Linseed : a valuable feedstuff for ruminants

– Linseeds are used in ruminant feeding for a long time, but this feedstu ﬀ knows now increasing interest. Linseeds are rich in alpha-linolenic acid, a fatty acid from the omega-3 series. Despite an extensive biohydrogenation of dietary alpha-linolenic acid in the rumen, its concentration in milk and beef meat increases with linseed incorporation in diets; this increase is accompanied by that of other fatty acids produced during biohydrogenation, especially conjugated linoleic acids and trans 18:1 fatty acids. The increase in cow fertility due to omega-3 fatty acids has not been demonstrated. Furthermore, linseed incorporation in ruminant diets is one of the most e ﬃ cient ways to decrease enteric methane emissions. In addition to a global mitigating e ﬀ ect of all lipid sources on methane, linseeds have a speciﬁc e ﬀ ect due to changes in rumen microbial ecosystem. The practical use of linseeds in ruminant feeding at a large scale requires the absence of negative e ﬀ ect at any step of the ruminant production system. An excessive supply of lipids from linseeds can have deleterious e ﬀ ects on digestive e ﬃ ciency, milk fat and protein content, beef susceptibility to oxidation, milk and beef fatty acid composition, but when linseed incorporation in the diet does not exceed ca. 3% of additional fat, only positive e ﬀ ects are remaining. A challenge is the increase in linseed cropping to meet increased needs for animal feeding.

1 Introduction 1 Although linseed is not commonly used nowadays in rumi-2 nant feeding, this is an ancient feedstuff which has been used 3 from the nineteenth century, as crude seed or cake (Grandeau,4 1876).In the first part of the twentieth century, linseed ex-5 peller cake has been used especially for beef fattening, and 6 was used not really for nutritional benefits but for giving a 7 shiny coat, and also a tasty meat (Dumont et al., 1997).The 8 Correspondence: michel.doreau@clermont.inra.frdevelopment of the use of fat sources in ruminant feeding in the 1990s as a mean to increase energy density of the diet concerned first palm oil, animal fat derivatives, and commonly used seeds such as cottonseed, soybean and rapeseed.A significant use of linseed is very recent and due to its richness in alpha-linolenic acid (18:3 n-3, or cis-9, cis-12, cis-15 18:3), potentially allowing an increase in omega-3 fatty acids (FA) in milk and meat.However, the extent of increase in omega-3 FA in these products is limited because of the wide biohydrogenation of polyunsaturated FA in the rumen, prior to absorption.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
3 Methane mitigation is a major issue for decreasing greenhouse 4 gases emissions from livestock.The Bleu-Blanc-Coeur initia-5 tive, born in France and aiming to develop omega-3 FA in hu-6 man foods through promoting feeding animals with omega-3, 7 considers this double interest of linseeds.Linseeds are now 8 used essentially as an extruded mixture of 50-70% linseeds 9 and 30-50% other feeds such as bran, in order to obtain a prod-10 uct which is easy to handle and to incorporate in concentrates.

11
This paper presents an overview of the interest of the incorpo-12 ration of linseed in diets for providing omega-3 FA to rumi-13 nants, then of the use of linseed for methane mitigation.In the 14 last part, the perspectives of increase in linseed use for animal reduce the risk of cardiovascular diseases (Mills et al., 2011).

29
Details on omega-3 FA effects on human health are reported in 30 a paper by Mourot (this issue).

31
A specificity of digestive processes in ruminants is an ex-32 tensive biohydrogenation of dietary FA in the rumen, prior to 33 absorption which occurs in the small intestine.As a conse-34 quence, the amount of omega-3 FA reaching the small intestine 35 is much lower than the dietary intake of omega-3 FA, resulting 36 in a quantitatively low transfer of these FA in milk and meat, thus absorbed and available for transfer into milk and meat.Different attempts have been made to decrease biohydrogenation through protection of lipids.The only one which has been proved to be efficient is the encapsulation of lipids in a coat of proteins treated with formaldehyde (Doreau et al., 2011;Fievez et al., 2007).However this technique is not used, in particular owing to its cost, to the use of formaldehyde, and to possible adverse effects of excessive amounts of polyunsaturated fats on animal health and product quality.
Concerning the FA metabolism, 18:3 n-3 represents on average 1.9% of 18-carbon FA reaching the duodenum because of its extensive biohydrogenation in the rumen.Nevertheless, the transfer rate from duodenum to milk is lower for 18:3 n-3 than that for other 18-carbon FA (Glasser et al., 2008b).In mammary gland and in muscle, an important de novo synthesis occurs from plasma acetate and butyrate, leading to a variety of short-and medium chain FA in milk fat.Moreover, the activity of a Δ9-desaturase leads to the formation of cis-9, trans-11 18:2 (rumenic acid) from vaccenic acid.In addition, a specific metabolic pathway occurs in the muscle, but not in the mammary gland: the elongation and desaturation of 18:3 n-3, leading to the formation of eicosapentaenoic acid (EPA, 20:5 n-3) and docosapentaenoic acid (DPA, 22:5 n-3) in muscle.However, the last step of desaturation towards docosahexaenoic acid (DHA, 22:6 n-3) is of very low extent in vertebrates (Doreau et al., 2011).

38
CLA, but the two former authors did not.In any case, the CLA 39 concentration in beef is too low for a possible effect on human health.Beef trans-18:1 FA comprise a significant amount of isomers other than trans-11, but few studies are available about the effect of linseeds on this pattern.With diets based on 30% straw and 70% concentrates, extruded linseed did not change the proportion of trans-11 (33%) but trans-12, -13, -14 and -15 increased at the expense of trans-9 and -10 (Habeanu et al., 2014).
There has been a steady decline of fertility in major dairy cow breeds associated with the improvement of genetic merit for milk production (Barbat et al., 2010;Butler, 2003).Part of this decline is due also to extended period of negative energy balance and intense mobilisation of body reserves during early lactation.The relationships among energy balance, body condition score and reproductive function are well documented (e.g.infrequent LH pulses, delayed ovarian activity, abnormal estrous cycles, poor follicular response to gonadotropins, reduction of oocyte quality and embryo survival (Butler, 2003, Chagas et al., 2007).Recent interest on lipid feeding to cows has focused on reproduction because of their high energy density and a supply of specific FA.Lipid supplementation could influence reproduction by altering the size of the dominant follicle, shortening the interval between calving and the first postpartum ovulation, increasing progesterone concentration during the luteal phase of the oestrous cycle, modulating uterine prostaglandin synthesis, and improving oocyte and embryo quality and maintenance of pregnancy (Santos et al., 2008).The omega-6 and omega-3 polyunsaturated FA seem to have the major effects on reproductive responses.Nevertheless, results from feeding linseeds on reproductive variables are inconsistent.Some authors reported an improved increased follicular and corpus luteum growth (Santos et al., 2008), oocyte (Moallem et al., 2013;Zachut et al., 2010) and embryo quality (Thangavelu et al., 2007), decreased pregnancy loss (Ambrose et al., 2006), reduced plasma prostaglandin (Petit et al., 2002), and increased serum progesterone concentration (Jahani-Moghadam et al., 2015), reduced interval from calving to ovulation (Colazo et al., 2009).In contrast, others noted no changes in milk progesterone concentration or corpus luteum activity (Ponter et al., 2006), or oocyte quality (Bilby et al., 2006, Fouladi-Nashta et al., 2009).The inconsistencies among these studies could be due to differences in the amounts of lipid supplements, duration of supplementation, and season.The global effect on cow fertility has not been evidenced: no effect of linseed feeding has been reported on conception rate (Ambrose et al., 2006;Bork et al., 2010;Petit and Twagiramungu, 2006;Petit et al., 2008), or pregnancy rate (Jahani-Moghadam et al., 2015).Further studies with a larger number of animals are necessary to be conducted in order to confirm these results.
3 Linseed, a way to mitigate methane emissions by ruminants Among greenhouse gases, which are responsible of global warming, methane is the major contributor for livestock activities: more than 40% of greenhouse gases, when they are expressed as carbon dioxide-equivalents.The major part of ???, page 3 of 9 "ocl150022" -2015/8/7 -10:45 -page 4 -#4 Doreau and A. Ferlay: OCL 2015, 22(6) methane is produced in the digestive tract of ruminants, especially in the rumen, which is the main site of digestion.In the rumen, dietary carbohydrates are fermented by bacteria and protozoa in volatile fatty acids, which are the main energy source for ruminants.During fermentation, hydrogen is produced, then is converted in methane by the action of another type of microbes, archaea methanogens.The abatement of methane emissions is a challenge for scientists.
Dietary lipids are considered now by the scientific community as the best way for enteric methane mitigation (reviews by Hristov et al., 2013 andMartin et al., 2010).Although their effect on methane emission is not systematic, lipids present advantages compared to other dietary options: chemicals and additives such as nitrates raise the issue of acceptability by consumers, tannins often reduce animal performances, highcereal diets question about the use of large amounts of cereals in ruminant feeding.When lipids are given in substitution to carbohydrates, methane is reduced because it is produced from carbohydrates, but not from lipids.In addition, some lipid sources decrease rumen protozoa which are important producers of hydrogen, which is the precursor of methane.The strongest decrease in rumen protozoa is obtained with linseeds on one hand, and coconut and palm kernel oil on the other hand.These latter lipid sources have the drawback to be rich in medium-chain saturated FA (12:0 and 14:0), which are considered as deleterious for human health.As a consequence, linseeds could be the best choice for methane mitigation.Review of experimental data show that on average linseeds reduce more methane emission than saturated sources (calcium salts of palm oil, tallow), and unsaturated sources containing oleic acid (rapeseed) or linoleic acid (sunflower, cottonseed) (Martin et al., 2010).However, between-experiments variability of response is high, so that some authors do not distinguish fat sources for their effect on methane emission (Grainger and Beauchemin, 2011).It has been shown that the effect of linseeds remains at least for one year after starting their distribution to cows (Martin et al., 2011).This long-term effect is especially interesting because products which decrease methane often have a short-term effect, due to the adaptation of rumen microbes to dietary changes.Increasing the proportion of linseeds in the diet until 5% additional fat results in a strong decrease in methane (Fig. 2).In practical conditions, a lower addition of linseeds is recommended, to avoid any risk of disturbances of fibre digestibility, which often occurs for high linseed supply, and any risk of excessive increase in some trans FA in products which may have a negative effect of human health.Although most results evidence the effect of linseed for methane mitigation, for an unknown reason, linseeds did not decrease methane emission in some experiments (Van Zijderveld et al., 2011).
For any option aiming to decrease methane emission by animals, it is mandatory to check that the decrease is not compensated for by an increase in the other greenhouse gases, carbon dioxide and nitrous oxide.For linseeds, there is a compensation for a minor part, due to the higher carbon footprint for linseed than for cereals that they replace.The effect of introducing linseeds in the diet has been calculated by life cycle assessment for the whole farming system, for beef cattle (Nguyen et al., 2012) and for dairy cattle (Nguyen et  trates could be fed lipids all year long, in order to provide 3.5% 71 additional fat.In this case, lipid supply can reduce total green-72 house gases emissions from cattle by 6%.However, this option 73 is expensive at present due to the higher cost of oleagineous 74 seeds compared to cereals (Doreau et al., 2014).Use of linseed in ruminant feeding could be developed if 78 linseed crops are developed.In several countries, the use of lin-79 seed in crop rotations is limited by a lower yield per ha than ce-80 reals, and by the relative price of cereals and linseeds.Among 81 crops which are frequently used in rotations in Europe, rape-82 seed is competitive, and grain legumes allow the decrease in 83 N fertilisation in the multiannual system.This is not the case 84 of linseed, for which average yield stagnates at 20 q/ha.For 85 France, national linseed production covers one half of present 86 needs for animal nutrition.The potential of increase in surfaces 87 is high, but a significant rise requires a strong coordination of 88 actors of the food chain (Charrier et al., 2013).Ways of im-89 provement which may lead in the short-term to tripling French 90 surfaces (30 000 ha instead of 10 000 ha now) have been pro-91 posed by Labalette et al. (2011), and include a larger choice 92 of varieties, better rotation choices and higher prices relative 93 to cereals.This latter can be achieved by feed industry, but the 94 price of milk and meat enriched in omega-3 should also be 95 higher.This is possible by a selective milk collection, which is 96 already organised in some dairy factories, by the development 97 of dairy and beef brands for niche markets, and by the pro-98 motion and lobbying such as the Bleu-Blanc-Coeur initiative, 99 ???, page 4 of 9 "ocl150022" -2015/8/7 -10:45 -page 5 -#5 Doreau and A. Ferlay: OCL 2015, 22(6) which is positively received by consumers.Incentives related 1 to public policies can be thought, owing to the environmental 2 interest on linseed use for the abatement of methane emission 3 by ruminants.

4
The positive effect of linseeds on omega-3 FA in milk and 5 beef, and the methane abatement, are two arguments for using 6 linseeds at a large scale.However, this practice will increase does not exceed 5% of dry matter; this corresponds to 3.5% 14 added FA from linseeds in diet DM.Higher proportion some-15 times decreases digestibility (Petit, 2010).rumen and then a decrease in milk fat content (Chilliard et al., 32 2009).A decrease in milk fat yield with linseed oil feeding is 33 often reported (Glasser et al., 2008a).Generally, feeding diets 34 with whole or crushed or micronized linseed had no effect on 35 the milk protein content in mid lactation (Petit, 2010) whereas 36 a decrease in protein content (0.5 g/kg) was observed with ex-37 truded linseed (Brunschwig et al., 2010).Concerning the long-38 term linseed supplementation, during the first year of experi-39 mentation, linseed diet had no effect on the milk and fat yields 40 compared to the control diet.Linseed supplement decreased 41 the milk protein content, without changing protein yield.Thus, 42 long-term effects of supplementation with linseeds were similar to those observed during short-term (1 to 3 months) studies 44 (Lerch et al., 2012a).With a moderate linseed incorporation in the diet (less than 3% additional fat), milk yield is unchanged 46 and the risk of decrease in milk fat or protein yield is low.

47
Linseed supply to diets has also been studied in fattening 48 cattle.Table 1 summarizes 20 comparisons between control 49 and supplemented diets.On average, animal liveweight gain is 50 higher by 9% with linseed-supplemented diets than with control diet, differences ranging between +25% and -15%.Within 52 experiment, differences are often non-significant.Difference  (2005): differences are very low (Tab.2).Whole linseeds have been used by Maddock et al. (2006) and Corazzin et al. (2012).Results suggest that linseed hull does not limit a normal digestion of the seed.It can be concluded that the incorporation of linseeds for finishing cattle has no effect or a slightly positive effect on performances.Although it has been shown that lipid supply in fattening diets generally increases carcass fat proportion (Clinquart et al., 1995), available data for linseed supply do not fully support this statement: linseeds may increase (Dufrasne et al., 1991) or not (Maddock et al., 2006;Normand et al., 2005;Razminowicz et al., 2008) carcass fatness.The reality of a difference between linseed and other lipid sources needs further research.
It is sometimes argued that linseeds contain cyanogenic compounds which could be toxic for animals.They are present as glycosides, and are likely to vary more with cultivar than with location or year (Oomah et al., 1992).Seed treatments can decrease cyanides.Pelleting decreases total cyanides, especially at high and prolonged temperatures (Feng et al., 2003).Extrusion divided cyanhydric acid by 4, whereas rolling divided them by 2 (one comparison, Normand et al., 2006); a very pronounced decrease in cyanhydric acid was observed with another extrusion technology: 10 mg/kg for extruded linseeds vs. 165 to 240 mg/kg for rolled linseeds (6 comparisons, Normand et al., 2005).However, cyanhydric acid content in plasma is not increased by rolled or extruded linseed inclusion in the diet, suggesting a possible detoxification in the rumen (Normand et al., 2006).Nevertheless, cyanogenic compounds are transferred to a low extent in milk, but according to Petit (2010), milk concentrations are too much low to result in a toxic effect for humans, if taking account the daily doses which are considered as safe by health authorities.
Due to their high amount of polyunsaturated FA, linseeds may be subject to oxidation.During a 120-day conservation, peroxide value and vitamin E content are stable for rolled linseeds, whereas the former increases and the latter decreases for extruded linseeds (Normand et al., 2005).It is recommended to use new batches of extruded linseeds every 2 months if there is no incorporation of antioxidant, in order to prevent a possible decrease in intake by animals.A concern related to the use of polyunsaturated FA is the susceptibility of lipids to oxidation (Durand et al., 2005).Milk and beef lipid oxidation may occur, when linseeds are incorporated in diets, but often there is no increased susceptibility to oxidation, for example when rolled or extruded linseeds are fed to fattening cattle in moderate amounts (750 g/day) (Normand et al., 2005).However, lipid oxidation may occur when animals have been submitted to oxidative stress during their lifetime, after inflammatory or infectious events, or in the pre-slaughter period, after an emotional or physical stress (Durand et al., 2013).For this reason, an additional supply of vitamin E or of vegetal antioxidants in the diet may reduce milk susceptibility to oxidation (Focant et al., 1998) and in beef meat after carcass ageing and meat display on shelfs (Gobert et al., 2010).
3 This negative judging is not observed when linseeds are un-4 protected (Wood et al., 2003, Normand et al., 2005), i.e. when to animals contain a high level of 19 oil (40%) with 55% of 18:3 n-3 (Glasser et al., 2008a, Pe-20 tit, 2010).Adding linseeds to ruminant diets is susceptible 21 to increase the concentration of polyunsaturated FA in dairy 22 products and beef.Ruminant products contain a variety of FA. 23 Some of them may be of potential benefits to human health, 24 including polyunsaturated FA of the omega-3 FA series.The 25 main omega-3 FA in milk fat is 18:3 n-3.In beef, omega-3 FA 26 are composed of both 18:3 n-3 and 20-and 22-carbon FA.The 27 omega-3 FA, and more particularly 20-and 22-carbon FA, can 28

31
Despite elongation process, very long-chain FA are present 32 in muscle in low proportions whatever the diet: less than 0.7 and 0.4% of total FA for DPA and EPA, respectively, and 34 this proportion is either unchanged or moderately increased 35 by linseed supply

7
only if animal performances (milk yield and composition for 8 dairy cows, liveweight gain and carcass characteristics) are 9 unchanged or improved.Lipid incorporation in diets may de-10 crease fibre digestibility, due to possible disturbances in rumen 11 microbial ecosystem and fermentation.However, most scien-12 tists agree that this risk is negligible when FA content of diets 13

16A
range of experiments has been carried out in dairy cows, 17 using linseeds in different forms and amounts.During most 18 short-term studies, feeding up to 15% linseed in diet dry mat-19 ter (DM) did not change DM intake (Ferlay et al., 2013; Petit, 20 2010).In early lactation, discrepancies among experiments on 21 the effect of whole or processed linseed supplementation on 22 milk yield could result from differences in diet composition 23 and length of experiment (Petit, 2010).The whole linseed sup-24 plementation did not modify milk yield and milk fat content 25 and yield in mid-or late lactation (Petit, 2010).Nevertheless, 26 linseed micronisation or extrusion results in variable effects 27 on milk fat concentration, with a possible decrease.One ex-28 planation could be the possible increasing rate of oil release 29 from extruded seeds into the rumen compared to whole seeds, 30 which could result in an increased production of trans FA in 31

53 between
experiments is due to the level of linseed supply, the 54 experimental design (addition of linseeds or substitution to 55 carbohydrates and protein) and the characteristics of substitu-56 tion, leading to differences in diet energy value between con-57 trol and supplemented diet.Five comparisons between rolled 58 and extruded linseeds have been performed byNormand et al.

5
biohydrogenation normally occurs.It can be concluded that at 6 normal levels of incorporation, linseeds do not affect milk or 7 beef taste.

9
The major interest of linseeds in ruminant nutrition is the 10 increase in omega-3 FA in milk and beef with a moderate 11 supply in cattle diet.Although this increase in quantitatively 12 slight, due to rumen biohydrogenation, it contributes to en-13 hance milk and beef nutritional quality, and the image of these 14 products for the consumer.This positive role of linseeds in ru-15 minant nutrition is reinforced by their role for enteric methane 16 mitigation.However, an excessive incorporation in diets may 17 increase some trans FA in products or decrease milk fat and 18 protein contents, and feed efficiency of the diet.It could be 19 recommended to limit linseed incorporation to ca. 3% addi-20 tional fat in the diet.However, a large increase in the use of 21 linseeds for feeding ruminant is limited by the possibilities of 22 increase in linseed cropping.23 Highlight 24 Linseed use in ruminant nutrition can be developed in the 25 future owing to interest in improving fatty acid composition 26 of milk and meat, and also in decreasing methane emissions.
al., In these studies, linseed supply was of limited extent 60 and given to high-producing animals (2% additional fat to lac-61 tating cows in winter for dairy, 3% of additional fat to the bull 62 fattening herd for beef), corresponding to present practices in 63 France for farmers who use linseeds.In both types of farms, 64 the use of linseeds slightly decreases greenhouse gases emis-65 sions, and slightly increases other environmental impacts as 66 energy use, due to extrusion process, and land use, because 67 crop yield per hectare is lower for linseeds than for cereals that 68 linseeds replace.If strong public policies for decreasing green-69 house gases are implemented, all ruminants receiving concen-70

Table 1 .
Effect of linseed supply on beef liveweight gain.