Conjugated linoleic acid (CLA) concentrations on beef according to breed, sex and age .a b Indicates a significant differences (at least p < 0.05) between breed, sex or age reported within each respective study. Abbreviations LD: Longissimus dorsi ; SM: Semimembranosus ; LL Longissimus lumborum; LT Longissimus thoracis; Sub: Subcutaneous fat.
Beef and lamb, are a food category with positive and negative nutritional attributes. Ruminant meats are major sources for many bioactive compounds including iron, zinc and B vitamins. However they are associated with nutrients and nutritional profiles that are considered negative including high levels of saturated fatty acids (SFA) and cholesterol. It is well know that the low PUFA/SFA and high n-6/n-3 ratio of meats contribute to the imbalance in the in the fatty acid intake of today consumers . Consumers are becoming more aware of the relationships between diet and health and this has increased consumer interest in the nutritional value of foods. Nutritionist advisers recommended a higher intake of polyunsaturated fatty acids (PUFA), especially n-3 PUFA at the expense of n-6 PUFA.
The nutritional beef and lamb profile could be further improved by addition of potentially health promoting nutrients. There are many references of improved fatty acid composition in grass fed beef. Besides the beneficial effects of n-3 fatty acids on human health one fatty acid that has drawn significant attention for its potential health benefits in the last two decades is conjugated linoleic acid (CLA). Conjugated linoleic acids (CLA) are implicated as anti-carcinogenic, anti-atherosclerosis, and anti-inflammatory agents in a variety of experimental model systems. It has been shown that in ruminants grazing have potential beneficial effects on PUFA/SFA and n-6/n-3 ratios, increasing the PUFA and CLA content and decreasing the SFA concentration of beef .
The total CLA content of beef varies from 0.17 to 1.35% of fat . This wide range is related to the type feed, breed differences, and management strategies used to raise cattle [3, 4]. Grazing beef steers on pasture or increasing the amounts of forage (grass or legumes hay) in the diet has been shown to increase the CLA content in the fat of cattle. Also, supplementing high-grain diets of beef cattle with oils (e.g., soybean oil, linseed oil, sunflower oil) may increase the CLA content of beef [3, 5].
There has been an increased interest in the substitution of animal fat sources with vegetable oils in animal nutrition. Vegetable oils have been attributed with reducing the level of saturation in monogastric animal tissues due to their unsaturated fatty acid concentration when compared with animal fat. In ruminants, dietary lipids were undergo two important transformations in the rumen. The initial transformation is the hydrolysis of the ester bond by microbial lipases. This initial step is a pre requisite for the second transformation, the biohydrogenation of unsaturated fatty acids [6, 7].
Several factors influence the CLA content of beef as breed, sex, seasonal variation, type of muscle, production practices but diet plays the most important role. Dietary CLA from beef can be increased by manipulation of animal diets. CLA concentration in beef can be influenced by dietary containing oils or oilseeds high in PUFA, usually linoleic or linolenic fatty acids.These dietary practices can increase CLA concentrations up to 3 fold [5, 8]. Moreover, trans-11 18:1 (vaccenic acid,VA) is the precursor of cis-9,trans-11 18:2 ( rumenic acid, RA) is the major CLA isomer in animal and humans and, therefore, it might be considered as a fatty acid with beneficial properties.
Soybean oil is one of the few plant sources providing ample amounts of both essential fatty acids 18:2 n-6 and 18:3 n-3. The fatty acid content of soy foods is often unrecognized by health professionals, perhaps because there is so much focus on soy proteins. Soybeans are used in cattle, poultry and pigs diets and could be a more important source of 18:3 n-3 for animal nutrition and also increase 18:3 n-3 and its fatty acids metabolites in meats. Genomics, specifically marker assisted plant breeding combined with recombinant DNA technology, provided powerful means for modifying the composition of oilseeds to improve their nutritional value and provide the functional properties required for various food oils .
Thus, the manipulation of the fatty acid composition in ruminant meat to reduce SFA content and the n-6/n-3 ratio whilst, simultaneously increasing the PUFA and CLA contents, is the major importance in meat research. The supplementation of ruminant diets with PUFA rich lipids is the most effective approach to decrease saturated FA and promote the enrichment of CLA and n-3 PUFA.
2. CLA structure, biosynthesis and potential beneficial effects on human health
The CLA acronym refers to a group of positional and geometric isomers of linoleic acid, in which the double bands are conjugated. At least twenty four different CLA isomers have been reported as occurring naturally in food, especially from ruminant origin . Isomerisation and incomplete hydrogenation of PUFA in the rumen produce several of octadecenoic, octadecadienoic and octadecatrienoic isomeric fatty acids  and, at least some of them, have powerful biological properties. The formation of conjugated dienes in the rumen during biohydrogenation of lipids in feed was observed previously, however, the anticarcinogenic effect of beef extracts was first observed and later identified [12, 13, 14].
The dominant CLA in ruminant meats is the cis-9, trans-11 isomer (RA) which has being identified as possessing a range of health promoting biological properties including antitumoral and anticarcinogenic activities . The rumenic acid is mostly produced in tissues by delta 9 desaturation of trans-11 18:1, (VA) and by ruminal biohydrogenation of dietary PUFA. The higher deposition of CLA in the neutral lipid fraction, 88% of total CLA relatively to phospholipid fraction, has been reported .The majority of the main natural isomer cis-9,trans-11 CLA does not originate directly from the rumen. Instead, only small amounts of CLA escape the rumen and trans-18:1 isomers are the main biohydrogenation intermediates available. El absorbed trans-11 18:1 is desaturated in the tissues by ∆9-desaturase to form RA . Stearoyl-CoA (SCD) is a rate-limiting enzyme responsible for the conversion of SFA into monounsaturated fatty acids (MUFA). This enzyme, located in the endoplasmic reticulum, inserts a double band between carbons 9 and 10 into SFA and affects the fatty acid composition of membrane phospholipids, triglycerides and cholesterol esters . SCD is also a key enzyme in the endogenous production of the cis-9,trans-11 isomer of conjugated linoleic acid (CLA). Trans octadecenoates (trans 18:1) are the major intermediates formed during rumen biohydrogenation of C18 PUFA. High trans-10 18:1 have been observed in tissues of concentrated-fed ruminants, whereas vaccenic acid is consistently associated with forage feeding [11, 19]. Evidence is accumulating that different trans 18:1 isomers have differential effects on plasma LDL cholesterol. Trans-9 and trans-10 18:1 are more powerful in increasing plasma LDL cholesterol than trans-11 18:1 . Comparison of antiproliferative activities of different CLA isomers present in beef on a set of human tumour cells demonstrates that all CLA isomers possess antiproliferative properties. It appears that important to determine the variations of the distribution of CLA isomers in beef since these proportions could influence the biological properties of bioformed CLA .
3. Factors influencing CLA concentrations on beef lipids
Amounts of CLA in beef vary mainly with feeding conditions, nature and quality of forages, proportions between forage and concentrate, oil-seed supplementations, but also with intrinsic factors such as breed and sex and age of animals .
3.1. Breed, sex and age (Table 1)
Breed or genotype and production system are determinant factors of the fatty acid composition of the ruminant meats. Breed affects the fat content of meat and fat content itself is a factor determining fatty acid composition. Genetic variability relates to differences between breeds or lines, variation due to the crossing of breeds and variation between animals within breeds reported that it can be difficult to assess the real contribution of genetics to variation in the CLA content.
|LD Limousin||2.24 g/100g|||
|LD Angus||1.96 g/100g|||
|LD Angus||0.51 b% FAME|||
|LD Charolais x AA||0.57 a% FAME|||
|LD Holando x AA||0.58a% FAME|||
|LD Nguni grass||0.34% FA|||
|LD Bonsmara grass||0.31% FA|||
|LD Angus grass||0.33% FA|||
|LD Holstein grass||0.84 % FA|||
|LD Simmental grass||0.87% FA|||
|LD Holstein concentrate||0.75% FA|||
|LD Simmental concentrate||0.72% FA|||
|SM Pasture and Silage Steers Longhorn||6.75a mg/100g|||
|SM Pasture and Silage Steers Charolais||3.29b mg/100g|||
|SM Pasture and Silage Steers Hereford||2.93b mg/100g|||
|SM Pasture and Silage Steers B. Gallowey||5.09a mg/100g|||
|SM Pasture and Silage Steers Beef Shorton||4.01ab mg/100g|||
|Sub Pasture and Silage Steers Longhorn||1210a mg/100g|||
|Sub Pasture and Silage Steers Charolais||651b mg/100g|||
|Sub Pasture and Silage Steers Hereford||584b mg/100g|||
|Sub Pasture and Silage Steers B. Gallowey||796 b mg/100g|||
|Sub Pasture and Silage Steers Beef Shorton||808b mg/100g|||
|Mertolenga PDO beef||0.39ab g/100g FA|||
|Mertolenga PDO veal||0.46a g/100g FA|||
|Vitela Tradicional do Montado PGI veal||0.35b g/100g FA|||
|LT & LL Veal Limousin||1.09% FAME|||
|LT & LL Veal Tudanka x Charolais||1.00% FAME|||
|LL bulls 14 month||0.37 % FA|||
|LL bulls 18 month||0.39% FA|||
|LL heifers 14 month||0.44% FA|||
|LL heifers 18 month||0.41 % FA|||
|L lumborum steers||0.20 % FA|||
|L.lumborum bulls||0.21 % FA|||
Significant between-breed differences in CLA content were observed in both muscle and subcutaneous adipose tissue of five breeds of cattle with the highest values in Longhorn and with the lowest in Hereford . German Holstein bulls accumulated a higher amount of CLA compared with German Simmental bulls . CLA percentages were affected by breed with the low values for Angus beef compared with Charolais x Angus and Holstein Argentine steers . The content of trans -10 C18:1 isomer tended to be higher in Limousin compared to Tudanca meat when expressed as mg/100g of meat, and the difference was only significant when expressed in terms of relative percent. The higher level of trans-10 C18:1 was consistent with the greater consumption of concentrate by Limousin calves . Within a similar production system the age/weight, gender and crossbreeding practices have minor effects on muscle FA composition but Mertolenga-PDO veal has higher total CLA contents that PDO beef and PGI veal [ 27]. On the contrary the cis-9, trans-11 CLA levels among steers of Nguni, Bonsmara and Angus breeds raised on natural pasture were similar . Similar results were found comparing the CLA content of Limousin and Aberdeen Angus beef .
Sex and age differences in muscle FA contents are often be explained by the degree of fatness and associated changes in the triacylglycerol/phospholipid ratio . Sex-dependent differences in the FA composition of muscle an adipose tissue from cattle slaughtered at different ages were demonstrated . Concentration CLA in meat beef not affected by castration .
3.2. Type muscle and anatomical location (Table 2)
Little work has been conducted to assess the effects of slaughter season and muscle type on meat CLA profile. The type of muscles strongly influenced proportions of total CLA and of all CLA isomers classes in intramuscular fatty acids (Table 2). CLA is mainly associated to the triacylglycerol fraction which is linked to the fat content of tissues . VA and CLA percentages were lower in lean muscle than subcutaneous fat or marbling . The CLA content of steaks differs depending on the location of the fat, CLA level was almost doubled in outer subcutaneous fat compared to lean muscle . There was significant differences in the concentration of CLA among depot sites through-out a bovine carcass. The brisket contained a higher concentration of cis-9, trans-11 CLA but no significant differences in the concentrations of trans-10, cis-12 CLA among the locations .
3.3. Season and pasture type (Table 2)
No differences between dietary grass silage and red clover silage were detected on CLA content of LD muscle of dairy cull cows . Total CLA content was lower (p< 0.05) in intensively produced beef than in Carnalentejana-PDO meat, which did not show significant differences (p<0.05) when the slaughter season was compared. Furthermore
|Steak muscle||0.30b % FA|||
|Steak marbling||0.50a % FA|||
|Outer subcutaneous fat||0.50a % FA|||
|Inner subcutaneous fat||0.50a% FA|||
|Seam||0.40ab % FA|||
|Adipose tissue brisket||0.70a g/100g FA|||
|Adipose tissue chuck||0.62ab g/100g FA|||
|Adipose tissue flank||0.56b g/100g FA|||
|Adipose tissue loin||0.53b g/100g FA|||
|Adipose tissue plate||0.57b g/100g FA|||
|Rib||0.52b g//100g FA|||
|Round||0.63ab g/100g FA|||
|Sirloin||0.57b g/100g FA|||
|LT concentrate||4.45 mg/g fat|||
|ST concentrate||3.88 mg/g fat|||
|LT Autumn||5.07 mg/g fat|||
|LT Spring||4.92 mg/g fat||]|
|ST Autumn||3.82 mg/g fat|||
|ST Spring||5.06 mg/g fat|||
|L L Spring||0.30 a g/100g FA|||
|L L Autumn||0.31a g/100g FA|||
|ST Spring||0.23 b g/100g FA|||
|ST Autumn||0.19b g/100g FA||]|
|LD Tall fescue||0.28%|||
|LD Red clover||0.30%|||
|LD cull cows grass silage||0.22 % TFA|||
|LD cull cows red clover silage||0.17 % TFA|||
A direct linear relation between grass percentage in cattle diet and meat CLA content has been described by  although the mechanism remains controversial. They suggested that grass in the diet enhances the growth of ruminal bacterium
|LD Grazing||10.8a mg/g fat|||
|LD Concentrate-fed||3.7b mg/g fat|||
|LD Grazing||5.3a mg/g fat|||
|LD Concentrate-fed||2.5 b mg/g fat|||
|LD Pasture||0.72 % FAME|||
|LD Pasture +0.7% corn||0.61 % FAME|||
|LD Pasture+1.0 %corn||0.58% FAME|||
|LD Feedlot||0.31 % FAME|||
|LD Grass silage (GS)||3.62% FA|||
|LD GS +Low concentrate||2.50% FA|||
|LD GS+ High concentrate||2.72% FA|||
|LT Semi-intensive 12 month||0.49a %|||
|LT Semi-intensive 14 month||0.49a %|||
|LT Intensive 12 month||0.25b %|||
|LT Intensive 14 month||0.29b %|||
|Ground control||0.50b g/100g|||
|Ground grass||0.94a g/100g|||
|Steaks control||0.38b g/100g|||
|Steaks grass||0.66a g/100g/|||
|Control||0.82 % FA|||
|Back fat 20% DDGS corn||0.88 % FA|||
|Back fat 20% DDGS wheat||0.88 % FA|||
|Back fat 40%DDGS corn||0.97 % FA|||
|Back fat 40% DDGS wheat||0.81 % FA|||
|LT concentrate||4.45 mg/g fat|||
|ST concentrate||3.88 mg/g fat|||
3.5. Oil supplementation (Tables 4 & 5)
The most common method of enhancing the CLA and VA content of ruminant meat and dairy products is to provide the animal with additional dietary unsaturated fatty acids, usually from plants oils such as soybean oil (SBO), for use as substrates for ruminal biohydrogenation . Steers fed a corn-based diet supplemented with SBO may enhance TVA without impacting CLA, while reducing the MUFA content of lean beef . Both oilseed and free oils affect CLA content in a similar manner. Free plant oils with high PUFA concentrations are normally not included in ruminant diets as high levels of dietary fat disturb the rumen environment and inhibit microbial activity. The main sources of supplementary fatty acids in ruminant rations are plant oils and oilseeds, fish oils, marine algae and fat supplements. Since dietary inclusion of fatty acids must be restricted to avoid impairment of rumen function, the capacity to manipulate the fatty acid composition by use of ruminally available fatty acids is limited . Many researchers have found higher CLA content in muscle lipids by supplementing with different oils. However, some studies reported no significant differences in CLA content due to oil supplementations. The differences in responses to plant oils were probably due to variations in stage of growth of cattle, levels of oil supplementation, levels of oil in total ration and amount of linoleic acid in oils. Researchers have successfully increased CLA content by supplementation of different oils [4,48,56]. Others  supplementing with 4% SBO to diets did not affect the CLA. Similar to  who reported that feeding 5% SBO no affected CLA but increased trans10-cis-12 CLA. The addition of different vegetable oils to the bulls diet (soybean or linseed, either protected or not protected from rumen digestion) increased the CLA content, with an average CLA value of 0.72 %. The increase of CLA was also due to the addition of oils presenting large quantities of its precursor LA in diets with unprotected soybean and linseed oils . Diets containing silage and concentrate or sugarcane and sunflower seeds fed Canchim- breed animals, produce an improvement in CLA levels (0.73g/100g vs. 0.34g/100) . Rapeseed oil and whole rapeseed do not seem to have positive effects. Of the three studied none showed increased CLA concentrations in the LDi after supplementation with 6% rapeseed oil . Soybean oil (SBO) has been used as a source de LA throughout the finishing period to promote greater CLA accretion in lean tissues with equivocal results [56, 41]. and where CLA accretion was increased with SBO addition, growth performance was reduced . Fed steers with 5% of soybean oil in a finishing experiment for 102 days had no effects in meat cis-9, trans, 11 CLA . In a study with steers, supplementation of 4% soybean oil to a finishing diet based on concentrate and forage (80:20) resulted in a depression of the CLA deposition in muscle tissues (2.5 vs. 3.1 mg/g FAME) compared to the same diet without soybean oil On the other hand, comparing 4% with 8% added soybean oil in a 60:40 concentrate : forage diet showed a numerical increase of the CLA content with the higher soybean supplementation (2.8/3.1 mg/g FAME) . The inclusion of sunflower oil in the diets (80% barley, 20% barley silage) of finishing cattle at 0%, 3%, or 6% increased the CLA content of the beef by 75% when cattle were fed 6% sunflower oil . Although supplementation with oil or oil seeds increased CLA content in muscle, the inclusion of linoleic acid –rich oil or oilseeds such as safflower or sunflower, in the diet of ruminants appears to be the most effective . Supplementation of cattle with a blend of oils rich in n-3 PUFA and linoleic acid results in a synergistic accumulation of ruminal and tissue concentrations of TVA . VA is the substrate for ∆9 –desaturase- catalyzed de novo tissue tissue synthesis of cis-9 trans-11 isomer of CLA. However, despite increases in its substrate, muscle tissue concentrations of cis-9, trans-11 CLA have not increased by using this strategy . Inclusion of extruded linseed in the diet of Limousin and Charolais cattle, increase CLA . The importance of the contribution of TVA to total CLA intake is further reinforced by a French study  in which a huge 233% increase of VA was shown, along with 117% increase of RA, which was caused by adding extruded linseeds into the animal fodder. Several authors reported that diets containing proportionally high levels of linolenic acid, such as fresh grass, grass silage, and concentrates containing linseed, resulted in increased deposition of the cis-9, trans-11 CLA isomer in muscle . The biohydrogenation by rumen microorganism does not include the cis-9, trans-11 CLA isomer as an intermediate. The trans-11 18:1 is the common intermediate during the biohydrogenation of dietary linoleic acid and linolenic acid to stearic acid . Since only a relatively small percentage the cis-9, trans-11 CLA isomer, formed in the rumen, is available for deposition on the muscles, the major source of this isomer in muscle results from the endogenous synthesis involving ∆ 9 desaturase and vaccenic acid .. Hereford steers cannulated in the proximal duodenum were used to evaluated the effects of forage and sunflower oil level on ruminal biohydrogenation and conjugated linoleic acid. Flow of trans-10 18:1 decreased linearly as dietary forage level increased whereas trans -11 18:1 flow to the duodenum increased linearly with increased dietary forage. Dietary forage or sunflower oil levels did not alter the outflow of cis-9, trans-11 CLA . Linseed supplementation was an efficient way to increase CLA proportion in beef (+22% to 36%) but was highly modulated by the nature of the basal diet, and by intrinsic factors as breed, age/sex, type of muscle, since these ones could modulate CLA proportions in beef from 24% to 47% . Soybean oil, which is rich in linoleic acid, has been found in several studied [66,67,] to be more efficient than linseed oil, which is rich in linolenic acid, in increasing the CLA content of milk. In beef cattle the addition of 3% and 6% sunflower oil to a barley based finishing diet results in increased CLA content in LD muscle: 2.0 vs 2.6 vs. 3.5 mg/g lipid for control, 3%,, and 6% sunflower oil, respectively. A more substantial increase in the CLA concentration was found when sunflower oil was added to both the growing and finishing diet of beef cattle.[68,69]. 4.3, 6,3 and 9.1 mg CLA / g FAME in LD muscle lipids of heifers, were found, after supplementing the feed with 0, 55, and 110 g sunflower oil per kg of the diet for 142 days before slaughter . Supplementation of a high forage fattening diet with either soybean oil or extruded full fat soybeans at a level of 33g added oil per kg of diet DM resulted in a 280-410 % increase in the concentration of CLA in the intramuscular and subcutaneous lipid depots of fattening Friesian bull calves The content of VA in both lipid depots were also increased about three-fold by this oil supplementation .
|Concentrate IMF fat||3.4 b mg/g fat|||
|Soybean oil IMF fat||13.0 a mg/g fat|||
|Extruded soybean IMF fat||15.4 a mg/g fat|||
|Concentrate Sub fat||5.2 c mg/g fat|||
|Soybean oil Sub fat||20.3 b mg/g fat|||
|Extruded soybean Sub fat||26.6 a mg/g fat|||
|LD concentrate / silage||0.41d % FA|||
|LD Grass||0.70c % FA|||
|LD grass +sunflower oil||1.34a % FA|||
|LD grass +linseed oil||0.93b% FA|||
|LD Wagyu Control||0.27 b % FA|||
|LD Wagyu 6% sunflower oil||1.29a % FA|||
|LD Limousin Control||0.28b % FA|||
|LD Limousin 6% sunflower oil||1.19a % FA|||
|LM grass||0.73c % FA|||
|LM grass+ sunflower oil||1.78a % FA|||
|LM grass+linseed oil||1.26b % FA|||
|LM Corn oil 0%||0.68b % FA|||
|LM Corn oil 0.75%||0.85a % FA|||
|LM Corn oil 1.5%||0.81ab % FA|||
|LT Control||0.33% FA|||
|LT Control + Vit E||0.36 % FA|||
|LT Control||0.34 % FA|||
|LT Control+ flaxseed||0.34 % FA|||
|LD Control||0.35 c mg/100g FA|||
|LD Soybean oil||0.94a mg/100g FA|||
|LD Linseed oil||0.80a mg/100g FA|||
|LD Protected linseed oil||0.55b mg/100g FA|||
|LM grass NL||0.78c g/100g FA|||
|LM grass+sunflower oil NL||1.90a g/100g FA|||
|LM grass+linseed oil NL||1,35b g/100g FA|||
|LM grass PL||0.32c g/100g FA|||
|LM grass+sunflower oil PL||0.71a g/100g FA|||
|LM grass+linseed oil PL||0.51b g/100g FA|||
|Grass silage (GS)||2.03a||Na|||
|GS +Low C||1.37b||Na|||
|GS+ High C||1.15b||Na|||
|20% DDGS corn||0.78||2.37|||
|40% DDGS corn||0.92||3.16|||
|LT et LL Tudanca x Charolais||2.68||0.36b|||
|LT et LL Limousin||2.24||1.01 a|||
4. Factors influencing CLA concentrations on lamb lipids
In lamb production, more than other species, each country or region has its own specific weight/age and type of carcass criteria, depending on the culture and the customs of the people. Many factors including breed, gender, age/body weight, fatness, depot site, environmental condition, diet and rearing management influence lamb fat deposition and composition. Further studied are needed to understand how animal circadian rhythms, diurnal rumination patterns and daily changes in herbage chemical composition could affect lamb fatty composition .
4.1. Production system (Tables 6 & 8)
No differences were detected in the muscle CLA/ trans-11 18:1 index of herbage or concentrate –fed lambs but the supplementation of tanino produced strong effects on the accumulation of fatty acids which are involved in the biohydrogenation pathway . During two years (Y1 and Y2) lambs were under four diets. Only silage both pre and post weaning (SS), only silage until weaning, silage plus concentrate thereafter (SC), silage plus concentrate both pre and post weaning (CC) and silage plus concentrate before weaning, only silage after (CS). Treatment differences for trans-11 18:1 were presented only in Y1, with muscle from the lamb fed silage before weaning having the highest levels. The same groups has the highest levels of cis-9, trans 11 CLA in Y1. Similar in Y2 the group SS has the highest CLA level, while the CC group has the lowest . The feeding strategy around parturition influence the CLA and VA content of lamb meat. Pre-partum grazing, regardless of post-partum feeding, can improve the fatty acid composition, increasing the CLA content in lamb meat . The meat of lambs slaughtered at Christmas has a higher CLA content than those reared in winter (slaughtered at Easter) as a result of the traditional feeding system which provided that lambs born and reared in autumn receive milk from ewes permanently pastured while those reared in winter are suckled by ewes permanently stall-fed . The grazing on
|LD Grass pellets||1.29a % FA|||
|LD Concentrate diet||1.02a % FA|||
|LD Concentrate diet ||0.74b % FA|||
|Muscle Concentrate+concentrate CC||0.46b g/100g lipids|||
|Muscle Silage+concentrate SC||0.61a g/100g lipids|||
|Muscle Concentrate+silage CS||0.45b g/100g lipids|||
|Muscle Silage+silage SS||0.65a g/100g lipids|||
|LT Pre-partum hay||1.42b % FA|||
|LT Pre-partum grazing||1.66a % FA|||
|LT Post-partum hay||1.35b % FA|||
|LT Post –partum grazing||1.73a % FA|||
|LD Grassed 9 am to 5 pm||1.85b g/100g FAME|||
|LD Grassed 9 am to 1 pm||1.45b g/100g FAME|||
|LD Grassed 1 pm to 5 pm||2.39a g/100g FAME|||
|LL Sucking lamb Autumn||1.10% IM Fat|||
|LL Sucking lamb Winter||0.56 % IM Fat|||
|LD Grazing subterraneous clover||0.46a % FA|||
|LD Grazing Italian rye grass||0.26 b % FA|||
|Pasture LD||0.90b % FAME|||
|Pasture Leg muscles||1.27a % FAME|||
|Pasture LD total lipids||0.90 % total FAME|||
|Pasture LD Triacylglycerols||0.62 %total FAME|||
|Pasture LD Phospholipids||0.11 % total FAME|||
Several strategies have been tested in recent years to improve CLA isomers in meat of intensively–reared lambs, keep indoors and fed high-concentrate diets rich linoleic acid and poor in linolenic. Incorporating linseed rich, in linolenic acid, the proportion of trans-11, 18:1 and cis-9, trans-11 18:2 were higher in the muscle and in the adipose tissues of linseed –fed lambs than in control lambs . This increased is in contrast to results of  but in agreement with . Discrepancias between these studies may due to differences in the level of intake the linoleic and linolenic acids or the different level of ∆9- desaturase inhibition as it has been shown that ∆9 desaturase is inhibited by PUFA with increasing inhibition as the degree of fatty acid unsaturation increases. Fed lambs from weaning to slaughter with diets that contained 5% supplemental from high oleic acid safflower or normal safflower increased the meat cis-9,trans,11 CLA compared with the control group  In lambs inclusion of 8% of soybean oil to a lucerne hay-based diet resulted in an intramuscular (M. L
|LD Sunflower oil||2.13a mg/100 g muscle|||
|LD Sunflower oil+ 33% linseed oil||2.06 a mg/100 g muscle|||
|LD Sunflower oil + 66% linseed oil||1.84b mg/100g muscle|||
|LD Linseed oil||1.56 c mg/100g muscle|||
|Leg control||1.78a mg/g fat|||
|Leg CLA||1,50a mg/g fat|||
|Leg Safflower oil||4.41b mg/g fat|||
|Adipose tissue Control||2.77 b mg/g fat|||
|Adipose tissue CLA||2.60 b mg/g fat|||
|Adipose tissue Safflower oil||7.33 a mg/g fat|||
|LD control||3955 b ppm in muscle|||
|LD Control + 5% sunflower oil||8491a ppm in muscle|||
|Fat control||4947b ppm in fat|||
|Fat control +5% sunflower oil||11313a ppm in fat|||
|LT Control||0.75c % of FA|||
|LT Control+Lucerne+10% soybean oil||1.21b % of FA|||
|LT Lucerne||1.28 b% of FA|||
|LT Lucerne+Lucerne+10% soyben oil||1.47 a% of FA|||
|Muscle Control no fat||0.05 b mg/g muscle|||
|Muscle control+wheat+linseed||0.11 a mg/g muscle|||
|Muscle control+corn+linseed||0.12 a mg/g muscle|||
|LL Control||0.60b g/100g FAME|||
|LL Linseed||0.72b g/100g FAME|||
|LL Rapeseed||0.70b g/100g FAME|||
|LL Safflower seed||0.96a g7100g FAME|||
|LL Sunflower seed||0.98a g/100g FAME|||
|LD Grazing subterraneous clover||4.22||Na|||
|LD Grazing Italian rye grass||3.65||Na|||
|LD Grass 9 am to 5 pm||1.55a||Na|||
|LD Grass 9 am to 1 pm||1.06b||Na|||
|LD Grass 1 pm to 5 pm||1.60a||Na|||
|LD grass pellets||2.25a||0.38b|||
|LD concentrate ad lib||0.85b||1.73a|||
|LM Pre Control||0.25||5.13b|||
|LM Pre Control +oil||0.29||6.02a|||
|LM Post Control||0.25||4.30b|||
|LM Post Control+ oil||0.29||6.81a|||
|Sub Pre Control||0.29||9.85b|||
|Sub Pre Control +oil||0.31||8.25b|||
|Sub Post Control||0.28||7.09b|||
|Sub Post Control+ oil||0.33||11.01a|||
Several factors influence the CLA content of ruminant meats as breed, sex, seasonal variation, type of muscle, production practices but diet plays the most important role. CLA concentration in beef and lamb can be influenced by dietary containing oils or oilseeds high in PUFA, usually linoleic or linolenic fatty acids. The supplementation of ruminant diets with PUFA rich lipids is the most effective approach to decrease saturated FA and promote the enrichment of CLA and n-3 PUFA. The differences in responses to plant oils were probably due to variations in stage of growth of animals, levels of oil supplementation, levels of oil in total ration and amount of linoleic acid in oils. Thus, the manipulation of the fatty acid composition in ruminant meat to reduce SFA content and the n-6/n-3 ratio whilst, simultaneously increasing the PUFA and CLA contents, is the major importance in meat research.
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