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Beynen AC, 2017. Flax in dog food

Creature Companion 2017; December: 32, 34.
Anton C. Beynen
Flax in dog food
Flax is a plant grown mainly for its oil and occasionally as linen-fiber crop. Flaxseeds, also known
as linseeds, are small, flat and oval-shaped. Flaxseed or its oil component is found in the ingredient
lists of many commercial dog foods. Dry foods may contain up to 10% flaxseed or 4% flaxseed oil.
Flaxseed meal (defatted seeds) is scarcely used.
Alpha-linolenic acid (ALA), an omega-3 fatty acid, is an essential nutrient that must be present in
the diet. Various ingredients provide ALA, but flaxseed (oil) has a uniquely rich content. The dog
can convert ALA into EPA (eicosapentaenoic acid), which elicits biological activity. The conversion
forms the basis for claims that flaxseed (oil) supports healthy skin, hair coat, joints and heart, but
these enhancements are unproven for flaxseed incorporated into an ALA-sufficient diet.
Supplemental flaxseed oil may ameliorate inflammatory skin disease.
Some internet discussions convey the impression that flaxseed causes food allergy. A manufacturer
offers a dog food line with an explicit flax-free claim. In fact, canine food allergy is rare (1),
rendering flaxseed allergy exceptionally rare. Another concern is that dietary flax releases
potentially toxic cyanide. No adverse cyanide-related effects have been reported for practical
flaxseed-containing dog diets, but this status quo awaits controlled study for confirmation (Note
Flaxseed is high in lignans, compounds that can imitate or oppose female sex hormone activity.
Some dog breeders use flaxseed supplements for reproductive health (2). In female rats, dietary
flaxseed altered reproductive development and reduced the risk of chemical-induced breast
cancer. These topics are still unaddressed in dogs. Flaxseed-containing dog foods might affect
long-term health positively or negatively. For now, flaxseed (oil) is a suitable, but dispensable
The approximate composition of whole flaxseed is 36% crude fat, 22% crude protein, 8% crude fiber,
4% ash and 8% moisture. The specialities, ALA and secoisolariciresinol diglucoside (SDG), constitute
about 20 and 1%. Total SDG (3) consists of various oligomers (4). Measurable amounts of undesired
cyanogenic glucosides, tannins and seed-coat mucilage fall markedly upon heat treatment (5, 6) such
as applied in the production of kibbled or canned food.
Flaxseeds have a tough hull. Human subjects consuming muffins with identical amounts of ALA as
whole flaxseed, milled seed or flax oil, had increasing plasma ALA concentrations, in this order (7).
Grinding seeds or isolating oil enhances ALA availability, but also its oxidation susceptibility. In stored
oil, oxidation (8) and bitter products (9) appear.
Total-tract digestibility
Incorporating flaxseed, presumably ground and at 5.6%, into an extruded food, without changing
macronutrient composition, lowered apparent protein and fat digestibility in dogs by about one
percent unit, while fecal moisture was unaffected (10). Flaxseed fermentation by canine fecal flora
gave uninterpretable results (11).
Solvent-extracted flaxseed meal, as component of extruded kibbles, had an apparent protein
digestibility of 79% (12). It was 77% for pressed flaxseed cake, soaked in hot water and then mixed
with wetted kibbles (13). Intake of dietary dry matter with 1% flaxseed mucilage, which matches
about 9% whole flaxseed (6, 14, 15), resulted in lower fat digestibility and more moist stools (16).
Alpha-linolenic acid
Feeding ground flaxseed or flax oil to dogs raises ALA, EPA and docosapentaenoic acid (DPA), but not
docosahexaenoic acid (DHA), in blood total lipids, phospholipids, triglycerides, erythrocytes,
neutrophils, and heart tissue (17-22). ALA intakes were increased up to 6.5 g per MJ metabolizable
energy for at least 4 weeks.
The fatty acid changes endorse that the dog is capable of converting ALA. The liver desaturates both
linoleic acid (LA) and ALA (23), releases arachidonic acid (24) and likely EPA and DPA also. Canine
retina and brain functionality requires DHA, plasma DPA serving as (co-)precursor (25). Milk fat from
dogs fed flax oil during gestation and lactation was enriched in ALA, but not in EPA, DPA and DHA
Eicosapentaenoic acid
EPA gives rise to eicosanoids with wide-ranging biological properties. Dogs gather bodily EPA more
efficiently from dietary EPA than from ALA (22) or ALA’s delta-6-desaturase product, stearidonic acid
(27). Using the observed (22) build-up of plasma phospholipid EPA as criterion, it follows (Note 2)
that 1.5 g of flaxseed oil (55% ALA) is as effective as 1 g of fish oil (10% EPA).
Skin health
Increasing the dietary ALA level from 0.08 g/MJ, which met the dog’s requirement (28, Note 3), to
0.56 g/MJ by inclusion of ground flaxseed, did not affect skin and hair coat condition in healthy dogs
(29, 30). Among four canine diets, the diet containing flax was not associated with healthier skin and
hair (31). Supplemental flaxseed oil (0.44 g ALA/MJ diet) improved canine atopic dermatitis
somewhat less than pure EPA (0.20 g/MJ diet) (32), while EPA amounted to twice the maximum
effective dose (33).
Heart and joint health
Fish oil (0.13 g EPA/MJ diet), but not flax oil (0.17 g ALA/MJ diet) supplementation, distinctly
elevated group-mean plasma EPA and reduced ventricular arrhythmia in Boxers (34). Fish oil (0.2-0.4
g EPA/MJ diet) has a small beneficial impact on canine osteoarthritis (35), but flax oil’s position
remains unknown.
In specific rat studies (36, 37), flaxseed mitigated cancer risk. Exposure to a diet with 10% ground
flaxseed or 0.02% SDG during suckling, reduced the incidence of dimetylbenzanthracene-induced
palpable mammary tumors later in life (37).
Reproductive development
Dietary flaxseed activated oestrogen-receptor signaling in murine mammary gland (38). Diets
containing 5 or 10% flaxseed delayed or accelerated puberty onset in female rats (39, 40).
Note 1
Cyanogenic glycosides (CG) are plant chemicals consisting of a nitrile aglycone and a carbohydrate
moiety (glucose or gentobiose). Upon destruction of the plant cell structure, CG’s are hydrolysed by
endogenous enzymes, yielding hydroxypropanenitrile, which decomposes in aqueous solution to
hydrogen cyanide. In flaxseed, the main CG’s are linamarin, linustatin and neolinustatin. The
contents differ among flaxseed varieties (41).
The releasable amount of cyanide in flaxseed, as determined by alkaline titration, is about 200
mg/kg (5, 6). This amount translates to 10 mg/kg dry petfood at 10% flaxseed inclusion level and
50% loss (5, 6) during processing. In young dogs fed a diet based on cooked rice and pork, the
addition of sodium cyanide to a level of 9 mg cyanide/kg dry matter markedly reduced body-weight
gain (42). In contrast, a diet containing cooked cassava instead of rice and providing 11 mg
cyanide/kg dry matter, had no effect on growth.
Note 2
Dogs were fed diets (1.9 MJ/100 g) containing either beef tallow (0.09 g ALA and 0 g EPA/MJ)
flaxseed oil (5.42 g ALA and 0 g EPA/MJ) or menhaden oil (0.12 g ALA and 1.62 g EPA/MJ) (22). After
feeding the diets for 28 days, the EPA contents of plasma phospholipids were 0.53, 4.42 and 10.17
mol% of total fatty acids. The diets with flaxseed and menhaden oil had increased phospholipid EPA
by 3.89 and 9.64 mol%, which was caused by the additional intakes of 5.33 g ALA and 1.62 g EPA/MJ,
respectively. Thus, 1 g ALA and 1 g EPA would raise phospholipid EPA by 0.73 and 5.95 mol%, while 1
g flaxseed oil (0.55 g ALA) and 1 g fish oil (0.10 g EPA) would induce increments of 0.40 and 0.60
mol%. In other words, 1.5 g flaxseed oil is equivalent to 1.0 g fish oil. Some of the flaxseed
inefficiency is likely due to its LA which competes with ALA for the delta-6-desaturase. The flaxseed
and menhaden-oil diets contained 2.11 and 0.69 g LA/MJ (22).
Note 3
The recommended LA and ALA allowances for adult dogs at maintenance have been set at 0.66 and
0.026 g/MJ while the LA:ALA ratio should be between 2.6 and 26 (28). Thus, the 0.026 g ALA/MJ
value is the minimum requirement at 0.66 g LA/MJ as the LA:ALA ratio results in 25.4. The role of the
ratio relates to the competition between LA and ALA for the delta-6-desaturase.
With regard to skin and hair coat condition in healthy dogs, diets containing ground sunflowerseed
(2.51 g LA and 0.12 g ALA/MJ, ratio 20.9) or ground flaxseed (1.97 g LA and 0.68 g ALA/MJ, ratio 2.9)
have been compared (29). Diets with either beef tallow (0.66 g LA and 0.05 g ALA/MJ, ratio 13.2),
sunflower oil (2.37 g LA and 0.07 g ALA, ratio 33.9) or ground flaxseed (2.37 g LA and 0.61 g ALA/MJ,
ratio 3.9) have also been compared (30). Two control diets within the comparisons can be
considered ALA sufficient. The sunflowerseed and tallow diets contained more than 0.026 g ALA/MJ
and had a LA:ALA ratio lower than 26. The sunflower-oil diet had a LA:ALA ratio of 33.9 so that the
ALA content of 0.07 g/MJ may be considered deficient. On the other hand, the 0.07 g ALA/MJ is 2.7
times higher than the minimum requirement at the LA:ALA ratio of 26.
The situation is further complicated by the fact that the diets differed as to contents of EPA, which
could be ALA’s mediator in potentially affecting skin and hair condition. The diets with
sunflowerseed and flaxseed contained 7 and 19 mg EPA/MJ (18, 29). The diets with beef tallow,
sunflower oil and flaxseed contained 11, 7 and 34 mg EPA/MJ (30). Thus, the flaxseed diets
contained more EPA than their control diets. The proposed requirement for EPA is 14 mg/MJ (28).
Even though the flaxseed versus sunflower-oil-diet increased both ALA and EPA intake above their
requirements, there was no improvement of skin and hair coat condition (30).
A third study was published in abstract form (31). The data show that dietary flax was not associated
with changes in skin and hair coat condition in healthy dogs. A diet containing flax as ALA source was
compared with three traditional canine diets. The ingredient and analysed compositions of the four
diets, including the fatty acid profiles, are not reported.
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Full-text available
The aim of the study was to determine quality and oxidative stability of selected cold pressed flaxseed oils, fresh (after producing, the beginning of shelf life) and stored at refrigerator temperature (after three months, the end of declared shelf life). The fresh oils were characterized by organoleptic assessment, fatty acids composition and bioactive compounds content (sterols, tocols, squalene, carotenoids, and phenols). For the fresh and stored oils oxidative stability in the Rancimat test, and the hydrolytic and oxidation degrees using standard methods were determined. It was found that fresh flaxseed oils were differentiated in fatty acid composition and content of bioactive compounds. Shares of saturated fatty acids, and content of squalene and phenolic compounds were most variable in the oils. At the end of shelf life flaxseed oils were characterized by 9-26% shorter induction time in compare to the initial state, and increased content of hydrolysis (acid value by 18-40%) and oxidation products (peroxide value by 16-37%, anisidine value by 13-41%, diene content by 10-21%, triene content by 23-42%) was detected.
Full-text available
The full-fat flaxseed (Linum usitatissimum L.) meal has obtained relatively new flourished concept as food or feedstuff for the development of healthier products. It provides favorable balance of polyunsaturated, monounsaturated and saturated fatty acids. However, flaxseed meal may be susceptible to oxidation by exposure to various storage conditions which is extremely undesirable and produces toxic compounds to human health. Another consideration in the application of flaxseed meal relates to the presence of anti-nutritional compounds that need to be minimized using appropriate processing method. The present research work was conducted to evaluate the impact of extrusion processing conditions and storage of full-fat flaxseed meal on functional characteristics such as α-linolenic acid content, lipid peroxidation and sensory attributes. The raw flaxseed meal was analyzed for cyanogenic glycosides, tannin and mucilage anti-nutritional compounds. Fatty acids composition was quantified by gas chromatography. The meal was extruded at barrel exit temperature (100-140 °C), screw speed (50-150 rpm), feed rate (30-90 kg/h) and feed moisture (10-30 %) for reduction of anti-nutritional compounds. The raw and extruded meals were stored for a ninety-day period under room conditions (20-25 °C). Lipid peroxidation was analyzed by peroxide, free fatty acids, conjugated dienes, total volatiles and malondialdehyde assay. Color, aroma and overall acceptability attributes were evaluated by sensory multiple comparison tests. The raw flaxseed meal possessed significant amount of anti-nutritional compounds, lipid and α-linolenic acid contents. The extrusion processing at high barrel exit temperature (140 °C) significantly reduced the cyanogenic compounds (84 %), tannin (73 %) and mucilage (27 %) in the flaxseed meal. The α-linolenic acid content and lipid peroxidation did not significantly change after extrusion processing or during storage at the end of 60 days. Fluctuations in sensory attributes occurred during storage, but at the end of 90 days, only the extruded samples presented negative effect and showed lowest consumer acceptability. The present study suggested that extrusion of flaxseed meal at optimum conditions and stored for 60 days did not change the stability of full-fat flaxseed meal and can be used as supplement or ingredient for the production of various healthier products.
Full-text available
Flaxseed meal from twenty-one varieties has been evaluated for content of cyanogenic glycosides (linamarin, linustatin and neolinustatin). Varieties belonging to three different groups of produc-tive attitude (oil, fiber and intermediate) were considered. The total content of cyanogenic glyco-sides ranged from 0.74 to 1.60 g • Kg −1 CN − . As expected, linamarin was a minority component ac-counting for only 2% -14% of total glycosides. Linustatin resulted statistically lower in the inter-mediate group than in the other groups and, in particular, it was the lowest in the Festival variety. Neolinustatin resulted lower in the fiber group although the variety Ventimiglia (belonging to oil group) showed a negligible level of this compound. Neolinustatin was positively correlated to total cyanogenic glycosides (r = 0.709) and inversely correlated to linustatin (r = −0.326). The variabil-ity observed in the content of the various forms of glycosides could be exploited in breeding pro-grams to reduce the content of these toxic compounds in flaxseed meal.
Background: In humans, dietary supplementation with flaxseed mucilage and calcium decrease apparent digestibility of fat and energy. These supplements could prove useful for weight management in dogs. Objective: To examine dry matter, energy and fat apparent digestibility and fecal characteristics following dietary flaxseed mucilage supplementation alone or in combination with calcium. Methods: A single-blinded crossover feeding trial was conducted on 11 privately owned dogs. During three consecutive 14 day periods, dogs where fed commercial dog food supplemented with potato starch (control diet), flaxseed mucilage or flaxseed mucilage and calcium. Feces from the last two days of each period were collected for analysis. Owners recorded fecal score (1-7: 1=very hard/dry feces. 2-3=ideal, 7=diarrhea). Results: Apparent digestibility of fat was lower in both flaxseed mucilage diet (94.5±0.8%) and flaxseed mucilage and calcium diet (92.9±0.9%) compared with control diet (96.9±0.2%, P<0.0001) with fat digestibility in flaxseed mucilage and calcium diet being significantly lower than the diet supplemented with only flaxseed mucilage. Dry matter and energy digestibility was not significantly affected by diet. Fecal wet weight, dry weight and dry matter percentage was not affected by diet despite a higher fecal score for test diets (3.7±0.3) compared with control (2.8±0.2, P<0.007). Conclusion: In dogs, flaxseed mucilage decreased fat apparent digestibility and this effect was enhanced when combined with calcium. Dry matter and energy apparent digestibility was not affected. Decreased fecal quality may limit the acceptable level of supplementation. Further studies on incorporating flaxseed mucilage in pet food products for weight management are needed.International Journal of Obesity accepted article preview online, 16 August 2016. doi:10.1038/ijo.2016.139.
Two basal diets and blends of these with one of 34 single ingredients were fed to groups of four Beagles for 21 days. The consistency of faeces was scored on the last 4 days of each period and the faecal dry matter was determined. The digestibility of organic matter and energy in the diets was determined by use of chromium sesquioxide as marker. No close correlation was found between the consistency and dry matter concentration of the faecal samples. Although the influences of individual feed ingredients on the faecal consistency and on faecal dry matter were obvious, these could not be explained by the digestibility of the organic matter or by the concentration of digestible energy in these feeds. Verdaulichkeit der organischen Substanz und verdaulichen Energie in einzelnen Komponenten extrudierter Hundefutter und deren Einfluß auf den Gehalt an Trockensubstanz und die Konsistenz des Hundekotes Zwei Grundmischungen, rein oder nach Verschneiden im Verhältnis zwischen 80:20 bis 60:40 mit 34 Einzelfuttermitteln, wurden als Extrudat an Gruppen von jeweils vier Beagles über 21 Tage gefüttert. An den letzten vier Tagen jeder Periode wurde jeweils die Konsistenz des Kotes nach dem Augenschein benotet, der Gehalt an Trockensubstanz wurde bestimmt. Die Verdaulichkeit der organischen Substanz und der Energie wurde indirekt mit Chromoxid als Marker bestimmt. Keine klare Korrelation wurde gefunden zwischen der Note für Konsistenz und dem Gehalt des Kotes an Trockensubstanz. Obwohl Einflüsse von Einzelfuttermitteln sowohl auf den Gehalt an Trockensubstanz als auch auf die Konsistenz des Kotes offenkundig waren, ließen diese sich nicht mit der Verdaulichkeit der organischen Substanz oder dem Gehalt an Verdaulicher Energie erklären.
A study was conducted to determine the effectiveness of reducing the hydrogen cyanide (HCN) content of flaxseed (FS) by processing. FS was processed by oven heating, single or repeated pelleting alone or in a mix with corn or other ingredients, autoclaving, and microwave roasting. The comparative effectiveness in reducing HCN in FS by these processes was monitored through HCN measurements by alkaline titration. The HCN content was 377 mg kg−1 in raw feed-grade FS and 139 mg kg−1 in a human food-grade FS. All processing methods tested significantly (p < 0.05) reduced the HCN content of FS. Autoclaving FS reduced its HCN content by 29.7%. Microwave roasting of FS reduced the HCN content by 83.3%. Because of the 5.7% water loss recorded after 4 min of FS roasting, this reduction could be related to more evaporation of the newly formed HCN. Pelleting FS once reduced HCN content by 13.3%, and three and six repeated pelleting processes reduced HCN content by 29.0% and 54.9% respectively. When FS was pelleted in a mix with 50% corn, the HCN reduction was even greater. After pelleting six times, HCN reduction reached 63.8%. However, the greatest reduction in HCN content was 73.8%, and was obtained when FS was mixed with several ingredients and pelleted twice. The HCN reduction could be the result of deactivation of the glycosidase, or the evaporation of HCN formed from cyanogenic glycosides. The HCN reduction increased as the number of pelletings and the temperature of the pelleted product increased. The greater and prolonged exposure to a higher temperature by several pelletings seems to promote a greater HCN reduction. The appropriate processing of FS is essential for the use of this oilseed in animal feeding. Copyright © 2003 Society of Chemical Industry
Registered Canadian cultivars of flax, and laboratory-prepared and commercially obtained samples of linseed meal (LM), were used to determine extract viscosity and mucilage, trypsin inhibitors and hydrocyanic acid (HCN) concentrations. The mucilage readily leached out from the seed coat (hull) fragments soaked in water, leaving behind pentagon-shaped cells that could be seen clearly in scanning electron micrographs. Extract viscosity significantly varied in the laboratory-prepared (23–48 cS) and commercially obtained (30–68 cS) samples of LM and may be used to obtain an indirect, qualitative estimate of flax mucilage. Mucilage was extracted from whole seed in 5.0–5.3% yields and contained 20–24% protein (about 10% ash and 30% total carbohydrates). Laboratory-prepared LM (raw) contained 42–51 units of trypsin inhibitor activity, commercially obtained samples, 14–37 units, and raw rapeseed and soybean meals, 99 and 1650 units, respectively. Picric acid tests (qualitative) showed only traces of HCN in ten cultivars of freshly ground flax. The acid silver nitrate titration procedure measured HCN quantitatively, but showed its presence only in three of the five cultivars investigated. HCN was conveniently measured by a colorimetric procedure (barbituric acidpyridine reaction), which may be used to screen flax cultivars. HCN content of flax was significantly influenced by environments (growth location and season) and, to a less extent, by cultivar.
Six laboratory-prepared (LM) and four commercially-obtained (CM) samples of linseed meal were analyzed for eleven proximate components, ten mineral elements, monosaccharides, amino acids, and seven vitamins (two samples only). Analysis of variance of LM data showed location had a greater influence on meal composition than did cultivar. LM and CM had similar composition, except for protein, total carbohydrates, acid-detergent fiber and lignin. Hull separated by a liquid cyclone process formed 37.5% of the seed and contained less than 1% oil, 20% protein and 32.9% total monosaccharides. Xylose and arabinose were the major sugars. Meal absorbed 8-fold, and the hull 13-fold their weights of water (water-hydration capacity), compared to less than 2-fold by similar fractions of canola (rapeseed) and soybean. Viscosities of aqueous extrats of hull were stable for 30 min at 25°C, and were concentration-dependent.
Total hepatectomy and abdominal evisceration were performed in two groups of dogs to determine if the liver is the only source of plasma arachidonic acid. Venous blood was drawn prior to surgery and hourly for 5–6 hours. Plasma lipids were fractionated by column chromatography into unesterified fatty acids, phospholipids, cholesterol esters, and triglycerides. The per cent composition of the individual fatty acids of these fractions and total esterified fatty acids were determined by gas-liquid chromatography. Hepatectomy resulted in progressive fall of the per cent composition of arachidonic acid of the unesterified fatty acid fraction only. There was no significant depression of any other fatty acid in this fraction, nor was there a change in any fatty acid including arachidonic acid in the phospholipid, cholesterol ester, and triglyceride fractions. Palmitoleic acid was significantly elevated in the unesterfied fatty acid fraction. Similar results were observed in the eviscerated group. There was no change of any fatty acid in the various lipid fractions of a group of sham operated dogs. Lipolysis of adipose tissue triglyceride supplies all fatty acids of the plasma unesterified fatty acid fraction except arachidonic acid which is virtually absent from this tissue. Thus, as the unesterified fatty acids were utilized by the peripheral tissues, all fatty acids except arachidonic acid were replenished by lipolysis of adipose tissue triglyceride. Since the liver was absent in both groups of animals, it was concluded that the liver is the source of plasma arachidonic acid in the fasting dog.