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METABOLISM AND NUTRITION |
* Department of Animal Science, University of Manitoba, Winnipeg, Canada R3T 2N2; Nutreco Canada Inc., Winnipeg, Canada R3P 2P2; and Canadian Bio-Systems Inc., Calgary, Canada T2C 0J7
1 Corresponding author: b_slominski{at}umanitoba.ca
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: laying hen • flaxseed • canola seed • Linpro • omega-3 egg
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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-linolenic acid (ALA). Flaxseed is being widely used in laying hen nutrition for n-3-enriched egg production, whereas canola seed and off-grades of canola seed are financially attractive and are becoming an interesting alternative to animal fats in poultry and swine feeding programs. Flax oil contains 48 to 58% of n-3 fatty acids, and it has been indicated that an increase of flaxseed in laying hen diets by 1% would result in an increase in n-3 fatty acid deposition by 40 mg per egg (Leeson and Summers, 2005). However, published research data on the effect of flaxseed on egg production parameters has been inconsistent. Jiang et al. (1991) and Caston et al. (1994) reported no effect of flaxseed on egg production, whereas Aymond and Van Elswyk (1995) suggested that flaxseed addition may have negative effects. There is also some evidence, and belief within the feed industry, that egg production could be significantly reduced in layer flocks when flaxseed inclusion rate is greater than 8% (Leeson et al., 2000). This has been attributed to low nutrient utilization or the response of birds to antinutritional factors (ANF) such as mucilage, cyanogenic glycosides, or trypsin inhibitors (Bhatty, 1995). Mucilage, a water-soluble nonstarch polysaccharide (NSP), significantly increases the intestinal viscosity, which has been shown to have a negative effect on nutrient digestion and absorption (Choct and Annison, 1992; Rodriguez et al., 2001). In addition, the decreased energy utilization from flaxseed-containing diets has been reported to result from incomplete rupture of the seed and nutrient encapsulation by the cell wall structure (Slominski et al., 2006). Careful examination of the literature concerned with the feeding of full-fat flaxseed and canola seeds clearly demonstrates that bird performance and nutrient utilization is affected more so by insufficient seed processing and ineffective cell opening for optimal nutrient utilization than by any negative effects associated with ANF. A common characteristic of flax and canola is the small seed size, which limits nutrient utilization, because there is no satisfactory practical grinding-processing technology available for an effective rupture of the tissue structure. Furthermore, the nutrient encapsulating effect of the cell walls cannot be overcome by monogastric animals, because they lack enzymes to digest the polysaccharides of the cell wall. Research studies, including our own data (Jiang, 1999), support this concept. As reported by Lee et al. (1995), availability of oil from canola seed has been questioned, because metabolizable energy values were lower than those for corresponding canola meal plus canola oil mixtures. This was further substantiated in the broiler chicken study in which poorer feed conversion, lower AMEn content (2,963 vs. 3,200 kcal/kg), and lower ileal fat (65.6 vs. 85.6%) and protein (75.6 vs. 81.2%) digestibilities were observed for the canola seed diet compared with the canola meal plus canola oil diet (Meng et al., 2006). A highly significant effect of particle size on apparent digestibility of nutrients by broiler chickens and laying hens fed full-fat canola seed has also been reported (Danicke et al., 1998). In a similar study with full-fat flaxseed, it was demonstrated that various seed rupture processes such as pelleting, autoclaving, or microwave roasting had a significant effect on fat and energy utilization, with TMEn values of flaxseed increasing by 22 to 25% (Shen et al., 2004). In addition to seed rupture, the advantage of using heat treatment would be that some heat-labile ANF (i.e., trypsin inhibitors, cyanogenic glycosides) can be inactivated during feed processing (Feng et al., 2003). The mucilage and the intact NSP associated with the cell wall structure, however, may still pose a problem.
Oilseeds are often added to poultry diets after grinding. Under the commercial conditions, high-diameter sieves (i.e., 4 mm) are used for seed processing to avoid sieve plugging due to high oil content. However, when the seeds are premixed with cereal grains to overcome this problem, the grinding may still be insufficient for an effective rupture of the seed structure. In addition, seed grinding before diet preparation would accelerate lipid oxidation and would result in a short shelf life of diets. Therefore, it would be advantageous to feed whole seed in the form of a pelleted diet, because this would eliminate the grinding cost and would reduce the potential for lipid oxidation during storage. The potential drawback could be a low deposition of n-3 fatty acids due to the cell wall physical barrier for effective nutrient utilization (Aymond and Van Elswyk, 1995).
Earlier research from this laboratory has demonstrated that the use of a multicarbohydrase enzyme containing cell wall-degrading and viscosity-reducing activities can improve oil utilization from full-fat oil-seeds in broiler chickens and adult roosters (Meng et al., 2006; Slominski et al., 2006). However, the effectiveness of enzyme addition on egg production and n-3 fatty acids deposition in hens fed oilseeds has not yet been investigated.
Therefore, the objective of this study was to evaluate the effects of a multicarbohydrase enzyme cocktail on performance parameters, egg fatty acid deposition, and nutrient digestibility in hens fed diets containing canola seed, flaxseed, and a Linpro product (Werner Agra Ltd., Regina, Saskatchewan, Canada; flaxseed:peas, 1:1 wt/wt; ground-extruded). Pelleting and crumbling of the diets was chosen as a means of rupturing the seeds for effective nutrient utilization.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Six hundred forty-eight Hy-Line CV-20 laying hens were kept in confinement housing under semicontrolled environmental conditions and were exposed to a 16-h photoperiod. Feed and water were available ad libitum. Each dietary treatment was replicated 6 times, and each replicate consisted of 18 adjacently caged birds (6 cages of 3 birds each) fed as a group with a total of 108 hens per treatment. The cage dimensions were 30.5 x 40.6 cm, providing 413 cm2 per bird. The birds were fed experimental diets through the production peak (39 to 63 wk of age) consisting of 2 phases and three 28-d periods in each phase. All birds were weighed individually at the start and the end of the experiment. Egg production was recorded daily and calculated as hen-day production. Feed consumption was measured on a 28-d basis and calculated as a mean for each 18-bird replicate. Eggs were weighed for 3 consecutive days in the middle of each period. All animal procedures were conducted according to the guidelines of the Canadian Council on Animal Care (1993). The protocol for this study was approved by the Animal Care Protocol Review Committee of the University of Manitoba.
Diets
Birds were randomly assigned to 6 test diets, containing 150 g/kg diet of canola seed, flaxseed, or Linpro (flaxseed:peas, 1:1 wt/wt; ground-extruded) each without and with a multicarbohydrase enzyme addition (Superzyme OM; Canadian Bio-Systems Inc., Calgary, Alberta, Canada; Table 1
). The enzyme preparation supplied 1,100 U of pectinase, 50 U of cellulase, 1,000 U of xylanase, 600 U of glucanase, 400 U of mannanase, 50 U of galactanase, and 2,500 U of amylase per kilogram of diet. Intact flax and canola seeds were added to the diets, and all diets were pelleted and crumbled. The diets were examined in the laboratory, and no intact seeds were found.
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At 43 and 63 wk, eggs were collected for specific gravity measurements using the saline flotation method (Holder and Bradford, 1979). Five eggs per cage unit and 30 eggs per treatment were collected at 51 wk, and yolks from 10 eggs were pooled to yield 3 replicates per treatment. The yolk samples were frozen at –20°C, freeze-dried, and finely ground before fatty acid analysis by the Lipid Analytical Laboratories, University of Guelph. The weights of fresh eggs as well as the weights of yolks before and after freeze-drying were recorded. At 59 wk, excreta samples from 6 cage units per treatment (108 birds) were collected over a 3-h period and immediately frozen at –20°C. The samples were freeze-dried, finely ground, and pooled to produce 3 replicates per treatment. The pooled samples were then subjected to analysis of acid insoluble ash (AIA), which served as an internal marker (McCarthy et al., 1974), fat (AOAC, 1990; 920.39), and NSP content. Total NSP were determined by gas-liquid chromatography (component neutral sugars) and by colorimetry (uronic acids) using the procedure described by Englyst and Cummings (1988) with some modifications (Slominski and Campbell, 1990). At the end of the study, 12 hens (2 hens per replicate) were randomly selected from each treatment group and killed by cervical dislocation. The contents of jejunum (from the end of the duodenum to Meckel’s diverticulum) were collected and pooled from 2 birds to yield 6 replicate samples per treatment. Fresh digesta were centrifuged at 3,600 x g for 10 min, and viscosity of the supernatant was determined at 40°C using the Brookfield digital viscometer (model DV-II+LV, Brook-field Engineering Laboratories, Stoughton, MA).
Calculations and Statistical Analysis
The following equation was used for calculation of the digestibility of fat and NSP (using fat calculation as an example):
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A 3 x 2 factorial arrangement of a completely randomized design was used for statistical analysis. Experimental unit was a replicate, previously defined as 18 adjacently caged birds fed as 1 group. All of the statistical analysis was conducted by the SAS program (version 9.1, SAS Institute Inc., Cary, NC). Digestibility of nutrients, digesta viscosity, and fatty acid profile parameters were analyzed by the GLM procedure. Main effects of diet and enzyme and the interaction between diet and enzyme were tested. Performance parameters (feed consumption, egg production, feed conversion ratio, egg weight, hen weight, and specific gravity) from each phase were analyzed as repeated measures by the MIXED procedure. This model included main effects (diet, enzyme, and phase) and the associated 2- and 3-way interactions (diet x enzyme, diet x phase, enzyme x phase, diet x enzyme x phase). Means were separated by Tukey’s honestly significance difference. Contrasts of enzyme effect (i.e., without vs. with enzyme addition) within each diet type and phase were made. All statements of significance are based on P < 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Diet had a significant effect on all the production parameters measured (Table 2). Hens fed the canola seed diet consumed less feed than those fed flaxseed and Linpro (94.2, 100.1, and 98.5 g/hen per day, respectively) with a similar effect observed for each phase. There was no significant difference in feed consumption between the flaxseed and Linpro diets, except for phase II, in which greater consumption of the flaxseed diet was observed. Enzyme supplementation of canola seed and flaxseed diets resulted in lower feed consumption in phase II and over the entire trial, with no significant effect in phase I. No significant effects of diet on egg production were observed until phase II, at which time hens consuming flaxseed had lower egg production compared with those consuming canola seed or Linpro. Enzyme supplementation had a more pronounced effect on egg production in hens fed flaxseed than the other diets, with a significant increase in egg production during phase II and over the entire trial. There was no difference in egg weight between any of the dietary treatments in phase I of the experiment. In phase II, eggs from the flaxseed group were heavier than those from the canola seed group but not different from those of the Linpro treatment. Enzyme had no significant effect on egg size except for hens fed the flaxseed diet, who laid slightly smaller eggs after enzyme addition in phase II of the experiment. As a result, hens consuming canola seed diets had better feed conversion than those consuming flaxseed during each phase. Hens consuming Linpro diets had superior feed conversion to those consuming flaxseed diets in phase II, and no significant difference was noted in phase I. The use of enzyme significantly improved feed conversion in the flaxseed diet during each phase and over the entire trial but had no effects on canola seed and Linpro diets.
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Hen Weight and Eggshell Quality
As shown in Table 3, flaxseed-fed hens were significantly lighter at the end of the trial than those from the other treatments. Enzyme supplementation had no effect on hen weight.
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). Adding enzyme to the flaxseed diet significantly increased the specific gravity measurements in phase I but not in phase II. Eggs from Linpro-fed hens had an intermediate shell quality between those from canola and flaxseed-fed hens only in phase I of the experiment, whereas in phase II, egg specific gravity from Linpro-fed hens was similar to that from canola diet, which was probably due to the adaptation of the birds to the flaxseed component of the Linpro diet. Digesta Viscosity and Total Tract Fat and NSP Digestibilities
Hens consuming flaxseed diets had the greatest jejunal digesta viscosity, whereas those fed canola seed had the lowest (Table 4). Diet had no significant effect on either NSP or fat digestibilities (Table 4). The NSP digestibility in hens fed flaxseed increased from 12 to 24% after enzyme supplementation, whereas NSP digestibility in hens fed canola seed or Linpro was not affected by enzyme addition. No statistically significant effect of enzyme addition on fat digestibility was noted.
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There was no difference in total fatty acid content among the treatments, although the fatty acid profile changed significantly (Tables 5 and 6). When compared with canola seed, incorporation of flaxseed and Linpro into the diets increased the contents of saturated fatty acids (SFA) and total n-3 fatty acids and decreased monounsaturated fatty acids (MUFA). The content of n-6 fatty acids was not affected by dietary treatments; hence, the n-6:n-3 fatty acid ratio was significantly lower in eggs produced by hens fed the flaxseed and Linpro. Eggs laid by the flaxseed group contained the greatest total n-3 fatty acids and the lowest MUFA. The decrease in egg MUFA content was mainly attributed to the decrease in oleic acid (C18:1n-9), although the palmitoleic acid (C16:1n-7) content increased when compared with that of the canola seed diets. Deposition of ALA (C18:3n-3), eicosapentaenoic acid (EPA, C20:5n-3), and docosahexaenoic acid (DHA, C22:6n-3) was significantly greater for the flaxseed-containing diets than that of the canola seed diet. As a result, the n-6:n-3 ratio differed significantly (Table 6).
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Enzyme had no effect on fatty acid deposition in eggs produced by hens fed canola seed. For the flaxseed diet, enzyme addition increased the egg DHA content from 91.8 to 101.9 mg/60 g of egg and tended to increase the contents of ALA (P = 0.06) and EPA (P = 0.09), hence significantly increasing the total n-3 fatty acid content from 546 to 578 mg/60 g of egg. For the Linpro group, EPA significantly increased from 6.5 to 7.2, DHA from 89.4 to 96.8, and total n-3 fatty acids from 415 to 438 mg/60 g of egg after enzyme supplementation. As well, the total fatty acids and stearic and oleic acids increased after enzyme supplementation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Lee et al. (1995) reported that although canola seed and flaxseed have similar contents of energy-contributing components, the AMEn and TMEn of flaxseed (3.75 and 3.75 kcal/g) were, respectively, lower (P < 0.05) than those of canola seed (4.46 and 4.56 kcal/g). They suggested that the seed size, hull coat thickness, high fiber, and other ANF may affect energy utilization. It is a well-known fact that energy utilization could be reduced due to the nutrient-encapsulating effect of the cell wall-NSP (Bedford, 2002). In this context, the total NSP content of flaxseed meal has been reported to average 271 g/kg (Slominski et al., 2006) and was much greater than that of canola meal (171 g/kg; Meng et al., 2005). In addition, water-soluble mucilage present in the hull fraction of flaxseed is known to significantly increase the intestinal viscosity (Rodriguez et al., 2001; Alzueta et al., 2003). Mucilage consists of 2 fractions, a neutral fraction composed of arabinoxylans and an acidic pectic-like fraction consisting of polysaccharides containing rhamnose, galactose, and galacturonic acid residues. The arabinoxylans are the major components responsible for the viscous properties of mucilage (Cui et al., 1994), which, similarly to viscous polysaccharides of cereal grains, could decrease nutrient availability by increasing the rate of feed passage and reducing the rates of diffusion of endogenous enzymes and nutrients (Classen and Bedford, 1991). Ortiz et al. (2001) concluded that deleterious components of flaxseed interact with dietary nutrients of flaxbased diets thereby decreasing energy (AMEn) utilization. This could explain an increase in feed consumption observed in the current study to compensate for low nutrient availability. In addition, the depressed egg production and body weight have been indicated to result from inadequate AMEn content of the flaxseed-containing diets (Leeson et al., 2000). In general, published research data on the effect of flaxseed on laying hen performance is inconsistent. Bean and Leeson (2003) suggested that duration of the trial could affect performance. Among the long-term studies, similar to our data, responses in feed consumption and hen weight were reported by Caston et al. (1994), Leeson et al. (2000), and Novak and Scheideler (2001), whereas a decrease in feed consumption was reported by Bean and Leeson (2003) for flaxseed-containing diets. Lower egg production observed in the current study is in agreement with the research data by Leeson et al. (2000) but in disagreement with findings by Caston et al. (1994), Novak and Scheideler (2001), and Bean and Leeson (2003), who reported no adverse effect of flaxseed addition, up to 20% of the diet, on egg production. Differences in diet composition or strain of hens could be partially responsible for such conflicting results. In the current study, eggs laid by hens consuming flaxseed were slightly but significantly heavier (P = 0.047) than those from birds fed canola seed (60.6 vs. 59.8 g). It has been demonstrated that there is a relationship between increased egg size and increased protein-amino acid intake (Waldroup and Hellwig, 1995). As discussed earlier, hens fed the flaxseed diets increased feed consumption to compensate for low energy utilization compared with those fed the canola seed diets. As a result, protein-amino acid intake increased as well, resulting in a bigger egg size.
Egg specific gravity has been used extensively as a measure of shell strength (Holder and Bradford, 1979). Because the egg contents (yolk and albumen) maintain a constant specific gravity, any difference in egg specific gravity relates to the amount of calcium deposition (shell thickness). In the current study, eggs from hens fed flaxseed had consistently the lowest specific gravity (Table 3). Therefore, it is possible that calcium absorption was impaired due to increased digesta viscosity associated with the flax mucilage.
Earlier research from this laboratory has demonstrated that multicarbohydrase enzymes can improve energy (lipids) utilization from ground full-fat flaxseed or extruded flaxseed products in adult roosters and broiler chickens (Slominski et al., 2006). In the present study, the addition of a multicarbohydrase enzyme (Superzyme OM) significantly increased egg production and improved feed conversion in hens consuming flaxseed (Table 2). The improved egg production parameters would suggest better energy utilization from the flaxseed diet, although only a trend in improved fat digestibility with enzyme supplementation was noted (Table 4). A significant increase in NSP digestibility indicates that the enzyme (Superzyme OM) was effective in flaxseed cell wall polysaccharide depolymerization and elimination, at least in part, of the nutrient encapsulating effect of the cell wall structure. The use of flaxseed markedly increased the viscosity of jejunum digesta compared with that of canola seed (18.8 vs. 5.0 mPa·s; Table 4). Enzyme addition failed to reduce the intestinal viscosity, although in our earlier research, a significant viscosity-reducing activity was demonstrated in vitro (data not shown). It would appear that flaxseed mucilage is much more difficult to degrade in vivo, and more effective enzyme combinations are needed to target this component. Egg specific gravity significantly increased with enzyme supplementation (Table 3), which could be indicative of improved calcium utilization.
Linpro is an extruded product consisting of full-fat flaxseed and peas (1:1 wt/wt). The flaxseed in Linpro is used as a whole seed and is ground with peas before extruding. In addition to providing nutrients, peas serve as a carrier to increase the flow of flaxseed during grinding. Hens fed the Linpro diets had overall similar feed consumption and egg size but greater egg production and greater feed conversion than those fed flaxseed (Table 2). This was not surprising, because the level of flaxseed in the Linpro diets was much lower than that present in the flaxseed diets (75 vs. 150 g/kg of diet). Hence, the Linpro diets contained lower levels of ANF, including mucilage, which as shown in Table 4 resulted in lower intestinal viscosity. It could be speculated that in addition to grinding, the pressure and heat used during the extrusion process could contribute to the effective rupture of the seed structure and elimination of the negative effect of some heat-labile ANF (i.e., trypsin inhibitors, cyanogenic glycosides). This, in turn, would increase the overall nutrient utilization (Thacker et al., 2005) and explain why in the current study enzyme addition showed no effect on most of the egg production and nutrient digestibility parameters in hens fed the Linpro diet.
In the present study, hens consuming flaxseed deposited significantly more n-3 fatty acids in the egg (562 mg/60 g of egg, equal to 11.6% of total yolk fat; the average of total fat per 60 g of egg was 4.85 g) than those fed canola seed (207 mg/egg, equal to 4.3% of total yolk fat). This is in agreement with research by Cherian and Sim (1991), who reported the total n-3 fatty acid content in the egg yolk fat to average 10.75 and 4.15%, respectively, in hens fed flaxseed or canola seeds both at 16% of the diet. In the current study, the increase in total n-3 fatty acids in eggs produced by hens consuming flaxseed resulted from the increase of not only ALA but also both EPA and DHA (Table 5). The EPA and DHA deposition in the egg is a consequence of in vivo metabolism, with ALA serving as a precursor for their synthesis through the desaturation-chain elongation pathway within the liver (Brenner, 1971). Conversion of ALA to EPA parallels that of linoleic acid (C18:2n-6) to arachidonic acid (C20:4n-6). Both fatty acids compete for the same enzyme 
6-desaturase in the first step of their respective conversions to form polyunsaturated 20-carbon derivatives (Brenner, 1971; Nettleton, 1991). The decrease in arachidonic acid deposition in eggs produced by birds fed flaxseed (Table 5) supports this well-known competitive inhibition between n-3 and n-6 fatty acids. The increase in SFA observed in the current study was most likely due to much greater SFA content of flax oil than canola oil (i.e., 10.2 vs. 6.0%; Vaisey-Genser, 1994). The lower level of MUFA in eggs produced by hens fed flaxseed resulted from either lower concentration of oleic acid in this ingredient or the inhibitory effects of polyunsaturated fatty acids, or both. Mahfouz et al. (1984) and Garg et al. (1988) have reported that polyunsaturated fatty acids inhibit the activity of 9-desaturase, which is involved in MUFA synthesis.
It is of interest to note that the egg enrichment with DHA, an important fatty acid for human health, was very effective in hens consuming canola seed and was only lower by 12 mg/60 g of egg (i.e., 82.9 vs. 95.0 mg/60 g of egg) from that of flaxseed and Linpro (Table 5). This could indicate that DHA deposition reaches the plateau at a much lower concentration of dietary n-3 fatty acids than that corresponding to the 15% inclusion rate of flaxseed. This is further substantiated by the fact that no difference in DHA deposition was observed between the flaxseed and the Linpro diets, both products included in the diets at 15% but Linpro contributing only 7.5% of the flaxseed. This finding is consistent with earlier studies indicating that the increase in EPA and DHA was not proportional to the level of ALA, which increased significantly in the eggs from hens fed flaxseed (Caston and Leeson, 1990; Cherian and Sim, 1991; Aymond and Van Elswyk, 1995). The poor conversion rate of ALA to DHA probably relates to the complexity of DHA biosynthesis. Recent studies have shown that the biosynthesis of polyunsaturated fatty acids is more complex than previously recognized, because enzymes from more than one intracellular compartment are required for the synthesis of 22-carbon polyunsaturated fatty acid with their first double bond at position 4 in a partial degradation-resynthesis cycle (Sprecher, 2000).
Enzyme addition significantly increased n-3 fatty acid deposition, particularly DHA, in eggs produced by hens fed both flaxseed and Linpro diets. This may be due to the depolymerization of the cell wall polysaccharides after enzyme supplementation, which resulted in more oil release and thus more oil exposure to digestive enzymes.
In conclusion, high levels of dietary flaxseed had adverse effects on hen production performance. Such negative effects were minimized by enzyme supplementation, which had a positive effect on feed utilization and n-3-enriched egg production in hens fed pelleted and crumbled diets containing flaxseed.
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ACKNOWLEDGMENTS |
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Received for publication November 22, 2007. Accepted for publication April 19, 2008.
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