Prediction of lamb meat fatty acid composition using near-infrared reflectance spectroscopy (NIRS).

The aim of this study was to assess the feasibility of near-infrared reflectance spectroscopy (NIRS) for predicting lamb meat fatty acid composition. We compared ground vs. intact non-ground meat samples to determine whether grinding and homogenisation of meat samples improved the performance of the predictions. We used 76 male lambs, of which 32 were pasture-fed and 44 stall-fed with concentrate and hay. The reflectance spectrum of Longissimus lumborum muscle was measured at wavelengths between 400 and 2500nm. Predictions were better with ground than with intact muscle samples. NIRS accurately predicts several individual fatty acids (FA) (16:0, 18:0, 16:1 Δ9 cis, 17:1 Δ9 cis, 18:1 Δ9 cis, 18:1 Δ11 cis and 16:1 Δ9 trans) and several FA groups (total linear saturated FA, total branched saturated FA, total saturated FA, total cis monounsaturated FA (MUFA), total trans MUFA, total MUFA and total polyunsaturated PUFA). These results show the potential of NIRS as a rapid, and convenient tool to predict the major FA in lamb meat.

Plant polyphenols associated with vitamin E can reduce plasma lipoperoxidation in dairy cows given n-3 polyunsaturated fatty acids.

Diets rich in n-3 polyunsaturated fatty acids (PUFA) improve the nutritional value of ruminant products but also increase the risk of lipoperoxidation in plasma and tissues. The relative effectiveness of dietary antioxidants such as vitamin E (vit E) given alone or with plant extracts rich in polyphenols (PERP) containing rosemary, grape, citrus, and marigold was investigated in the plasma of mid-lactation dairy cows given diets enriched in 18:3 n-3. For a 30-d period, the animals were given a maize silage-based diet (control group C, n = 6) or the same basal diet supplemented with extruded linseed rich in 18:3 n-3 [50 g of oil/kg of diet dry matter (DM); group L, n = 6], extruded linseed + vit E (375 international units/kg of diet DM; 7,500 IU/cow per day; group LE, n = 6), or extruded linseed + vit E + PERP (10 g/kg of diet DM; group LEP, n = 5). Plasma susceptibility to lipoperoxidation was evaluated using in vitro parameters of conjugated diene formation (lag phase and maximum oxidation rate). Plasma indicators of lipoperoxidation and antioxidant status were analyzed in the 4 experimental groups as well as the fatty acid (FA) composition of total plasma lipids. At d 30, group L significantly increased plasma cholesterol esters (+57%) and phospholipids (+35%) compared with group C. It also increased plasma n-3 PUFA (4.7-fold increase) to the detriment of n-6 PUFA (-30%), leading to a higher peroxidizability index (+20%). Plasma in vitro lipoperoxidation was higher in group L (rich in 18:3 n-3) than in group C. Vitamin E alone had no effect on lipoperoxidation, whereas vit E in association with PERP lowered lipoperoxidation by increasing the resistance time against peroxidation (+47%) and by decreasing the oxidation rate (-48%) compared with group L at d 30. Surprisingly, in vivo plasma lipoperoxidation estimated by the plasma level of the major lipoperoxidation product (malondialdehyde) was not significantly increased in group L. This study shows, for the first time, that PERP supplied in association with vit E were able to reduce lipoperoxidation in lactating cows given a diet rich in 18:3 n-3, thereby helping to protect cows against the deleterious consequences of lipoperoxidation and potentially ensuring antioxidant potential for 18:3 n-3-enriched dairy products.

Indoor fattening of lambs raised on pasture: 2. Influence of stall finishing duration on triglyceride and phospholipid fatty acids in the longissimus thoracis muscle.

Twenty-four male Ile-de-France lambs (six blocks of homologous lambs) were used to study the effect of four feeding systems on muscle triglyceride (TG) and phospholipid (PL) fatty acids (FA) from the longissimus thoracis (LT): raised and finished on cool season grasses (G), raised on the same grasses and stall-finished, indoors, on concentrates and hay, respectively, for 22 (GSS) and 41 days (GSL), and stall-feeding, indoors, on concentrate and hay during both growing and finishing periods (S). In TG, similar decreases (P<0.05) of proportions of linolenic acid were observed after changing from grass feeding to stall feeding (GSS and GSL), and a decrease (P<0.05) in proportions of conjugated C18:2 cis9, trans11 (CLA cis9, trans11) was obtained after a long period of concentrate feeding (GSL). In PL, C22:5 n-3 achieved a significantly (P<0.05) lower level in GSL lambs compared both G and S lambs. A similar non-significant tendency was observed in the case of the other very long chain n-3 polyunsaturated FA. The separate analysis of fatty acids of TG and PL from the LT muscle underlined that TG afforded a more significant lowering effect than PL on the overall ratio between C18:2 n-6 and C18:2 n-3 in muscle lipids and on the health potential of meat for the consumer. A PCA analysis combining FA composition of TG and PL, and growth performances of the lambs allowed an efficient discrimination between the four feeding systems.

Indoor fattening of lambs raised on pasture. Part 1: Influence of stall finishing duration on lipid classes and fatty acids in the longissimus thoracis muscle.

Forty male Ile-de-France lambs (10 blocks of 4 homologous lambs) were used to study the effects of four feeding systems on muscle fatty acids (FA): raising and finishing on cool-season grasses (G), raising on the same grasses and stall-finishing, indoors, on concentrates and hay, respectively, for 22 (GSS) or 41 days (GSL), and stall-feeding indoors on concentrates and hay during both growing and finishing periods (S). Twenty-four lambs only (6 blocks) were retained for comparison of growth performances, lipid content in the longissimus thoracis muscle (LT) and their FA composition according to treatment. The 16 other lambs (4 blocks) were removed from the comparison, due to a large spread in the growth of the lambs towards the end of the trial. No significant effects of treatment were seen on the rate of growth (221, 228, 243 and 245±SE 8.0g/d, respectively, for G, GSS, GSL and S groups), and the lipid contents of the LT (2.22, 2.16, 2.17 and 2.52±SE 0.11g/100g fresh tissue). Grazing, lowered n-6 PUFA (polyunsaturated fatty acids), and increased n-3 PUFA and C18:2 c9t11 (conjugated linoleic acid cis9, trans11) compared to concentrate feeding. The main effects of grazing were not removed by a short period of finish indoors on concentrate (GSS group), but C20:4 n-6 and C22:6 n-3 contents achieved the lowest contents in this group, with significant differences from the values observed for GSL and S groups (C20:4 n-6) or from the three other groups (C22:6 n-3). After a longer period of finish on concentrate (GSL group), C18:3 n-3 (linolenic acid), C18:2 c9t11 and long chain (LC) n-3 PUFA were brought to the levels observed in the S group. In terms of adequacy for human health, the C18:2 n-6/C18:3 n-3 ratios were favourably low in the four groups (2.6, 3.6, 4.9 and 5.2±SE 0.7, respectively, for G, GSS, GSL and S groups), the level observed in the case of G group being significantly lower than for the three other groups and the level observed for GSS group being significantly lower than for the GSL and S groups.

Factors influencing proportion and composition of CLA in beef.

Bovine meat is criticised for the bad nutritional image of its lipids and fatty acids. However, with dairy products, beef is the major source of conjugated linoleic acid (CLA) which could have several human health benefits. The present study compared, from data of five nutritional experiments on bovine animals performed by the laboratory, the impact of factors linked to the animals (breed, age, sex, type of muscle) and to feeding conditions (basal diet, lipid supplements) on the CLA proportion and composition in muscles. Among these factors, 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 (breed, age/sex, type of muscle) since these ones could modulate CLA proportion in beef from 24% to 47%. Moreover, these factors modified also the proportion of cis,trans-CLA, related to cis,cis- and trans,trans-isomers. Specific biological properties of these latter isomers should be determine to understand the consequences of intramuscular CLA isomer variations for the health of consumers.

Influence of maturation and cooking treatments on the nutritional value of bovine meats: Water losses and vitamin B12.

The aim of the study was to determine the influence of maturation and of cooking processes on water losses and on the vitamin B12 content of meat. Three types of muscle (Longissimus lumborum, Longissimus thoracis and Triceps brachii) were sampled from a total of 16 animals, representative of animals raised for meat production in France. Three durations of maturation were compared: 1, 3 and 14 days. Different cooking processes were applied: Longissimus lumborum was deep-fat fried or roasted, Longissimus thoracis was pan fried or grilled and Triceps brachii was braised. The cooking yield averaged 55-56% for Triceps brachii, 73-77% for Longissimus lumborum and 85-87% for Longissimus thoracis. Vitamin B12 concentration in raw meat was significantly higher in Triceps brachii than in Longissimus lumborum and Longissimus thoracis (20.86, 11.53 and 9.21ng/g wet tissue, in the same respective order). When expressed on a wet weight basis, all concentrations were significantly increased by cooking. When expressed on a lipid-free dry basis, significant losses in vitamin B12 were measured only in the braised Triceps brachii (-25%) and in the deep-fat fried Longissimus lumborum (-5.5%) as a result of long duration and high temperature of cooking, respectively. Maturation did not affect the vitamin B12 content of meat, whether raw or cooked.

Plasma lipid transport in the preruminant calf, Bos spp: primary structure of bovine apolipoprotein A-I.

The preruminant calf (Bos spp.) is a model of considerable interest with regard to hepatic and intestinal lipoprotein metabolism (Bauchart et al., J. Lipid Res. (1989) 30, 1499-1514 and Laplaud et al., J. Lipid Res. (1990) 31, 1781-1792). As a preliminary step towards future experiments dealing with HDL metabolism in the calf, we have purified apoA-I from this animal and determined its complete amino acid sequence. Thus, approx. 10% of calf apoA-I was shown to contain a propeptide, with the sequence Arg-His-Phe-Trp-Gln-Gln. Enzymatic cleavage of apoA-I resulted in 10 proteolytic peptides. The complete apoA-I sequence was obtained after alignment of peptides on the basis of their homologies with those from rabbit apoA-I. Thus calf apoA-I consists of 241 amino acid residues, and exhibits high sequence homology with all mammalian apoA-I's studied to date. The bovine protein contained 10 hydrophobic amphipathic helical regions, occurring between residues 43-64, 65-86, 87-97, 98-119, 120-141, 142-163, 164-184, 185-206, 207-217 and 218-241. A computer-constructed phylogenetic tree showed that bovine apoA-I was more closely related to its dog counterpart, including the presence of a single methionine, than to the corresponding macaque and human proteins. Comparative predictions of the respective antigenic structures of human and bovine apoA-I's using the Hopp-Woods algorithm indicated similar positions for all 13 detectable antigenic sites, among which 7 were of identical, or closely related, amino acid composition. This finding was confirmed by demonstration of partial immunological identity between the two proteins upon immunodiffusion analysis, a result obtained using a monospecific rabbit antiserum against bovine apoA-I. Finally, comparison of sequence homology between bovine apoA-I and the lecithin:cholesterol acyl transferase (LCAT) activating region of human apoC-I suggests that several LCAT activating domains may be present in calf apoA-I.

Modeling of intramuscular lipids in different muscles in bulls, steers, and cows.

Intramuscular fat depot is of major interest for consumers, producers, and the industry. To predict intramuscular (i.m.) lipid deposition in cattle of continental breeds, different models were constructed for different muscles in bulls, steers, and cows. Two independent databases (DB1 and DB2) were developed with homogeneous individual data collected in the same slaughterhouse and total lipids, phospholipids, and triglycerides were analyzed in the same lab with the same procedures. Database DB1 was used with the meta-analysis methodology to fit the predictive models of i.m. lipids, phospholipids, and triglycerides with carcass fatness. Database DB2 was used to evaluate the accuracy of the models predicted. Total lipid and triglyceride contents varied linearly with carcass fatness in bulls, steers, and cows, but phospholipids were more independent of carcass fatness, regardless of the type of cattle studied. In bulls, LM had a lower minimal value (intercept in the model) and greater slope than semitendinosus (ST) and triceps brachii (TB) muscles. In cows, LM showed a greater intercept than ST and TB muscles but a similar slope. In steers, lipid content increased similarly in LM, rectus abdominis (RA) muscle, and ST muscle with carcass fatness. Bulls had a lower intercept than steers but showed a similar trend with carcass fatness. According to the external evaluation using DB2, the models obtained to predict total lipids in LM were more accurate than those obtained in the ST muscle in bulls and cows and in the RA muscle in steers. The models proposed for cows should be used only in the range of carcass fatness used to fit the equations, and further data are needed to fully validate them.

Fattening performance, metabolic indicators, and muscle composition of bulls fed fiber-rich versus starch-plus-lipid-rich concentrate diets.

The aim of this study was to compare the responses in fattening performance and meat composition for high-concentrate diets rich in either starch and lipids (especially omega-3 fatty acids) or fibrous by-products. A total of 140 Charolais bulls (initially 319 ± 27 kg BW) were allocated to 3 high-concentrate diets and were fattened for up to 18 mo. The diet treatments included concentrate mixtures rich in either fiber (FR; n = 56) or starch plus linseed (diets SL and SLR; n = 56 and n = 28, respectively) and barley straw. The concentrate mix was offered ad libitum in SL and FR diets but was kept isoenergetic to the FR diet in the SLR diet. Bulls were weighed every 15 d. Feed intake was measured daily. Carcass composition was assessed for all animals slaughtered at 699 ± 65 kg BW. Meat nutritional quality traits (e.g., fat content and fatty acid composition focusing on n-6 and n-3 polyunsaturated fatty acids) were measured on the longissimus thoracis, rectus abdominis, and semitendinosus muscles. Metabolic enzyme activity (phosphofructokinase, lactate dehydrogenase, and cytochrome-c oxidase) was measured on these muscles and on liver. The SL diet bulls had greater fattening performance, BW gain (P = 0.006), and efficiency for growth (P = 0.025) at an energy intake similar to that of FR diet bulls. They also had heavier carcasses with a greater proportion of fat. However, liver samples showed no difference in specific metabolic activity. Compared to bulls fed the SL diet, bulls fed SLR consumed 15% less energy and had lower BW gain (P < 0.001) but were slightly more efficient for growth (P = 0.010). They had lower carcass weight but a greater muscle-to-fat ratio. Compared to bulls fed the FR diet, SLR bulls had lower than planned NEg intake and lower BW gain but did not have differences in body composition. Compared to the FR diet, the SL diet led to a greater omega-3 fatty acid content because of a greater supply of dietary linoleic acid, especially in lean muscle.

Fatty acid metabolism and very low density lipoprotein secretion in liver slices from rats and preruminant calves.

The liver of bovine animals possesses a low ability to secrete triglycerides (TG) as part of the very low density lipoproteins (VLDL) compared with rat liver. We compared hepatic fatty acid (FA) metabolism between rat and calf in order to determine the limiting steps of TG-VLDL secretion in bovine animals. Liver slices from young Sprague-Dawley rats and preruminant Holstein x Friesian calves were incubated for 7 h with increasing concentrations (0.1, 0.2, 0.4, and 0.8 mM) of [14C]oleate. The oxidation of oleate to CO2 and acid-soluble products was 2- to 3-fold higher in rat than in calf liver slices. Since oleate uptake was 2-fold higher in rat than in calf, the oxidation rate represented 20-29% of oleate uptake in both animal species. Oleate was essentially incorporated into the neutral lipids (75-87% of total lipids) that were stored mainly in the cytosol in both animal species (81-90% of neutral lipids). The accumulation of neutral lipids in the cytosol was 3.4-fold higher while VLDL secretion was 6- to 18-fold more efficient in rat than in calf liver slices. Our results indicate that the slow rate of VLDL secretion by bovine liver is probably due to the limited availability of TG for VLDL packaging rather than to the preferential oxidation of FA.

Apolipoprotein B production and very low density lipoprotein secretion by calf liver slices.

Secretion of triglycerides by the liver in ruminants as components of very low density lipoproteins particles is low as compared with that in primates or rodents. The rate-limiting steps for the hepatic export of very low density lipoproteins have been studied in liver slices to determine the origin of the low lipotropic capacity of calf liver compared to that of rat liver. The rates of production of apolipoprotein B (apo B) and albumin as well as the rate of secretion of VLDL-apolipoproteins were measured during 12-h incubation of liver slices in organo-culture using [35S]methionine-cysteine labeling. Hepatic apo B production was similar in the two animal species but the VLDL-apolipoprotein secretion rate for calf liver slices amounted to only 20% of that observed for rat liver slices. Although calf and rat liver slices synthesized similar amounts of total protein, the hepatic production of albumin, measured in cells and media, was much higher in calf than rat liver slices (around 2.7-fold), whereas the rate secretion of albumin was similar in the two species. Our results showed that the slow rate of secretion of VLDL by calf liver cells was not consecutive to a low rate of synthesis of apo B but rather to a defect in VLDL assembly and/or secretion.

Dietary coconut oil affects more lipoprotein lipase activity than the mitochondria oxidative capacities in muscles of preruminant calves.

The presence of coconut oil in a milk replacer stimulates the growth rate of calves, suggesting a better oxidation of fatty acid in muscles. Because dietary fatty acid composition influences carnitine palmitoyltransferase I (CPT I) activity in rat muscles, this study was designed to examine the effects of a milk replacer containing either tallow (TA) or coconut oil (CO) on fatty acid utilization and oxidation and on the characteristics of intermyofibrillar (IM) and subsarcolemmal (SS) mitochondria in the heart and skeletal muscles of preruminant calves. Feeding CO did not affect palmitate oxidation rate by whole homogenates, but induced higher palmitate oxidation by IM mitochondria (+37%, P < 0.05). CPT I activity did not significantly differ between the two groups of calves. Heart and longissimus thoracis muscle of calves fed CO had higher lipoprotein lipase activity (+27% and 58%, respectively; P < 0.05) but showed no differences in fatty acid binding protein content or activity of oxidative enzymes. Whatever the muscle and the diet, IM mitochondria had higher respiration rates and enzyme activities than those of SS mitochondria (P < 0.05). Furthermore, CPT I activity of the heart was 28-fold less sensitive to malonyl-coenzyme A inhibition in IM mitochondria than in SS mitochondria. In conclusion, dietary CO marginally affected the activity of the two mitochondrial populations and the oxidative activity of muscles in the preruminant calf. In addition, this study showed that differences between IM and SS mitochondria in the heart and muscles were higher in calves than in other species studied so far.

Daily metabolism and hepatic balance studies of plasma cortisol and aldosterone in the preruminant calf.

Intestinal and hepatic catabolism of cortisol and aldosterone were studied in the calf using blood samples from the mesenteric artery and portal and hepatic veins collected over 24 h, the hepatic blood flow being continuously recorded during this period. The total hepatic blood flow remained broadly constant over the 24 h, although meals were followed by decreasing flow in the portal vein and by increasing flow in the hepatic artery. The intestinal tract catabolizes cortisol as intensively as the liver (both 13% of cortisol reaching the organ). The part played by the gut and the liver in the catabolism of aldosterone were also equivalent (both 30% of aldosterone reaching the organ). This 24-h study demonstrated that a constant ratio existed between secretion and catabolism of cortisol while the hepatic balance of aldosterone seemed to be modified during the night.

Nycthemeral changes in plasma cortisol levels in preruminant calves with different milk proteins.

Preruminant calves bearing indwelling catheters in the hepatic artery, the portal and the hepatic veins were fed with two kinds of diets, a conventional curdled milk diet and a milk diet which was uncurdled in the abomasum. Measurements of plasma cortisol in blood sampled regularly during the 24 hr of the day indicated that with curdled milk, cortisol concentrations were significantly higher than with uncurdled milk. Nycthemeral changes were characterized by high values before meals and by postprandial decreases. Between meals, several peak values were observed and in the night a regular increase occurred. With both kinds of meals, cortisol evolutions were similar though peak values were higher with the curdled milk.

Contribution of mitochondria and peroxisomes to palmitate oxidation in rat and bovine tissues.

Total and peroxisomal palmitate oxidation capacities and mitochondrial enzyme activities were compared in tissues from growing rats, preruminant calves and 15-month-old bulls. Total palmitate oxidation rates were 1.9-5.2-fold higher in rat than in bovine tissues and 1.7-fold higher in the heart and muscles from calves than from growing bulls. The peroxisomal contribution to palmitate oxidation was similar between rats and bovines (i.e. calves and bulls) in liver (35-51%), heart (26%) but not in muscles (14 +/- 3% in rats vs 33 +/- 4.5% in bovines, P < 0.05). Mitochondrial enzyme activities were 1.8-4.8-fold higher in rat than in bovine tissues but the citrate synthase to cytochrome-c oxidase ratio was the highest in the liver (17-38), intermediate in the heart and muscles from calves and rats (6-10) and the lowest in heart and muscles from bulls (2-3, P < 0.05). In all tissues and animal groups, palmitate oxidation rates were similar per unit cytochrome-c oxidase activity, but not always per unit citrate synthase activity. Therefore, differences in mitochondrial contents (as between rats and bovines) or in mitochondrial characteristics (as between liver and muscles) relate to the differences in palmitate oxidation capacity.

Lipids of three microsporidian species and multivariate analysis of the host-parasite relationship.

Sporal lipids of 3 microsporidia, Encephalitozoon cuniculi from mammals and Glugea atherinae and Spraguea lophii from fishes, were investigated. High phospholipid levels were found (54.8-64.5% of total lipids), which is in agreement with the presence of highly developed internal membranes in microsporidian spores. Sphingomyelin was not detected in G. atherinae. Triglycerides (less than 10% of total lipids), cholesterol, and free fatty acids were identified in all species. Analysis of fatty acids from the phospholipid fraction revealed the predominance of docosahexaenoic acid (30-40% of total phospholipid fatty acids) in G. atherinae and S. lophii and oleic acid (25.8% of total phospholipid fatty acids) in E. cuniculi. The 3 microsporidia possessed a significant amount of branched-chain fatty acids (iso and anteiso forms) not found in the hosts, supporting the existence of some parasite-specific metabolic steps for these fatty acids. On the basis of phospholipid fatty acid profiles, host-parasite relationships were investigated through correspondence factorial analysis. It shows 3 distinct clusters with the first corresponding to fishes, the second to fish parasites, and the third to E. cuniculi and its host cell. These data suggest that the mammal microsporidia developing within parasitophorous vacuoles are more dependent on host cells than the fish microsporidia that induce cystlike structures.

Effect of a supply of raw or extruded rapeseeds on digestion in dairy cows.

The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility.

Effect of grass or concentrate feeding systems and rate of growth on triglyceride and phospholipid and their fatty acids in the M. longissimus thoracis of lambs.

Thirty-two male Ile-de-France lambs were used in a factorial 2×2 design to analyse the effects of feeding systems (grass outdoor, G, or concentrate and hay indoor: stall, S) and of growth rate (low, L, or high, H) on total lipids, triglyceride (TG) and phospholipid (PL) contents and their fatty acid composition in the longissimus thoracis muscle (L.T.). Contents were lower for TG (10.4 vs. 15.8 mg/100 g fresh tissue, P<0.05) and higher for PL (6.4 vs. 5.8 mg/100 g fresh tissue, P <0.05) in grass-fed lambs compared to stall-fed ones. TG of grass fed lambs displayed lower proportions of palmitic acid (C16:0), monounsaturated fatty acids (MUFAs), linoleic acid (C18:2n-6) and other (n-6) polyunsaturated fatty acids (PUFA) and higher proportions of stearic acid (C18:0), linolenic acid (C18:3n-3), cis 9, 11 trans C18:2 and trans monounsaturated fatty acids. In PL of the same lambs only lower MUFA, C18:2n-6 and (n-6) PUFA and higher C18:3n-3, (n-3) PUFA and cis 9, 11 trans C18:2 were observed. Growth rate had no effect on lipid, TG or PL contents of longissimus thoracis. However C18:0 proportions were higher in TG and lower in PL for low growth rate lambs. Low growth rate lambs had also lower cis 9, 11 trans C18:2 in TG. Thus, irrespective of growth rate, the muscle lipids characteristic of grass fed lambs fulfilled the recommended features of human food components much better than that of stall fed lambs, namely for CLA and C18:3n-3. The lower ratios of (n-6) to (n-3) PUFA displayed in grass fed lambs both in TG and in PL were also useful to discriminate all the grass fed lambs from all the stall fed animals.

Breed and dietary linseed affect gene expression of enzymes and transcription factors involved in n-3 long chain polyunsaturated fatty acids synthesis in longissimus thoracis muscle of bulls.

N-3 long-chain (LC) PUFA are known to be beneficial for human development and health. These properties explain the increasing interest in promoting n-3 LC PUFA deposition in bovine muscles, leading to healthier meats. In this context, this study aimed to identify possible limiting steps in the bioconversion of 18:3n-3 into n-3 LC PUFA in the longissimus thoracis (LT) muscle of 36 Aberdeen Angus, Limousin, and Blond d'Aquitaine bulls (n = 12 per breed) that were fed, for the 105-d finishing period, either a concentrate-based diet (25% molasses straw to 75% concentrate, on a raw basis; CON) or the same CON diet supplemented with extruded linseed (44.5 g lipid/kg diet DM) mixed into the concentrate (LINS). The fatty acid (FA) composition of the LT muscle was determined by GLC, and the mRNA abundances for enzymes and transcription factors involved in n-3 LC PUFA synthesis were determined by quantitative real-time PCR. The total lipid concentration in the LT muscle was approximately 2.4-fold greater (P < 0.001) in Angus bulls than in the other breeds and composed of the greatest n-3 PUFA content (P < 0.001) including 18:3n-3 (P < 0.001) and n-3 LC PUFA (P < 0.02), primarily 20:5n-3 (P < 0.007) and 22:5n-3 (P < 0.04). These data were associated with a lesser gene expression (P < 0.02) of 2 enzymes [acyl-CoA oxidase 1 (ACOX1) and L-bifunctional protein (L-PBE)] and 2 transcription factors [liver X receptors (LXR) α and ß] in the LT muscle of Angus bulls compared with gene expression in Limousin bulls. Moreover, the mRNA of elongase 5 was only present in trace amounts in the LT muscle of the 3 breeds. The addition of linseed to the diet resulted in greater deposition of 18:3n-3 (P < 0.001) in the LT muscles of the 3 breeds, without any major changes (P > 0.34) in the n-3 LC PUFA content. Dietary linseed stimulated (P < 0.04) the gene expression of all enzymes and transcription factors involved in n-3 LC PUFA synthesis except elongases 2 and 5 (P > 0.19), the expression of which remained weak and was not inducible. These results reveal a limited capacity for n-3 LC PUFA synthesis from 18:4n-3 (substrate of elongase 5) in the LT muscles of Blond d'Aquitaine, Limousin, and Angus bulls. Therefore, further investigations on the cellular regulation of elongase gene expression are needed to identify the physiological or nutritional factors that efficiently stimulate elongase expression in beef cattle.

A grass-based diet favours muscle n-3 long-chain PUFA deposition without modifying gene expression of proteins involved in their synthesis or uptake in Charolais steers.

N-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) are subject of growing interest as they are of particular relevance for meat quality and human health. However, their content in the muscles of cattle is generally low probably as the complex result of their biosynthesis from dietary n-3 PUFA in the muscle and/or in other tissues/organs and of their subsequent uptake by the muscle. In view of this, this study aimed at understanding whether the changes in the muscle n-3 LCPUFA content, depending on the diet (maize silage v. grass) or the muscle type (Rectus abdominis, RA v. Semitendinosus, ST) in 12 Charolais steers, were related to variations in the gene expression of proteins involved in n-3 LCPUFA biosynthesis or cellular uptake. Tissue fatty acid composition was analysed by gas-liquid chromatography and mRNA abundance of proteins by quantitative real-time PCR. The grass-based diet resulted in a 2.3-fold (P < 0.0002) increase in both RA and ST n-3 LCPUFA content compared with the maize silage-based diet, whereas no difference in the expression of genes involved in n-3 LCPUFA biosynthesis and uptake was observed between diets. ST exhibited a 1.5-fold higher n-3 LCPUFA content than RA (P < 0.003), whereas the gene expression of proteins involved in n-3 LCPUFA biosynthesis and uptake was 1.3- to 18-fold higher in RA than in ST (P < 0.05). In conclusion, diet- or muscle type-dependent changes in the muscle n-3 LCPUFA content of Charolais steers did not seem to be mediated by the gene expression regulation of proteins involved in the biosynthesis or uptake of these fatty acids.