Ruminal degradability and intestinal digestibility
of protein and amino acids in barley and oats
expander-treated at various intensities
Egil Prestlùkken
*Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 AÊ s, Norway
Received 11 December 1998; received in revised form 23 August 1999; accepted 8 September 1999
Abstract
The objectives of the experiment were to study effects of pelleting or expander treatment at various intensities (mild, medium, hard or maximum) prior to pelleting at two temperatures in the mixer-conditioner (60 and 758C) on ruminal degradation and intestinal digestibility of protein and amino acids in barley and oats, using nylon bag methods. Temperatures achieved were 85±95, 100± 110 and 115±1258C at mild, medium and hard intensity, whereas maximum temperature achieved was 1258C for barley and 1408C for oats. Thus, temperatures higher than 130±1358C appeared unrealistic under commercial conditions.
Pelleting decreased ruminal degradation of protein, especially at high temperature in the mixer-conditioner. Expander treatment decreased ruminal degradation of protein further and the lowest effective protein degradability (EPD) achieved was 30% for barley and 29% for oats, both obtained at maximum temperature in the expander and high temperature in the mixer-conditioner. These values are low compared to previous results and need to be verified. No negative effects of treatment on digestibility of protein were observed. This indicates that the treatments shifted site of protein digestion from the rumen to the small intestine.
Expander treatment did not alter the contents of any individual amino acid either in barley or in oats. Expander treatment reduced ruminal degradation of total amino acids to the same extent as protein. The variation in ruminal degradation among amino acids was considerable. Thus, ruminal degradation of protein cannot be used for determination of ruminal degradation of all individual amino acids. Expander treatment did not increase the content of indigestible amino acids in barley or oats, indicating that amino acids were not heat-damaged.# 1999 Elsevier Science B.V. All rights reserved.
Keywords: Expander treatment; Nylon bags methods; Ruminants; Protein; Amino acids Animal Feed Science and Technology
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*Tel.:47-64-94-80-57; fax:47-64-94-79-60 E-mail address: ihfegp@ihf.nlh.no (E. Prestlùkken)
1. Introduction
Cereal grains, such as barley and oats, serve as an energy constituent in diets for ruminants. Although the content is low, protein from these grains constitutes a significant part of the dietary protein. However, the protein in barley and oats is extensively degraded in the rumen, resulting in a rather low protein value. Nylon bag studies have shown that expander treatment can protect protein in barley or oats against ruminal degradation (Weisbjerg et al., 1996; Lund, 1997; Prestlùkken, 1999) and thereby increasing their protein value by shifting the site of protein digestion from the rumen to the small intestine.
The major parameters affecting nutrients in thermo-mechanical processes as the expander treatment are temperature, moisture content, residence time and mechanical shear (Voragen et al., 1995). Of them, only the influence of temperature during the expansion process have been discussed earlier. Moreover, the effects of the expander treatment have not been properly verified under commercial processing conditions. In addition, steam is usually added in the mixer-conditioner located prior to the expander. To what extent the addition of steam in the mixer-conditioner influence effects of the expander process has not been studied previously.
Modern systems for protein evaluation in ruminants are moving in the direction of predicting the absorption of individual amino acids from the small intestine (Rulquin and VeÁriteÁ, 1993). Several studies (Susmel et al., 1989; Erasmus et al., 1994; O'Mara et al., 1997; van Straalen et al., 1997) indicate that ruminal degradability of amino acids are not similar to protein. Thus, knowledge to ruminal degradability of individual amino acids is required when protein value is to be expressed on the basis of individual amino acids. Excessive heat treatment may reduce the availability of certain amino acids. Lysine, in particular, is susceptible to heat treatment through the reaction with reducing sugars and the formation of Maillard products (Broderick et al., 1991). The determination of intestinal digestibility of individual amino acids is, therefore, of special importance in heat-treated feedstuffs.
The objectives of the experiment were (1) to study effects of pelleting or expander treatment at various intensities prior to pelleting at two temperatures in the mixer-conditioner on ruminal degradation and intestinal digestibility of protein, and (2) to study effects of the treatments on ruminal degradation and intestinal digestibility of individual amino acids in barley and oats.
2. Material and methods
2.1. Animals and diets
Three non-lactating dairy cows fitted with a flexible rumen cannulae (Bar Diamond, Parma, ID, USA; 100 mm i.d.) and a simple T-type PVC cannulae (20 mm i.d.) located in the duodenum 50±60 cm distal to pylorus (distal to the bile duct entrance), were used. At 06:00 and 15:00 hours, the cows were fed equal amounts of a standardised diet consisting of grass hay (4 kg per day; 120 g CP, 60 g ash, 25 g fat, 600 g neutral detergent fibre
(NDF), g kgÿ1
DM) and a concentrate mixture (1.8 kg per day; 175 g CP, 55 g ash, 50 g fat, 195 g NDF and 440 g starch plus sugar, g kgÿ1
DM). The cows were housed in tie-stalls in a metabolism unit. Animal care was conducted according to laws and regulations controlling experiments with live animals and the experiment was approved by the Norwegian Animal Research Authority.
2.2. Experimental feedstuffs and treatments
The experimental feedstuffs were barley and oats. The feedstuffs were ground on a horizontal shaft hammer mill and a sample was taken as an untreated control. Experimental samples were produced at 60 and 758C in the mixer-conditioner. After the mixer-conditioner, the feedstuffs were either subjected to traditional pelleting (75±808C) or heat treatment with a Kahl OE 23 Expander (A. Kahl GmbH, Reinbek, Germany) at various intensities (mild, medium, hard or maximum) prior to pelleting. In the samples only pelleted, the expander acted as a screw feeder from the mixer-conditioner to the pellet press. In the samples expander-treated prior to pelleting, treatment intensity was regulated by adjusting the hydraulic pressure on the conical-shaped resistor in the outlet of the expander, and at highest temperature stage in the mixer-conditioner, also through addition of steam in the expander. Monitored treatment conditions are listed in Table 1.
2.3. Nylon bag measurements
Ruminal degradation and intestinal digestibility measurements were carried out using nylon bag methods mainly as described by Madsen et al. (1995) and Prestlùkken (1999). In the mobile bag experiment, original feed and residues after 16 h rumen incubation were used. Except for 16 h residues for determination of intestinal digestibility, all residues were milled for 1 min at frequency 80 with the MM2000 Mixer Mill (RETCH GmbH & Co. KG, Haan, Germany).
2.4. Chemical analysis
The feedstuff samples were milled through a 1 mm screen before analysis. In all samples, nitrogen (Kjeldahl-N) and dry matter were determined as described by AOAC (1990). Within feedstuff, four samples were selected for additional chemical analysis. Ash and fat (acid hydrolysis with petroleum ether extraction) were determined using AOAC (1990) methods. Acid detergent fibre (ADF) and NDF were determined according to van Soest et al. (1991) using the ANKOM220 Fiber Analyzer (ANKOM Technol., Fairport, NY). Starch was analysed according to the method of McCleary et al. (1994) without correction for sugar. Amino acid analysis was performed according to Directive 98/64/EC (EEC, 1998), using acid hydrolysis. The amino acids were separated with ion-exchange chromatography and quantified by UV-detection at 570 nm (440 nm for proline) after post-column derivatisation with ninhydrin using the Biochrom 20 Amino Acid Analyser (Pharmacia Biotech, Cambridge, UK). Tyrosine was analysed in oxidised samples although oxidation reduces the content of tyrosine (Mason et al., 1980). Based on unpublished results from our laboratory, tyrosine was increased by 10% to compensate
Table 1
Processing conditions
Treatmenta Pelleted Mild Medium Hard Max Pelleted Mild Medium Hard Max
608C in mixer-conditioner 758C in mixer-conditioner
Barley, Sample No. 2 3 4 5 6 7 8 9 10 11
Capacity, expander (t, hÿ1) ± 2.0 2.0 2.0 2.0 ± 2.8 3.0 3.0 3.0
Pressure, expander (bar)b ± 15 25 42 42 ± 10 25 33 33
Temp., mixer (8C) 60 60 60 62 62 74 72 76 75 75
Temp., expander (8C) ± 80 95 116 125 ± 90 102 114 125
H2OFeed(%)c 14.4 14.4 14.4 14.5 14.5 15.4 16.4 16.9 16.9 16.9
Oats, Sample No. 13 14 15 16 17 18 19 20 21 22
Capacity, expander (t, hÿ1) ± 3.3 2.7 2.1 2.1 ± 2.6 2.9 2.8 2.7
Pressure, expander (bar)b ± 20 42 46 50 ± 10 33 45 50
Temp., mixer (8C) 59 63 62 59 60 74 76 75 74 75
Temp., expander (8C) ± 86 105 120 135 ± 92 108 126 140
H2OFeed(%)c 12.9 13.2 13.2 12.9 13.0 14.0 15.5 15.5 15.5 15.5
aOrdinary pelleting and expander treatment at mild, medium, hard or maximum treatment intensity. bHydraulic pressure required to keep the cone in position.
cCalculated water content in the feed samples based on 10.9 and 9.5% water in untreated barley and oats (Table 2), assuming a 0.7% increase in feed moisture
content for every 108C increase in temperature (A. Kahl, pers. commun.).
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for losses during oxidation. The content of serine, valine and isoleucine was increased by 6% for incomplete recovery after hydrolysis (Rudemo et al., 1980). Nitrogen in residues after ruminal and intestinal incubation was determined according to Dumas method (AOAC, 1990) using the EA 1108 Elemental Analyser (Fison Instruments S.p.A, Rudano Milan, Italy).
2.5. Calculations and statistical analysis
Amino acid protein (AA-protein) was calculated using water-corrected molecular weights. Ruminal degradation characteristics of CP were calculated as described by érskov and McDonald (1979) using the PROC NLIN procedure in the statistical analysis systems (SAS, 1990). Effective rumen degradability of protein (EPD) was calculated assuming a rumen outflow rate of 8% hÿ1
. Disappearance of amino acids from the rumen nylon bag was calculated on animal basis as the mean of disappearance after 8, 16 and 24 h incubation time. Digestibility of rumen undegraded protein (dUDP) was calculated according to Hvelplund et al. (1992). True indigestible residue of protein and amino acids after intestinal incubation was calculated as a percentage of intact feed. Increase in the moisture content of the feedstuffs during processing (H2OFeed) was calculated assuming
that 108C increase in temperature by the steam addition increased the water content with 0.7% units (A. Kahl GmbH, pers. commun.).
Analysis of variance (ANOVA) was performed with the GLM procedure in SAS (1990) with effect of treatment and cow in the model. Means were separated with the PDIFF statement. Means among treatments and among amino acids within treatment were separated with the Duncan multiple range comparison statement. The significance level wasP< 0.05 unless stated otherwise.
3. Results and discussion
3.1. Effect of treatment on chemical composition and amino acids
In general, the chemical composition of the feedstuff samples was within expected ranges (Table 2). The expander treatment did not appear to severely affect the composition of feedstuffs except for a tendency to reduced NDF and ADF content. Heat treatment increases the solubility of fibres (Shinnick et al., 1988; Vranjes and Wenk, 1995). Thus, the observed effect might be analytical rather than nutritional. Compared to the Danish amino acid table (Kristensen et al., 1996), the content of amino acid nitrogen in barley and oats was high (Table 3). However, the proportions of individual amino acids were within the expected range in all samples. Furthermore, the expander treatment did not influence the proportion of lysine or other essential amino acids relative to non-essential amino acids (Table 3). This indicates that amino acids, and lysin in particular, were not heat damaged as might expected (Broderick et al., 1991; Schwab, 1995; Voragen et al., 1995). However, the amino acid analysis may hydrolyse bonds that are not hydrolysed by intestinal enzymes (Dworschak, 1980; Mauron, 1990). If this happens, amino acid analysis will overestimated bioavailability of e.g., lysine.
Table 2
Chemical composition (g kgÿ1DM if not stated otherwise) and content of amino acid protein (AA-protein)ain
samples of barley and oats
Barley Oats
Sample No.
1 6 8 11 12 17 19 22
Treatmentsb Untreated 62/125 72/90 75/125 Untreated 60/135 76/92 75/140
DM (g kgÿ1) 891 930 910 905 905 924 910 912
Ash 27 26 27 26 32 29 29 29
Fat 26 19 26 23 41 39 44 43
NDF 196 173 195 172 308 271 279 245
ADF 49 43 40 46 136 114 115 100
Starch 578 585 589 585 478 523 490 495
CP 107 109 114 110 109 108 106 108
AA-proteina 95 92 100 96 89 88 90 87
aAA-protein calculated using water-corrected molecular weights.
bProcessing conditions: Untreated control and temperatures monitored in mixer-conditioner/expander (8C).
See also Table 1 for explanation.
Treatmentsb Control 62/125 72/90 75/125 SEMc Control 60/135 76/92 75/140 SEMc
Total AAN 83.3 78.5 84.7 82.2 1.58 80.3 80.0 82.5 79.9 1.25
Essential AA (EAA)
Phenylalanine 5.6 5.6 5.5 5.7 0.06 5.4 5.4 5.4 5.3 0.03
Threonine 3.7 3.7 3.8 3.6 0.10 3.8 3.9 3.9 3.9 0.08
Tyrosine 3.0 3.0 3.0 3.3 0.11 3.4 3.5 3.7 3.5 0.18
Valine 5.4 5.5 5.4 5.4 0.07 5.9 ab 5.8 abc 5.5 c 6.0 a 0.08 Sum EAA 42.3 42.4 42.2 42.4 0.15 45.5 45.6 45.3 45.7 0.14
Non essential AA (NEAA)
Alanine 4.3 4.3 4.3 4.4 0.07 5.2 5.0 4.8 5.3 0.14
Aspartic acid 6.2 6.2 6.4 6.1 0.13 8.4 8.3 8.3 8.2 0.15 Cystein 2.5 2.5 2.4 2.5 0.03 3.2 ab 3.1 b 3.3 a 3.2 ab 0.05 Glutamic acid 24.6 a 24.2 b 24.3 ab 24.2 ab 0.10 21.5 21.2 21.3 20.9 0.24 Glycine 4.2 b 4.4 a 4.4 a 4.4 a 0.03 5.4 5.4 5.2 5.4 0.11 Proline 11.3 11.5 11.3 11.3 0.07 5.5 c 6.3 ab 6.5 a 6.0 bc 0.11
Serine 4.6 4.7 4.8 4.6 0.13 5.2 5.3 5.3 5.3 0.09
Sum NEAA 57.7 57.6 57.8 57.6 0.15 54.5 54.4 54.7 54.3 0.14
aDifferent letters within grain type indicates statistical differences (p< 0.05). bSee Tables 1 and 2 for explanation.
cSEM: standard error mean.
3.2. Effect of treatment on ruminal degradation of protein
It is well known that unfolding and denaturation of proteins at moderate heat can increase digestibility of protein by making anti-nutritional proteins inactive. When heat is added, bonds that stabilise the three-dimensional structure of proteins will break. If hydrophobic groups are exposed, this will result in reduced solubility of proteins (Voragen et al., 1995), and consequently reduced ruminal degradation of protein. Consistent with Weisbjerg et al. (1996), Lund (1997) and Prestlùkken (1999), the expander treatment, and even ordinary pelleting, reduced EPD markedly in barley (Fig. 1) and oats (Fig. 2). Except for the ordinary pelleted samples, increased temperature in the mixer-conditioner had no effect on EPD. In fact, in oats, EPD tended to be lower at the low temperature in the mixer-conditioner (Fig. 2). This observation indicates that input of mechanical energy is the main factor determining the effect of the expander treatment. Thus, addition of thermal energy as steam probably plays a role only when input of mechanical energy is low. Expander treatment of barley beyond mild intensity had only a minor effect on EPD, whereas increased treatment intensity gradually decreased EPD in oats. These findings are in agreement with Prestlùkken (1999), and have also been shown for barley by Lund (1997). McNiven et al. (1995) and Prestlùkken (1999) have discussed mechanisms for the different response of barley and oats to heat treatments. Differences in morphologic configuration of the starch-protein matrix probably play an important role.
3.3. Effect of treatment on ruminal degradation of amino acids
Numerous publications exist on the effect of ruminal exposure on degradation of amino acids in feedstuffs for ruminants (Varvikko et al., 1983; Mir et al., 1984; Varvikko, 1986;
Fig. 1. Effective protein degradability (EPD) in untreated (Untr.), pelleted (Pell.) and different intensities of expander treatment of barley at two temperatures in the mixer-conditioner. Different letters indicate statistical differences between treatments (p< 0.05, MSE3.9).
Crooker et al. (1986, 1987); Susmel et al., 1989; Erasmus et al., 1994; Weisbjerg et al., 1996; Lund, 1997; O'Mara et al., 1997; van Straalen et al., 1997; Zebrowska et al., 1997) and rapeseed meal, soybean meal and fish meal seem to be the most commonly studied. Of the literature studied, only three references determined ruminal degradation of individual amino acids of barley or oats (Weisbjerg et al., 1996; Lund, 1997; Zebrowska et al., 1997), and only Weisbjerg et al. (1996) and Lund (1997) included heat-treated barley in the study.
Ruminal degradation of individual amino acids in the untreated and the expander-treated samples of barley and oats are shown in Figs. 3 and 4, respectively. In general, the expander treatment reduced ruminal degradation of total amino acids to the same extent as protein, indicating that ruminal degradation of protein can be used for the determination of ruminal degradation of total amino acids. However, among the individual amino acids there was considerable variation in ruminal degradation. Thus, ruminal degradation of protein or total amino acids cannot be used for determination of ruminal degradation of the individual amino acids. In the present experiment, arginine, glutamic acid, cysteine and, to some extent, histidine were degraded to a relatively high degree, whereas isoleucine, leucine, methionine, tyrosine, valine, and to some extent, phenylalanine and alanine were degraded to a relatively low degree. In general, these observations are in agreement with the literature referred earlier. However, considerable variation among studies, and among feedstuffs within study, make it difficult to make unambiguous conclusions on ruminal degradation of individual amino acids. Romagnolo et al. (1994) suggested that hydrophobicity of proteins might be associated with reduced degradability in the rumen. Although that study was on protein fractions, it is interesting to observe that hydrophobic amino acids as leucine, isoleucine, phenylalanine, methionine, valine, alanine and tyrosine, in the present study in general were degraded to a lower extent than more hydrophilic amino acids as histidine, arginine, lysine,
Fig. 2. Effective protein degradability (EPD) in untreated (Untr.), pelleted (Pell.) and different intensities of expander treatment of oats at two temperatures in the mixer-conditioner. Different letters indicate statistical differences between treatments (p< 0.05, MSE4.4).
Fig. 3. Ruminal degradation of protein (N), amino acids (AA), essential AA (EAA), none essential AA (NEAA) and individual amino acids in untreated and expander-treated barley. Within sample, mean value for AA is shown as a horizontal line. Different letters indicate significant differences (p< 0.05) among AA within treatment. MSEmean square error.
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Fig. 4. Ruminal degradation of protein (N), amino acids (AA), essential AA (EAA), none essential AA (NEAA) and individual amino acids in untreated and expander-treated oats. Within sample, mean value for AA is shown as a horizontal line. Different letters indicate significant differences (p< 0.05) among AA within treatment. MSEmean square error.
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cysteine, glutamic acid, glycine and serine (Figs. 3 and 4). Thus, their suggestion may be of some relevance for individual amino acids as well.
As mentioned earlier, heat treatment may create Maillard products. If Maillard products are formed, a reduced ruminal degradation of lysine might be expected. Lund (1997), studying barley and seven other feedstuffs, concluded that the expander treatment had no specific effect on ruminal degradation of lysine compared to total amino acids. In the present study, the expander treatment tended to reduce ruminal degradation of lysine relative to the mean for amino acids in barley (Fig. 3), whereas in oats, the opposite was observed with a tendency to increased degradation of lysine compared to the mean of amino acids (Fig. 4). Thus, treatment effects may vary among feedstuffs. However, the expander treatment tended to reduce ruminal degradation of total essential amino acids both in barley and in oats compared to total non-essential amino acids. If the decrease in ruminal degradation is not followed by reduced intestinal digestibility of essential amino acids, the expander treatment may improve the amino acid profile of escape protein.
3.4. Effect of treatment on intestinal digestion of protein
Hvelplund et al. (1992) proposed that feedstuffs contain a constant amount of indigestible protein and that intestinal digestibility of rumen undegraded protein can be calculated from nylon bag studies with intact feed. However, in barley, oats and several other feedstuffs, the hypothesis of a constant indigestible protein residue does not seems to be true (Volden and Harstad, 1995). Thus, digestibility of rumen undegraded protein should be calculated on the basis of residues pre-incubated in the rumen (Madsen et al., 1995). In the present experiment, indigestible protein was measured on intact feed and on residues pre-incubated in the rumen for 16 h. In agreement with Volden and Harstad (1995) and Prestlùkken (1999), rumen pre-incubation reduced indigestible protein, especially in barley (Table 4). Furthermore, for intact barley, the content of indigestible protein decreased in all expander-treated samples compared to the untreated. Since the indigestible content of protein in the untreated sample was in agreement with that determined by Volden and Harstad (1995), a positive effect of treatment on digestibility of protein in intact barley cannot be excluded. However, this was not confirmed in the study of Prestlùkken (1999). In oats, there was a tendency for treatment intensity to increase the content of indigestible protein. Prestlùkken (1999) also observed this. The increase was, however, marginal even at the highest treatment intensity. In fact, due to the considerable reduction in ruminal degradation of protein, the expander treatment increased digestibility of rumen undegraded protein, especially in oats (Table 4). Therefore, as described by Satter (1986), the expander treatment seems to maximise the amount of protein that can escape rumen degradation and still be digested in the intestine. However, as shown by McNiven et al. (1994), with oats roasted at 1688C, the risk for reducing digestibility of protein by heat treatment cannot be ignored.
3.5. Effect of treatment on intestinal digestion of amino acids
Although the mobile nylon bag experiment indicates that the expander treatment does not decrease intestinal digestibility of protein (Table 4), severe heat treatment may have
Table 4
Indigestible protein in intact feed (IF) and residues after 16 h rumen pre-incubation (IF16). Values in % of intact feed. Digestibility (%) of rumen undegraded proteina,b
(dUDP)
Treatmentsc Untr. Pell. Mild Medium Hard Max Pell. Mild Medium Hard Max MSEd
608C in mixer-conditioner 758C in mixer-conditioner
Barley, No. 1 2 3 4 5 6 7 8 9 10 11
IF 6.07 a 3.35 d 3.28 d 4.52 bcd 3.92 cd 4.31 bcd 4.72 abcd 4.15 bcd 4.10 bcd 4.93 abc 5.47 ab 0.59
IF16 1.73 1.97 1.81 2.08 2.22 1.98 1.92 2.07 2.07 2.29 2.08 0.11
dUDP 95.8 b 96.1 ab 97.2 a 96.8 ab 96.6 ab 97.2 a 96.5 ab 96.7 ab 97.0 ab 96.5 ab 97.0 a 0.38
Oats, No. 12 13 14 15 16 17 18 19 20 21 22
IF 2.42 b 2.92 ab 2.91 ab 2.87 ab 3.12 ab 2.98 ab 3.14 ab 2.79 ab 3.70 a 3.40 ab 3.79 a 0.30 IF16 1.88 cd 1.83 d 1.93 cd 2.07 abcd 2.18 abc 2.29 ab 1.87 d 1.96 cd 2.01 bcd 2.32 a 2.18 abc 0.03 dUDP 87.8 e 90.1 d 95.9 ab 96.9 a 96.8 a 96.7 a 93.8 c 95.4 b 96.7 a 96.5 a 96.8 a 0.30
aEstimated according to Hvelplund et al. (1992) using indigestible residues after 16 h rumen pre-incubation. bDifferent letters within row indicates statistical differences (p< 0.05).
cSee Table 1 for explanation. dMSE: mean square error.
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specific effects on certain amino acids (Broderick et al., 1991; Schwab, 1995; Voragen et al., 1995). In agreement with Lund (1997), the results presented do not indicate that heat treatment with an expander decreased the content of digestible lysine or any other amino acid. However, the indigestible residues among amino acids varied considerably and among the essential amino acids, lysine was one with a relatively high indigestible residue (Table 5). Consequently, digestibility of lysine probably was low compared to most other amino acids. A relative low digestibility of lysine was also observed by Weisbjerg et al. (1996), studying 15 feedstuffs. However, as shown in Table 5, indigestible residues were in general low. Thus, in practice, digestibility of dietary amino acids was high both in untreated and treated barley and oats.
3.6. Amino acid profiles of ruminal and intestinal residues
Intestinal incubation markedly reduced the content of amino acids nitrogen both in untreated and expander-treated barley (Table 6) and oats (Table 7). Reduced
Table 5
Indigestible protein and amino acids (AA) measured in residues after 16 h rumen pre-incubation. Values in % of intact feeda
Barley Oats
Sample No.
1 6 8 11 12 17 19 22
Treatmentsb Control 62/125 72/90 75/125 SEMc Control 60/135 76/92 75/140 SEMc
Protein 2.28 2.04 2.08 2.16 0.08 2.07 b 2.42 a 2.10 b 2.42 a 0.10 Amino acids 1.72 1.75 1.73 1.71 0.06 1.47 bc 1.57 ab 1.32 c 1.66 a 0.05
Essential AA (EAA)
Arginine 1.50 1.54 1.64 1.53 0.06 0.84 ab 0.91 ab 0.73 b 1.05 a 0.06 Histidine 1.59 1.67 1.65 1.62 0.05 1.66 bc 1.87 ab 1.60 c 1.92 a 0.07 Isoleucine 1.83 1.84 1.84 1.92 0.07 1.32 bc 1.65 ab 1.26 c 1.74 a 0.11 Leucine 1.83 1.86 1.88 1.81 0.07 1.65 ab 1.75 a 1.54 b 1.78 a 0.06 Lysine 2.03 1.90 2.09 2.03 0.09 1.70 ab 1.69 ab 1.52 b 1.86 a 0.09 Methionine 1.65 1.65 1.51 1.67 0.11 1.56 a 1.40 b 1.33 b 1.57 a 0.04 Phenylalanine 1.70 1.72 1.73 1.67 0.06 1.28 b 1.53 ab 1.32 b 1.69 a 0.08 Threonine 2.27 2.38 2.16 2.15 0.12 1.68 ab 1.53 b 1.50 b 1.88 a 0.10 Tyrosine 1.87 1.64 1.84 1.74 0.06 1.26 1.74 1.30 1.58 0.17 Valine 1.98 2.05 1.88 1.88 0.09 1.54 ab 1.70 a 1.49 b 1.80 a 0.07 Sum EAA 1.78 1.77 1.81 1.76 0.07 1.36 bc 1.43 ab 1.22 c 1.52 a 0.05
Non essential AA (NEAA)
Alanin 2.69 2.80 2.72 2.77 0.09 1.93 2.29 2.03 2.26 0.12 Aspartic acid 2.69 2.78 2.53 2.60 0.10 1.51 bc 1.70 ab 1.39 c 1.78 a 0.07 Cystein 2.01 1.83 1.95 1.91 0.07 1.55 b 1.96 a 1.57 b 2.07 a 0.10 Glutamic acid 0.75 0.82 0.80 0.77 0.03 0.86 ab 0.97 a 0.78 b 1.07 a 0.04 Glysin 3.03 3.04 2.88 3.00 0.09 2.40 ab 2.58 a 2.26 b 2.61 a 0.07 Prolin 1.14 1.15 1.12 1.11 0.04 1.99 a 1.95 a 1.44 b 2.11 a 0.12 Serin 2.09 2.18 2.19 2.08 0.08 2.06 a 1.90 ab 1.50 b 1.82 ab 0.13 Sum NEAA 1.65 1.71 1.65 1.66 0.06 1.62 ab 1.73 ab 1.43 b 1.80 a 0.05
aDifferent letters within grain type indicates statistical differences (p< 0.05). bSee Tables 1 and 2 for explanation.
cSEM: standard error mean.
Table 6
Amino acid N (g AAN 100 gÿ1N), amino acid profile (g AA 100 gÿ1AA) of intact feed (IF), residues after washing in machine (W), residues after 16 h rumen
incubation (R) and residues after intestinal incubation of 16 h rumen residues (I) in untreated and expander-treated barleya
SEM Contrasts
Untreated barley Expander-treated barley Untreated vs. expanded
IF W R I IF W R I IF W R I
Aamino acid N 83.6 a 81.6 a 78.2 a 62.9 b 78.8 a 79.8 a 81.7 a 68.0 b 2.46 n.s. n.s. n.s. n.s.
Essential AA (EAA)
Arginine 5.4 a 5.2 a 4.5 c 4.9 b 5.4 a 5.3 a 5.3 a 4.9 b 0.05 n.s. n.s. 0.01 n.s.
Histidine 2.5 a 2.4 a 2.2 b 2.4 a 2.5 2.5 2.5 2.5 0.06 n.s. n.s. 0.01 n.s.
Isoleucine 4.0 c 4.0 c 4.8 a 4.5 b 4.0 b 4.1 b 4.3 a 4.4 a 0.05 n.s. n.s. 0.01 n.s.
Leucine 7.3 bc 7.1 c 7.6 b 8.2 a 7.3 b 7.1 b 7.9 a 8.1 a 0.11 n.s. n.s. n.s. n.s.
Lysine 3.9 bc 3.6 c 4.0 b 4.9 a 3.8 b 3.9 b 3.8 b 4.4 a 0.14 n.s. n.s. n.s. 0.02
Methionine 1.8 1.7 1.8 1.8 1.8 1.8 1.9 1.8 0.09 n.s. n.s. n.s. n.s.
Phenylalanine 5.7 b 5.7 b 6.1 a 5.9 ab 5.6 5.6 5.6 5.8 0.09 n.s. n.s. 0.01 n.s.
Threonine 3.7 b 3.5 b 3.7 b 5.1 a 3.7 b 3.7 b 3.7 b 5.1 a 0.10 n.s. n.s. n.s. n.s. Tyrosine 3.0 abc 2.9 bc 3.5 a 3.3 ab 3.0 b 3.4 ab 3.6 a 3.3 ab 0.15 n.s. 0.02 n.s. n.s.
Valine 5.4 b 5.3 b 5.4 b 6.5 a 5.5 c 5.6 bc 5.9 b 6.6 a 0.1 3 n.s. n.s. 0.03 n.s.
Sum EAA 42.6 b 41.4 c 43.5 b 47.5 a 42.6 c 42.9 c 44.5 b 47.0 a 0.36 n.s. 0.01 0.08 n.s.
Non essential AA (NEAA)
Alanine 4.2 b 4.1 b 4.4 b 7.0 a 4.2 c 4.4 bc 4.6 b 7.0 a 0.10 n.s. 0.06 0.10 n.s.
Aspartic acid 6.0 b 5.5 c 6.4 b 10.1 a 6.2 b 5.6 c 6.4 b 10.1 a 0.18 n.s. 0.09 n.s. n.s.
Cysteine 2.5 b 2.2 c 1.7 d 2.9 a 2.4 b 2.3 b 2.2 c 2.7 a 0.04 n.s. 0.05 0.01 0.01
Glutamic acid 24.6 b 25.8 a 24.7 b 11.2 c 24.2 a 23.9 ab 22.9 b 11.7 c 0.33 n.s. 0.01 0.01 n.s.
Glycine 4.2 b 4.1 b 3.6 c 7.7 a 4.3 b 4.3 b 4.1 b 7.8 a 0.09 n.s. n.s. 0.01 n.s.
Proline 11.2 b 12.5 a 11.4 b 7.7 c 11.4 a 11.7 a 10.5 b 7.7 c 0.22 n.s. 0.02 0.01 n.s.
Serine 4.6 b 4.5 bc 4.3 bc 5.9 a 4.7 b 4.7 b 4.8 b 6.1 a 0.10 n.s. n.s. 0.01 n.s.
Sum NEAA 57.4 b 58.6 a 56.4 b 52.5 c 57.4 a 57.2 a 55.5 b 53.0 c 0.36 n.s. 0.01 0.08 n.s.
aDifferent letters within treatment indicates statistical differences (p< 0.05). Significance level in contrastsP< 0.10. SEM: standard error mean; n.s.: indicates not
significant.
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Table 7
Amino acid N (g AAN 100 gÿ1N), amino acid profile (g AA 100 gÿ1AA) of intact feed (IF), residues after washing in machine (W), residues after 16 h rumen
incubation (R) and residues after intestinal incubation of 16 h rumen residues (I) in untreated and expander-treated oatsa
SEM Contrasts
Untreated oats Expander-treated oats Untreated vs. expanded
IF W R I IF W R I IF W R I
Amino acid N 80.3 a 78.5 a 71.4 b 57.4 c 80.0 a 79.7 a 75.0 b 52.5 c 2.10 n.s. n.s. 0.08 0.09
Essential AA (EAA)
Arginine 7.1 a 7.5 a 6.1 b 3.9 c 7.2 a 6.9 a 7.0 a 4.2 b 0.26 n.s. n.s. 0.01 n.s.
Histidine 2.4 bc 2.5 b 2.3 c 2.9 a 2.5 b 2.5 b 2.5 b 2.8 a 0.08 n.s. n.s. 0.02 n.s. Isoleucine 4.1 b 4.4 b 5.1 a 4.0 b 4.0 b 4.3 ab 4.4 a 4.3 a 0.10 n.s. n.s. 0.01 0.04
Leucine 7.6 b 7.7 b 8.2 a 8.2 a 7.5 b 7.5 b 8.1 a 8.2 a 0.16 n.s. n.s. n.s. n.s.
Lysine 4.1 b 4.1 b 5.2 a 5.0 a 4.1 4.4 3.9 4.3 0.17 n.s. n.s. 0.01 0.01
Methionine 1.7 b 1.8 b 2.1 a 1.6 c 1.8 b 1.9 ab 1.9 a 1.5 c 0.04 n.s. 0.08 0.01 n.s. Phenylalanine 5.4 ab 5.6 a 5.7 a 5.2 b 5.4 b 5.3 b 5.7 a 5.4 b 0.08 n.s. 0.04 n.s. 0.06
Threonine 3.8 b 3.8 b 4.7 a 4.6 a 3.9 4.0 3.9 4.2 0.19 n.s. n.s. 0.01 0.09
Tyrosine 3.4 a 3.3 a 2.8 b 3.3 a 3.5 3.7 3.7 3.5 0.13 n.s. n.s. 0.01 n.s.
Valine 5.9 c 6.5 ab 6.7 a 6.2 bc 5.8 b 6.1 ab 6.3 a 6.4 a 0.19 n.s. n.s. 0.03 n.s. Sum EAA 45.5 c 47.2 b 49.3 a 44.8 c 45.6 bc 46.6 ab 47.4 a 44.7 c 0.38 n.s. n.s. 0.01 n.s.
Non essential AA (NEAA)
Alanine 5.2 c 5.1 c 6.3 b 7.0 a 5.0 b 5.2 b 5.2 b 7.3 a 0.16 n.s. n.s. 0.01 n.s.
Aspartic acid 8.4 c 8.0 c 9.8 a 9.1 b 8.3 b 8.2 b 8.1 b 8.9 a 0.21 n.s. n.s. 0.01 n.s.
Cystein 3.2 a 2.5 b 1.9 c 3.4 a 3.1 b 3.0 b 2.4 c 3.5 a 0.06 n.s. 0.01 0.01 n.s.
Glutamic acid 21.5 a 21.6 a 16.7 b 12.4 c 21.2 a 20.4 a 21.4 a 13.1 b 0.45 n.s. n.s. 0.01 n.s.
Glycine 5.4 bc 5.2 c 5.6b 8.7 a 5.4 b 5.3 b 4.8 c 8.7 a 0.14 n.s. n.s. 0.01 n.s.
Proline 5.5 b 5.5 b 5.3 b 7.6 a 6.3 b 6.1 b 5.9 b 7.7 a 0.13 0.01 0.02 0.01 n.s.
Serine 5.2 b 5.0 b 5.2 b 7.0 a 5.3 b 5.3 b 4.9 b 6.2 a 0.34 n.s. n.s. n.s. 0.06
Sum NEAA 54.5 a 52.8 b 50.8 c 55.2 a 54.4 ab 53.4 bc 52.6 c 55.3 a 0.38 n.s. n.s. 0.01 n.s.
aDifferent letters within treatment indicates statistical differences (p< 0.05). Significance level in contrastsP< 0.10. SEM: standard error mean; n.s. indicate not
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157±175
concentration of amino acids shows that digestibility of amino acids was high relative to other nitrogen components. The amino acid profile after intestinal incubation differed to a great extent from the profile of the intact feed as well as the residues after washing and ruminal incubation. This observation confirm that digestibility varied among individual amino acids. No major differences between the amino acid profile of residues after intestinal incubation of untreated and expander-treated samples was found, supporting the statement that expander treatment does not decrease digestibility of specific individual amino acids.
To obtain true ruminal degradation of protein and amino acids, correction for microbial contamination of nylon bag residues are recommend (Varvikko, 1986; Nocek, 1988; Erasmus et al., 1994). Since amino acid profile of the rumen microbes differs from that of barley and oats, severe microbial contamination would alter amino acid profile of the rumen nylon bag residues. Thus, differences in amino acid profile between intact feed and the rumen nylon bag residues might be explained by microbial contamination. However, except for untreated oats, ruminal incubation did not increase the relative proportion of e.g., lysine compared to intact feed. The concentration of lysine in protein from particle adherent bacteria is almost twice the concentration found in protein from barley and oats. Erasmus et al. (1994), washing the nylon bags for 10 min in a washing machine, found on average only 3.9% microbial contamination in residues after 16 h rumen incubation for 12 feedstuffs. In the present study, the bags were washed for 10 min three times in a washing machine. Thus, microbial contamination was probably not severe in the present study either. Consequently, the difference in amino acid profile between intact feed and nylon bag residues most likely was attributed to different ruminal degradation among dietary amino acids. Moreover, the similarity in amino acid profile between intact feed and residues after ruminal incubation was greater for expander-treated samples than for untreated samples. This shows that dietary protein was protected from being degraded in the rumen, confirming that increased rumen escape of dietary amino acids can be expected when expander-treating barley and oats.
3.7. Processing conditions
In a previous experiment conducted at the A. Kahl pilot plant, the expander temperatures ranged from 1308C at mild to 1708C at hard treatment intensity (Prestlùkken, 1999). In the present experiment conducted at a commercial production plant, the expander temperatures ranged from 85±95, 100±110 and 115±1258C at mild, medium and hard treatment intensity, respectively (Table 1). The maximum temperature achieved was 1258C for barley and 1408C for oats. However, increasing the temperature above 1208C was dependent on the skill of the operator. In addition, to achieve these high temperatures, the expander must be well maintained with low mechanical wear. Therefore, in agreement with the experience of the Norwegian compound feed industry, which has used expanders for many years, processing temperatures above 130±1358C usually are unrealistic under commercial conditions.
With 108C as a start temperature, the addition of steam increased the temperature by about 50 and 658C at low and high temperature in the mixer-conditioner, respectively. This accounted for a 3.5 and 4.5% increase of water in the feed material. Thus, at the low
temperature in the mixer-conditioner, the water content was around 14.5% in barley and 13.0% in oats during the expander processing (Table 1). The increase in temperature caused by the addition of steam in the expander was not monitored. Assuming that the temperature increased from 75 to 958C, 1.4% water was added in the expander as steam. Consequently, content of water in the feed material were around 2.5% units higher during the expander treatment at the high compared to the low temperature in the mixer-conditioner. Since the presence of water is important in hydrothermal reactions (Voragen et al., 1995), increased water content was expected to increase the treatment effects of the expander process. However, this seemed not to be the case in the present study. Moreover, with respect to the parameters studied, shifting the administration of energy in the expander process from mainly mechanical energy at low temperature in the mixer-conditioner to more hydrothermal energy at high temperature in the mixer mixer-conditioner, seemed not to be crucial for the treatment effects. The through-put of the expander increased from around 2.0 tonnes hÿ1
at the low temperature to around 3.0 tonnes hÿ1
at the high temperature in the mixer-conditioner, indicating that the water content of the feed material is important for the through-put of the expander. However, increased through-put resulted in decreased residence time, which again affects time dependent reactions. Thus, the effects caused by reduced residence time may confound the expected increase in treatment effects caused by addition of water. Nevertheless, the results confirm that expander treatment is an excellent method to alter the site and extent of digestion of protein and amino acids in ruminants. It must, however, be emphasised that the values observed for EPD at the medium, hard and maximum treatment intensities are lower than previous results (Prestlùkken, 1999). The values need to be verified in additional experiments before implementing the results in commercial feed production.
4. Conclusions
Expander treatment and even ordinary pelleting reduced ruminal degradation of protein in barley and oats considerably. In general, the treatments reduced ruminal degradation of total amino acids to the same extent as protein, indicating that ruminal degradation of protein can be used for the determination of total amino acid degradation. However, among the individual amino acids there was considerable variation in ruminal degradation. Thus, ruminal degradation of protein cannot be used for determination of ruminal degradation of all of the individual amino acids. Expander treatments did not increase the indigestible residue of protein or individual amino acids. Thus, the risk that expander treatment thereby reduces digestibility of protein or amino acids seems to be slight in practice. Consequently, the treatments seemed to shift site of protein and amino acid digestion from the rumen to the intestine. The observed values for EPD in expander-treated samples were low and need to be verified in additional experiments. Expander processing at temperatures above 130±1358C is probably unrealistic under commercial conditions.
Acknowledgements
The author gratefully acknowledges the staff at Eiker Mùlle Inc., Hokksund, Norway, for production of experimental feedstuff samples, O.M. Harstad and H. Volden for taking
part in the planning of the experiment, K. Hove for surgery of animals, M. Bratberg, M. Henne and R. évstegaÊrd for assistance in nylon bag experiments and care-taking of animals, L.T. Mydland and W. Eckhardt for help with the amino acid analysis, and, finally, N.P. Kjos and M.A. McNiven for critical review of the manuscript. The research was financed by the Norwegian Research Council, Statkorn AS, Denofa AS, Felleskjùpet FoÃrutvikling, Stormùllen AS, Norkorn and the Department of Animal Science, NLH.
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