Evaluation of the effects of different diets on microbiome diversity and fatty acid composition of rumen liquor in dairy goat

Fat supplementation plays an important role in defining milk fatty acids (FA) composition of ruminant products. The use of sources rich in linoleic and α-linolenic acid favors the accumulation of conjugated linoleic acids isomers, increasing the healthy properties of milk. Ruminal microbiota plays a pivotal role in defining milk FA composition, and its profile is affected by diet composition. The aim of this study was to investigate the responses of rumen FA production and microbial structure to hemp or linseed supplementation in diets of dairy goats. Ruminal microbiota composition was determined by 16S amplicon sequencing, whereas FA composition was obtained by gas-chromatography technique. In all, 18 pluriparous Alpine goats fed the same pre-treatment diet for 40±7 days were, then, arranged to three dietary treatments consisting of control, linseed and hemp seeds supplemented diets. Independently from sampling time and diets, bacterial community of ruminal fluid was dominated by Bacteroidetes (about 61.2%) and Firmicutes (24.2%) with a high abundance of Prevotellaceae (41.0%) and Veillonellaceae (9.4%) and a low presence of Ruminococcaceae (5.0%) and Lachnospiraceae (4.3%). Linseed supplementation affected ruminal bacteria population, with a significant reduction of biodiversity; in particular, relative abundance of Prevotella was reduced (−12.0%), whereas that of Succinivibrio and Fibrobacter was increased (+50.0% and +75.0%, respectively). No statistically significant differences were found among the average relative abundance of archaeal genera between each dietary group. Moreover, the addition of linseed and hemp seed induced significant changes in FA concentration in the rumen, as a consequence of shift from C18 : 2n-6 to C18 : 3n-3 biohydrogenation pathway. Furthermore, dimethylacetal composition was affected by fat supplementation, as consequence of ruminal bacteria population modification. Finally, the association study between the rumen FA profile and the bacterial microbiome revealed that Fibrobacteriaceae is the bacterial family showing the highest and significant correlation with FA involved in the biohydrogenation pathway of C18 : 3n-3.     

The role of microbes in rumen lipolysis and biohydrogenation and their manipulation

Despite the fact that the ruminant diet is rich in polyunsaturated fatty acids (PUFA), ruminant products – meat, milk and dairy – contain mainly saturated fatty acids (SFA) because of bacterial lipolysis and subsequent biohydrogenation of ingested PUFA in the rumen. The link between SFA consumption by man and coronary heart disease is well established. In contrast, ruminant products also contain fatty acids that are known to be beneficial to human health, namely conjugated linoleic acids (CLAs). The aims of research in this field have been to understand the microbial ecology of lipolysis and biohydrogenation and to find ways of manipulating ruminal microbes to increase the flow of PUFA and CLA from the rumen into meat and milk. This review describes our present understanding of the microbial ecology of ruminal lipid metabolism, including some apparently anomalous and paradoxical observations, and the status of how the metabolism may be manipulated and the possible consequential effects on other aspects of ruminal digestion. Intuitively, it may appear that inhibiting the ruminal lipase would cause more dietary PUFA to reach the mammary gland. However, lipolysis releases the non-esterified fatty acids that form the substrates for biohydrogenation, but which can, if they accumulate, inhibit the whole process. Thus, increasing lipase activity could be beneficial if the increased release of non-esterified PUFA inhibited the metabolism of CLA. Rumen ciliate protozoa do not carry out biohydrogenation, yet protozoal lipids are much more highly enriched in CLA than bacterial lipids. How could this happen if protozoa do not metabolise PUFA? The answer seems to lie in the ingestion of plant organelles, particularly chloroplasts, and the partial metabolism of the fatty acids by contaminating bacteria. Bacteria related to Butyrivibrio fibrisolvens are by far the most active and numerous biohydrogenating bacteria isolated from the rumen. But do we misunderstand the role of different bacterial species in biohydrogenation because there are uncultivated species that we need to understand and include in the analysis? Manipulation methods include dietary vegetable and fish oils and plant-derived chemicals. Their usefulness, efficacy and possible effects on fatty acid metabolism and on ruminal microorganisms and other areas of their metabolism are described, and areas of opportunity identified.     

Effect of fish oil on ruminal biohydrogenation of C18 unsaturated fatty acids in steers fed grass or red clover silages

Red clover and fish oil (FO) are known to alter ruminal lipid biohydrogenation leading to an increase in the polyunsaturated fatty acid (PUFA) and conjugated linoleic acid (CLA) content of ruminant-derived foods, respectively. The potential to exploit these beneficial effects were examined using eight Hereford × Friesian steers fitted with rumen and duodenal cannulae. Treatments consisted of grass silage or red clover silage fed at 90% of ad libitum intake and FO supplementation at 0, 10, 20 or 30 g/kg diet dry matter (DM). The experiment was conducted with two animals per FO level and treatments formed extra-period Latin squares. Flows of fatty acids at the duodenum were assessed using ytterbium acetate and chromium ethylene diamine tetra-acetic acid as indigestible markers. Intakes of DM were higher (P < 0.001) for red clover silage than grass silage (5.98 v. 5.09 kg/day). There was a linear interaction effect (P = 0.004) to FO with a reduction in DM intake in steers fed red clover silage supplemented with 30 g FO/kg diet DM. Apparent ruminal biohydrogenation of C18:2n-6 and C18:3n-3 were lower (P < 0.001) for red clover silage than grass silage (0.83 and 0.79 v. 0.87 and 0.87, respectively), whilst FO increased the extent of biohydrogenation on both diets. Ruminal biohydrogenation of C20:5n-3 and C22:6n-3 was extensive on both silage diets, averaging 0.94 and 0.97, respectively. Inclusion of FO in the diet enhanced the flow of total CLA leaving the rumen with an average across silages of 0.22, 0.31, 0.41 and 0.44 g/day for 0, 10, 20 or 30 g FO/kg, respectively, with a linear interaction effect between the two silages (P = 0.03). FO also showed a dose-dependent increase in the flow of trans-C18:1 intermediates at the duodenum from 4.6 to 15.0 g/day on grass silage and from 9.4 to 22.5 g/day for red clover silage. Concentrations of trans-C18:1 with double bonds from Δ4-16 in duodenal digesta were all elevated in response to FO in both diets, with trans-11 being the predominant isomer. FO inhibited the complete biohydrogenation of dietary PUFA on both diets, whilst red clover increased the flow of C18:2n-6 and C18:3n-3 compared with grass silage. In conclusion, supplementing red clover silage-based diets with FO represents a novel nutritional strategy for enhancing the concentrations of beneficial fatty acids in ruminant milk and meat.     

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 linoleic acid by rumen fungi compared with rumen bacteria

AIMS: To investigate biohydrogenation of linoleic acid by rumen fungi compared with rumen bacteria, and to identify the fungus with the fastest biohydrogenation rate. METHODS AND RESULTS: Biohydrogenation of linoleic acid by mixed rumen fungi and mixed rumen bacteria were compared in vitro. With mixed rumen bacteria, all biohydrogenation reactions were finished within 100 min of incubation and the end product of biohydrogenation was stearic acid. With mixed rumen fungi, biohydrogenation proceeded more slowly over a 24-h period. Conjugated linoleic acid (CLA; cis-9, trans-11 C18 : 2) was an intermediate product, and vaccenic acid (VA; trans-11 C18 : 1) was the end product of biohydrogenation. Fourteen pure fungal isolates were tested for biohydrogenation rate. DNA sequencing showed that the isolate with the fastest rate belonged to the Orpinomyces genus. CONCLUSIONS: It is concluded that rumen fungi have the ability to biohydrogenate linoleic acid, but biohydrogenation is slower in rumen fungi than in rumen bacteria. The end product of fungal biohydrogenation is VA, as for group A rumen bacteria. Orpinomyces is the most active biohydrogenating fungus. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to demonstrate that rumen fungi can biohydrogenate fatty acids. Fungi could influence CLA content of ruminant products.     

Accumulation of trans C18:1 Fatty Acids in the Rumen after Dietary Algal Supplementation Is Associated with Changes in the Butyrivibrio Community

Optimization of the fatty acid composition of ruminant milk and meat is desirable. Dietary supplementation of algae was previously shown to inhibit rumen biohydrogenation, resulting in an altered milk fatty acid profile. Bacteria involved in biohydrogenation belong to the Butyrivibrio group. This study was aimed at relating accumulation of biohydrogenation intermediates with shifts in Butyrivibrio spp. in the rumen of dairy cows. Therefore, an experiment was performed with three rumen-fistulated dairy cows receiving a concentrate containing algae (9.35 g/kg total dry matter [DM] intake) for 20 days. Supplementation of the diet with algae inhibited biohydrogenation of C_18:2 omega 6 (n-6) and C_18:3 n-3, resulting in increased concentrations of biohydrogenation intermediates, whereas C_18:0 decreased. Addition of algae increased ruminal C_18:1 trans fatty acid concentrations, mainly due to 6- and 20-fold increases in C_18:1 trans 11 (t11) and C_18:1 t10. The number of ciliates (5.37 log copies/g rumen digesta) and the composition of the ciliate community were unaffected by dietary algae. In contrast, supplementation of the diet with algae changed the composition of the bacterial community. Primers for the Butyrivibrio group, including the genera Butyrivibrio and Pseudobutyrivibrio, were specifically designed. Denaturing gradient gel electrophoresis showed community changes upon addition of algae without affecting the total amount of Butyrivibrio bacteria (7.06 log copies/g rumen DM). Clone libraries showed that algae affected noncultivated species, which cluster taxonomically between the genera Butyrivibrio and Pseudobutyrivibrio and might play a role in biohydrogenation. In addition, 20% of the clones from a randomly selected rumen sample were related to the C_18:0-producing branch, although the associated C_18:0 concentration decreased through supplementation of the diet with algae.     

As yet uncultured bacteria phylogenetically classified as Prevotella, Lachnospiraceae incertae sedis and unclassified Bacteroidales, Clostridiales and Ruminococcaceae may play a predominant role in ruminal biohydrogenation

Microbial biohydrogenation of dietary poly‐unsaturated fatty acids (PUFA) to saturated fatty acids (SFA) in the rumen results in the high ratio of SFA/PUFA in ruminant products, such as meat and milk. In vitro, Butyrivibrio proteoclasticus‐related bacteria extensively biohydrogenate PUFA to SFA, yet their contribution in the rumen has not been confirmed. The aim of this study was to evaluate the role of Butyrivibrio proteoclasticus group bacteria in ruminal biohydrogenation and to assess the possible role of other bacteria. Fish oil at 0%, 1.5% and 3% dry matter intake was fed to eight Holstein × Friesian steers, in order to elicit changes in the extent of PUFA biohydrogenation. Fatty acid and B. proteoclasticus group 16S rRNA concentrations in rumen digesta were determined. Correlation between digesta 18:0 concentration and B. proteoclasticus group 16S rRNA concentration was low. Terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis (DGGE) coupled with multivariate statistics revealed that many terminal restriction fragments (T‐RFs) and DGGE bands were linked to cis‐9, trans‐11 conjugated linoleic acid (CLA), 18:1 trans‐11 and 18:0 ruminal concentrations. MiCA T‐RF predictive identification software showed that these linked T‐RFs were likely to originate from as yet uncultured bacteria classified as Prevotella, Lachnospiraceae incertae sedis, and unclassified Bacteroidales, Clostridiales and Ruminococcaceae. Sequencing of linked DGGE bands also revealed that as yet uncultured bacteria classified as Prevotella, Anaerovoax (member of the Lachnospiraceae incertae sedis family), and unclassified Clostridiales and Ruminococcaceae may play a role in biohydrogenation.     

In vitro biohydrogenation of four dietary fats

This study was designed to determine in vitro rates of biohydrogenation of dietary unsaturated fatty acids by a mixed population of rumen microbes. The four dietary fats [Alifet High-Energy^® (AHE), Alifet-Repro^® (AR), Megalac^® (MG), and Energy Booster^® (EB)] differ in method of preparation, fatty acid composition, or both of these factors. Dietary fats (20 mg) were incubated with 4 mL strained rumen fluid diluted with 16 mL of medium, 0.8 mL of reducing solution buffer, and 200 mg of a synthetic diet (370 g cellulose, 370 g starch, and 160 g casein per kg DM) at 37 °C. Total contents were collected after 0, 6, 12, 24, or 36 h and change in fatty acid content determined. Disappearance of oleic acid was minimal (0.05–0.20) in AR and MG but moderate (about 0.60) in AHE and EB after 36 h of incubation. Rate of biohydrogenation of linoleic and linolenic acids from AR were similar (0.025 ± 0.009 h⁻¹) and 0.65 of these fatty acids remained intact after 36 h. Rate of biohydrogenation of linoleic acid was four times greater than for oleic acid (0.040 ± 0.013 h⁻¹ versus 0.009 ± 0.002 h⁻¹) in MG. Thus, 0.65 of the linoleic acid but only 0.20 of the oleic acid had disappeared from MG after 36 h. Trans-11 and trans-12 were the predominant trans-isomers in AHE and AR cultures whereas trans-9 and trans-10 were the predominant trans-isomers in EB and MG cultures. None of the dietary fats contained conjugated linoleic acid (CLA) but CLA was present in the incubation inoculum. The amount of CLA decreased with time but this was not affected by source of dietary fat. Most (0.90–0.95) of the long-chain fatty acids eicosapentaenoic (EPA) and docosahexaenoic (DHA) in AR remained after 36 h of incubation. Results demonstrate that biohydrogenation varied among fatty acids and among source of dietary fat and indicate that AR can be used to increase post-ruminal supply of linolenic, EPA and DHA.     

Comparative studies on the metabolism of linoleic acid by rumen bacteria,protozoa, and their mixture in vitro

Linoleic acid was differentially catabolized by the various rumen microbial fractions, such as rumen bacteria (B), protozoa (P), and their mixture (BP). The predominant isomer of conjugated linoleic acids (CLA) synthesized by B, P, and BP from linoleic acid was 9c11t-CLA. The formation of 9c11t-CLA was higher (P < 0.05) in P suspension (53.6 μg/mg microbial nitrogen) compared with B (38.3 μg/mg microbial nitrogen) and BP (28.8 μg/mg microbial nitrogen) suspensions by 12 h of incubation. The second most abundant CLA isomer was 10t12c. The accumulation of 10t12c-CLA in BP suspension was 2.3 times lower (P < 0.05) than that in B suspension (84.8 μg/mg microbial nitrogen) by 12 h of incubation. The accumulation of 10t-18:1 in BP suspension during 6- and 12-h incubation periods were not different (P > 0.05) than that in B suspension (6.8 and 14.0 μg/mg microbial nitrogen, respectively). However, the accumulation of 11t-18:1 in BP suspension at 6- and 12-h incubations were 2.7 and 3.3 times higher (P < 0.05), respectively, than that in B suspension. There were no significant accumulations of 11t-18:1, 10t-18:1, and 18:0 in P suspension throughout the incubation period. It was concluded that B, P, and BP metabolized linoleic acid to different isomers of CLA, whereas B, including BP, was only capable of biohydrogenating the CLA isomers to 18:0 by the reduction of 18:1 isomers. P was incapable of biohydrogenating LA, but its association with B in the BP suspension altered the biohydrogenation of LA significantly compared with B alone.     

Differential incorporation of dietary conjugated linolenic and linoleic acids into milk lipids and liver phospholipids in lactating and suckling rats

Interest in health benefits of conjugated fatty acids is growing. The present study compared the incorporation pattern of dietary conjugated linolenic acids (CLnA) into milk with that of conjugated linoleic acids (CLA). Lactating Sprague-Dawley rats (Day 1) were divided into five groups fed the control diet (n=4) or one of four experimental diets supplemented with 1–2% CLA or CLnA mixture (n=8 each). Supplementation of 1% and 2% CLA led to enrichment of 4.17% and 8.57% CLA, respectively, while supplementation of 1% and 2% CLnA resulted in enrichment of only 0.98% and 1.71% CLnA in the milk lipids, demonstrating the transfer of CLnA from maternal diet to milk was discriminated. When the lactating rats were given a diet containing a CLnA mixture of 9t,11t,13t-, 9c,11t,13t- and 9c,11t,13c-CLnA isomers, two CLA isomers, namely, 9t,11t (0.59–0.90%) and 9c,11t (1.21–1.96%), were found in the milk, suggesting that three CLnA isomers were Δ-13 saturated. Dietary CLnA at 1–2% had no effect on liver phospholipid (PL) fatty acid composition of both maternal and suckling rats, whereas dietary CLA increased docosahexaenoic acid (4c,7c,10c,13c,16c,19c-22:6) and palmitic acid (16:0) proportionally in the PL of maternal rats, but it suppressed 16:0 in the PL of suckling rats. It is concluded that maternal rats incorporate CLnA isomers into milk differently from that of CLA isomers. Most interesting is that maternal rats can metabolically convert CLnA to CLA.     

Inclusion of sunflower seed and wheat dried distillers’ grains with solubles in a red clover silage-based diet enhances steers performance,meat quality and fatty acid profiles

The current study compared beef production, quality and fatty acid (FA) profiles of yearling steers fed a control diet containing 70 : 30 red clover silage (RCS) : barley-based concentrate, a diet containing 11% sunflower seed (SS) substituted for barley, and diets containing SS with15% or 30% wheat dried distillers’ grain with solubles (DDGS). Additions of DDGS were balanced by reductions in RCS and SS to maintain crude fat levels in diets. A total of two pens of eight animals were fed per diet for an average period of 208 days. Relative to the control diet, feeding the SS diet increased (P<0.05) average daily gain, final live weight and proportions of total n-6 FA, non-conjugated 18:2 biohydrogenation products (i.e. atypical dienes) with the first double bond at carbon 8 or 9 from the carboxyl end, conjugated linoleic acid isomers with the first double bond from carbon 7 to 10 from the carboxyl end, t-18:1 isomers, and reduced (P<0.05) the proportions of total n-3 FA, conjugated linolenic acids, branched-chain FA, odd-chain FA and 16:0. Feeding DDGS-15 and DDGS-30 diets v. the SS diet further increased (P<0.05) average daily gains, final live weight, carcass weight, hot dressing percentage, fat thickness, rib-eye muscle area, and improved instrumental and sensory panel meat tenderness. However, in general feeding DGGS-15 or DDGS-30 diets did not change FA proportions relative to feeding the SS diet. Overall, adding SS to a RCS-based diet enhanced muscle proportions of 18:2n-6 biohydrogenation products, and further substitutions of DDGS in the diet improved beef production, and quality while maintaining proportions of potentially functional bioactive FA including vaccenic and rumenic acids.     

Milk fatty acid profile of Peruvian Criollo and Brown Swiss cows in response to different diet qualities fed at low and high altitude

Two identical experimental protocols were followed at 200 and 3,600 m above sea level (a.s.l.) determining the changes of the milk fatty acid (FA) profile of Brown Swiss (BS) and indigenous Peruvian Criollo cows (CR) as a response to diets which were designed to cover the variation in feed quality caused by season. At each site (altitude), six BS and six CR cows, adapted to >3,500 m a.s.l., were fed three dietary treatments (DS, dry-season forage; RS rainy-season forage; OC, diet optimised to meet the cow's requirements) in a 2 × 2 × 3-factorial arrangement. Intakes of FA and milk yield increased from diet DS (low quality diet) to RS and OC (high quality diet) for both cow types. Milk fat proportions of conjugated linoleic acid (CLA), C18:3 c9,c12,c15, total n-3 and polyunsaturated FA (PUFA) were highest (p < 0.05) with diet OC and higher in the lowlands than in the highlands. Low intakes of diet DS obviously resulted in a ruminal energy deficiency and body lipid mobilisation. The ruminal energy deficiency with diet DS was especially pronounced in BS, apparently reducing biohydrogenation rate and leading to lower proportions of C18:0 and higher proportions of C18:3 c9,c12,c15 in milk fat (p < 0.05). Especially C18:3 c9,c12,c15 intake did not concur with its proportion in milk fat, suggesting a strong dependence on energy status. Milk yield and FA excretion with milk were higher for BS than for CR (p < 0.05) with all three diets although milk fat content was lower (p < 0.05) for BS than CR. Milk fat of BS was richer in CLA and PUFA than milk fat of CR (p < 0.05). The desaturase indices for 18 FA were also higher for BS than CR (p < 0.05), suggesting a slightly higher Δ9-desaturase activity for BS, especially with diet DS. Milk fat content was generally higher at the high altitude than at the lowland site (p < 0.05), whereas the FA profile was unexpectedly similar across sites. Various interactions were found among diet type, cow type and altitude (site) indicating that a combination of these factors contributes to the characteristic FA profile of the respective milk.     

Comparison of fatty acid composition of bacterial and protozoal fractions in rumen fluid of sheep fed diet supplemented with sunflower, rapeseed and linseed oils

The objective of this study was to investigate effects of oil supplements on the composition of fatty acids (FA), especially of trans11-C18:1 (vaccenic acid, TVA) and cis9, trans11-C18:2 conjugated linoleic acid (c9,t11-CLA), in bacterial (BF) and protozoal (PF) fractions of rumen fluid of sheep that was fractionated centrifugation. Four sheep were fed a diet consisting of meadow hay (960 g dry matter (DM)/day) and of barley grain (240 g DM/day), with sunflower oil (SO), rapeseed oil (RO) or linseed oil (LO) as supplements (60 g/day) in a Latin square design. The oils were used as they are rich in linoleic acid (SO, 533 g/kg of FA), oleic acid (RO, 605 g/kg of FA) and α-linolenic acid (LO, 504 g/kg of FA). Compared to the control (i.e., without oils), oil supplements influenced the concentration of unsaturated (UFA) and saturated fatty acids (SFA). In both BF and PF, the main fatty acids were palmitic and stearic, but PF contained a higher proportion of TVA and c9,t11-CLA than BF. In PF, TVA concentrations, ranked by oil supplement, were SO > RO > LO > Control (174, 150, 118, 74 g/kg of FA, respectively) and the c9,t11-CLA concentrations were RO > SO > LO > Control (59, 51, 27 and 15 g/kg of FA, respectively). Concentrations of c9,t11-CLA in PF were two to three times higher than in BF with all the oil supplements versus the control. Oil treatments impacted the c9,t11-CLA concentration in the fractions, especially SO and RO. The protozoal fraction contained a higher proportion of TVA and c9,t11-CLA than did the bacterial fraction, and dietary addition of SO, RO and LO resulted in a higher incorporation of TVA into both bacterial and protozoal microbial fractions, which probably positively affected TVA flow from the rumen.     

Slow Absorption of Conjugated Linoleic Acid in Rat Intestines,and Similar Absorption Rates of 9c,11t-Conjugated Linoleic Acid and 10t,12c-Conjugated Linoleic Acid

We have previously shown that the 9c,11t-conjugated linoleic acid (CLA) concentration was always significantly higher than the 10t,12c-CLA concentration following the administration of these compounds to mice and rats, and considered that structural differences between the conjugated double bonds in these isomers affected absorption in the small intestine. This study investigates the absorption of CLA in the rat intestine by a lipid absorption assay of lymph from the thoracic duct. In Study 1, we used safflower oil and a triacylglycerol form of CLA (CLA-TG), while in Study 2, we used 9c,11t-CLA and 10t,12c-CLA. The cumulative recovery of CLA was lower than that of linoleic acid until two hours after sample administration. There was no difference in the extent of lymphatic recovery of 9c,11t-CLA and 10t,12c-CLA after the administration of CLA-TG, 9c,11t-CLA, and 10t,12c-CLA to the rats, suggesting that geometrical and positional isomerism of the conjugated double bonds did not influence the absorption.     

The fatty acid composition of milk fat as influenced by feeding oilseeds

The fatty acid composition of bovine milk fat can be substantially altered by feeding lipid sources which alter the fatty acid profile of lipid entering the intestine from the rumen. As long-chain fatty acids of dietary origin can be incorporated directly into milk fat the opportunity exists to alter the ratio of short and long-chain fatty acids as well as the degree of saturation of milk fat. In practice our ability to alter the fatty acid profile of milk fat is limited not by the synthetic capacity of the mammary gland, but rather by the challenge of achieving effective protection of unsaturated dietary fatty acids from biohydrogenation in the rumen, as well as keeping the level of polyunsaturated fatty acids within the range where the organoleptic quality and shelf-life of milk and dairy products are not compromised. The fatty acid composition of oilseeds such as canola are considered desirable from a human health perspective and thus their inclusion in the diet of dairy cattle as a means of achieving a more desirable fatty acid profile in milk fat may enhance the nutritive quality of milk.     

Effect of fish oil and sunflower oil supplementation on milk conjugated linoleic acid content for grazing dairy cows

The objective of this study was to determine the effect of adding fish oil (FO) and sunflower oil (SFO) to grazing dairy cows’ diets on the temporal changes in milk conjugated linoleic acid (cis-9, trans-11 CLA). Sixteen Holstein cows were divided into two diet regimen groups. One group (CONT) was fed a basal diet (7.6 kg DM basis) plus 400 g animal fat. The other group (FOSFO) were fed a basal diet plus 100 g of FO and 300 g of SFO (FOSFO). The cows were milked twice a day and milk samples were collected every 3-day for a period of 21 days. Both groups grazed together on pasture ad libitum and fed treatment diets after the morning and afternoon milking. Milk production, milk fat percentages, milk fat yield, milk protein percentages, and milk protein yield were not affected (P>0.05) by treatment diets. The concentrations of cis-9 trans-11 CLA and vaccenic acid (VA) in milk fat were higher (P<0.05) for cows fed the FOSFO over 3 week of lipid supplementation. The concentration of cis-9 trans-11 CLA in milk fat reached maximum on day 3 with both diets and remained relatively constant thereafter. The concentration of VA in milk fat followed the same pattern of temporal changes as cis-9 trans-11 CLA. In conclusion, milk cis-9, trans-11 CLA and VA concentrations increased with FO and SFO supplementation compared with the CONT diet and the increase reached a plateau on day 3 of supplementation and remained relatively constant throughout the remainder of the study.     

Rumen microbiota and dietary fat: a mutual shaping

Although fat content in usual ruminant diets is very low, fat supplements can be given to farm ruminants to modulate rumen activity or the fatty acid (FA) profile of meat and milk. Unsaturated FAs, which are dominant in common fat sources for ruminants, have negative effects on microbial growth, especially protozoa and fibrolytic bacteria. In turn, the rumen microbiota detoxifies unsaturated FAs (UFAs) through a biohydrogenation (BH) process, transforming dietary UFAs with cis geometrical double‐bonds into mainly trans UFAs and, finally, into saturated FAs. Culture studies have provided a large amount of data regarding bacterial species and strains that are affected by UFAs or involved in lipolysis or BH, with a major focus on the Butyrivibrio genus. More recent data using molecular approaches to rumen microbiota extend and challenge these data, but further research will be necessary to improve our understanding of fat and rumen microbiota interactions.     

Factors influencing biohydrogenation and conjugated linoleic acid production by mixed rumen fungi

The objective of this study was to evaluate the effect of soluble carbohydrates (glucose, cellobiose), pH (6.0, 6.5, 7.0), and rumen microbial growth factors (VFA, vitamins) on biohydrogenation of linoleic acid (LA) by mixed rumen fungi. Addition of glucose or cellobiose to culture media slowed the rate of biohydrogenation;only 35-40% of LA was converted to conjugated linoleic acid (CLA) or vaccenic acid (VA) within 24 h of incubation, whereas in the control treatment, 100% of LA was converted within 24 h. Addition of VFA or vitamins did not affect biohydrogenation activity or CLA production. Culturing rumen fungi at pH 6.0 slowed biohydrogenation compared with pH 6.5 or 7.0. CLA production was reduced by pH 6.0 compared with control (pH 6.5), but was higher with pH 7.0. Biohydrogenation of LA to VA was complete within 72 h at pH 6.0, 24 h at pH 6.5, and 48 h at pH 7.0. It is concluded that optimum conditions for biohydrogenation of LA and for CLA production by rumen fungi were provided without addition of soluble carbohydrates, VFA or vitamins to the culture medium; optimum pH was 6.5 for biohydrogenation and 7.0 for CLA production.     

Increased expression of a molecular chaperone GroEL in response to unsaturated fatty acids by the biohydrogenating ruminal bacterium, Butyrivibrio fibrisolvens

Butyrivibrio fibrisolvens is the most active bacterial species in the biohydrogenation of polyunsaturated fatty acids (PUFA) in the rumen. It needs to remove the unsaturated bonds in order to detoxify the PUFA to enable the growth of the bacterium. Here, we investigated the response of cell membrane-associated proteins in B. fibrisolvens to growth in the presence of PUFA. Numerous changes were observed in the cell membrane-associated proteome. One of the main modifications occurring when the 18:2 fatty acids, linoleic acid and conjugated linoleic acid, were added, was an increased expression of the molecular chaperone GroEL.