes vs. lambs from PFAD ewes. mRNA expression of stearoyl-CoA desaturase (P < 0.01), fatty acid synthase (P = 0.01), Δ5-desaturase (P < 0.01), and Δ6-desaturase (P < 0.01) were decreased in liver of EPA + DHA lambs. A significant lamb × dam diet interaction was observed for elongation of very long chain fatty acid 2 in adipose tissue (P = 0.01); lambs supplemented with the same FA as their dams had lower expression. Expression of HSL tended (P = 0.08) to be decreased in adipose of EPA + DHA lambs born from EPA + DHA ewes. The changes in mRNA expression suggest that lipogenesis decreased, and lipolysis increased in lamb liver with EPA + DHA vs. PFAD supplementation during the finishing period. In adipose tissue, changes suggest that lipogenesis decreased in lambs born from EPA + DHA supplemented dams and supplemented with EPA + DHA during the finishing period. In addition, these results suggest an interaction between supplementation of FA to dams during late gestation on lamb response of adipose tissue, but not liver, to FA supplementation during the finishing period.

Toxicity of unsaturated fatty acids to the biohydrogenating ruminal bacterium, Butyrivibrio fibrisolvens

BACKGROUND

Health-promoting polyunsaturated fatty acids (PUFA) are abundant in forages grazed by ruminants and in vegetable and fish oils used as dietary supplements, but only a small proportion of PUFA finds its way into meat and milk, because of biohydrogenation in the rumen. Butyrivibrio fibrisolvens plays a major role in this activity. The aim of this study was to investigate the mechanisms by which PUFA affect the growth of B. fibrisolvens, how PUFA are metabolized and the metabolic response to growth in the presence of PUFA.

RESULTS

Linoleic acid (LA; cis-9, cis-12-18:2) and alpha-linolenic acid (LNA; cis-9, cis-12, cis-15-18:3) increased the lag phase of B. fibrisolvens JW11, LNA having the greater effect. Growth was initiated only when the PUFA had been converted to vaccenic acid (VA; trans-11-18:1). The major fish oil fatty acids, eicosapentaenoic acid (EPA; 20:5(n-3)) and docosahexaenoic acid (DHA; 22:6(n-3)), were not metabolized and prevented growth. Cellular integrity, as determined fluorimetrically by propidium iodide (PI) ingression, was affected as much by 18:1 fatty acids, including VA, as 18:2 fatty acids. The methyl esters of LNA, LA, EPA and DHA had no effect on growth or other measurements. The ATP pool decreased by 2/3 when LA was added to growing bacteria, whereas most acyl CoA pools decreased by >96%.

CONCLUSIONS

It was concluded that biohydrogenation occurs to enable B. fibrisolvens to survive the bacteriostatic effects of PUFA, and that the toxicity of PUFA is probably mediated via a metabolic effect rather than disruption of membrane integrity.

Ecophysiology of syntrophic communities that degrade saturated and unsaturated long-chain fatty acids

Syntrophic relationships are the key for biodegradation in methanogenic environments. We review the ecological and physiological features of syntrophic communities involved in the degradation of saturated and unsaturated long-chain fatty acids (LCFA), as well as their potential application to convert lipids/fats containing waste to biogas. Presently, about 14 species have been described with the ability to grow on fatty acids in syntrophy with methanogens, all belonging to the families Syntrophomonadaceae and Syntrophaceae. The principle pathway of LCFA degradation is through beta-oxidation, but the initial steps in the conversion of unsaturated LCFA are unclear. Communities enriched on unsaturated LCFA also degrade saturated LCFA, but the opposite generally is not the case. For efficient methane formation, the physical and inhibitory effects of LCFA on methanogenesis need to be considered. LCFA adsorbs strongly to biomass, which causes encapsulation of active syntrophic communities and hampers diffusion of substrate and products in and out of the biomass. Quantification of archaea by real-time PCR analysis suggests that potential LCFA inhibitory effect towards methanogens might be reversible. Rather, the conversion of adsorbed LCFA in batch assays was shown to result in a significant increase of archaeal cell numbers in anaerobic sludge samples.

Isolation and biochemical characterization of two lipases from a metagenomic library of China Holstein cow rumen

Two novel lipase genes RlipE1 and RlipE2 which encoded 361- and 265-amino acid peptides, respectively, were recovered from a metagenomic library of the rumen microbiota of Chinese Holstein cows. A BLAST search revealed a high similarity (90%) between RlipE2 and a carboxylesterase from Thermosinus carboxydivorans Nor1, while there was a low similarity (below 50%) between RlipE1 and other lipases. Phylogenetic analysis indicated that RlipE2 clustered with the lipolytic enzymes from family V while RlipE1 clustered with six other putative bacterial lipases which might constitute a new subfamily. The recombinant lipases were thermally unstable and retained 60% activity over a pH range of 6.5-8.5. Substrate specificity assay indicated that both enzymes had higher hydrolytic activity toward laurate (C(12)), palmitate (C(16)) and stearate (C(18)). The novel phylogenetic affiliation and high specificity of both enzymes for long-chain fatty acid make them interesting targets for manipulation of rumen lipid metabolism.

Effect of incremental levels of sunflower-seed oil in the diet on ruminal lipid metabolism in lactating cows

Based on the potential benefits ofcis-9,trans-11-conjugated linoleic acid (CLA) for human health there is interest in developing sustainable nutritional strategies for enhancing the concentration of this fatty acid in ruminant-derived foods. Most evidence to date suggests that endogenous synthesis is the major source ofcis-9,trans-11 in milk fat and ruminal outflow is limited and largely independent of dietary 18 : 2n-6 supply. Four lactating cows fitted with a rumen cannula were used in a 4 × 4 Latin square with 14 d experimental periods to examine the effects of sunflower-seed oil (SFO) as a source of 18 : 2n-6 on ruminal lipid metabolism. Cows were offered grass silage-based diets supplemented with 0, 250, 500 or 750 g SFO/d. Supplements of SFO had no effect on DM intake, milk fat or protein secretion, but increased linearly (P < 0·01) milk yield and milk lactose output and shifted (P < 0·001) rumen fermentation towards propionate at the expense of acetate. SFO supplements increased linearly (P < 0·05) the flow of 18 : 0, 18 : 1, 18 : 2n-6 and total CLA at the omasum and enhanced ruminalcis-9-18 : 1, 18 : 2n-6 and 18 : 3n-3 metabolism. Flows of all-trans- (Δ4–16) andcis- (Δ9–16) 18 : 1 isomers were elevated, while increases in ruminal CLA outflow were confined totrans-8,trans-10 and geometric 9,11 and 10,12 isomers. It is concluded that supplementing grass silage-based diets with plant oils rich in 18 : 2n-6 enhances ruminal outflow oftrans-11-18 : 1 andcis-9,trans-11-CLA in lactating cows.

Evaluating the conjugated linoleic acid and trans 18:1 isomers in milk fat of dairy cows fed increasing amounts of sunflower oil and a constant level of fish oil

The objective was to evaluate different levels of sun-flower oil (SFO) in dairy rations to increase vaccenic (trans-11-18:1) and rumenic acids (cis-9,trans-11-18:2) in milk fat, and assess the content and composition of other trans-octadecenoic (trans-18:1) and conjugated linoleic acids (CLA) isomers. Eighty lactating Holstein cows were fed control diets for 4 wk and then placed on 4 diets for 38 d; milk fat was analyzed after 10 and 38 d. The treatments were: control, 1.5% SFO plus 0.5% fish oil (FO), 3% SFO plus 0.5% FO, and 4.5% SFO plus 0.5% FO. The forage-to-concentrate ratio was 50:50 and consisted of barley/alfalfa/hay silage and corn/barley grain concentrate. There were no differences in milk production. Supplementation of SFO/FO reduced milk fat compared with respective pretreatment periods, but milk protein and lactose levels were not affected. There was a linear decrease in all short- and medium-chain saturated fatty acids (SFA) in milk fat after 10 d (25.5, 24.1, 20.2, and 16.7%) and a corresponding linear increase in total trans-18:1 (5.2, 9.1, 14.1, and 21.3%) and total CLA (0.7, 1.9, 2.4, and 3.9%). The other FA in milk fat were not affected. Separation of trans-18:1 isomers was achieved by combination of gas chromatography (GC; 100-m highly polar capillary column) and prior separation of trans FA by silver ion-thin layer chromatography followed by GC. The CLA isomers were resolved by a combination of GC and silver ion-HPLC. The trans-11- and trans-10-18:1 isomers accounted for approximately 50% of the total trans-18:1 increase when SFO/FO diets were fed. On continued feeding to 38 d, trans-11-18:1 increased with 1.5% SFO/FO, stayed the same with 3%, and declined with 4.5% SFO/FO. Rumenic acid showed a similar pattern on continued feeding as trans-11-18:2; levels increased to 0.43, 1.5, 1.9, and 3.4% at 10 d and to 0.42, 2.15, 2.09, and 2.78% at 38 d. Rumenic acid was the major CLA isomer in all 4 diets: 66, 77, 78 and 85%. The CLA isomers trans-7,cis-9-, trans-9,cis-11-, trans-10,cis-12-, trans-11,trans-13-, and trans-9,trans-11-/trans-10,trans-12-18:2 also increased from 0.18 (control) to 0.52% (4.5% SFO/FO). Milk fat produced from 3% SFO/FO appeared most promising: trans-11-18:1 and cis-9,trans-11-18:2 increased 4.5-fold, total SFA reduced 18%, and moderate levels of trans-10-18:1 (3.2%), other trans-18:1 (6.6%) and CLA isomers (0.5%) were observed, and that composition remained unchanged to 38 d. The 4.5% SFO/FO diet produced higher levels of trans-11-18:1 and cis-9,trans-11-18:2, a 28% reduction in SFA, and similar levels of other trans-18:1 (9.2%) and CLA isomers (0.52%), but the higher levels of trans-11-18:1 and cis-9,trans-11-18:2 were not sustained. A stable milk fat quality was achieved by feeding moderate amounts of SFO (3% of DM) in the presence of 0.5% FO that had 4% vaccenic and 2% rumenic acids.

Dynamic Features of the Rumen Metabolism of Linoleic Acid, Linolenic Acid and Linseed Oil Measured in Vitro

The lipid quality of ruminant products is largely determined by the extent of rumen microbial biohydrogenation (BH) of polyunsaturated fatty acids (FAs) and the substances formed thereby. In vitro batch incubations with mixed rumen bacteria were tracked over 24 h to characterize the profiles and kinetics of the BH products from three lipid sources: pure linoleic acid (c9,c12-18:2), pure linolenic acid (c9,c12,c15-18:3) and linseed oil (mainly c9,c12,c15-18:3 in triacylglycerols). After 24 h of incubation biohydrogenation was more complete for c9,c12-18:2, which gave mainly stearic acid (18:0), than for c9,c12,c15-18:3, which yielded mainly trans-18:1 FAs. This suggests inhibition of the final BH step (18:1 to 18:0). Incubations of c9,c12-18:2 resulted in high levels of carbon 10- and 12-desaturated 18:1, t10,c12- and c9,t11-CLAs. Incubations of c9,c12,c15-18:3 resulted in high levels of t11-18:1, carbon 13- and 15-desaturated 18:1 as well as t11,c15-18:2 and 11,13-CLAs. A comparative study of linolenic acid and linseed oil kinetics revealed that the BH process was not significantly slowed by the esterification of polyunsaturated FAs, but may have been limited by the isomerization step in which the cis12 double bond goes to the trans11 position. The disappearance rates of c9,c12-18:2 and c9,c12,c15-18:3 ranged from 23.6 to 44.6%/h. The wide variety of BH intermediates found here underlines the large number of possible BH pathways. These data help provide a basis for dynamic approaches to BH processes.

The production of 10-hydroxystearic and 10-ketostearic acids is an alternative route of oleic acid transformation by the ruminal microbiota in cattle

The formation of hydroxystearic acid (HSA) and ketostearic acid (KSA) from oleic acid transformation has been documented in a variety of microbial species, including several isolated from the rumen of domesticated ruminant species. However, their ruminal production rates have not been established as influenced by fatty acid source. Dosing continuous cultures of mixed ruminal microorganisms with 1-(13C)-oleic acid increased the 13C enrichment of both HSA and KSA at 24 h postdosing, and showed that the majority (96 and 85%, respectively) of the HSA and KSA present in the 24-h samples originated from oleic acid. Several experiments using batch cultures of ruminal microorganisms showed that production of HSA and KSA was directly related to oleic acid input but was not affected by elaidic acid input, and that HSA was further metabolized to KSA but not to other fatty acids. When continuous cultures of ruminal microorganisms were supplemented with soybean oil or canola oil, production of 10-HSA + 10-KSA was related to oleic acid input but not to linoleic acid input. Daily production of 10-HSA + 10-KSA across treatments was 14.4 micromol/100 micromol oleic acid input into the cultures or 31.1 micromol/100 micromol oleic acid net loss. The results of this study quantify the formation of 10-HSA and 10-KSA from oleic acid transformation by ruminal microorganisms, and show that their accumulation in ruminal contents is directly related to the extent of oleic acid input and biotransformation by the rumen microbiota.

Factors affecting conjugated linoleic acid content in milk and meat

Conjugated linoleic acid (CLA) has been recently studied mainly because of its potential in protecting against cancer, atherogenesis, and diabetes. Conjugated linoleic acid (CLA) is a collective term for a series of conjugated dienoic positional and geometrical isomers of linoleic acid, which are found in relative abundance in milk and tissue fat of ruminants compared with other foods. The cis-9, trans-11 isomer is the principle dietary form of CLA found in ruminant products and is produced by partial ruminal biohydrogenation of linoleic acid or by endogenous synthesis in the tissues themselves. The CLA content in milk and meat is affected by several factors, such as animal's breed, age, diet, and management factors related to feed supplements affecting the diet. Conjugated linoleic acid in milk or meat has been shown to be a stable compound under normal cooking and storage conditions. Total CLA content in milk or dairy products ranges from 0.34 to 1.07% of total fat. Total CLA content in raw or processed beef ranges from 0.12 to 0.68% of total fat. It is currently estimated that the average adult consumes only one third to one half of the amount of CLA that has been shown to reduce cancer in animal studies. For this reason, increasing the CLA contents of milk and meat has the potential to raise the nutritive and therapeutic values of dairy products and meat.

Effects of nutrition and management on the production and composition of milk fat and protein: a review

The composition and functional properties of cow’s milk are of considerable importance to the dairy farmer, manufacturer, and consumer. Broadly, there are 3 options for altering the composition and/or functional properties of milk: cow nutrition and management, cow genetics, and dairy manufacturing technologies. This review considers the effects of nutrition and management on the composition and production of milk fat and protein, and the relevance of these effects to the feeding systems used in the Australian dairy industry. Dairy cows on herbage-based diets derive fatty acids for milk fat synthesis from the diet/rumen microorganisms (400–450 g/kg), from adipose tissues (<100 g/kg), and from de novo synthesis in the mammary gland (about 500 g/kg). However, the relative contributions of these sources of fatty acids to milk fat production are highly dependent upon feed intake, diet composition, and stage of lactation. Feed intake, the amount of starch relative to fibre, the amount and composition of long chain fatty acids in the diet, and energy balance are particularly important. Significant differences in these factors exist between pasture-based dairy production systems and those based on total mixed ration, leading to differences in milk fat composition between the two. High intakes of starch are associated with higher levels of de novo synthesis of fat in the mammary gland, resulting in milk fat with a higher concentration of saturated fatty acids. In contrast, higher intakes of polyunsaturated fatty acids from pasture and/or lipid supplements result in higher concentrations of unsaturated fatty acids, particularly oleate, trans-vaccenate, and conjugated linoleic acid (CLA) in milk fat. A decline in milk fat concentration associated with increased feeding with starch-based concentrates can be attributed to changes in the ratios of lipogenic to glucogenic volatile fatty acids produced in the rumen. Milk fat depression, however, is likely the result of increased rates of production of long chain fatty acids containing a trans-10 double bond in the rumen, in particular trans-10 18 : 1 and trans-10-cis-12 18 : 2 in response to diets that contain a high concentration of polyunsaturated fatty acids and/or starch. Low rumen fluid pH can also be a factor. The concentration and composition of protein in milk are largely unresponsive to variation in nutrition and management. Exceptions to this are the effects of very low intakes of metabolisable energy (ME) and/or metabolisable protein (MP) on the concentration of total protein in milk, and the effects of feeding with supplements that contain organic Se on the concentration of Se, as selenoprotein, in milk. In general, the first limitation for the synthesis of milk protein in Australian dairy production systems is availability of ME since pasture usually provides an excess of MP. However, low concentrations of protein in milk produced in Queensland and Western Australia, associated with seasonal variations in the nutritional value of herbage, may be a response to low intakes of both ME and MP. Stage of lactation is important in determining milk protein concentration, but has little influence on protein composition. The exception to this is in very late lactation where stage of lactation and low ME intake can interact to reduce the casein fraction and increase the whey fraction in milk and, consequently, reduce the yield of cheese per unit of milk. Milk and dairy products could also provide significant amounts of Se, as selenoproteins, in human diets. Feeding organic Se supplements to dairy cows grazing pastures that are low in Se may also benefit cow health. Research into targetted feeding strategies that make use of feed supplements including oil seeds, vegetable and fish oils, and organic Se supplements would increase the management options available to dairy farmers for the production of milks that differ in their composition. Given appropriate market signals, milk could be produced with lower concentrations of fat or higher levels of unsaturated fats, including CLA, and/or high concentrations of selenoproteins. This has the potential to allow the farmer to find a higher value market for milk and improve the competitiveness of the dairy manufacturer by enabling better matching of the supply of dairy products to the demands of the market.

Biohydrogenation of C18 unsaturated fatty acids to stearic acid by a strain of Butyrivibrio hungatei from the bovine rumen

AIMS

To identify a ruminal isolate which transforms oleic, linoleic and linolenic acids to stearic acid and to identify transient intermediates formed during biohydrogenation.

METHODS AND RESULTS

The stearic acid-forming bacterium, isolated from the rumen of a grazing cow, was a Gram-negative motile rod which utilized a range of growth substrates including starch and pectin but not cellulose or xylan. From its 16S rRNA gene sequence, the isolate was identified as a strain of Butyrivibrio hungatei. During conversion of linoleic acid, 9,11-conjugated linoleic acid formed as a transient intermediate before trans-vaccenic acid accumulated together with stearic acid. Unlike previously studied ruminal biohydrogenating bacteria, B. hungatei Su6 was able to convert alpha-linolenic acid to stearic acid. Linolenic acid was converted to stearic via conjugated linolenic acid, linoleic acid and trans-vaccenic acid as intermediates. Oleic acid and cis-vaccenic acid were converted to a series of trans monounsaturated isomers as well as stearic acid. An investigation of these isomers indicated that mixed trans positional isomers are intermediate in the biohydrogenation of cis monounsaturated fatty acids to stearic acid.

CONCLUSION

This, the first rigorous identification and characterization of a ruminal bacterium which forms stearic acid, shows that B. hungatei plays an important role in unsaturated fatty acid transformations in the rumen.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biohydrogenating bacteria which convert C18 unsaturated fatty acids to stearic acid have not been available for study for many years. Access to B. hungatei Su6 now provides a fresh opportunity for understanding biohydrogenation mechanisms and rumen processes which lead to saturated fat in ruminant products.

Biohydrogenation of unsaturated fatty acids in continuous culture fermenters during digestion of orchardgrass or red clover with three levels of ground corn supplementation

Diet digestibility and outputs of biohydrogenation intermediates were assessed in a continuous culture of ruminal microorganisms. Orchardgrass or red clover harvested and frozen during spring or fall served as the primary substrates for fermentation. During 10-d incubations, fermenters were fed thawed forage (50 g of DM/d), forage (42 g/d) plus 8 g/d of corn, or forage (34 g/d) plus 16 g/d of corn. Effluents from the last 3 d of incubation were composited for analyses. Starch input increased from 5 to 27% of DM as corn input increased from 0 to 16 g/d. Corn input reduced (P < 0.01) pH, increased (P < 0.01) microbial DM yield, and increased (P = 0.01) digestibility of DM, NDF, CP, and nonstructural carbohydrates. Overall, apparent hydrogenation (percentage) of cis9-18:1, 18:2n-6, and 18:3n-3 was greater (P < 0.05) with orchardgrass than clover. Hydrogenation of cis9-18:1 and 18:2n-6 increased (P = 0.01), but hydrogenation of 18:3n-3 decreased (P = 0.01) linearly due to corn input, regardless of forage. As a result, output of trans11, cis15-18:2 also decreased (P = 0.01). Average output of cis9,trans11-18:2 was greater (P = 0.01) for clover (1.3 mg/d) compared with orchardgrass (0.6 mg/d), but corn input with either forage increased (P = 0.01) cis9,trans11-18:2 output by 205%. Output of trans11-18:1 was greater (P = 0.01) from orchardgrass compared with clover (174 vs. 90 mg/d), but corn increased (P = 0.01) trans11-18:1 output only from clover fermentations. Output of trans10-18:1 was greater (P = 0.01) in response to orchardgrass compared with clover (10 vs. 4 mg/d), but corn addition doubled the output regardless of forage type. Output of trans10,cis12-18:2, which did not differ due to forage type, increased (P = 0.01) twofold in response to corn. Cis9,cis11-18:2 was a primary conjugated isomer produced from forage fermentations, but its output decreased (P = 0.03) in response to corn input. When inputs of 18:2n-6 plus 18:3n-3 were less than 0.9% of total DM (clover), hydrogenation was low (87%). When 18:2n-6 plus 18:3n-3 inputs were from 1.2 to 1.5% of total DM (orchardgrass), hydrogenation averaged 96%. Despite greater hydrogenation, incremental additions of cis9-18:1 and 18:2n-6 from corn grain increased (P < 0.05) outputs of trans10-18:1, trans11-18:1, trans10,cis12-18:2, cis9,trans11-18:2, and trans,trans-18:2 in effluent. Results suggest that forage species alone or in combination with corn grain can alter hydrogenation and profiles of intermediates to varying degrees.

Isomerization of stable isotopically labeled elaidic acid to cis and trans monoenes by ruminal microbes

A previous study showed that oleic acid was converted by mixed ruminal microbes to stearic acid and also converted to a multitude of trans octadecenoic acid isomers. This study traced the metabolism of one of these trans C18:1 isomers upon its incubation with mixed ruminal microbes. Unlabeled and labeled (18-[13C]trans-9 C18:1) elaidic acid were each added to four in vitro batch cultures with three cultures inoculated with mixed ruminal bacteria and one uninoculated culture. Samples were taken at 0, 12, 24, and 48 h and analyzed for 13C enrichment in component fatty acids by gas chromatography-mass spectrometry. At 0 h of incubation, enrichment was detected only in elaidic acid. By 48 h of incubation, 13C enrichment was 18% (P < 0.01) for stearic acid, 7% to 30% (P < 0.01) for all trans C18:1 isomers having double bonds between carbons six through 16, and 5% to 10% for cis-9 and cis-11 monoenes. After 48 h, 13C enrichment in the uninoculated cultures was only detected in the added elaidic acid. This study shows trans fatty acids exposed to active ruminal cultures are converted to stearic acid but also undergo enzymic isomerization yielding a multitude of positional and geometric isomers.

Characterization of 18:1 and 18:2 isomers produced during microbial biohydrogenation of unsaturated fatty acids from canola and soya bean oil in the rumen of lactating cows

Ruminal production of biohydrogenation intermediates in response to unsaturated oils was assessed using 24 Jersey cows fed a control diet or the control diet supplemented at 35 g/kg dry matter (DM) with canola, soya bean, or a mixture of equal amounts of canola plus soya bean oil for 4-weeks. Total fatty acid content averaged 63 or 35 g/kg DM for oil-supplemented diets or control. Oleic acid accounted for 6, 29, 21 or 12 g/kg DM in the control, canola, mixture, or soya bean oil diet, respectively. Linoleic acid averaged 17, 19, 26, or 33 g/kg DM and linolenic acid 5, 5, 6 or 8 g/kg DM for control, canola, mixture, or soya bean oil. Concentrations of cis12-, trans11-, trans13+14, and trans15-18:1 were 0.81, 2.99, 2.24, and 0.73 mg/g rumen fluid, respectively, in response to soya bean oil and were 126, 90, 45, and 38% greater compared with other diets. Trans11cis15-, cis9trans11- and cis9 cis11-18:2 also were greater when soya bean oil (0.30, 0.34 and 0.01 mg/g, respectively) was fed compared with other treatments (0.12, 0.21 and 0.004 mg/g, respectively). Feeding canola oil resulted in greater concentrations of trans4-, trans5-, trans6+7+8-, trans9- and trans10-18:1 (0.20, 0.25, 0.87, 0.39 and 0.70 mg/g, respectively) compared with other diets (0.09, 0.15, 0.36, 0.20 and 0.46 mg/g, respectively). Trans10cis12-18:2 concentration did not differ as a result of diet and averaged 0.002 mg/g rumen contents. The pattern of 18:1 and 18:2 isomers formed during ruminal biohydrogenation depends greatly on dietary profile of unsaturated fatty acids.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.

Biotransformation of Unsaturated Long-Chain Fatty Acids by Eubacterium lentum

Eubacterium lentum (33 strains) isomerized the 12- cis double bond of C 18 fatty acids with cis double bonds at C-9 and C-12 into an 11- trans double bond before reduction of the 9- cis double bond. The 14- cis double bond of homo-γ-linolenic acid was isomerized by 29 strains into a 13- trans double bond. The same strains isomerized the 14- cis double bond of arachidonic acid into a 13- trans double bond and then isomerized the 8- cis double bond into a 7- trans double bond; the 13- cis double bond of 10- cis , 13- cis -nonadecadienoic acid was isomerized into a 12- trans double bond. None of these isomerization products was further reduced. Studies with resting cells showed optimal isomerization velocity at a linoleic acid concentration of 37.5 μM; higher concentrations were inhibitory. The pH optimum for isomerization was 7.5 to 8.5. The isomerase was inhibited by the sulfhydryl reagents iodoacetamide, bromoacetate, and N -ethylmaleimide and by the chelators EDTA and 1,10-phenanthroline.

The hydrogenation of the series of methylene-interrupted cis,cis-octadecadienoic acids by pure cultures of six rumen bacteria

The hydrogenation of all the methylene-interrupted cis,cis-octadecadienoic acids was examined using pure cultures of six rumen bacteria able to hydrogenate linoleic acid to stearic acid or its immediate precursor, trans-11-octadecenoic acid, after first conjugating the linoleic acid to cis,trans-9,11-octadecadienoic acid. Only the delta 14-cis,17-cis-isomer was not hydrogenated by at least one of the bacteria and no evidence was found that conjugation was necessary before hydrogenation except for the delta 2-cis,5-cis- and delta 9-cis,12-cis-isomers. Several isomers were hydrogenated to an extent close to that achieved with linoleic acid (delta 9-cis,12-cis). Those bacteria only able to hydrogenate linoleic to trans-11-octadecenoic acid gave only octadecenoic acid products and those bacteria able to hydrogenate linoleic acid to stearic gave variable yields of octadecenoic acids and stearic acid except with the isomers delta 12-cis,15-cis and delta 13-cis,16-cis when only octadecenoic acids were detected. At the substrate levels used (20 micrograms/ml), both inhibition and stimulation of growth were found but no common pattern emerged, nor was the growth consistently related to the extent of hydrogenation.