Inhibition of the biohydrogenation of dietary C18 unsaturated fatty acids by rumen bacteria using some inhibitors of methanogenesis.
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Animals↗
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Modifying milk fat composition of dairy cows to enhance fatty acids beneficial to human health.
There is increased consumer awareness that foods contain microcomponents that may have beneficial effects on health maintenance and disease prevention. In milk fat these functional food components include EPA, DHA, and CLA. The opportunity to enhance the content of these FA in milk has improved as a result of recent advances that have better defined the interrelationships between rumen fermentation, lipid metabolism, and milk fat synthesis. Dietary lipids undergo extensive hydrolysis and biohydrogenation in the rumen. Milk fat is predominantly TG, and de novo FA synthesis and the uptake of circulating FA contribute nearly equal amounts (molar basis) to the FA in milk fat. Transfer of dietary EPA and DHA to milk fat is very low (<4%); this is, to a large extent, related to their extensive biohydrogenation in the rumen, and also partly due to the fact that they are not transported in the plasma lipid fractions that serve as major mammary sources of FA uptake (TG and nonesterified FA). Milk contains over 20 isomers of CLA but the predominant one is cis-9,trans-11 (75-90% of total CLA). Biomedical studies with animal models have shown that this isomer has anticarcinogenic and anti-atherogenic activities. cis-9,trans-11-CLA is produced as an intermediate in the rumen biohydrogenation of linoleic acid but not of linolenic acid. However, it is only a transient intermediate, and the major source of milk fat CLA is from endogenous synthesis. Vaccenic acid, produced as a rumen biohydrogenation intermediate from both linoleic acid and linolenic acid, is the substrate, and delta9-desaturase in the mammary gland and other tissues catalyzes the reaction. Diet can markedly affect milk fat CLA content, and there are also substantial differences among individual cows. Thus, strategies to enhance milk fat CLA involve increasing rumen outflow of vaccenic acid and increasing delta9-desaturase activity, and through these, several-fold increases in the content of CLA in milk fat can be routinely achieved. Overall, concentrations of CLA, and to a lesser extent EPA and DHA, can be significantly enhanced through the use of diet formulation and nutritional management of dairy cows.
Animals↗
Effect of linoleic acid concentration on conjugated linoleic acid production by Butyrivibrio fibrisolvens A38.
Butyrivibrio fibrisolvens A38 inocula were inhibited by as little as 15 microM linoleic acid (LA), but growing cultures tolerated 10-fold more LA before growth was inhibited. Growing cultures did not produce significant amounts of cis-9, trans-11 conjugated linoleic acid (CLA) until the LA concentration was high enough to inhibit biohydrogenation, growth was inhibited, and lysis was enhanced. Washed-cell suspensions that were incubated anaerobically with 350 microM LA converted most of the LA to hydrogenated products, and little CLA was detected. When the washed-cell suspensions were incubated aerobically, biohydrogenation was inhibited, CLA production was at least twofold greater, and CLA persisted. The LA isomerase reaction was very rapid, but the LA isomerase did not recycle like a normal enzyme to catalyze more substrate. Cells that were preincubated with CLA lost their ability to produce more CLA from LA, and the CLA accumulation was directly proportional (r(2) = 0.98) to the initial cell density. Growing cells were as sensitive to CLA as LA, the LA isomerase and reductases of biohydrogenation were linked, and free CLA was not released. Because growing cultures of B. fibrisolvens A38 did not produce significant amounts of CLA until the LA concentration was high, biohydrogenation was arrested, and the cell density had declined, the flow of CLA from the rumen may be due to LA-dependent bacterial inactivation, death, or lysis.
Animals↗
Comprehensive analysis of the factors for propionic acid accumulation in acidogenic phase of anaerobic process.
The accumulation of propionic acid in the anaerobic process often leads to a low efficiency of the methanogenic phase due to the low acetogenic rate of propionic acid, and hence the low wastewater treatment efficiency. Three acidogenic reactors were used to study the reasons for propionic acid accumulation in the acidogenic phase and its control strategy. The experimental results indicated that in the micro-aerobic circumstance (ORP>-100 mV) the accumulation of propionic acid in the acidogenic reactor always occurred at any pH value. Under strict anaerobic circumstances (ORP < -150 mV), typical propionic acid-type fermentation commonly occurred at pH about 5.5 regardless of ORP value. However, at pH about 5.0, either propionic acid-type or butyric acid-type fermentation might occur depending on whether ORP was high or low. Higher hydrogen production rate was found to have no direct relationship to the accumulation of propionic acid in the acidogenic reactors. In fact, great yield of NADH maybe the major reason for simultaneous accumulation of propionic acid and higher biohydrogen generation rate in the traditional anaerobic process. The highest biohydrogen generation rate occurred during the ethanol-type fermentation without the accumulation of propionic acid. Ethanol-type fermentation is a better choice when using an anaerobic acidogenic reactor of a two-phase separated anaerobic process to efficiently produce biohydrogen simultaneously with organic wastewater pre-treatment.
Bacteria, Anaerobic↗
Dietary and ruminally derived trans-18:1 fatty acids alter bovine milk lipids.
The objectives of this study were to determine whether dietary fish oil enhances production of trans-18:1 isomers in the bovine rumen and whether flow of ruminally derived and/or dietary trans-18:1 to the small intestine is correlated with milk fat production. Four lactating Holstein cows with cannulas in the rumen and proximal duodenum were fed diets with 0% supplemental fat (control diet), 3% hydrogenated tallow fatty acids (HTFA diet), 1.5% menhaden oil plus 1.5% stearic acid (MO+SA diet), or 1.5% soybean oil plus 1.5% partially hydrogenated soybean oil (SBO+HSBO diet) in a 4 x 4 Latin square design. Intakes of trans-18:1 were 0, 12, 0 and 69 g/d when cows were fed the control, HTFA, MO+SA and SBO+HSBO diets, respectively. However, the extent of 18:1 + 18:2(n-6) + 18: 3(n-3) biohydrogenation in the rumen was reduced by consumption of the MO+SA and SBO+HSBO diets. As a result, flow of trans-18:1 to the duodenum was 163 g/d for MO+SA-fed cows and 152 g/d for SBO+HSBO-fed cows compared with 38 g/d for cows fed the HTFA and control diets. Incomplete biohydrogenation accounted for all of the trans-18:1 flow when the MO+SA diet was fed. Compared with results when the HTFA and control diets were fed, milk fat percentage was lower and concentration of trans-18:1 in milk fat was higher when the MO+SA and SBO+HSBO diets were fed. Across all treatments, milk fat percentage decreased linearly with the amount of trans-18:1 flowing to the duodenum and the concentration of trans-18:1 in milk fat. Results indicate that bovine milk fat percentage is depressed by trans-18:1, whether derived from the diet or from incomplete biohydrogenation of unsaturated fatty acids.
Animals↗
Dietary soybean oil changes lipolytic rate and composition of fatty acids in plasma membranes of ovine adipocytes.
A study was conducted to determine which fatty acids in plasma membranes of adipose tissue from ruminants are changed when the diet is supplemented with unsaturated fatty acids and to determine the effect of the fat supplement on adipocyte metabolism. Ten sheep were randomly assigned to two isonitrogenous diets containing either no added fat (control) or 5 g soybean oil/100 g diet. Perirenal fat was removed at slaughter, adipocytes isolated by collagenase digestion, and plasma membranes prepared by centrifugation on a Percoll gradient. Feeding soybean oil to the sheep increased (P < 0.05) linoleic acid [18: 2(n-6)] concentration in subcutaneous fat and isolated adipocytes, suggesting partial escape of dietary unsaturated fatty acids from ruminal biohydrogenation. Soybean oil consumption also decreased (P < 0.05) concentrations of myristic acid, arachidonic acid [20: 4(n-6)] and anteiso 17:0 in plasma membranes, but increased (P < 0.05) trans 18:1. Lipogenesis was not affected by diet, but lipolysis tended to be greater (P = 0.07) in sheep fed the soybean oil-containing diet than in those fed the control diet. In ruminants, fatty acids of ruminal origin, namely trans intermediates of biohydrogenation or branched-chain fatty acids of microbial lipid, may account for as much change in the composition of plasma membranes and in cellular metabolism as do the small quantities of unsaturated fatty acids in the diet that escape biohydrogenation.
Adipocytes↗
Nutritional regulation of milk fat synthesis.
Certain diets cause a marked reduction in milk fat production in ruminants. Commonly referred to as milk fat depression (MFD), the mechanism involves an interrelationship between rumen microbial processes and tissue metabolism. Numerous theories to explain this interrelationship have been proposed and investigations offer little support for theories that are based on a limitation in the supply of lipogenic precursors. Rather, the basis involves alterations in rumen biohydrogenation of dietary polyunsaturated fatty acids and a specific inhibition of mammary synthesis of milk fat. The biohydrogenation theory proposes that under certain dietary conditions, typical pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates that inhibit milk fat synthesis. Trans-10, cis-12 conjugated linoleic acid (CLA) has been identified as one example that is correlated with the reduction in milk fat. Investigations with pure isomers have shown that trans-10, cis-12 CLA is a potent inhibitor of milk fat synthesis, and similar to diet-induced MFD, the mechanism involves a coordinated reduction in mRNA abundance for key enzymes involved in the biochemical pathways of fat synthesis. A more complete identification of these naturally produced inhibitors of fat synthesis and delineation of cellular mechanisms may offer broader opportunities for application and understanding of the regulation of lipid metabolism.
Animal Feed↗
Influence of supplemental cracked high-linoleate or high-oleate safflower seeds on site and extent of digestion in beef cattle.
Our objectives were to evaluate ruminal fermentation patterns, apparent ruminal biohydrogenation, and site and extent of nutrient disappearance in cattle fed supplemental cracked safflower seeds differing in 18 C fatty acid profile. Nine Angus x Gelbvieh heifers (641 +/- 9.6 kg) fitted with ruminal and duodenal cannulas were used in a triplicated 3 x 3 Latin square. Cattle were fed (OM basis) 9.1 kg of bromegrass hay and either 1) 1.8 kg of corn and 0.20 kg of soybean meal (Control); 2) 0.13 kg of soybean meal and 1.5 kg of cracked high-linoleate (67.2% 18:2) safflower seeds (Linoleate); or 3) 1.5 kg of cracked high-oleate (72.7% 18:1) safflower seeds (Oleate). Safflower seed supplements were formulated to provide similar quantities of N and TDN and 5% dietary fat. Single degree of freedom orthogonal contrasts (Control vs. Linoleate and Oleate; Linoleate vs. Oleate) were used to evaluate treatment effects. True ruminal OM and ruminal NDF disappearances (percentage of intake) were greater (P < or =0.02) for Control than Linoleate and Oleate. True ruminal N degradability (% of intake) was not different (P = 0.38) among treatments. Apparent ruminal biohydrogenation of dietary 18:2 was greatest (Linoleate vs. Oleate, P < 0.001) for Linoleate, whereas biohydrogenation of dietary 18:1 was greatest (Linoleate vs. Oleate, P = 0.02) for Oleate. Duodenal flow of 18:0 was least (P < 0.001) for Control but did not differ (P = 0.92) between Oleate and Linoleate. Total flow of unsaturated fatty acid to the duodenum was greatest (P < 0.001) in cattle fed safflower seeds, and was greater with Linoleate (P < 0.001) than with Oleate. Duodenal flow of 18:1 and 18:2 increased (P < 0.001) in Oleate and Linoleate, respectively. Duodenal flow of 18:1trans-11 was greater (P < 0.001) in cattle fed safflower seeds and in Linoleate than in Oleate. Postruminal disappearance of saturated fatty acids was greatest (P < 0.001) for Control; however, postruminal disappearance of total unsaturated fatty acids was greater (P = 0.002) for Linoleate vs. Oleate. Supplemental high-linoleate or high-oleate safflower seeds to cattle fed forage-based diets may negatively affect ruminal OM and fiber disappearance but not N disappearance. Provision of supplemental fat in the form of safflower seeds that are high in linoleic acid increased intestinal supply and postruminal disappearance of unsaturated fatty acids, indicating that the fatty acids apparently available for metabolism are affected by dietary fat source.
Animal Feed↗
Analysis of variation in cis-9, trans-11 conjugated linoleic acid (CLA) in milk fat of dairy cows.
Conjugated linoleic acid (CLA) is a fatty acid with numerous putative health benefits and is a natural component of ruminant-derived food products. An intermediate in rumen biohydrogenation is cis-9, trans-11 CLA, the major CLA isomer in milk fat. However, the major source of cis-9, trans-11 CLA in milk is endogenous synthesis by delta 9-desaturase conversion of trans-11 C18:1, another rumen biohydrogenation intermediate. The desaturase indices serve as a proxy for delta 9-desaturase activity and are calculated from the ratios of fatty acid pairs that represent product/substrate for this enzyme. This study analyzed individual animal variation in milk fat content of cis-9, trans-11 CLA and in desaturase indices in milk fat. Thirty lactating Holstein cows were allocated to one of three treatment groups: one received a standard total mixed ration, one received a diet that produced an elevated milk fat content of CLA, and a third treatment group was alternated between these diets at 3-wk intervals over the 12-wk study. There was a two- to threefold variation among individuals on the same diet for both milk fat content of CLA and desaturase indices in milk fat. This hierarchy was maintained to a large extent over the 12-wk study even in the variable treatment group that alternated between the two diets. Within the variable diet treatment, some animals consistently had a substantial response in milk fat content of CLA to dietary shifts, whereas other cows had little or no response. We conclude that while diet is a major determinant of the CLA content in milk fat, individual animal differences also have a substantial effect. The variation among individuals includes differences related to both rumen biohydrogenation and delta 9-desaturase activity in the mammary gland.
Analysis of Variance↗
Examination of the persistency of milk fatty acid composition responses to fish oil and sunflower oil in the diet of dairy cows.
Based on the potential benefits of cis-9, trans-11 conjugated linoleic acid (CLA) for human health, there is a need to develop effective strategies for enhancing milk fat CLA concentrations. Levels of cis-9, trans-11 CLA in milk can be increased by supplements of fish oil (FO) and sunflower oil (SO), but there is considerable variation in the response. Part of this variance may reflect time-dependent ruminal adaptations to high levels of lipid in the diet, which lead to alterations in the formation of specific biohydrogenation intermediates. To test this hypothesis, 16 late lactation Holstein-British Friesian cows were used in a repeated measures randomized block design to examine milk fatty acid composition responses to FO and SO in the diet over a 28-d period. Cows were allocated at random to corn silage-based rations (8 per treatment) containing 0 (control) or 45 g of oil supplement/kg of dry matter consisting (1:2; wt/wt) of FO and SO (FSO), and milk composition was determined on alternate days from d 1. Compared with the control, the FSO diet decreased mean dry matter intake (21.1 vs. 17.9 kg/d), milk fat (47.7 vs. 32.6 g/kg), and protein content (36.1 vs. 33.3 g/kg), but had no effect on milk yield (27.1 vs. 26.4 kg/d). Reductions in milk fat content relative to the FSO diet were associated with increases in milk trans-10 18:1, trans-10, cis-12 CLA, and trans-9, cis-11 CLA concentrations (r(2) = 0.74, 0.57, and 0.80, respectively). Compared with the control, the FSO diet reduced milk 4:0 to 18:0 and cis 18:1 content and increased trans 18:1, trans 18:2, cis-9, trans-11 CLA, 20:5 n-3, and 22:6 n-3 concentrations. The FSO diet caused a rapid elevation in milk cis-9, trans-11 CLA content, reaching a maximum of 5.37 g/100 g of fatty acids on d 5, but these increases were transient, declining to 2.35 g/100 g of fatty acids by d 15. They remained relatively constant thereafter. Even though concentrations of trans-11 18:1 followed the same pattern of temporal changes as cis-9, trans-11 CLA, the total trans 18:1 content of FSO milk was unchanged because of the concomitant increases in the concentration of other isomers (Delta(4-10) and Delta(12-15)), predominantely trans-10 18:1. In conclusion, supplementing diets with FSO enhances milk fat cis-9, trans-11 CLA content, but the high level of enrichment declines because of changes in ruminal biohydrogenation that result in trans-10 replacing trans-11 as the major 18:1 biohydrogenation intermediate formed in the rumen.
Animal Nutritional Physiological Phenomena↗
Major advances in nutrition: impact on milk composition.
A number of major scientific advances have been realized in the last 25 yr in determining the opportunities and limitations of altering milk composition through nutritional manipulation. Because of the greater sensitivity of milk fat to dietary manipulation than either protein or lactose, nutritional control of milk fat content and fatty acid composition received a great deal of attention. New information emerged linking ruminal production of trans fatty acid isomers with milk fat depression. As a result, research on fatty acid biohydrogenation intensified yielding new insight on the origin of specific trans fatty acid isomers originating from ruminal biohydrogenation and how these isomers were modified by the action of mammary enzymes. The discovery of conjugated linoleic acid (CLA) as a potent anticarcinogen also led to extensive work on enhancing its concentration in milk through nutritional manipulation and discovering the physiological effects of specific CLA isomers. New protected fats were developed in recent years that were designed to resist biohydrogenation and enhance the concentration of unsaturated fatty acids in milk. The nutritional factors receiving the most attention during the last 25 yr for their influence on milk protein content were forage-to-concentrate ratio, the amount and source of dietary protein, and the amount and source of dietary fat. New insights were tested on modes of action whereby fat supplements caused a decline in protein concentration. Changes in milk lactose concentration occur only in extreme and unusual feeding situations, but the basic biology of lactose synthesis and regulation are still being explored using modern molecular techniques. This paper highlights the major advances in controlling milk composition by dietary manipulation and how it influences the entire animal system from practical feeding studies to basic cellular work on mammary tissue metabolism.
Animal Feed↗
[Factors of effecting hydrogen production from anaerobic fermentation of excess sewage sludge].
Large amounts of sewage sludge is produced from the treatment of wastewater by biological processes, which is usually treated by anaerobic digestion to produce methane gas. Acetogenesis and hydrogen are an intermediate phase during the anaerobic digestion. Batch tests of fermentative hydrogen production under different initial pH (3.0 - 12.5) were compared using the raw sludge and alkaline pretreated sludge. The influences of the characteristics and concentration of sludge were also examined thereafter. Results show that the optimal initial pH for biohydrogen production from sewage sludge was around 11.0. Under this optimal condition, the biohydrogen yield of raw sludge was 8.1 mL/g, and it would reach to 16.9 mL/g when the sludge was pretreated by alkali. Furthermore, there is no methane generation during the biohydrogen fermentation of the alkaline pretreatment sludge in 4 days and the hydrogen consumption is also slowed down. In addition, a low VSS/SS rate will reduce the hydrogen yield, while the concentrations of sludge have no obvious compact on it.
Bacteria, Anaerobic↗
Incorporation of n-3 fatty acids of fish oil into tissue and serum lipids of ruminants.
This study examines the biohydrogenation and utilization of the C20 and C22 polyenoic fatty acids in ruminants. Eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids were not biohydrogenated to any significant extent by rumen microorganisms, whereas C18 polyenoic fatty acids were extensively hydrogenated. The feeding of protected fish oil increased the proportion of 20:5 from 1% to 13-18% and 22:6 from 2% to 7-9% in serum lipids and there were reductions in the proportion of stearic (18:0) and linoleic (18:2) acids. The proportion of 20:5 in muscle phospholipids (PL) increased from 1.5% to 14.7% and 22:6 from 1.0% to 4.2%; these acids were not incorporated into muscle or adipose tissue triacylglycerols (TAG). In the total PL of muscle, the incorporated 20:5 and 22:6 substituted primarily for oleic (18:1) and/or linoleic (18:2) acid, and there was no consistent change in the porportion of arachidonic (20:4) acid.
Adipose Tissue↗
A comparison between feeding systems (pasture and TMR) and the effect of vitamin E supplementation on plasma and milk fatty acid profiles in dairy cows.
Unidentified constituents in fresh pasture increase milk fat cis-9, trans-11 conjugated linoleic acid (CLA) concentration, and prevent milk fat depression, even though ruminal conditions conducive to reducing milk fat synthesis exist. One possible explanation is vitamin E (kappa-tocopherol), a constituent high in fresh pasture, but naturally low in conserved/dried forages and cereal grains. Twenty late-lactating dairy cows previously consuming a total mixed ration (TMR) were randomly allocated to one of two dietary treatments for 21 d: TMR (control; n=10); and TMR plus an additional 10,000 i.u. alpha-tocopherol/d (VIT E; n = 10). These cows were simultaneously compared with 13 late-lactation dairy cows previously grazing fresh pasture (PAS) balanced for age, parity and genetic merit. Average daily alpha-tocopherol intakes were approximately 468, 10,520 and 1,590 i.u./cow for the control, VIT E and PAS treatments, respectively. Dietary alpha-tocopherol supplementation (VIT E v. control) slightly increased milk fat content by 0.23 percentage units, but did not significantly alter milk fatty acid composition. Plasma trans-11 18:1 (VA) content tended to increase and trans-10 18:1 levels numerically declined following alpha-tocopherol supplementation suggesting possible changes in rumen biohydrogenation products. In addition, increased alpha-tocopherol intake in TMR-fed cows decreased serum urea levels and tended to alter milk fat 15:0 suggesting changes in rumen microbial populations. However, when compared with cows grazing pasture, TMR-fed cows supplemented with alpha-tocopherol, still produced milk with lower cis-9, trans-11 CLA and VA, and higher trans-10 18:1 concentrations suggesting alpha-tocopherol is not a primary reason for milk fatty acid profile differences between pasture and TMR-fed cows. Therefore, additional unknown pasture constituents favour production of fatty acids originating from the cis-9, trans-11 instead of the trans-10, cis-12 CLA biohydrogenation pathways.
Animal Feed↗
Targets and procedures for altering ruminant meat and milk lipids.
Beef and dairy products suffer from a negative health image, related to the nature of their lipid fraction. Rumen lipid metabolism involves the presence of saturated lipids in ruminant tissues. Lipolysis, fatty acid biohydrogenation and formation of microbial fatty acids in the rumen and their effects on rumen outflow of fatty acids are discussed. Special emphasis is given to the formation of trans-fatty acids and the possibilities of decreasing biohydrogenation. Small differences in intestinal digestibilities of fatty acids are mentioned, followed by a discussion on transfer of absorbed fatty acids into milk and adipose tissue lipids. The preferential retention of polyunsaturated fatty acids as well as the balance between synthesis and incorporation of fatty acids in tissues is described. Dietary means for the modification of milk fat are listed, with special emphasis on the possibilities for enrichment in polyunsaturated fatty acids and the presence of conjugated linoleic acids. A description of the nature and development of fat depots in beef cattle is followed by a discussion of breed, conformation and feed effects on adipose tissue distribution and fatty acid composition. Special emphasis is given to the very lean Belgian Blue double-muscled breed. The review ends with a consideration of the limits to the modification of ruminant fats, involving considerations of consumer acceptance as well as animal welfare and environmental effects.
Adipose Tissue↗
Conjugated linoleic acid is synthesized endogenously in lactating dairy cows by Delta(9)-desaturase.
Conjugated linoleic acid (CLA) is a naturally occurring anticarcinogen found in milk fat and body fat of ruminants. Although CLA is an intermediate in ruminal biohydrogenation of linoleic acid, we hypothesized that its primary source was from endogenous synthesis. This would involve Delta(9)-desaturase and synthesis from trans-11 18:1, another intermediate in ruminal biohydrogenation. Our first experiment supplied lactating cows (n = 3) with trans-11 18:1 by abomasal infusion and examined the potential for endogenous synthesis by measuring changes in milk fat CLA. By d 3, infusion of trans-11 18:1 resulted in a 31% increase in concentration of cis-9, trans-11 CLA in milk fat, demonstrating that an active pathway for endogenous synthesis of CLA exists. Our second experiment examined the quantitative importance of endogenous synthesis of CLA in lactating cows (n = 3) by abomasally infusing a putative stimulator (retinol palmitate) or an inhibitor (sterculic oil) of Delta(9)-desaturase. Infusion of retinol palmitate had no influence on milk fatty acid desaturation, and yield of CLA in milk fat was not altered. However, sterculic oil infusion decreased the concentration of CLA in milk fat by 45%. Consistent with Delta(9)-desaturase inhibition, the sterculic oil treatment also altered the milk fat concentration of other Delta(9)-desaturase products as indicated by the two- to threefold increase in the ratios of 14:0 to 14:1(,) 16:0 to 16:1 and 18:0 to cis-18:1. Using changes in the ratio of 14:0 to 14:1 as an indication of the extent of Delta(9)-desaturase inhibition with the sterculic oil treatment, an estimated 64% of the CLA in milk fat was of endogenous origin. Overall, results demonstrate that endogenous synthesis of CLA from trans-11 18:1 represented the primary source of CLA in milk fat of lactating cows.
Animals↗
Diet-induced milk fat depression in dairy cows results in increased trans-10, cis-12 CLA in milk fat and coordinate suppression of mRNA abundance for mammary enzymes involved in milk fat synthesis.
Milk composition can be altered by diet, and one example is milk fat depression (MFD) in dairy cows. The biohydrogenation theory of MFD has implicated unique fatty acids formed by altered rumen biohydrogenation of PUFA; one example is trans-10, cis-12 conjugated linoleic acid (CLA). In the present study, we induced MFD with a high concentrate/low forage (HC/LF) diet and examined milk composition, milk fatty acid changes and mammary lipogenic mRNA abundance to determine the mechanism involved. The HC/LF diet reduced milk fat percentage by 25% and yield by 27% with no effect on dietary intake, milk production, protein or lactose. Milk fatty acids synthesized de novo in the mammary gland and fatty acids taken up from circulation were reduced to a similar extent (molar basis). MFD was also characterized by the appearance of trans-10, cis-12 CLA in the milk fat. We analyzed mammary mRNA abundance for lipogenic genes and detected reductions for acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), fatty acyl CoA ligase, glycerol phosphate acyltransferase (GPAT) and acylglycerol phosphate acyltransferase (AGPAT). There was no effect on the milk protein gene, kappa-casein. The reductions in mRNA were also correlated with the appearance of trans-10, cis-12 CLA in the milk fat for ACC, FAS, lipoprotein lipase and GPAT. This study demonstrates that diet-induced MFD involves coordinated effects on mRNA for mammary lipid synthesis pathways, and provides support for a mechanism involving alterations in transcriptional activation of these genes.
Acetyl-CoA Carboxylase↗
Biotransformation of linoleic acid and bile acids by Eubacterium lentum.
Eubacterium lentum is a gram-positive, nonsporeforming, nonmotile, asaccharolytic anaerobe. In the present investigations, 3 E. lentum strains (group E) isolated from rat feces were compared with 30 E. lentum strains (groups A, B, C, and D) previously studied by Macdonald et al. (I. A. Macdonald, J. F. Jellet, D. E. Mahony, and L. V. Holdeman, Appl. Environ. Microbiol. 37:992-1000, 1979). All strains alkalized (pH 8 to 8.5) arginine-containing (2 to 15 mg/ml) culture media, and growth of the majority of the strains was stimulated by arginine. All strains converted linoleic acid into transvaccenic acid by shifting the 12,13-cis double bond of linoleic acid into an 11,12-trans(?) double bond followed by biohydrogenation of the 9,10-cis double bond. Hence, biohydrogenation of linoleic acid is a new general characteristic of E. lentum. The 33 strains were also studied for bile acid deconjugase and hydroxysteroid dehydrogenase (HSDH) activities. The 6 strains in group D were steroid inactive; the 27 strains in groups A, B, C, and E were steroid active. The steroid-active group contained bile acid deconjugase-producing strains (groups C and E, plus strain 116 in group A) and nondeconjugating strains. All nondeconjugating strains of groups A and B developed 7 alpha- and 12 alpha-HSDH activities and contained 3 alpha-HSDH-positive strains and 3 alpha-HSDH-negative strains. Deconjugating strains varied in HSDH activities.
Arginine↗