Synopsis

The dietary considerations concerning the fatty acid (FA) profile of red meat are presented from two perspectives: 1) from the perspective of prescribing ruminant animal diets to effect desired alterations in red meat fatty acid profiles and 2) from the perspective of the influence of different kinds of animal diet on the fatty acid profile in red meat. How can they have effects on the red meat properties?

Commentary

We are pleased to release the latest issue Part (5!) five summarizes the results of the intrinsic character of red meat and how they can be modulated, this collection of (5) five E-letters summarize the biology of each extrinsic trait to set the stage for discussions of production system elements that impact each trait. Because of the pervasive impact of total fat content and fatty acid profile on beef quality, especially aspects concerning appearance, tenderness, juiciness, flavor, and healthfulness, the biological considerations and the production system elements impacting these issues are distributed throughout this text.  Among the components within are that of feed, namely feeding flaxseed to cattle, which has beneficial roles with a mixed resulting focus for the development of benefits.  Providing a dietary source of long-chain n-3 polyunsaturated fatty acid is one subject of feed; another is allowing for a rumen environment conducive to partial biohydrogenation. A third is in providing a substrate for the biosynthesis of vaccenic and rumenic acids (Nassu et al., 2011).

The limits of each of the issues are supportive of specific work for each region of service to correlate with the regional population concerning implementation. Diets in relation to Vaccenic Acid also reported that including a percentage of soybean oil in with a ground barley diet with barley straw as the roughage source led to even greater proportions of t10-18:1 in beef, reaching (11.6%) eleven-point six percent in backfat. Meaningful measures of steps in feed can support results with a formidable change in the metrics costs.

Analysis

Pasture vs. Feedyard

Pasture-fed steers have been shown to have greater concentrations of n – 3 PUFA, (C18:3n − 3 and C20:3n − 3) in the intramuscular fat of the longissimus, resulting in a greater total ratio of n − 3 fatty acids than concentrate-fed steers (French et al., 2000; Nuernberg et al., 2005 a, b; Pordomingo et al., 2012; Realini et al., 2004; Yang et al., 2002; and DeFreitas et al., 2014).  Alfaia et al. (2009) indicated that these effects resulted from the higher ruminal protection from bio-hydrogenation of fatty acids in fresh pastures as compared to grains and silage.

There is consensus among researchers cited that the higher PUFA C18:3 content in pastures accounts for the deposition of C18:3n − 3 in the meat. Beef from pasture-finished steers had (2.2) two-point two times more α-linolenic acid than those finished in the feed yard (DeFreitas et al., 2014). Although a large part of PUFA C18:3 is hydrogenated in the rumen to stearic acid, a proportion escapes ruminal fermentation and is absorbed in the small intestine (Sañudo et al., 2000). Animals consuming high concentrate diets produce beef having higher PUFA n – 6 content (Alfaia et al., 2009; French et al., 2000; and Nuernberg et al., 2005 a, b).

Beef from steers finished on pasture has been reported to have a better omega-6 to omega-3 ratio (n − 6/n − 3) than for those finished on concentrate (French et al., 2000; DeFreitas et al., 2014). As stated above, French et al. (2000) reported that a decreasing concentrate level in the diet resulted in a linear increase in intramuscular conjugated linoleic acid. Dannenberger et al. (2005) and DeFreitas et al. (2014), however, found no advantage to pasture-fed cattle for C18:2cis-9 trans-11 content in the longissimus intramuscular fat or in the subcutaneous fat. Scerra et al. (2011) and Medeiros (2008) reported that short finishing periods (Scerra et al., 2011) or the feeding of small amounts of supplementation on an Avena strigosa Schreb. And Lolium multiflorum Lam. pasture (Medeiros, 2008) did not erase the fatty acid profiles established through pasture feeding, whereas longer periods of concentrate feeding or high levels of supplementation on pasture altered the profile generated on pasture-feeding.

Organic and Grass-fed Beef

Alterations of production system elements designed to improve beef fat composition typically involve forage feeding or supplementation with oil seeds rich in PUFA — to increase ALA (and to a lesser extent LA) intake, reducing rumen hydrogenation, and thereby, providing precursors for elongation and/or desaturation into n−3 LC and CLA in the adipose tissue (Daley et al., 2010; and Scollan et al., 2006). Fatty acid profiles of beef from cattle grown on forage diets is preferred in some health-conscious markets to beef from animals fed concentrates. A benefit has been reported to grazing cattle on pasture as compared to feeding of harvested forage (French et al., 2000; Kraft et al., 2008; and Warren et al., 2008a, b).  

Although there are no studies concerning the impact of grass- or forage-based meat consumption on long term human health, grass-fed beef and lamb consumption for (4) four weeks increased plasma and platelet n−3 LC (DHA and EPA) when compared to consumption of equal amounts of meat from silage and concentrate-feed regimes (McAfee et al., 2011). Kamihiro et al. (2015) reported that beef fat from organic and summer finished grass-fed cattle contained higher concentrations of conjugated linoleic acid, its precursor Vaccenic acid, and individual omega-3 fatty acids and had a lower ratio of omega-6 to omega-3 fatty acids compared with non-organic and winter finished cattle respectively.

Dried Distiller’s Grain Plus Solubles

Increasing levels of dried distiller’s grain plus solubles (DDGS) in-ground barley finishing diets of cattle has been reported to increase vaccenic acid and reduce t10-18:1 in subcutaneous fat (Dugan et al., 2010). Production of ethanol from grain fermentation removes much of the starch from the grain, leaving a residue relatively high in protein, fiber, and oil (Walter et al., 2010). Substituting corn DDGS for ground barley has been found to increase the t10/t11-18:1 ratio (Aldai et al., 2010b). 

Flaxseed and Linseed

Flaxseed is a feed candidate for cattle that might improve the long-chain n-3 polyunsaturated fatty acid content of beef. Flaxseed contains about (40%) forty percent oil, of which (50–60%) fifty to sixty percent is linolenic acid, making it one of the richest plant sources of n-3 fatty acids. Feeding flaxseed has been shown to increase levels of n-3 fatty acids in pork, poultry, and dairy products. Human consumption of products from animals consuming flaxseed has been demonstrated to help maintain red blood cell n-3 fatty acid levels (Legrand et al., 2010).

Feeding cattle flaxseed or flaxseed products has also been shown to increase n-3 fatty acids in beef (Kronberg et al., 2006; and Scollan et al., 2001 a, b), but enrichment in adipose tissue and meat is limited by bacterial biohydrogenation in the rumen (Raes, De Smet, and Demeyer, 2004). As discussed earlier, ruminal biohydrogenation means little unsaturated fatty acids are available for absorption, but under ruminal conditions of incomplete biohydrogenation, partially hydrogenated products such as the beneficial vaccenic acid (trans (t)11-18:1) and rumenic acid (cis (c)9, t11-18:2) are available for absorption (Field et al., 2009 ). Therefore, feeding flaxseed to cattle has beneficial roles of 1) providing a dietary source of long-chain n-3 polyunsaturated fatty acid; 2) allowing for a rumen environment conducive to partial biohydrogenation; and 3) providing a substrate for the biosynthesis of vaccenic and rumenic acids (Nassu et al., 2011).

Jua´ rez et al. (2011a) fed (10%) ten percent rolled flaxseed in a (63%) sixty-three percent ground barley, (22%) twenty-two percent alfalfa brome hay diet to steers for a 90-d finishing period. The addition of flaxseed increased total omega-3 fatty acids in beef loin muscle from (0.95 to 2.05%) point nine five to two-point zero five percent of total fatty acids. These workers also reported increased concentrations of polyunsaturated fatty acid biohydrogenation products in beef when flaxseed was included in the diet, but only marginal increases in vaccenic acid (from 0.64 to 0.78%) from point six four to point seven eight percent), and rumenic acid was not affected. Instead, there was a decrease in t10-18:1 accompanied by relatively large increases in other trans-18:1 isomers (t13/t14, t15, t16-18:1) and atypical C18:2 isomers (c9, t13/t8, c12-, t8, c13-, t11, c15- c9, c15- and c12, c15-18:2) derived from the biohydrogenation of linolenic acid. Some increase in beef conjugated linoleic acid has been reported when flaxseed is fed in high forage diets (Enser et al. 1999; Raes et al. 2003; De La Torre et al. 2006; and Barton et al. 2007).

The type of forage in diets containing flaxseed has been found to influence the deposition of biohydrogenation intermediates in beef (Nassu et al., 2011). Inclusion of (15%) fifteen percent flaxseed in a grass hay ration increased the rumenic acid proportion of fatty acids in beef loin from (0.26 to 0.55%) point two six to point fifty-five percent and for vaccenic acid from (0.6 to 2.2%) point six to two-point two percent; whereas, inclusion in a barley silage ration only increased rumenic acid from (0.2 to 0.28%) point two to point two eight percent and vaccenic acid from (0.48 to 0.8%) point four eight to point eight percent of total fatty acids. These workers also reported that feeding flaxseed to cattle, regardless of forage source, resulted in relatively large increases in the concentrations of unique metabolites of linolenic acid biohydrogenation that have unknown impacts on human health (Nassu et al., 2011).

In summary, Nassu et al. (2011) concluded that feeding flaxseed in combination with grass hay appears to be a method to increase concentrations of vaccenic and rumenic acids in beef, but these benefits were muted by increases in other linolenic acid metabolites of unknown physiological consequence and health outcomes.

Alberti et al. (2014) reported that adding (5%) five percent linseed to the concentrate increased the percentage of n−3 fatty acids, primarily α-linolenic acid in the intramuscular fat, and lowered the n−6/n−3 ratio resulting in beef considered to be more healthful.  The addition of 200IU Vitamin E appeared to act synergistically with linseed in improving fatty acid profile. Animals fed linseed, and vitamin E that were fatter at slaughter also exhibited greater percentage of monounsaturated fatty acid content primarily due to increased oleic acid (Alberti et al., 2014).

Dietary Fat Source and Monensin

Soybean and rumen-protected fat (RPF) or calcium soaps are sometimes used as lipid sources in ruminant diets. These lipid sources can increase the amount of unsaturated fatty acids bypassing the rumen for absorption in the small intestine. Also, feed additives that modify the rumen microbial population and, consequently, the nature of ruminal biohydrogenation can alter the availability of unsaturated fatty acids entering the small intestine (Fellner et al., 1997). Of these additives, ionophores (e.g., monensin) are important due to their high efficacy in modifying ruminal fermentation and thus their widespread use in finishing diets.

Oliveira et al. (2014) proposed that feeding highly unsaturated lipid sources in conjunction with monensin will increase unsaturated fatty acid availability to muscles, which will, in turn, increase mRNA synthesis of transcription factors and other important proteins involved in lipid metabolism. They analyzed the gene expression of PPAR-α, SREBP-1c, stearoyl-CoA desaturase (SCD), acetyl CoA carboxylase α (ACACA), lipoprotein lipase (LPL), fatty acid-binding protein 4 (FABP4), and glutathione peroxidase (GPX1) in the muscle of young bulls fed diets containing soybean or RPF with or without monensin. Oliveira et al. (2014) performed a correlation analysis among gene expressions and the fatty acid profile of beef.

They concluded that lipid sources and monensin differentially impact mRNA expression of PPAR-α, SCD, ACACA, LPL, FABP4, and GPX1 in the LD tissue. Only SREBP-1c expression was not affected by the diets. All genes had greater expression when animals were fed ground soybean plus monensin, indicating that soybeans increased the amount of activating fatty acids that reached tissues compared to rumen-protected fat and that monensin had an additive effect (Oliveira et al., 2014). Therefore, alterations of dietary lipid source and rumen metabolism can be utilized to change fatty acid absorption and, consequently, expression of genes involved in lipid metabolism in the Longissimus dorsi (Oliveira et al., 2014). Arachidonic acid and α-linolenic acid had the greatest number of correlations with the genes evaluated, and those correlations were mostly negative. Lipid sources and monensin interact and alter the expression of PPAR-α, SCD, ACACA, LPL, FABP4, and GPX1 (Oliveira et al., 2014). These changes in gene expression were most associated with arachidonic and α-linolenic acids and the ability of lipid sources and monensin to increase these fatty acids in tissues (Oliveira et al., 2014).

Fat Encapsulation

Supplementation with unprotected lipids has minimal effects on the composition of FA in ruminants due to the biohydrogenation of unsaturated fatty acids (UFA) by microorganisms in the rumen ((Ekeren et al., 1992; St. John et al., 1987; and Chang, Lunt, and Smith, 1992). However, the feeding of protected lipids bypasses ruminal FA biohydrogenation, resulting in unsaturated fatty acid absorption in the small intestine and their incorporation in the adipose and muscle tissues of ruminants (Oltjen and Dinius, 1975). A method protecting polyunsaturated fatty acids, primarily the omega-3 (ω-3) fatty acids, from rumen biohydrogenation has been demonstrated to improve the omega-6: omega-3 (ω6: ω3) ratio (Oliveira et al., 2012; and Alvarado-Gilis et al., 2015 a, b).

An encapsulating matrix to affect this ruminal by-pass can be created by mixing feed particles with a suitable matrix material that is resistant to microbial digestion that subsequently forms encapsulating prills. In contrast with encapsulation, when the matrix incurs physical damage, exposure of the core material is confined to the broken surface, and the remainder of the matrix retains its ruminal stability. Alvarado-Gilis et al. (2015 a, b) reported that a matrix consisting of dolomitic lime hydrate is an effective barrier to ruminal biohydrogenation of unsaturated fats although the adverse effects of lime hydrates on feed intake may limit the application of the technology to use with ingredients that are fed in relatively small quantities. Andrade et al. (2014) reported that supplementation with rumen-protected lipids did not affect most beef quality parameters. Meat polyunsaturated fatty acid content was, however, reduced by the inclusion of protected lipids in the diet during the fatting period but the ω6/ω3, Σ hypocholesterolemic/Σ hypercholesterolemic and atherogenicity indexes were increased (Andrade et al., 2014). However, supplementation with rumen-protected lipids during the rearing period resulted in darker beef, higher fat contents, and increased beef tenderness in meat aged for (28 d) twenty-eight days compared to those that received mineral supplementation (Andrade et al., 2014).

A variety of procedures to protect dietary lipids from ruminal degradation have been explored including the use of intact oilseeds, heat/chemical treatment of intact/processed oilseeds, chemical treatment of oils to form calcium soaps or amides, and emulsification/encapsulation of oils with protein and subsequent chemical protection (Scollan et al., 2014; and Gulati, Garg, and Scott, 2005). Physical treatment methods do not greatly alter the proportional loss of dietary PUFA but can increase the total amount of PUFA escaping from the rumen when cattle are fed PUFA-supplemented rations (Jenkins and Bridges, 2007).

Using the emulsification/encapsulation of oils with protein technology, Scollan et al. (2004) showed that a protected plant oil supplement with n−6: n−3 PUFA ratio of 1:1 decreased the n−6: n−3 PUFA ratio in the muscle (from 3.59 to 1.88) three-point five nine to one point eighty-eight while maintaining the high PUFA: SFA ratio. No effect was observed on the concentration of docosahexaenoic acid (DHA). Ruminal protection of fish oil using this technology, however, increased the concentration of Eicosapentaenoic Acid EPA and DHA in tissue but had little effect on the PUFA: SFA ratio (Richardson et al., 2004). Moloney, Shingfield, and Dunne (2011) reported that long term (17) seventeen months supplementation of beef cattle with a similar product employing emulsification/encapsulation of oils with protein technology increased the proportion of EPA and DHA in muscle phospholipids from 2.51 and 0.45 to 8.89 and 2.79 g/100 g fatty acids, respectively, compared to an un-supplemented group. While this emulsification/encapsulation of oils with protein technology seems the most effective protection strategy to date, it has not been used on a commercial scale and involves formaldehyde, the use of which may not be permitted by some regulatory authorities (Scollan et al., 2014).

Fish oil encapsulated in a pH-sensitive matrix that remained intact at rumen pH but eroded in the lower pH of the abomasum was shown to be effective in delivering fish oil, effecting a 3-fold increase in EPA and a 2-fold increase in DHA (Dunne et al., 2011). A procedure involving a whey protein gel complex has also been reported to be effective in protecting PUFA from rumen degradation (Carroll, DePeters, and Rosenberg, 2006; and van Vuuren et al., 2010). Kronberg et al. (2013) reported that a supplement of flaxseed treated with a proprietary, formaldehyde-free process increased muscle C18:3n−3 and EPA proportion in muscle from forage-fed lambs but not in muscle from concentrate-fed cattle.

Oliveira et al. (2012) reported an increase in C18:2n−6 in the bovine muscle when soybean oil was replaced by a commercial product containing calcium salts of soybean oil. A version of this product applied to linseed oil, however, did not protect C18:3n−3 from ruminal biohydrogenation (Oliveira et al., 2012). Noci, Monahan, and Moloney (2011) reported that an amide derivative of camelina oil (a mixture of C18:2n−6 and C18:3n−3) increased the concentration of both C18:2n−6 and C18:3n−3 fatty acids in lamb muscle but this technology has not been investigated in cattle. Kim et al. (201 0a, b, c) reported that supplementing grass silage-fed cattle with a lipid-rich plant extract did not enhance the concentration of either C18:3n−3, EPA, or DHA in muscle possibly indicating that this extract did not provide ruminal protection.

Ruminants incorporate long-chain n−3 PUFA primarily into membrane phospholipids, not into triacylglycerols (Scollan et al., 2014). In addition, there is a possibility for manipulating the intramuscular fatty acid composition of red meat without largely increasing the level of fatness (Scollan et al., 2014). Since the concentrations of EPA and DHA in fish oil are species-dependent and represent up to (25%) twenty-five percent of fish oil fatty acids (Givens et al., 2000), it may be possible to concentrate these fatty acids prior to ruminal protection. Also, algae that are enriched in long-chain n−3 PUFA during culture, when fed to lactating cows, has been reported to cause a five-fold increase in DHA muscle concentration (Angulo et al., 2012).

Prescriptive Diets

Beef with enhanced levels of fatty acids beneficial to human health is of considerable interest to health-conscious consumers, especially in the West (Prieto et al., 2013). Levels of n _ 3 PUFA in ruminant tissues can be increased by feeding dietary lipids which is “protected” from biohydrogenation in the rumen using formaldehyde treatment of linseed (Wood et al., 2008). Scollan et al. (200 6a, b) demonstrated that feeding a protected lipid supplement comprised of soybean, linseed, and sunflower seeds produced a higher efficiency of incorporation of C18:2n _ 6 into intramuscular fat compared with C18:3n _ 3.

Changes in grassland management, such as harvesting at different times during the growing season (harvesting at different levels of maturity) or allowing the grass to wilt before harvesting and conservation apparently have an effect on fatty acid proportions, not only in the grass but also in the meat of cattle and sheep (Wood et al., 200 8). Different grasses and pasture plants also produce different concentrations of PUFA in intramuscular fat either due to variation in levels of certain PUFA among plant species or because of differences in the way the feed is processed in the rumen (Wood et al., 2008). Scollan et al. (2006b) showed that the proportions of both C18:2n _ 6 and C18:3n _ 3 in muscle were increased when steers were fed red clover silage as compared to perennial ryegrass silage. Lee et al. (2004) suggested that the pattern of rumen fermentation and biohydrogenation for red clover is different from that of perennial ryegrass due to the inhibition of lipolysis in clover by the plant enzyme polyphenol oxidase.

Animal Diets to Enhance CLA

There is much evidence that the physiological properties of CLA are isomer specific (Scollan et al., 2014). The CLA isomer and trans-18:1 fatty acid concentration in beef adipose and muscle tissues may be affected by factors such as the animal’s diet, species, level of fatness, age/weight, gender, and breed, as well as fat depot site (Scollan et al., 2014). Strategies to increase the main CLA isomer, cis-9, trans-11 CLA, in beef adipose tissues include pasture- and grass silage-based diets with or without dietary supplements of linseed/linseed oil, rapeseed oil/cakes containing elevated levels of C18:3n−3, fish oil, or marine algae (Scollan et al., 2014). French et al. (2000) and Wood et al. (2008) reported work showing that the process of rumen biohydrogenation is different between fresh and conserved grass, resulting in increased proportions of CLA in intramuscular fat.

CLA isomer patterns in the beef muscle are affected by both diet and, if used, the type of supplement (Scollan et al., 2014). Pasture-based diets (rich in C18:3n−3) with/without supplements containing linseed/rapeseed cake or oil result in higher muscle concentrations of trans, trans-CLA isomers (primarily trans-11, trans-13; trans-12, trans-14; trans-9, trans-11) and trans-11, cis-13 CLA (Alfaia et al., 2009; and Dannenberger et al., 2005). In contrast, n−6 PUFA-based diets (lipids rich in C18:2n−6 like grains or corn silage) led to higher muscle concentrations of trans-10, cis-12 CLA; trans-7, cis-9 CLA; and trans-8, cis-10 CLA (Shingfield et al., 2013). The greatest reported level of cis-9, trans-11 CLA (including trans-7, cis-9 CLA) concentration of 134 mg/100 g muscle was measured in the muscle of Wagyu steers fed a high barley diet supplemented with sunflower oil at the rate of (6%) six percent of dry matter. (Mir et al., 2002).

Options for cuisines, where the seafood is limited, red meat can be the primary source of the perceived beneficial unsaturated fatty acids. Development of red meats with enhanced levels of total n-3 fatty acids could, therefore, contribute to substantial increases in long-chain n-3 polyunsaturated fatty acid intake for these cultures thereby adding value to beef. As a result of their demonstrated beneficial health effects and their natural occurrence in ruminant animals, many attempts have been made to increase omega−3, rumenic (C9, t11-18:2) and vaccenic acids (C9, t11-18:1) in beef (Benjamin and Spener, 2009; and Field et al., 2009). Rumenic acid has been reported as instrumental in the prevention and possible treatment of several diseases, including diabetes, obesity, and some types of cancer (Belury, 2002; and Masso-Welch, 2003). Vaccenic acid has the same role because, upon ingestion, the human body can desaturate it to form rumenic acid (Turpeinen et al., 2002). Ingestion of vaccenic acid has also been shown to reduce blood triglycerides (Wang et al., 2008).

Animal Diets to Enhance Vaccenic Acid

Because of their perceived health benefits, research emphasis is the discovery of means to increase vaccenic and rumenic acids as ruminal fermentation products (Ip et al., 1994; Buccioni et al., 2012; and Koba et al., 2007; and Simopoulos, 1999 ). Vaccenic acid (C18:1trans-11) is the most abundant trans-18:1 fatty acid isomer in beef from pasture-based fed cattle; however, barley-based diets of British × Continental crossbred steers result in higher concentrations of C18:1 trans-10 compared to vaccenic acid and replaced vaccenic acid as the major isomer in beef muscle (Mapiye et al., 2012 b). Also, the muscle from feedyard-fed bulls, intensive indoor-fed Limousine bulls, and Normand cull cows had higher C18:1trans-10 compared to vaccenic acid contents (Alfaia et al., 2009; Bauchart et al., 2010; and Kraft et al., 2008).

Wood (1983) and Purchas, Knight, and Busboom (2005 )  found a greater accumulation of t10-18:1 than vaccenic acid in cattle finished on a high barley diet. Grain-fed beef has been reported to have less conjugated linoleic acid and more t10-18:1 than vaccenic acid as compared with grass-finished beef (in U.S., Leheska et al. 2008 and in Germany, Dannenberger et al. 2004). Raes et al. (2004) reported that when the concentrate was fed with limited barley (13%) thirteen percent and wheat (20%) twenty percent with straw as a roughage source, a high proportion of vaccenic acid to t10-18:1 was maintained in both rumen contents and adipose tissue. Limiting the amount of barley in the concentrate portion of the diet to (34%) thirty-four percent in a (60:40) sixty forty roughage to concentrate diet (DM basis) was also found to maintain a higher concentration of vaccenic acid than t10-18:1 in duodenal digesta (Lee et al. 2005).

A summary of the literature indicates that C18:1trans-10 is a “potentially negative TFA isomers” in terms of human health (Wang et al., 2012). Feeding forages supplemented with linseed- or sunflower oil and algae results in elevated vaccenic acid levels but also higher levels of C18:1trans-9 and C18:1trans-10 isomer concentrations in muscle of German Holstein cows (Angulo et al., 2012). Pasture and grass silage-based diets alter the trans-18:1 fatty acid isomer pattern resulting in a decrease of C18:1trans-6/7/8, C18:1trans-9, and C18:1trans-10 and a enrichment of C18:1trans- 13/14 and C18:1trans-16 compared to corn silage-based diets (Aldai et al., 2011; and Dannenberger et al., 2004).

In summary, if cattle are fed too high a level of grain with highly fermentable starch, the resultant shift in rumen microflora creates a cascade involving a reduction in rumen pH and a shift in the biohydrogenation pathways towards producing C18:1trans-10(t10-18:1) instead of vaccenic acid (Bauman and Griinari 2003). Accentuated increases in C18:1trans-10 may also occur when feeding grains since the final step in the biohydrogenation that leads to stearic acid is precipitated by acidic ruminal conditions (Troegeler-Meynadier et al. 2006). The type of grain and degree of grain processing can also be important as a determinant of the isomeric profile of trans-18:1 produced in the rumen (Mohammed et al., 2010).

The shift from the production of vaccenic acid to C18:1trans-10 occurs rapidly when cattle are moved from pasture to a high barley diet (Aldai et al., 2011). Corn is generally thought to have a slower rate of ruminal fermentation than barley or wheat. When Fritsche et al. (2001) fed a diet with (70%) seventy percent corn, they observed (0.7%) point seven percent vaccenic acid and (0.22%) point two two percent t10-18:1 in beef subcutaneous fat. Duckett et al. (2002) reported that the concentration of vaccenic acid was greater when high-oil corn was substituted for conventional corn, but when corn oil was added to conventional corn at the same rate as in the high-oil corn diet, the flow of t10-18:1 was more than (300%) three hundred percent greater than the flow of vaccenic acid.

Beaulieu et al. (2002) and Dhiman et al. (2005) added soybean oil to a corn-based diet and found greater concentrations of total trans-18:1 in adipose tissue, but they observed no change in rumenic acid leading them to hypothesize that the increase in trans fatty acids was related to isomers other than vaccenic acid. When Madron et al. (2002) added as much as (26%) twenty-six percent extruded full-fat soybeans to a corn-based diet, however, muscle concentrations of t10- and t11-18:1 increased, but vaccenic acid remained the predominant isomer. In contrast, when Hristov et al. (2005) fed diets with (79%) seventy-nine percent dry rolled barley containing either (5%) five percent safflower or high oleic acid safflower, they found only (0.6%) point six percent vaccenic acid and more than (5%) five percent t10-18:1 in adipose tissue for both diets. Aldai et al. (2010c ) also reported that including (3%) three percent soybean oil in an (85%) eighty-five percent ground barley diet with barley straw as the roughage source led to even greater proportions of t10-18:1 in beef, reaching (11.6%) eleven-point six percent in backfat.

As previously mentioned, the accumulation of trans-18:1 isomer can be related to the effects of low pH on biohydrogenation pathways, but the type and level of oil can also inhibit biohydrogenation (Troegeler-Meynadier et al. 2006) further increasing trans-18:1 in beef. The longer-chain polyunsaturated fatty acids in fish oil (i.e., docosahexaenoic acid) have been shown to be effective at reducing biohydrogenation rates (Lee et al. 2005), but their effectiveness is also associated with the composition of other oils in the diet (Duckett and Gillis 2010). The accumulation of trans-18:1 when feeding polyunsaturated fatty acids may reflect inhibition at the enzymatic level (Troegleler-Meynaidier et al. 2006) or direct inhibition of the bacteria involved in the final step of hydrogenation of trans-18:1 to stearic acid (Lourenc o et al., 2010).

Conclusion

Among others, there are numerous animal diets, each with their advantages and downsides. Namely, the primary challenge with each of these diets is to allow the best absorption of fatty acids while reducing or bypassing the constraining effect from the bacterial biohydrogenation taking place in the rumen. The second challenge is how a diet would affect the concentrations of the crucial vaccenic and rumenic acids since they have proven healthy properties. Nevertheless, many factors and consequences are entangled when influencing them. It means that fluctuations in dietary lipid supply and rumen metabolism may be used to modify the absorption of fatty acid and, thus, the expression of lipid metabolism genes. Please join us on the (1) first and (15) fifteenth of each month for our fortnightly delivery of insightful, informative must-reads from some of the world’s scientific thinkers. Selected by our editors. Thank you for reading our publication entirely; please share it with others who also care. We look forward to your comments and having you with us again next month; we will be thrilled in having you with us; thus, we will take your trust in us with great honor and appreciation.