Archives of Animal Nutrition, 2015 Vol. 69, No. 3, 177–186, http://dx.doi.org/10.1080/1745039X.2015.1034520
Effects of different processing methods of flaxseed on ruminal degradability and in vitro post-ruminal nutrient disappearance Saman Lashkari, Osman Azizi* and Hossein Jahani-Azizabadi Department of Animal Science, Faculty of Agriculture, University of Kurdistan, Sanandaj, Iran (Received 29 November 2014; accepted 19 March 2015) The aim of the study was to determine the effects of different heat-processing methods of flaxseed on the in situ effective dry matter degradability (EDMD) and the in situ effective crude protein degradability (ECPD). The treatments included roasting, steep roasting, rolled roasting, rolled steep roasting, microwave irradiation and extrusion. Three rumen-fistulated sheep were used for in situ incubations. Furthermore, the effects of heat-processing methods on post-ruminal in vitro nutrient disappearance and total tract disappearance were measured by a three-step in vitro technique. The seeds were roasted and extruded at 140°C to 145°C. One lot of roasted seeds was gradually cooled for about 1 h (roasting) and another lot was held in temperature isolated barrels for 45 min (steep roasting). Moreover, roasted and steep roasted flaxseed was rolled in a roller mill. The lowest and highest EDMD was observed for unheated and extruded flaxseed, respectively (p < 0.05). The highest ECPD was observed for extruded flaxseed (p < 0.05). Roasting and microwave irradiation reduced ECPD of flaxseed (p < 0.05). In vitro post-ruminal disappearance of crude nutrients including fibre fractions was highest for rolled-roasted and rolled steep-roasted flaxseed (p < 0.05). The lowest and highest total tract disappearance rates of crude nutrients and fibre fractions were estimated for unheated and extruded flaxseed, respectively (p < 0.05). The post-ruminal disappearance of crude nutrients was also increased by roasting, in which rolling enhanced this effect. In conclusion, all investigated heat treatments had significant effects on in situ and in vitro degradability of nutrients. As well, rolling of roasted flaxseed enhanced the respective effects. Therefore, different methods of heat processing can be used to modify the feed value of flaxseed for specific purposes. Keywords: degradation; flaxseed; heat processing; in situ, in vitro; nutrients; sheep
1. Introduction Flaxseed is an oilseed which can be used as source of high-quality protein and fat for ruminants, especially for dairy cows (Neveu et al. 2014). On a dry matter (DM) basis, flaxseed contains 20% crude protein (CP), 18% neutral detergent fibre (NDF) and 40% ether extract (EE) (Mustafa et al. 2002). Flaxseed contains high levels of linolenic acid, averaging 18% of the total seed weight and 53% of the total fatty acids (Mustafa et al. 2002). Recently, there has been a renewed interest in using flaxseed in animal rations as it can be used to alter the fatty acid composition of milk and meat products and, therefore, provide functional health benefits for the consumer (Petit 2010). The concept of supplying bypass nutrients to growing or lactating ruminants has received a great deal of attention in the past decade. Various chemical and physical *Corresponding author. Email: [email protected] © 2015 Taylor & Francis
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processing has been suggested to protect oilseeds from ruminal degradation and biohydrogenation by denaturating the protein matrix surrounding the fat droplets (Kennelly 1996). Heat processing is the most commonly used physical method to protect oilseeds and oilseed meals from ruminal degradation. Heat treatment of oilseeds can also alter site of nutrient digestion in the gastrointestinal tract of ruminants (Mustafa et al. 2002). Heat processing has been widely used to decrease protein degradation in the rumen and increase the supply of dietary protein at the duodenum. Heat processing makes proteins more resistant to ruminal degradation and result in a more gradual releasing of NH3-N, peptides and branched-chain volatile fatty acids (Veen 1986). Therefore, these essential growth factors are made available to the ruminal cellulolytic bacteria for a longer period of time after feeding. Also, it has been suggested that decreasing ruminal CP degradation of the diet by using heat processing increased ruminal fibre digestion (Aldrich et al. 1995). The application of heat to a high fat product such as flaxseed might also protect polyunsaturated fatty acid from microbial biohydrogenation and thus increase the concentration of polyunsaturated fatty acids in milk (Jones et al. 2001). Data on the effects of roasting and steep roasting, combination of roasting and rolling, combination of steep roasting and rolling, microwave heating and extrusion as a common methods of heat processing on ruminal in situ degradation and post-ruminal nutrient disappearance of flaxseed are lacking, and therefore, the objectives of this study were to determine the effects of different heat-processing methods of flaxseed on ruminal kinetic parameters of DM and CP and to determine in vitro post-ruminal disappearance of ruminal undegraded nutrients of unheated and heated flaxseed using the three-step in vitro technique.
2. Material and methods 2.1. Heat processing of flaxseed The flaxseed used in the study was a feed-grade product of unknown cultivar and was provided by a commercial company. In the present study, the investigated flaxseed was unheated (raw) or in six different ways heat processed (roasted, steep roasted, rolled roasting, rolled steep roasting, microwave irradiated and extruded). Flaxseeds were roasted in an industrial roaster with a flame and blower at 140 to 145°C (turning speed of 2.5 circles per minute; diameter of tunnel of 50 cm). One lot was gradually cooled for about 1 h (roasting) and the other lot was immediately placed, without cooling, in barrels and covered with canvas for 45 min before being allowed to cool (steep roasting) (Faldet et al. 1992). Furthermore, roasted and steep-roasted flaxseed was processed in a roller mill equipped with rollers that were 22.9 cm in diameter and 76.2 cm long, with 12 grooves per 2.54 cm2 (rolled-roasted and rolled steep-roasted flaxseed). The rollers were adjusted to provide the coarsest roll possible, while ensuring that the seed coat was broken. Moreover, flaxseeds were subjected to microwave irradiation at a power of 800 W for 4 min under agitation. Extrusion of flaxseed was performed at 140 to 145°C with a resident time of 43 s using a multipurpose twin-screw extrusion system.
2.2. Chemical composition The feed samples were dried using an oven at 60°C for 48 h, ground to pass through a 2mm screen. DM, CP and EE of flaxseed were determined using the methods recommended by AOAC (2005). Neutral detergent-insoluble CP (NDICP) and acid detergent-
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insoluble CP (ADICP) were determined using standardisation and recommendations published by Licitra et al. (1996).
2.3. In situ study In situ ruminal disappearance of DM and CP of unheated and heated flaxseed were determined using a nylon bag technique (Ørskov and McDonald 1979). Each feed sample was incubated in six replicates (two replicates per each sheep) in the rumen of three wethers (mean weight 32.9 ± 4 kg). Animals were fed 0.6 kg alfalfa hay and 0.4 kg concentrate containing 24% corn grain, 20.4 barley grains, 27% soybean meal, 13.8% canola meal, 13.8% wheat bran, 0.3% calcium carbonate, 0.5% mineral and vitamin premix and 0.2% salt. The diet was offered twice a day at 08:30 h and 15:30 h in equal amounts after collecting the refusals. The incubation times for flaxseed samples were 0, 2, 4, 8, 12, 16, 24, 48 and 72 h. The nylon bags with 50 μm pore size were suspended in the rumen in a polyester mesh bag and were removed from the rumen at the same time, so that all bags could be washed simultaneously. The bags were then removed from the mesh bag and washed with washing machine until the rinse water remained clear. Bags were then dried in oven at 55°C until a constant weight was achieved before determination of DM disappearance and CP analysis. The kinetics of in situ DM and CP disappearance were estimated using a non-linear procedure of SAS (1991). The model of Ørskov and McDonald (1979) was fitted to the percentage of DM and CP disappearance as: Y ¼ a þ bð1 ect Þ; where a is the soluble fraction, b is the slowly disappearing fraction, c is the fractional rate of disappearance [%/h] and t is the incubation time [h]. Effective ruminal disappearance was estimated using the following model: Y ¼ a þ bc=ðc þ k Þ; where k is the fractional rate of particulate passage, assumed to be 0.03 h−1 (Ørskov and McDonald 1979).
2.4. Three-step in vitro procedure This stage of the experiment followed the procedure of Gargallo et al. (2006). Approximately, 5 g of sample was weighed into a 5 cm × 10 cm nylon bags, 50-μm pore size Dacron polyester bag (six bags per sample) and suspended in the rumen of three sheep fitted with permanent rumen fistula for 12 h. Bags were then removed and washed with a washing machine and dried in an oven at 55°C for 48 h and weighed. Samples from each bag were taken for N analysis using the Kjeldahl method (Kjeltec 2300 Autoanalyzer, Foss Tecator). After weighing, residue (0.5 g) was placed in an in situ bag (5 × 5 cm with a pore size 50 μm) and placed in an ANKOM Daisy incubator for determination of post-ruminal digestibility (Gargallo et al. 2006). Briefly, samples were incubated in a pepsin/HCl solution for 1 h, followed by incubation in a pancreatin/ KH2PO4 solution for 24 h. After 24 h, the liquid was drained from the bottles and bags were again rinsed until the run-off was clear. Bags were allowed to drain and were dried in
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an oven at 55°C for 48 h. The dry weights of the samples and bags were recorded and bags were opened and pooled by sample for CP, OM, EE, NDF and ADF analysis. The approximated total tract disappearance is based on in situ incubation and three-step in vitro technique.
2.5. Statistical analysis Experimental data were analysed in a completely randomised design using the general linear method procedure of SAS (SAS Institute, 1991). Heat-processing methods were considered as the only sources of variation and the statistical model was: Yij ¼ μ þ T þ eij where μ is the mean, T is the treatment and eij is the residual. The dependent variable represents the response for the ith treatment. Means were compared using Duncan’s multiple range tests.
3. Results and discussion 3.1. Chemical composition of the feed Chemical analysis of unheated and heat-processed flaxseed is shown in Table 1. Because both unheated and heat-processed flaxseed samples were derived from a single batch, it was not possible to test differences of chemical composition between the different heatprocessing methods statistically. However, it was evident that heat processing altered the chemical composition of flaxseed (Table 1). The contents of NDF and ADF in heatprocessed flaxseed were lower than in unheated flaxseed. The decrease in NDF and ADF content can be attributed to the loss of different proportions of flaxseed hulls due to shattering during extruding, roasting or rolling (Ganesh and Grieve 1990). In agreement Table 1.
Chemical composition of heat-processed flaxseed (n = 6). Type of heat processing Rolled Steep Rolled steep Microwave Unheated Roasted roasted roasted roasted irradiated Extruded SEM*
Nutrients [g/kg DM] Organic matter 956 Crude protein 198 Ether extract 345 NDF† 240 226 ADF‡ Hemicelluloses 14.0 NFC# 171 Nutrients [g/kg crude protein] 28.1 NDICP+ 18.0 ADICP§
955 198 361 221 199 22.5 174
950 195 384 219 195 24.0 150
954 194 384 220 171 49.2 154
951 198 358 215 181 34.0 178
949 195 383 221 186 34.8 149
953 197 384 217 174 42.8 153
0.67 1.06 3.31 3.76 3.84 4.12 4.56
33.8 22.0
34.7 30.5
35.6 26.3
35.3 31.5
35.4 33.3
37.3 25.4
0.70 1.06
Notes: *SEM, standard error of means; †NDF, Neutral detergent fibre; ‡ADF, Acid detergent fibre; #NFC, Nonfibre carbohydrates; +NDICP, Neutral detergent-insoluble crude protein; §ADICP, Acid detergent-insoluble crude protein.
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with these findings, Fathi Nasri et al. (2008) reported that roasting reduced also the NDF contents of whole soybean. Rolled flaxseed contained the lowest amounts of ADF and physical changes were evident. In contrast, Faldet et al. (1991) found similar NDF and ADF concentrations when raw whole soybeans were roasted at 165°C and then rolled. Furthermore, heat processing caused an increase of the NDICP and ADICP contents when compared to unheated flaxseed. In agreement with these findings, it has been reported already earlier that heat processing such as roasting (Hussein et al. 1995), extruding (Moshtaghi Nia and Ingalls 1992) and micronisation (Mustafa et al. 2002) increased the amounts of NDICP and ADICP.
3.2. In situ dry matter degradability and estimated parameters of degradability The estimated parameters of degradability, including soluble (a), insoluble potentially degradable (b) fractions, degradation rate (c) and in situ effective DM degradability (EDMD), are shown in Table 2. EDMD of unheated and extruded flaxseed was the lowest and highest, respectively (p < 0.05). The low EDMD of raw flaxseed could be explained by the hard pericarp surrounding the seed. As reported by Leeson and Caston (2004), the hull of flaxseed represents about 25% of the seed weight; it is largely composed of fibre and contains about 18.5% lignin, which is highly indigestible. This fibrous material keeps the integrity of raw flaxseed, which would prevent ruminal degradation and could explain the low in situ degradability of raw flaxseed observed in the present study. Heat processing markedly improved EDMD of flaxseed. It can be concluded that hard pericarp of the seed must be broken for better utilisation; therefore, heat and mechanical processing of flaxseed significantly enhanced the EDMD of flaxseed. In comparison with unheated flaxseed and all other treatments, extrusion caused the largest increase of EDMD and estimated degradation parameters with the exception of degradation rate. In agreement with our findings, also Mustafa et al. (2002) found that extrusion increased soluble, insoluble potentially degradable DM fraction and EDMD of flaxseed. All variations of roasting and microwave irradiation increased the EDMD also significantly compared to the unheated samples, but between these treatments rolling of roasted flaxseed was more effective than roasting, steep roasting and microwave irradiation (p < 0.05). The higher EDMD of rolled flaxseed might be due to the break of seed coat and the exposure of the internal material to rumen microorganisms. The present study Table 2. flaxseed.
Estimated degradation parameters and dry matter degradability of heat-processed Type of heat processing Steep Rolled Unheated Roasted roasted roasted
a† [g/kg DM] b‡ [g/kg DM] c# [%/h] EDMD§ [g/kg DM]
79.4d 188d 4.1a 186d
89.8c 288c 2.4b 218c
90.4c 295c 2.3b 221c
113.8b 413b 1.2c 237b
Rolled Microsteep wave roasted irradiated Extruded SEM* 119.7b 421ab 1.2c 238b
70.0e 399b 1.8bc 219c
326.1a 453a 3.6a 570a
12.9 14.6 0.17 19.3
Notes: *SEM, Standard error of the mean; †a, Rapidly degraded fraction, ‡b, Slowly degraded fraction; #c, Rate of degradation; §EDMD, in situ effective dry matter degradability with a passage rate of 0.03/h. a–d Means in the same row not sharing the same superscript are significantly different (p < 0.05).
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agrees with the results of Huard et al. (1998) who found that rolling of canola seeds increased the ruminally EDMD compared with whole canola seeds from 6.32% to 38.68%, respectively. In contrast to other treatments, the microwave irradiation of flaxseed decreased the soluble fraction significantly but increased EDMD in a similar way as steep roasting and rolled roasting. These results agreed with findings of Sadeghi and Shawrang (2007).
3.3. In situ crude protein degradability and estimated parameters Estimated parameters including soluble (a), insoluble potentially degradable (b) fractions, degradation rate (c) and in situ effective crude protein degradability (ECPD) are shown in Table 3. The soluble fraction was the highest in extruded flaxseed and lowest in microwave heated flaxseed (p < 0.05). Extrusion of flaxseed increased the ECPD more effectively as other heat treatments (p < 0.05). It has been suggested that extrusion caused the break of fat micelles and disrupt the protein matrix of the flaxseed endosperm. This permits a more rapid degradation of nutrients by rumen microbes (Mustafa et al. 2003). Similar extrusion effects on the degradation of CP in the rumen have been reported previously (Mustafa et al. 2002). The ECPD for roasted and steep-roasted flaxseed was lower than unheated and extruded flaxseed. Similarly, McNiven et al. (1994) found that roasting results in denaturation of protein and probably transform the proteins to a more resistant structure to rumen degradability. Also, a reduction in ECPD due to steeping suggests that more heat was able to penetrate the flaxseed possibly rendering some proteins (albumins and globulins) more insoluble. Similar effects with steep-roasted soybean meals have been reported by Mosimanyana and Mowat (1992). Lower ECPD of rolled flaxseed as compared to unheated flaxseed indicated that after rolling of flaxseed, roasting could effectively reduce the rumen degradability. Microwave heating of flaxseed effectively decreased the soluble fraction and ECPD. These results are in agreement with those of Sadeghi and Shawrang (2007) who reported that microwave irradiation decreased the water-soluble fraction and ECPD. Reduction of soluble fraction and ECPD might be due to the cross-linking of chains and protein aggregation through heating. Microwave irradiation and roasting effectively reduced CP degradation rate as compared to unheated flaxseed (p < 0.05). The significant reduction in the CP degradation rate Table 3. Estimated degradation parameters and crude protein degradability of heat-processed flaxseed. Type of heat processing Steep Rolled Unheated Roasted roasted roasted a† [g/kg CP] b‡ [g/kg CP] c# [%/h] EDMD§ [g/kg CP]
91.5b 188.9b 7.0a 223b
81.8cd 174.0c 4.7bc 187e
75.8de 169.9c 5.5b 185ef
87.4bc 165.8c 7.8a 207c
Rolled steep roasted 90.5b 152.8d 8.0a 201d
Microwave irradiated Extruded SEM 69.7e 197.0b 4.1c 184f
194.2a 238.4a 4.0c 330a
6.24 4.18 0.27 7.49
Notes: *SEM, Standard error of the mean; †a, Rapidly degraded fraction, ‡b, Slowly degraded fraction, #c, Rate of degradation, §ECPD, Effective crude protein degradability with passage rate of 0.03/h [g/kg DM]. a–f Means in the same row not sharing the same superscript are significantly different (p < 0.05).
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of flaxseed by heat processing might increase bypass protein and therefore increase the amount of available amino acids in the small intestine. Also previous studies reported that heat processing such as roasting (Fathi Nasri et al. 2008), extruding (Kibelolaud et al. 1993) and micronisation (Mustafa et al. 2002) reduced the degradation rate of CP. The lower CP degradation rate of heat-processed flaxseed is likely a reflection of the increased levels of NDICP. Reduction in the ruminal degradation rate of CP would decrease ruminal NH3-N production and the cost of urea synthesis (Lashkari and Taghizadeh 2013).
3.4. Ruminal in situ and post-ruminal in vitro nutrient disappearance Ruminal in situ and post-ruminal in vitro disappearance of DM, OM, CP, EE, NDF and ADF of unheated and heat-processed flaxseed is shown in Table 4. The highest level of DM, OM, CP, EE, NDF and ADF disappearance after 12 h of in situ rumen incubation was observed for extruded flaxseed (p < 0.05). Extrusion of flaxseed increased the disappearance of DM, OM, CP, EE, NDF and ADF by 68, 72, 33, 55, 56 and 50%, respectively. The results are in agreement with the data obtained by Mustafa et al. (2003) who reported that extrusion of flaxseed increased the DM and CP disappearance after 12 h of rumen incubation. The lowest CP disappearance after 12 h of rumen incubation was
Table 4. Ruminal in situ, post-ruminal in vitro and approximation of total tract nutrient disappearance [%]. Type of heat processing Steep Rolled Unheated Roasted roasted roasted Ruminal† Dry matter Organic matter Crude protein Ether extract NDF # ADF§ Post-ruminal Dry matter Organic matter Crude protein Ether extract NDF ADF Total tract‡ Dry matter Organic matter Crude protein Ether extract NDF ADF
Rolled steep roasted
Microwave irradiated Extruded SEM*
14.9cd 13.1cd 19.1b 26.9d 13.5e 11.7e
15.7bc 13.1cd 15.7d 28.0c 15.4d 14.4c
15.6bc 12.8d 15.6d 27.7cd 16.0d 14.4c
16.7b 15.0b 18.6bc 31.1b 19.4b 16.2b
16.8b 14.4bc 18.4c 30.3b 19.4b 17.1b
14.1d 12.1d 14.9e 18.6e 17.7c 13.9c
48.8a 48.6a 28.7a 59.9a 30.1a 23.7a
1.82 1.93 0.69 1.72 0.81 0.59
51.2e 45.4d 41.1c 12.7d 11.9c 11.2c
57.6d 52.4b 56.5b 33.5c 15.4b 15.7b
58.8cd 52.2b 56.8b 36.1bc 15.1b 15.9b
61.6ab 63.2a 62.0a 43.3a 21.5a 18.7a
62.9a 62.9a 62.3a 46.4a 21.6a 18.9a
60.4bc 49.9c 57.4b 38.3b 15.3b 14.9b
41.8f 43.9d 55.6b 33.1e 17.9b 14.5b
1.09 1.13 1.08 1.63 0.64 0.44
66.2d 58.6d 60.3d 39.7e 25.5d 23.0d
73.3c 65.6c 72.3c 61.6c 30.8c 30.2c
74.5c 65.0c 72.5c 63.9c 31.1c 30.3c
78.4b 78.2b 80.6b 74.5b 40.9b 34.9b
79.7b 77.4b 80.7b 76.8b 41.0b 36.1b
74.6c 62.1c 72.3c 56.8d 33.1c 28.9c
90.6a 92.6a 84.4a 93.1a 48.0a 38.2a
0.52 0.32 0.63 2.48 1.38 0.22
Notes: *SEM, Standard error of the mean. †Determined after 12 h of ruminal incubation; #NDF, Neutral detergent fibre; §ADF, Acid detergent fibre; ‡Approximation of total tract disappearance based on in situ incubation and three-step in vitro technique. a–e Means in the same row not sharing the same superscript are different (p < 0.05).
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observed for roasted, steep-roasted and microwave-irradiated flaxseed. This suggests that these treatments change the internal constituents of flaxseed which increased their resistance to ruminal degradation. The EE disappearance after 12 h of rumen incubation of microwave-irradiated, as well as roasted and steep-roasted flaxseed was significantly lower than the other heat-processed flaxseeds (p < 0.05). These results demonstrated that also roasting of flaxseed is a suitable way to protect polyunsaturated fatty acids from microbial biohydrogenation and thus increase the concentration of polyunsaturated fatty acids in dairy products (Jones et al. 2001). The lowest and highest NDF and ADF disappearance after 12 h of rumen incubation were observed for unheated and extruded flaxseed, respectively (p < 0.05). These findings are in agreement with those of Mustafa et al. (2003) who stated that extrusion of flaxseed increased the NDF disappearance after 12 h of rumen incubation of flaxseed. Furthermore, rolling of roasted flaxseed effectively increased the NDF and ADF disappearance after 12 h of rumen incubation as compared to roasted and steep-roasted flaxseed (p < 0.05). The high NDF and ADF disappearance of rolled flaxseed might be due to break of the seed coat. Post-ruminal in vitro CP disappearance was the highest for rolled-roasted and rolled steep-roasted flaxseed; intermediate for roasted, steep-roasted, extruded and microwaveirradiated flaxseed and lowest for unheated flaxseed (p < 0.05). Higher post-ruminal in vitro CP disappearance after heat processing confirms the hypothesis that only primary Maillard products were formed and that there was no formation of intestinally indigestible terminal Maillard products (Von Keyserlingk et al. 2000). The highest post-ruminal in vitro CP, EE, NDF and ADF disappearance of rolled flaxseed might be due to associate effects of roasting and rolling. Significant difference between post-ruminal in vitro nutrient disappearance of roasted and rolled-roasted flaxseed showed that breaking the seed coat via roasting may be insufficient for effective digestion by ruminants. Wang et al. (1997) reported similar observations in a study comparing micronised and ground micronised canola seed. Post-ruminal in vitro CP disappearance of extruded flaxseed was higher than the untreated flaxseed. Post-ruminal in vitro CP disappearance of roasted and steeproasted flaxseed was higher than the unheated flaxseed. Similarly, Fathi Nasri et al. (2008) reported that post-ruminal CP disappearance of whole soybean was enhanced by roasting and steep roasting. Compared to unheated flaxseed, also microwave-heated flaxseed increased the post-ruminal in vitro CP disappearance (p < 0.05). It has been suggested that microwave irradiation may induce the unfolding of proteins and their denaturation. This would expose hydrophobic amino acids (especially aromatic amino acids), which allows an effective protein digestion by pepsin and trypsin (Murray et al. 2003). 3.5. Approximation of total tract nutrient disappearance Approximation of total tract nutrient disappearance of DM, OM, CP, EE, NDF and ADF of unheated and heat-processed flaxseed is shown in Table 4. The total tract disappearance of DM, OM, CP, EE, NDF and ADF of extruded flaxseed was the highest. This was expected because the highest ruminal in situ disappearance of extruded flaxseed caused this elevated total tract disappearance. A significant increase of total tract disappearance of DM, NDF and ADF was also observed after roasting, rolled roasting and microwave heating. 4. Conclusions All investigated heat treatments of flaxseed had significant effects on in situ and in vitro degradability of nutrients. Based upon the in situ studies, roasting and microwave
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irradiation would be expected to enhance the amount of protein escaping the rumen and to increase NDF and ADF degradability. Rolling of roasted flaxseed enhanced the respective effects. On the other hand, extrusion increased the rumen and total tract degradability of nutrients considerably and decreased the post-ruminal supply of nutrients from flaxseed. Therefore, different methods of heat processing can be used to modify the feed value of flaxseed for specific purposes.
Disclosure statement No potential conflict of interest was reported by the authors.
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Effects of different processing methods of flaxseed on ruminal degradability and in vitro post-ruminal nutrient disappearance Saman Lashkari, Osman Azizi* and Hossein Jahani-Azizabadi Department of Animal Science, Faculty of Agriculture, University of Kurdistan, Sanandaj, Iran (Received 29 November 2014; accepted 19 March 2015) The aim of the study was to determine the effects of different heat-processing methods of flaxseed on the in situ effective dry matter degradability (EDMD) and the in situ effective crude protein degradability (ECPD). The treatments included roasting, steep roasting, rolled roasting, rolled steep roasting, microwave irradiation and extrusion. Three rumen-fistulated sheep were used for in situ incubations. Furthermore, the effects of heat-processing methods on post-ruminal in vitro nutrient disappearance and total tract disappearance were measured by a three-step in vitro technique. The seeds were roasted and extruded at 140°C to 145°C. One lot of roasted seeds was gradually cooled for about 1 h (roasting) and another lot was held in temperature isolated barrels for 45 min (steep roasting). Moreover, roasted and steep roasted flaxseed was rolled in a roller mill. The lowest and highest EDMD was observed for unheated and extruded flaxseed, respectively (p < 0.05). The highest ECPD was observed for extruded flaxseed (p < 0.05). Roasting and microwave irradiation reduced ECPD of flaxseed (p < 0.05). In vitro post-ruminal disappearance of crude nutrients including fibre fractions was highest for rolled-roasted and rolled steep-roasted flaxseed (p < 0.05). The lowest and highest total tract disappearance rates of crude nutrients and fibre fractions were estimated for unheated and extruded flaxseed, respectively (p < 0.05). The post-ruminal disappearance of crude nutrients was also increased by roasting, in which rolling enhanced this effect. In conclusion, all investigated heat treatments had significant effects on in situ and in vitro degradability of nutrients. As well, rolling of roasted flaxseed enhanced the respective effects. Therefore, different methods of heat processing can be used to modify the feed value of flaxseed for specific purposes. Keywords: degradation; flaxseed; heat processing; in situ, in vitro; nutrients; sheep
1. Introduction Flaxseed is an oilseed which can be used as source of high-quality protein and fat for ruminants, especially for dairy cows (Neveu et al. 2014). On a dry matter (DM) basis, flaxseed contains 20% crude protein (CP), 18% neutral detergent fibre (NDF) and 40% ether extract (EE) (Mustafa et al. 2002). Flaxseed contains high levels of linolenic acid, averaging 18% of the total seed weight and 53% of the total fatty acids (Mustafa et al. 2002). Recently, there has been a renewed interest in using flaxseed in animal rations as it can be used to alter the fatty acid composition of milk and meat products and, therefore, provide functional health benefits for the consumer (Petit 2010). The concept of supplying bypass nutrients to growing or lactating ruminants has received a great deal of attention in the past decade. Various chemical and physical *Corresponding author. Email: [email protected] © 2015 Taylor & Francis
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processing has been suggested to protect oilseeds from ruminal degradation and biohydrogenation by denaturating the protein matrix surrounding the fat droplets (Kennelly 1996). Heat processing is the most commonly used physical method to protect oilseeds and oilseed meals from ruminal degradation. Heat treatment of oilseeds can also alter site of nutrient digestion in the gastrointestinal tract of ruminants (Mustafa et al. 2002). Heat processing has been widely used to decrease protein degradation in the rumen and increase the supply of dietary protein at the duodenum. Heat processing makes proteins more resistant to ruminal degradation and result in a more gradual releasing of NH3-N, peptides and branched-chain volatile fatty acids (Veen 1986). Therefore, these essential growth factors are made available to the ruminal cellulolytic bacteria for a longer period of time after feeding. Also, it has been suggested that decreasing ruminal CP degradation of the diet by using heat processing increased ruminal fibre digestion (Aldrich et al. 1995). The application of heat to a high fat product such as flaxseed might also protect polyunsaturated fatty acid from microbial biohydrogenation and thus increase the concentration of polyunsaturated fatty acids in milk (Jones et al. 2001). Data on the effects of roasting and steep roasting, combination of roasting and rolling, combination of steep roasting and rolling, microwave heating and extrusion as a common methods of heat processing on ruminal in situ degradation and post-ruminal nutrient disappearance of flaxseed are lacking, and therefore, the objectives of this study were to determine the effects of different heat-processing methods of flaxseed on ruminal kinetic parameters of DM and CP and to determine in vitro post-ruminal disappearance of ruminal undegraded nutrients of unheated and heated flaxseed using the three-step in vitro technique.
2. Material and methods 2.1. Heat processing of flaxseed The flaxseed used in the study was a feed-grade product of unknown cultivar and was provided by a commercial company. In the present study, the investigated flaxseed was unheated (raw) or in six different ways heat processed (roasted, steep roasted, rolled roasting, rolled steep roasting, microwave irradiated and extruded). Flaxseeds were roasted in an industrial roaster with a flame and blower at 140 to 145°C (turning speed of 2.5 circles per minute; diameter of tunnel of 50 cm). One lot was gradually cooled for about 1 h (roasting) and the other lot was immediately placed, without cooling, in barrels and covered with canvas for 45 min before being allowed to cool (steep roasting) (Faldet et al. 1992). Furthermore, roasted and steep-roasted flaxseed was processed in a roller mill equipped with rollers that were 22.9 cm in diameter and 76.2 cm long, with 12 grooves per 2.54 cm2 (rolled-roasted and rolled steep-roasted flaxseed). The rollers were adjusted to provide the coarsest roll possible, while ensuring that the seed coat was broken. Moreover, flaxseeds were subjected to microwave irradiation at a power of 800 W for 4 min under agitation. Extrusion of flaxseed was performed at 140 to 145°C with a resident time of 43 s using a multipurpose twin-screw extrusion system.
2.2. Chemical composition The feed samples were dried using an oven at 60°C for 48 h, ground to pass through a 2mm screen. DM, CP and EE of flaxseed were determined using the methods recommended by AOAC (2005). Neutral detergent-insoluble CP (NDICP) and acid detergent-
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insoluble CP (ADICP) were determined using standardisation and recommendations published by Licitra et al. (1996).
2.3. In situ study In situ ruminal disappearance of DM and CP of unheated and heated flaxseed were determined using a nylon bag technique (Ørskov and McDonald 1979). Each feed sample was incubated in six replicates (two replicates per each sheep) in the rumen of three wethers (mean weight 32.9 ± 4 kg). Animals were fed 0.6 kg alfalfa hay and 0.4 kg concentrate containing 24% corn grain, 20.4 barley grains, 27% soybean meal, 13.8% canola meal, 13.8% wheat bran, 0.3% calcium carbonate, 0.5% mineral and vitamin premix and 0.2% salt. The diet was offered twice a day at 08:30 h and 15:30 h in equal amounts after collecting the refusals. The incubation times for flaxseed samples were 0, 2, 4, 8, 12, 16, 24, 48 and 72 h. The nylon bags with 50 μm pore size were suspended in the rumen in a polyester mesh bag and were removed from the rumen at the same time, so that all bags could be washed simultaneously. The bags were then removed from the mesh bag and washed with washing machine until the rinse water remained clear. Bags were then dried in oven at 55°C until a constant weight was achieved before determination of DM disappearance and CP analysis. The kinetics of in situ DM and CP disappearance were estimated using a non-linear procedure of SAS (1991). The model of Ørskov and McDonald (1979) was fitted to the percentage of DM and CP disappearance as: Y ¼ a þ bð1 ect Þ; where a is the soluble fraction, b is the slowly disappearing fraction, c is the fractional rate of disappearance [%/h] and t is the incubation time [h]. Effective ruminal disappearance was estimated using the following model: Y ¼ a þ bc=ðc þ k Þ; where k is the fractional rate of particulate passage, assumed to be 0.03 h−1 (Ørskov and McDonald 1979).
2.4. Three-step in vitro procedure This stage of the experiment followed the procedure of Gargallo et al. (2006). Approximately, 5 g of sample was weighed into a 5 cm × 10 cm nylon bags, 50-μm pore size Dacron polyester bag (six bags per sample) and suspended in the rumen of three sheep fitted with permanent rumen fistula for 12 h. Bags were then removed and washed with a washing machine and dried in an oven at 55°C for 48 h and weighed. Samples from each bag were taken for N analysis using the Kjeldahl method (Kjeltec 2300 Autoanalyzer, Foss Tecator). After weighing, residue (0.5 g) was placed in an in situ bag (5 × 5 cm with a pore size 50 μm) and placed in an ANKOM Daisy incubator for determination of post-ruminal digestibility (Gargallo et al. 2006). Briefly, samples were incubated in a pepsin/HCl solution for 1 h, followed by incubation in a pancreatin/ KH2PO4 solution for 24 h. After 24 h, the liquid was drained from the bottles and bags were again rinsed until the run-off was clear. Bags were allowed to drain and were dried in
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an oven at 55°C for 48 h. The dry weights of the samples and bags were recorded and bags were opened and pooled by sample for CP, OM, EE, NDF and ADF analysis. The approximated total tract disappearance is based on in situ incubation and three-step in vitro technique.
2.5. Statistical analysis Experimental data were analysed in a completely randomised design using the general linear method procedure of SAS (SAS Institute, 1991). Heat-processing methods were considered as the only sources of variation and the statistical model was: Yij ¼ μ þ T þ eij where μ is the mean, T is the treatment and eij is the residual. The dependent variable represents the response for the ith treatment. Means were compared using Duncan’s multiple range tests.
3. Results and discussion 3.1. Chemical composition of the feed Chemical analysis of unheated and heat-processed flaxseed is shown in Table 1. Because both unheated and heat-processed flaxseed samples were derived from a single batch, it was not possible to test differences of chemical composition between the different heatprocessing methods statistically. However, it was evident that heat processing altered the chemical composition of flaxseed (Table 1). The contents of NDF and ADF in heatprocessed flaxseed were lower than in unheated flaxseed. The decrease in NDF and ADF content can be attributed to the loss of different proportions of flaxseed hulls due to shattering during extruding, roasting or rolling (Ganesh and Grieve 1990). In agreement Table 1.
Chemical composition of heat-processed flaxseed (n = 6). Type of heat processing Rolled Steep Rolled steep Microwave Unheated Roasted roasted roasted roasted irradiated Extruded SEM*
Nutrients [g/kg DM] Organic matter 956 Crude protein 198 Ether extract 345 NDF† 240 226 ADF‡ Hemicelluloses 14.0 NFC# 171 Nutrients [g/kg crude protein] 28.1 NDICP+ 18.0 ADICP§
955 198 361 221 199 22.5 174
950 195 384 219 195 24.0 150
954 194 384 220 171 49.2 154
951 198 358 215 181 34.0 178
949 195 383 221 186 34.8 149
953 197 384 217 174 42.8 153
0.67 1.06 3.31 3.76 3.84 4.12 4.56
33.8 22.0
34.7 30.5
35.6 26.3
35.3 31.5
35.4 33.3
37.3 25.4
0.70 1.06
Notes: *SEM, standard error of means; †NDF, Neutral detergent fibre; ‡ADF, Acid detergent fibre; #NFC, Nonfibre carbohydrates; +NDICP, Neutral detergent-insoluble crude protein; §ADICP, Acid detergent-insoluble crude protein.
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with these findings, Fathi Nasri et al. (2008) reported that roasting reduced also the NDF contents of whole soybean. Rolled flaxseed contained the lowest amounts of ADF and physical changes were evident. In contrast, Faldet et al. (1991) found similar NDF and ADF concentrations when raw whole soybeans were roasted at 165°C and then rolled. Furthermore, heat processing caused an increase of the NDICP and ADICP contents when compared to unheated flaxseed. In agreement with these findings, it has been reported already earlier that heat processing such as roasting (Hussein et al. 1995), extruding (Moshtaghi Nia and Ingalls 1992) and micronisation (Mustafa et al. 2002) increased the amounts of NDICP and ADICP.
3.2. In situ dry matter degradability and estimated parameters of degradability The estimated parameters of degradability, including soluble (a), insoluble potentially degradable (b) fractions, degradation rate (c) and in situ effective DM degradability (EDMD), are shown in Table 2. EDMD of unheated and extruded flaxseed was the lowest and highest, respectively (p < 0.05). The low EDMD of raw flaxseed could be explained by the hard pericarp surrounding the seed. As reported by Leeson and Caston (2004), the hull of flaxseed represents about 25% of the seed weight; it is largely composed of fibre and contains about 18.5% lignin, which is highly indigestible. This fibrous material keeps the integrity of raw flaxseed, which would prevent ruminal degradation and could explain the low in situ degradability of raw flaxseed observed in the present study. Heat processing markedly improved EDMD of flaxseed. It can be concluded that hard pericarp of the seed must be broken for better utilisation; therefore, heat and mechanical processing of flaxseed significantly enhanced the EDMD of flaxseed. In comparison with unheated flaxseed and all other treatments, extrusion caused the largest increase of EDMD and estimated degradation parameters with the exception of degradation rate. In agreement with our findings, also Mustafa et al. (2002) found that extrusion increased soluble, insoluble potentially degradable DM fraction and EDMD of flaxseed. All variations of roasting and microwave irradiation increased the EDMD also significantly compared to the unheated samples, but between these treatments rolling of roasted flaxseed was more effective than roasting, steep roasting and microwave irradiation (p < 0.05). The higher EDMD of rolled flaxseed might be due to the break of seed coat and the exposure of the internal material to rumen microorganisms. The present study Table 2. flaxseed.
Estimated degradation parameters and dry matter degradability of heat-processed Type of heat processing Steep Rolled Unheated Roasted roasted roasted
a† [g/kg DM] b‡ [g/kg DM] c# [%/h] EDMD§ [g/kg DM]
79.4d 188d 4.1a 186d
89.8c 288c 2.4b 218c
90.4c 295c 2.3b 221c
113.8b 413b 1.2c 237b
Rolled Microsteep wave roasted irradiated Extruded SEM* 119.7b 421ab 1.2c 238b
70.0e 399b 1.8bc 219c
326.1a 453a 3.6a 570a
12.9 14.6 0.17 19.3
Notes: *SEM, Standard error of the mean; †a, Rapidly degraded fraction, ‡b, Slowly degraded fraction; #c, Rate of degradation; §EDMD, in situ effective dry matter degradability with a passage rate of 0.03/h. a–d Means in the same row not sharing the same superscript are significantly different (p < 0.05).
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agrees with the results of Huard et al. (1998) who found that rolling of canola seeds increased the ruminally EDMD compared with whole canola seeds from 6.32% to 38.68%, respectively. In contrast to other treatments, the microwave irradiation of flaxseed decreased the soluble fraction significantly but increased EDMD in a similar way as steep roasting and rolled roasting. These results agreed with findings of Sadeghi and Shawrang (2007).
3.3. In situ crude protein degradability and estimated parameters Estimated parameters including soluble (a), insoluble potentially degradable (b) fractions, degradation rate (c) and in situ effective crude protein degradability (ECPD) are shown in Table 3. The soluble fraction was the highest in extruded flaxseed and lowest in microwave heated flaxseed (p < 0.05). Extrusion of flaxseed increased the ECPD more effectively as other heat treatments (p < 0.05). It has been suggested that extrusion caused the break of fat micelles and disrupt the protein matrix of the flaxseed endosperm. This permits a more rapid degradation of nutrients by rumen microbes (Mustafa et al. 2003). Similar extrusion effects on the degradation of CP in the rumen have been reported previously (Mustafa et al. 2002). The ECPD for roasted and steep-roasted flaxseed was lower than unheated and extruded flaxseed. Similarly, McNiven et al. (1994) found that roasting results in denaturation of protein and probably transform the proteins to a more resistant structure to rumen degradability. Also, a reduction in ECPD due to steeping suggests that more heat was able to penetrate the flaxseed possibly rendering some proteins (albumins and globulins) more insoluble. Similar effects with steep-roasted soybean meals have been reported by Mosimanyana and Mowat (1992). Lower ECPD of rolled flaxseed as compared to unheated flaxseed indicated that after rolling of flaxseed, roasting could effectively reduce the rumen degradability. Microwave heating of flaxseed effectively decreased the soluble fraction and ECPD. These results are in agreement with those of Sadeghi and Shawrang (2007) who reported that microwave irradiation decreased the water-soluble fraction and ECPD. Reduction of soluble fraction and ECPD might be due to the cross-linking of chains and protein aggregation through heating. Microwave irradiation and roasting effectively reduced CP degradation rate as compared to unheated flaxseed (p < 0.05). The significant reduction in the CP degradation rate Table 3. Estimated degradation parameters and crude protein degradability of heat-processed flaxseed. Type of heat processing Steep Rolled Unheated Roasted roasted roasted a† [g/kg CP] b‡ [g/kg CP] c# [%/h] EDMD§ [g/kg CP]
91.5b 188.9b 7.0a 223b
81.8cd 174.0c 4.7bc 187e
75.8de 169.9c 5.5b 185ef
87.4bc 165.8c 7.8a 207c
Rolled steep roasted 90.5b 152.8d 8.0a 201d
Microwave irradiated Extruded SEM 69.7e 197.0b 4.1c 184f
194.2a 238.4a 4.0c 330a
6.24 4.18 0.27 7.49
Notes: *SEM, Standard error of the mean; †a, Rapidly degraded fraction, ‡b, Slowly degraded fraction, #c, Rate of degradation, §ECPD, Effective crude protein degradability with passage rate of 0.03/h [g/kg DM]. a–f Means in the same row not sharing the same superscript are significantly different (p < 0.05).
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of flaxseed by heat processing might increase bypass protein and therefore increase the amount of available amino acids in the small intestine. Also previous studies reported that heat processing such as roasting (Fathi Nasri et al. 2008), extruding (Kibelolaud et al. 1993) and micronisation (Mustafa et al. 2002) reduced the degradation rate of CP. The lower CP degradation rate of heat-processed flaxseed is likely a reflection of the increased levels of NDICP. Reduction in the ruminal degradation rate of CP would decrease ruminal NH3-N production and the cost of urea synthesis (Lashkari and Taghizadeh 2013).
3.4. Ruminal in situ and post-ruminal in vitro nutrient disappearance Ruminal in situ and post-ruminal in vitro disappearance of DM, OM, CP, EE, NDF and ADF of unheated and heat-processed flaxseed is shown in Table 4. The highest level of DM, OM, CP, EE, NDF and ADF disappearance after 12 h of in situ rumen incubation was observed for extruded flaxseed (p < 0.05). Extrusion of flaxseed increased the disappearance of DM, OM, CP, EE, NDF and ADF by 68, 72, 33, 55, 56 and 50%, respectively. The results are in agreement with the data obtained by Mustafa et al. (2003) who reported that extrusion of flaxseed increased the DM and CP disappearance after 12 h of rumen incubation. The lowest CP disappearance after 12 h of rumen incubation was
Table 4. Ruminal in situ, post-ruminal in vitro and approximation of total tract nutrient disappearance [%]. Type of heat processing Steep Rolled Unheated Roasted roasted roasted Ruminal† Dry matter Organic matter Crude protein Ether extract NDF # ADF§ Post-ruminal Dry matter Organic matter Crude protein Ether extract NDF ADF Total tract‡ Dry matter Organic matter Crude protein Ether extract NDF ADF
Rolled steep roasted
Microwave irradiated Extruded SEM*
14.9cd 13.1cd 19.1b 26.9d 13.5e 11.7e
15.7bc 13.1cd 15.7d 28.0c 15.4d 14.4c
15.6bc 12.8d 15.6d 27.7cd 16.0d 14.4c
16.7b 15.0b 18.6bc 31.1b 19.4b 16.2b
16.8b 14.4bc 18.4c 30.3b 19.4b 17.1b
14.1d 12.1d 14.9e 18.6e 17.7c 13.9c
48.8a 48.6a 28.7a 59.9a 30.1a 23.7a
1.82 1.93 0.69 1.72 0.81 0.59
51.2e 45.4d 41.1c 12.7d 11.9c 11.2c
57.6d 52.4b 56.5b 33.5c 15.4b 15.7b
58.8cd 52.2b 56.8b 36.1bc 15.1b 15.9b
61.6ab 63.2a 62.0a 43.3a 21.5a 18.7a
62.9a 62.9a 62.3a 46.4a 21.6a 18.9a
60.4bc 49.9c 57.4b 38.3b 15.3b 14.9b
41.8f 43.9d 55.6b 33.1e 17.9b 14.5b
1.09 1.13 1.08 1.63 0.64 0.44
66.2d 58.6d 60.3d 39.7e 25.5d 23.0d
73.3c 65.6c 72.3c 61.6c 30.8c 30.2c
74.5c 65.0c 72.5c 63.9c 31.1c 30.3c
78.4b 78.2b 80.6b 74.5b 40.9b 34.9b
79.7b 77.4b 80.7b 76.8b 41.0b 36.1b
74.6c 62.1c 72.3c 56.8d 33.1c 28.9c
90.6a 92.6a 84.4a 93.1a 48.0a 38.2a
0.52 0.32 0.63 2.48 1.38 0.22
Notes: *SEM, Standard error of the mean. †Determined after 12 h of ruminal incubation; #NDF, Neutral detergent fibre; §ADF, Acid detergent fibre; ‡Approximation of total tract disappearance based on in situ incubation and three-step in vitro technique. a–e Means in the same row not sharing the same superscript are different (p < 0.05).
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observed for roasted, steep-roasted and microwave-irradiated flaxseed. This suggests that these treatments change the internal constituents of flaxseed which increased their resistance to ruminal degradation. The EE disappearance after 12 h of rumen incubation of microwave-irradiated, as well as roasted and steep-roasted flaxseed was significantly lower than the other heat-processed flaxseeds (p < 0.05). These results demonstrated that also roasting of flaxseed is a suitable way to protect polyunsaturated fatty acids from microbial biohydrogenation and thus increase the concentration of polyunsaturated fatty acids in dairy products (Jones et al. 2001). The lowest and highest NDF and ADF disappearance after 12 h of rumen incubation were observed for unheated and extruded flaxseed, respectively (p < 0.05). These findings are in agreement with those of Mustafa et al. (2003) who stated that extrusion of flaxseed increased the NDF disappearance after 12 h of rumen incubation of flaxseed. Furthermore, rolling of roasted flaxseed effectively increased the NDF and ADF disappearance after 12 h of rumen incubation as compared to roasted and steep-roasted flaxseed (p < 0.05). The high NDF and ADF disappearance of rolled flaxseed might be due to break of the seed coat. Post-ruminal in vitro CP disappearance was the highest for rolled-roasted and rolled steep-roasted flaxseed; intermediate for roasted, steep-roasted, extruded and microwaveirradiated flaxseed and lowest for unheated flaxseed (p < 0.05). Higher post-ruminal in vitro CP disappearance after heat processing confirms the hypothesis that only primary Maillard products were formed and that there was no formation of intestinally indigestible terminal Maillard products (Von Keyserlingk et al. 2000). The highest post-ruminal in vitro CP, EE, NDF and ADF disappearance of rolled flaxseed might be due to associate effects of roasting and rolling. Significant difference between post-ruminal in vitro nutrient disappearance of roasted and rolled-roasted flaxseed showed that breaking the seed coat via roasting may be insufficient for effective digestion by ruminants. Wang et al. (1997) reported similar observations in a study comparing micronised and ground micronised canola seed. Post-ruminal in vitro CP disappearance of extruded flaxseed was higher than the untreated flaxseed. Post-ruminal in vitro CP disappearance of roasted and steeproasted flaxseed was higher than the unheated flaxseed. Similarly, Fathi Nasri et al. (2008) reported that post-ruminal CP disappearance of whole soybean was enhanced by roasting and steep roasting. Compared to unheated flaxseed, also microwave-heated flaxseed increased the post-ruminal in vitro CP disappearance (p < 0.05). It has been suggested that microwave irradiation may induce the unfolding of proteins and their denaturation. This would expose hydrophobic amino acids (especially aromatic amino acids), which allows an effective protein digestion by pepsin and trypsin (Murray et al. 2003). 3.5. Approximation of total tract nutrient disappearance Approximation of total tract nutrient disappearance of DM, OM, CP, EE, NDF and ADF of unheated and heat-processed flaxseed is shown in Table 4. The total tract disappearance of DM, OM, CP, EE, NDF and ADF of extruded flaxseed was the highest. This was expected because the highest ruminal in situ disappearance of extruded flaxseed caused this elevated total tract disappearance. A significant increase of total tract disappearance of DM, NDF and ADF was also observed after roasting, rolled roasting and microwave heating. 4. Conclusions All investigated heat treatments of flaxseed had significant effects on in situ and in vitro degradability of nutrients. Based upon the in situ studies, roasting and microwave
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irradiation would be expected to enhance the amount of protein escaping the rumen and to increase NDF and ADF degradability. Rolling of roasted flaxseed enhanced the respective effects. On the other hand, extrusion increased the rumen and total tract degradability of nutrients considerably and decreased the post-ruminal supply of nutrients from flaxseed. Therefore, different methods of heat processing can be used to modify the feed value of flaxseed for specific purposes.
Disclosure statement No potential conflict of interest was reported by the authors.
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