In situ ruminal degradation and intestinal digestibility of dry matter and protein in expanded feedstuffs

Animal Feed Science and Technology 77 (1999) 1±23

In situ ruminal degradation and intestinal digestibility of dry matter and protein in expanded feedstuffs Egil Prestlùkken* Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 As, Norway Received 3 March 1998; accepted 19 August 1998

Abstract Barley, oats, soybean meal (SBM), rapeseed meal (RSM), a cereal mixture containing barley, oats, SBM and RSM (40 : 40 : 10 : 10) and a protein mixture containing barley, oats, SBM and RSM (10 : 10 : 40 : 40), were expanded (Kahl-expander) at three treatment intensities; mild (1308C), medium (1558C), and high (1708C). Ruminal degradation of dry matter (DM) and protein, and intestinal digestibility of protein was measured with nylon bag methods (in situ). In addition, particle loss of protein associated with washing of the nylon bags, and aspects concerning the assessment of protein value of individual feedstuffs for feed mixtures, were studied. The expander treatment tended to reduce effective DM degradability (EDMD) in barley, oats, SBM and the cereal mixture, but not in RSM and the protein mixture. The expander treatment considerably reduced effective protein degradability (EPD) in barley, oats, SBM, the cereal mixture and to some extent in the protein mixture. In RSM, expander treatment reduced EPD only at high treatment intensity. The intestinal digestibility of protein was not reduced by the expander treatment in any of the feedstuffs. The expander treatment will therefore shift the site of protein digestion from the rumen to the small intestine. The particle loss of protein was high in barley and oats, but was reduced by the expander treatment, especially in oats. In SBM and RSM, expander treatment tended to increase the particle loss. Except for oats, correction for the particle loss did not reduce the effect of the expander treatment on EPD. In the mixtures, EPD predicted from individual feedstuffs was higher than measured EPD, but predicted reduction in EPD from individual feedstuffs by the expander treatment was in agreement with the measured values. Differences in EPD between expandertreated feed mixtures, and corresponding mixtures of feedstuffs expanded individually, were small. This result indicates that feed mixtures can be expanded as a whole and that there is no need for expanding each ingredient separately. # 1999 Elsevier Science B.V. Keywords: Ruminants; Nylon bags; Expander; Nitrogen; Ruminal degradation; Intestinal digestibility

* Tel.: +47-6494-8057; fax: +47-6494-7960; e-mail: [email protected] 0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved PII: S 0 3 7 7 - 8 4 0 1 ( 9 8 ) 0 0 2 4 6 - 6

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1. Introduction In ruminants, the protein value of a feedstuff is determined by the amount of amino acids from microbial protein and rumen undegraded dietary protein (UDP) absorbed in the small intestine. The requirement of UDP increases with the production level of the animal. The fact that processing can increase the amount of UDP in proteinaceous feedstuffs is well documented (Kaufmann and LuÈpping, 1982; Satter, 1986; Broderick et al., 1991; Schwab, 1995). However, excessive processing can reduce the protein value by making the protein indigestible in the small intestine (Hvelplund, 1985; Stern et al., 1985; Broderick et al., 1991). Therefore, intestinal digestibility should always be determined in processed feedstuffs. Methods for determining intestinal digestibility have recently been reviewed by Stern et al. (1997). In many parts of the world, cereal grain is an important ingredient in diets for ruminants and serves mainly as an energy component, with starch as an excellent nutrient for synthesis of microbial protein in the rumen. The effect of processing cereal grains has been reviewed by several authors (Hale, 1973; érskov, 1976, 1979, 1986; Theurer, 1986; Campling, 1991; Mathison, 1996). Emphasis has generally been on studying how processing affects the utilisation of starch. In contrast, the effect of processing on the utilisation of protein in cereal grains has received limited attention. In diets high in cereal grains, a significant amount of the dietary feed protein is of cereal grain origin. Therefore, in such diets, increased protein value of cereal grains is of interest. Since its introduction in the late 1980s (Pipa and Frank, 1989), the annular gap expander has achieved a remarkable acceptance by the compound feed industry throughout the world. However, surprisingly limited information regarding the effect of expander treatments on the nutritive value of feedstuffs exists. The main purpose of this study was to focus on the effect the expander treatment has on ruminal degradation and intestinal digestibility of protein, and to determine if the expander treatment is a suitable method for improving the protein value of some commonly used feedstuffs for ruminants. In several feedstuffs, the losses of fine particles through the pores associated with washing of the nylon bags, are considerable (Weisbjerg et al., 1990; Dewhurst et al., 1995). These particles are considered to be immediately degraded in the rumen. However, if the particles lost from the nylon bags are degraded at the same rate as the particles left in the bags, losses of particles in the washing of the nylon bags will lead to an overestimation of ruminal degradation (Weisbjerg et al., 1990). In the formulation of feed mixtures, it is assumed that each individual feedstuff makes an additive contribution to the nutritive value. Interactions (positive or negative) between individual feedstuffs resulting from the exposure of a feedstuff mixture to a particular treatment are usually neglected, if ever studied. Therefore, the present experiment was designed to assess how the expander treatment affected the protein value of individual feedstuffs as well as the feed mixtures. 2. Materials and methods 2.1. Animals and feeding Three non-lactating dairy cows fitted with a flexible rumen cannula (Bar Diamond, Parma, ID, 100 mm i.d.) and a simple T-type PVC cannula (20 mm i.d.) located in the

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duodenum 50±60 cm distal to pylorus, were used. At 08:00 and 15:00 hours the cows were fed with the same amount of a standardised diet consisting of grass hay (4 kg dayÿ1; ca. 100 g CP, 60 g ash, 25 g fat and 625 g neutral detergent fibre (NDF), g kg DMÿ1), and a concentrate mixture (1.8 kg dayÿ1; ca. 150 g CP, 60 g ash, 50 g fat, 210 g NDF and 450 g starch plus sugar, g kg DMÿ1). 2.2. Experimental feedstuffs Two cereal grains, that is, barley and oats; two protein feedstuffs, that is, solventextracted soybean meal (SBM) and solvent-extracted rapeseed meal (RSM); and two feedstuff mixtures, that is, one cereal mixture containing barley, oats, SBM and RSM (40 : 40 : 10 : 10) and one protein mixture containing barley, oats, SBM and RSM (10 : 10 : 40 : 40), were used in the experiment (contents on as is basis). 2.3. Treatments Each of the experimental feedstuffs and the feed mixtures was expanded at three treatment intensities with the annular gap expander at Kahl's pilot plant in Reinbek, Germany. The annular gap expander can be considered as a simplified single screw extruder and is classified among the high-temperature-short-time (HTST) processes. The main factors determining the treatment effects are temperature, moisture content, shear forces, pH and residence time (Voragen et al., 1995). In the present experiment, only temperature (8C) at the outlet of the expander and hydraulic pressure (bar; 1 bar ˆ 105 Pa) required to keep a conical shaped piston head at the outlet of the expander in position, were monitored. The temperature sensor was located in the metal jacket of the expander. The monitored temperature thereby represents the temperature of the heated metal rather than that of the feedstuff. At mild, medium and hard treatments the temperature was maintained around 1308C, 1558C, and 1708C, respectively. For each feedstuff, an untreated sample was kept as a control. All expanded samples were formed into 10 mm pellets in a flat-die pellet mill located just at the outlet of the expander. After pelleting, the feed material was immediately transported to a belt cooler where it was allowed to cool and dry for approximately 15 min. The feedstuff samples were taken from the end of the cooler belt. After air stabilisation, the samples were sealed in plastic bags and stored at 48C until analysis. 2.4. Nylon bag experiments The in sacco procedure for measuring rumen degradation and the mobile bag procedure for measuring intestinal digestibility were as described by Madsen et al. (1995). Three cows were used for determination of ruminal degradation, whereas two cows were used for the determination of intestinal digestibility. All feedstuffs were milled through a 1.6 mm screen. In the in sacco experiment, 2 g of feed material was placed in 6  12 cm2 polyester bags (ZBF, AG, CH-8803, RuÈschlicon, Switzerland) with a pore size of 36 mm. Bags in 4, 3, 3, 4, 4, 6 and 8 replicates were incubated in the rumen for 0, 2, 4, 8, 16, 24 and 48 h,

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respectively. Except for the 16 h bags, which were placed at 16:00 hours, all bags were placed in the rumen at 08:00 hours. After removal from the rumen, the bags were immediately rinsed in cold tap water, washed for 10 min three times and spun in a domestic washing machine. The zero-hour bags were washed in the washing machine only. The bags were dried at 458C for 48 h, and then weighed, whereupon the residues of replicates were pooled within incubation time and animal. The residues were stored at room temperature in air-tight glass jars before determination of nitrogen (N). In the mobile bag experiment, duplicates of 1 g of the original feed or 1 g of residues after 0, 2, 8 24 and 48 h rumen incubation were placed in 6  6 cm2 polyester bags (ZBF, AG, CH-8803, RuÈschlicon, Switzerland) with a pore size of 11 mm. All bags were heatsealed and pre-incubated in 1 l of 1 M HCl (pH 2.4) under continuous stirring for 1 h, and in 2 l of 1 M HCl (pH 2.4) and pepsin (Sigma P7000, 100 mg lÿ1) in a shaking water bath at 388C for 2 h. In total, 24 bags per day were introduced into the intestine via the duodenal cannulae at a rate of four bags every 15 min, starting at 12:00 hours. The bags were recovered from faeces at 08:00 hours and 12:00 hours the following morning and washed in cold tap water in a sieve bucket for 2 h before drying at 458C for 48 h. The bags were weighed and pooled within incubation time and animal. The residues were stored at room temperature in air-tight plastic tubes before determination of N. 2.5. Determination of particle losses from rumen nylon bags The procedure for determining particle losses from rumen nylon bags was derived from Weisbjerg et al. (1990). One gram of feed material was weighed in duplicate into 90 ml centrifugation tubes whereupon 20 ml distilled water was added. The tubes were incubated for 1 h at room temperature with manual stirring every 15 min. After incubation, the feed material was washed with 4  20 ml distilled water through a nitrogen-free filter paper (5891 black ribbon, Schleicher and Schuell) under vacuum. The feedstuff residues remaining on the filter paper were dried at 458C for 48 h and weighed before the determination of N. 2.6. Assessing protein value of individual feedstuffs for feed mixtures Estimated values for ruminal degradation of protein in the feed mixtures were based on the content of protein determined in the individual ingredients, their inclusion ratio in the mixtures, and degradation of protein measured in situ. These values were compared with those actually obtained for the feed mixtures in the nylon bag experiment. In addition, to test for interactions, ruminal degradation of protein was measured in mixtures of feedstuffs that had been individually treated prior to mixing. 2.7. Chemical analysis The feedstuff samples were milled through a 1 mm screen and DM, ash, ether extracts (EE), Kjeldahl-N, crude fibre and nitrogen-free extracts (NFE) were determined according to the Weende method using standard procedures as described by AOAC (1980). Acid detergent fibre (ADF) and NDF were determined according to Goering and

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van Soest (1970), following a sequential analysis of hemicellulose, cellulose and lignin (with use of sodium sulphite without use of amylase). The method of McCleary et al. (1994) was used for determination of starch. No correction for sugar was carried out. Thus, the determined content of starch represents starch plus sugar. Residues from the nylon bags were analysed for Kjeldahl-N according to AOAC (1980). 2.8. Calculations Crude protein was calculated as N*6.25. Degradation values of DM and protein in the rumen were calculated as described by érskov and McDonald (1979) using the PROC NLIN procedure in the Statistical Analysis Systems (SAS, 1990). Data were fitted to the equation P ˆ A ‡ B(1 ÿ eÿCt), where P is degradation after t hours, A is the material immediately degraded (%), B is the material degraded over time (%), C is the fractional degradation rate of B (hÿ1) and t is time. Bounds in the PROC NLIN model were A ‡ B  100. Effective degradability values (ED) of DM (EDMD) and protein (EPD) in the rumen were calculated as ED ˆ A ‡ [(B*C)/C ‡ k)], assuming a rate of particulate outflow from the rumen (k) of 8% hÿ1 (Harstad, 1992). Assuming that feed particles lost from the nylon bags are degraded at the same rate as those remaining in the bag, rumen degradation was corrected for particle loss as described by Weisbjerg et al. (1990) using the equation K(ti) ˆ M(ti)ÿPL(1ÿ((M(ti)ÿ(PL ‡WSfilter))/ (1ÿ(PL ‡ WSfilter)))); where K(ti) is corrected degradation at time t, M(ti) is measured degradation at time t, PL is particle loss and WSfilter is the true water-soluble fraction measured with filter paper. Effective degradability of protein corrected for particle loss (EPDcorr), was calculated as described earlier assuming k ˆ5% hÿ1 (Madsen et al., 1995). Digestibility of protein was determined as the fraction of indigestible protein left in the nylon bags after intestinal incubation in percentage of total feed protein. Indigestible protein in residues after ruminal incubation was calculated in percent of total feed protein. 2.9. Statistical analysis Variance analyses were performed with the GLM procedure in the Statistical Analysis System (SAS, 1990) with treatment and cow included in the model. The Ryan±Einot± Gabriel±Welsch multiple F-test (REGWF) was conducted to separate means between treatments within feedstuffs (SAS, 1990). The significance level was P < 0.05 unless stated otherwise. 3. Results 3.1. Chemical composition Among the individual feedstuffs, total CP content varied between 133 g kgÿ1 DM (barley) and 450 g kgÿ1 DM (SBM), while the content of NDF varied between 179 (barley) and 314 g kgÿ1 DM (oats) (Table 1). The content of CP was 200 g kgÿ1 DM in

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Table 1 Chemical composition of feedstuffs and feed mixtures (g kgÿ1 DM) Material

DM

ASH

CP

EE

CF

NFE

NDF

Barley Oats Soybean meal Rapeseed meal Cereal mixturea Protein mixtureb

892 905 897 897 900 887

21 31 62 70 38 69

133 150 450 388 200 355

25 51 13 37 31 30

45 118 75 122 74 81

776 650 400 383 657 465

179 314 123 255 222 219

ADF 43 124 68 168 81 118

Starch 598 416 85 30 472 142

DM, dry matter (g kgÿ1); ASH, ash; CP, crude protein; EE, ether extracts; CF, crude fibre; NFE, nitrogen free extracts; ADF, acid detergent fibre; NDF, Neutral detergent fibre; Starch, starch plus sugar. a Cereal mixture; barley, oats, soybean meal and rapeseed meal in the ratio 40 : 40 : 10 : 10 (as is basis). b Protein mixture; barley, oats, soybean meal and rapeseed meal in ratio 10 : 10 : 40 : 40 (as is basis).

the cereal mixture and 355 g kgÿ1 DM in the protein mixture, while the content of NDF was close to 220 g kgÿ1 DM in both mixtures. The content of starch varied between 598 in barley and 30 g kgÿ1 DM in RSM. 3.2. Treatments The temperature measured at the outlet of the expander was maintained at about 1308C and 1558C for the mild and medium treatments, respectively (Table 2). The hydraulic pressure required to keep the conical shaped piston head in the outlet of the expander in position varied between 23 (barley) and 44 bar (SBM) for the mild treatment, and between 50 (oats, RSM and the protein mixture) and 80 bar (SBM) for the medium treatment. In the hard treatment, the temperature varied between 160 (barley) and 1908C (RSM), while the pressure varied between 94 (cereal mixture) and 120 bar (barley). 3.3. Effect of treatment on ruminal degradation of dry matter Effective rumen dry matter degradability and degradation characteristics are presented in Table 3. The expander treatment reduced EDMD by 5% units in barley, and no effect Table 2 Measured temperature (8C) and hydraulic pressureb (bar) Treatmentsa

Mild

Material

8C

Bar

8C

Bar

8C

Barley Oats Soybean meal Rapeseed meal Cereal mixturec Protein mixturec

128 131 129 132 130 128

23 35 44 40 33 32

155 158 155 155 155 157

60 50 80 50 51 50

160 169 173 190 163 172

a

Medium

Hard

Expander-treated (Kahl Expander), Kahl's pilot plant, Germany. Hydraulic pressure required to keep the cone in position, 1 bar ˆ 105 Pa. c See notes a and b of Table 1 for explanation. b

Bar 120 100 100 100 94 100

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of increasing treatment intensity above mild treatment was observed. In oats, mild treatment decreased EDMD by 3% units. In contrast to barley, increased treatment intensity gave an additional decrease in EDMD and at hard treatment, EDMD was reduced to 62%. In barley and oats, the immediately degraded DM fraction (A) decreased and the degradable DM fraction (B) increased, especially for the medium and hard treatments. The fractional degradation rate (c) was initially decreased by the mild treatment, but increased again for the medium and high treatments. Effective dry matter degradability decreased by 3, 9 and 5% units by expanding SBM at mild, medium and hard treatments, respectively. In RSM, expanding at mild or medium treatment increased EDMD by 2% units, whereas EDMD decreased by 2% units for the hard treatment. In the cereal mixture, EDMD was reduced from 73 to 66% for the hard treatment, whereas expanding the protein mixture had no effect on EDMD.

Table 3 In sacco rumen dry matter degradation characteristics Material

Barley

Oats

Soybean meal

Rapeseed meal

Cereal mixturec

Protein mixturec

Itema

A B C EDMD A B C EDMD A B C EDMD A B C EDMD A B C EDMD A B C EDMD

Untreated

36.6b 52.4c 0.401a 80.3a 56.8a 17.5c 0.219ab 69.2a 30.1a 69.7b 0.091a 66.7a 26.0b 60.9 0.091 58.2ab 38.2a 43.9b 0.299 72.8 30.4 58.4 0.114 64.4

Treatmentsb Mild

Medium

Hard

37.2a 51.5c 0.223c 75.0b 54.1a 25.8b 0.075b 66.4b 30.1a 69.9b 0.075ab 63.6b 28.4a 58.0 0.100 60.0a n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

26.4c 60.6b 0.312b 74.7b 47.1b 27.3b 0.142b 63.7c 28.5b 71.5a 0.058b 58.3c 29.3a 60.3 0.083 59.6a n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

24.8d 62.3a 0.304b 74.1b 32.4c 37.6a 0.319a 61.5d 30.4a 69.6b 0.067b 62.0b 26.2b 62.1 0.076 56.4b 32.5b 48.3a 0.187 66.2 33.6 55.1 0.103 64.4

Root MSE

P

0.19 0.53 0.0213 0.69 1.17 1.48 0.0548 0.79 0.58 0.59 0.0076 1.14 0.72 2.49 0.0080 0.87 0.10 0.16 0.0165 0.54 2.11 2.44 0.0022 0.85

0.001 0.001 0.001 0.001 0.001 0.001 0.008 0.001 0.024 0.022 0.009 0.001 0.003 0.326 0.059 0.009 0.011 0.023 0.093 0.052 0.366 0.406 0.121 0.968

a A, immediately degraded dry matter (%); B, dry matter degraded over time (%); C, fractional rate of degradation of B (hÿ1); EDMD, effective dry matter degradability (%) at passage rate (k) 8% hÿ1. b See Table 2 for explanation. c See notes a and b of Table 1 for explanation. d Means followed by different letters indicate statistical difference at P < 0.05. n.d. indicates not determined.

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Fig. 1. Degradation of protein as a function of rumen incubation time in expander-treated feedstuffs (See Table 2 for explanation of treatment intensities).

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3.4. Effect of treatment on ruminal degradation of protein In barley, oats and the cereal mixture, degradation of protein in the rumen was reduced by the expander treatment, especially for the shorter incubation times, and in the zerohour sample (Fig. 1). In oats, rumen degradation decreased with increasing treatment intensity, whereas in barley, treatment intensity beyond mild treatment had no effect on ruminal degradation of protein. In SBM, expander treatment reduced the ruminal degradation of protein in the 2, 4, 8, 16 and 24 h rumen incubation times, whereas no differences were found between treatments in the zero-hour sample or in the 48 h incubation. Rumen degradation of RSM and the protein mixture was only slightly affected by treatment intensity. In barley, the expander treatment reduced EPD by 15, 19 and 19% units in mild, medium and hard treatments, respectively (Table 4). This decrease in EPD was due to a reduction in the A fraction and the fractional degradation rate (c) of the B fraction. In oats, Table 4 In sacco rumen protein degradation characteristics Material

Barley

Oats

Soybean meal

Rapeseed meal

Cereal mixturec

Protein mixturec

Itema

A B C EPD A B C EPD A B C EPD A B C EPD A B C EPD A B C EPD

Untreated

30.1a 62.2c 0.167a 72.0a 69.0a 27.0d 0.289a 89.1a 18.2a 81.8b 0.098a 62.4a 20.1c 74.4ab 0.108ab 62.5a 28.0 69.1 0.115 68.6a 18.1 80.5 0.094 61.3a

Treatmentsb Mild

Medium

Hard

23.5b 75.1b 0.063b 56.6b 45.3b 51.8c 0.070b 68.6b 13.0b 87.0a 0.073b 54.2b 29.6a 66.1b 0.114a 66.4b n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

18.3c 81.0a 0.065b 53.0b 37.6c 61.8b 0.044b 59.4c 10.4b 89.6a 0.053b 45.8c 25.1b 72.7ab 0.084bc 61.8a n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

17.2c 81.7a 0.061b 53.4b 22.0d 78.0a 0.038b 46.9d 12.0b 88.0a 0.061b 49.6c 20.2c 78.2a 0.073c 57.2c 19.7 80.3 0.045 48.7b 17.5 80.5 0.080 57.5b

Root MSE

P

1.57 2.16 0.0118 2.38 2.16 2.49 0.0654 1.65 1.17 1.17 0.0098 1.84 1.26 3.43 0.0117 1.33 5.24 5.08 0.0222 0.22 2.42 1.64 0.0041 0.04

0.001 0.001 0.001 0.001 0.001 0.001 0.009 0.001 0.001 0.001 0.006 0.001 0.001 0.027 0.016 0.001 0.356 0.269 0.196 0.007 0.583 0.978 0.190 0.007

a A, immediately degraded protein (%); B, protein degraded over time (%); C, fractional rate of degradation of B (hÿ1); EPD, effective protein degradability (%) at rate of passage (k) 8% hÿ1. b See Table 2 for explanation. c See notes a and b of Table 1 for explanation. d Means followed by different letters indicate statistical difference at P < 0.05. n.d. indicates not determined.

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expanding at mild, medium and hard treatments reduced EPD by 21, 30 and 42% units, respectively. As in barley, the decrease in EPD was mainly due to a decrease in the A fraction and in the fractional degradation rate (c). The A fraction decreased by 47% units from 69% in the untreated to 22% in the hard treatment, whereas the degradable B fraction increased from only 27% in the untreated to 78% in the hard treatment. The fractional degradation rate decreased from 0.29 in the untreated to 0.04 in the hard treatment. The effective protein degradability of SBM decreased to below 50% by the medium and the hard treatments, due to reductions in the A fraction and in the fractional degradation rate (c). Except for the hard treatment, expanding RSM did not reduce EPD. In fact, the mild treatment of RSM increased EPD, compared with the untreated. In the cereal mixture, EPD decreased by 20% units from 69% in the untreated to 49% in the hard treatment. In the protein mixture the corresponding reduction in EPD was 4% units. In the cereal mixture both the A fraction and the fractional degradation rate (c), decreased by the expander treatment. These effects were not observed in the protein mixture. 3.5. Intestinal digestibility Washing in water (zero-hour bags) had no effect on the indigestible protein fraction in mobile nylon bags (Table 5). However, for all feedstuffs, the indigestible protein fraction decreased after rumen pre-incubation. The incubation time required to reach a reduction varied, being longest for RSM and the protein mixture. Compared with the original feed, after only 2 h pre-incubation, the indigestible protein fraction was almost halved in barley, oats and the cereal mixture. Measured as the mean value of original feed and the residues after 0, 2, 8,24 and 48 h rumen incubation, no significant increase in the indigestible protein fraction by increasing treatment intensity was observed in barley (Table 5). In oats, however, the indigestible protein fraction increased significantly between untreated and hard treatment. In SBM, the expander treatment reduced the content of indigestible protein. In RSM, there was no significant increase in indigestible protein between untreated and the hard treatment. However, the indigestible fraction varied, being highest in the hard treatment (7.1%) and lowest in the medium treatment (6.1%). No differences in content of indigestible protein between the untreated and hard treatment were observed in the feedstuff mixtures. 3.6. Correction for particle loss of protein The particle loss of protein from the nylon bags was considerable and varied from 5% in untreated SBM and RSM to 57% in untreated oats (Table 6). Therefore, the immediately degraded A fraction, corrected for particle loss of protein (Acorr), was reduced compared to the uncorrected A-values (Table 4). In oats, the particle loss of protein was considerably decreased by expanding. The difference between the Acorr fraction and the A fraction was therefore only 15% in the hard treatment compared to 57% in the untreated. Also, in barley, the expander treatment reduced particle loss of protein compared to untreated barley, whereas there was an opposite effect in SBM and RSM. In the feedstuff mixtures, there was no effect of the expander treatment on the particle loss of protein.

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Table 5 Mobile bag intestinal digestibility of protein (indigestible N in % of original feed N) Material

Barley

Oats

Soybean meal

Rapeseed meal

Cereal mixtured

Protein mixtured

a

Itema

Original 0 2 8 24 48 Meanc Original 0 2 8 24 48 Meanc Original 0 2 8 24 48 Meanc Original 0 2 8 24 48 Meanc Original 0 2 8 24 48 Meanc Original 0 2 8 24 48 Meanc

Untreated

feed

feed

feed

feed

feed

feed

5.83b 7.58ab 3.64 2.29 1.85 2.43 3.93 4.44c 4.37 2.45 1.83b 1.44c 1.48b 2.67b 1.99a 2.19a 2.48a 4.61a 0.21b 0.53b 2.46a 7.88 8.14 8.00 3.54b 5.96a 4.60a 6.20ab 5.33b 5.64 3.15 2.30b 1.86 1.65b 3.41 6.67a 5.64 5.57 4.24 3.03 2.39 4.64

Treatmentsb Mild

Medium

Hard

8.15a 6.19b 3.13 2.49 1.82 1.30 3.84 4.91bc 4.63 2.70 2.02b 1.60b 1.32c 2.89ab 1.11b 1.07c 1.50b 2.99ab 0.75a 0.37c 1.45b 9.04 8.00 8.48 6.84a 5.46ab 4.23b 6.95ab n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

7.77ab 9.31a 3.84 2.56 1.79 1.30 4.43 5.91a 3.92 2.56 2.43a 1.65b 1.49b 2.99ab 1.64ab 1.74a 1.52b 0.98bc 0.85a 0.61a 1.22b 6.10 7.77 7.49 6.68ab 4.66b 3.74c 6.07b n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

6.18ab 6.72b 3.24 2.69 1.88 1.42 3.89 5.27b 4.26 2.91 2.55a 1.97a 1.69a 3.11a 1.32ab 1.26c 1.31b 0.73c 0.59ab 0.38c 0.98b 8.62 8.33 8.02 7.77a 5.38ab 4.71a 7.13a 5.87a 5.87 3.41 2.95a 1.78 1.74a 3.50 3.82b 5.02 4.72 4.17 3.04 2.28 4.07

Measured on original feed and on residues after 0, 2, 8, 24 and 48 h rumen incubation. See Table 2 for explanation. c Mean of original feed and the different rumen incubation times. d See notes a and b of Table 1 for explanation. Means followed by different letters indicate statistical difference at P < 0.05. n.d. indicates not determined. b

Root MSE

P

1.13 1.07 0.35 0.26 0.07 1.43 1.01 0.27 0.40 0.41 0.14 0.07 0.04 0.51 0.32 0.21 0.45 1.16 0.14 0.03 0.82 1.96 0.60 0.88 1.74 0.50 0.11 1.36 0.26 0.52 0.25 0.07 0.24 0.02 0.28 1.67 0.65 0.71 0.24 0.10 0.01 1.03

0.054 0.018 0.056 0.375 0.382 0.676 0.082 0.001 0.158 0.435 0.001 0.001 0.001 0.024 0.021 0.001 0.029 0.002 0.024 0.001 0.001 0.213 0.594 0.555 0.034 0.030 0.001 0.015 0.035 0.656 0.198 0.001 0.637 0.003 0.299 0.045 0.181 0.150 0.707 0.880 0.814 0.073

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Table 6 In sacco rumen protein degradation characteristics corrected for particle loss Material

Barley

Oats

Soybean meal

Rapeseed meal

Cereal mixturec

Protein mixturec

Itema

PL Acorr Bcorr EPDcorr PL Acorr Bcorr EPDcorr PL Acorr Bcorr EPDcorr PL Acorr Bcorr EPDcorr PL Acorr Bcorr EPDcorr PL Acorr Bcorr EPDcorr

Untreated

19.2 10.8 80.2b 72.4a 57.3 12.4a 61.5b 63.2a 5.2 13.1a 86.9b 69.5a 5.1 15.2b 78.7ab 68.7ab 19.5 7.9 88.7 69.4a 10.9 7.3 90.6 66.1a

Treatmentsb

Root

Mild

Medium

Hard

17.5 6.1 92.9a 58.1b 42.7 2.9b 91.6a 54.9b 9.6 3.3b 96.7a 60.0b 8.8 19.9a 73.7b 70.0a n.d n.d. n.d. n.d. n.d n.d. n.d. n.d.

10.3 7.0 91.0a 57.9b 33.5 6.0ab 94.0a 50.3bc 11.4 0.1b 99.9a 50.5c 10.7 14.5b 82.5ab 65.5b n.d n.d. n.d. n.d. n.d n.d. n.d. n.d.

12.7 6.0 94.0a 57.9b 15.1 7.8ab 92.6a 47.5c 10.7 1.7b 98.3a 54.7c 9.9 10.4c 87.3b 61.7c 18.2 1.8 98.2 48.2b 10.8 6.8 90.8 62.2b

MSE

P

1.94 2.49 2.70

0.072 0.002 0.001

2.84 2.49 2.13

0.032 0.001 0.001

1.46 1.46 1.98

0.001 0.001 0.001

1.41 3.91 1.44

0.001 0.026 0.002

6.70 6.49 0.39

0.533 0.381 0.012

2.75 1.73 0.18

0.894 0.934 0.029

a

PL, particle loss of protein (%); Acorr, immediately degraded protein corrected for PL (%); Bcorr, protein degraded over time corrected for PL (%); EPDcorr, effective protein degradability corrected for PL (%) at rate of passage (k) 5% hÿ1. b See Table 2 for explanation. c See notes a and b of Table 1 for explanation. Means followed by different letters indicate statistical difference at P < 0.05. n.d. indicates not determined.

In barley, the reduction in effective protein degradability corrected for particle loss of protein (EPDcorr) was 14% units at all treatment intensities (Table 6). In oats and SBM the reduction in EPDcorr was 8, 13 and 15% units (oats) and 10, 19 and 15% units (SBM) at mild, medium and hard treatment intensities, respectively. In RSM, expanding at mild intensity increased EPDcorr by 1% unit, whereas expanding at medium and hard treatment intensity reduced EPDcorr by 3 and 7% units, respectively. In the cereal mixture, EPDcorr decreased by 20% units in the hard treatment, whereas EPDcorr decreased by 4% units in the protein mixture. 3.7. Determination of EPD on feedstuff mixtures versus individual feedstuffs Based on values for EPD measured in each individual feedstuff, the predicted reduction in EPD by the expander treatment was approximately 20% units in the cereal mixture and

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Table 7 Predicted and measured effective protein degradabilitya (EPD) in feed mixtures (%) Material

Treatmentc

Mixed before Expandingd

Mixed after Expandinge

Predictedb

Cereal mixturef

Untreated Hard Untreated Hard

68.6 48.9 61.3 57.5

66.3 47.4 59.9 50.0

73.2 52.2 64.0 54.3

Protein mixturef a

All values uncorrected for particle loss. Predicted values based on additivity of measured values for individual feedstuffs. c See Table 2 for explanation. d Measured value on feed mixtures mixed at a commercial plant. Total mixture expanded. e Measured value on feed mixtures mixed at the laboratory. Mixture of feedstuffs expanded individually. f See notes 1 and 2 of Table 1 for explanation. b

10% units in the protein mixture (Table 7). Measured reduction in EPD by expanding the complete mixture was 20% units in the cereal mixture and 4% units in the protein mixture. Furthermore, the EPD values of the expanded feedstuff mixtures and the mixtures of expanded individual feedstuffs were in good agreement, especially in the cereal mixture (68.6 versus 66.3 in the untreated, and 48.9 versus 47.4 in the hard treatment). The actual measured EPD values were, however, 4 to 5% units lower than that predicted for both of the untreated mixtures (73 versus 68%) and the expanded mixtures (52 versus 48%). 4. Discussion 4.1. Ruminal degradation in expander-treated barley and oats Barley and oats differed in their rate and extent of ruminal DM degradation, with barley being degraded to a greater extent than oats (Table 3). This result is in contrast to Herrera-Saldana et al. (1990) who ranked oats (highest degradation) before barley. Low ruminal degradation of DM in oats could be explained by the high content of fibre fractions in oats compared to barley (Table 1). The expander treatment reduced EDMD by 5% units in barley and by 3±8% units in oats (Table 3). Most of this reduction in EDMD can be attributed to the reduction in EPD. However, after subtracting the protein, the DM in barley and oats consists mainly of carbohydrates, in which starch is predominant. Since heat treatment of starchy feedstuffs will normally result in gelatinization of starch making it more accessible to enzymatic breakdown, it is somewhat surprising that the heat treatment did not increase ruminal degradation of DM in barley and oats. Several contradictory reports exist concerning the effect of heat treatment of cereals. Arieli et al. (1995) found no reduction in ruminal degradation of DM measured in sacco in barley expanded at 1158C compared to untreated barley, whereas ruminal degradation of starch was considerably reduced by the treatment. Cone et al. (1989) found that steam rolling of barley decreased the nylon bag degradation of DM and starch compared with dry rolling. In contrast, Malcolm and Kiesling (1993) reported that steam flaking of

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barley tended to increase rumen DMD in sacco. Furthermore, reduced ruminal degradation of DM in barley as a result of flame roasting (McNiven et al., 1994, 1995) or steam flaking (Fiems et al., 1990) has been reported. Mathison et al. (1991) found higher enzymatic degradation of starch in steam-rolled barley than in dry-rolled barley after 24 h incubation in vitro. In the study of Engstrùm et al. (1992), the amyloglucosidase-induced release of glucose in vitro was higher for steam-rolled barley than for dry-rolled barley, whereas the rates of disappearance of DM and starch in sacco were higher for dry-rolled barley than for steam-rolled barley. The reason for the discrepancy in the results, both between in sacco experiments and between in sacco and in vitro experiments, is not clear. In general, grinding of cereals increases the total surface area rendering nutrients more accessible for microbial attack (Nocek, 1988; Michalet-Doreau and Ould-Bah, 1992). Variation in grinding and particle size may explain some of this discrepancy. However, the reason why heat treatment tends to increase ruminal degradation of DM in some situations, while the same or a similar treatment tends to decrease ruminal degradation in other situations, is difficult to explain. When barley and oats are treated with heat and pressure in the expander, starch and protein are transformed into a dough in which the total surface area is decreased. This may limit the extent of microbial attachment and thereby ruminal degradation. Excessive heat treatment can also reduce the digestibility of starch through the formation of dextrans or through retrogradation (Rooney and Pflugfelder, 1986). As discussed by McNiven et al. (1995), the effect of heat treatment may depend upon the time allowed for cooling and the physical treatment following the heat treatment. In other words, the effects of a certain heat treatment on the ruminal degradation of DM and starch is complex. Therefore, when processing feedstuffs, great care and effort should be taken when monitoring processing conditions. In addition to starch, barley and oats contain significant amounts of soluble and insoluble fibres (Bach Knudsen, 1997). Unfortunately, the effects of the expander treatment on the fibre components were not monitored in the present experiment. However, the soluble fibres have been reported to increase after pelleting (Graham et al., 1989) and extrusion (Shinnick et al., 1988; Vranjes and Wenk, 1995). Engstrùm et al. (1992), however, found no differences in content of b-glucans between steam-rolled and dry-rolled barley. In addition, in their study, nylon bag disappearance of b-glucans after washing and 8 h rumen incubation was lowest for steam-rolled barley. Excessive heat treatment may increase lignin-like components that can analytically be determined as insoluble fibre (van Soest and Mason, 1991). In the study of Engstrùm et al. (1992), the content of ADF was higher after steam-rolling than after dry-rolling. In addition, steamrolling more than tripled the content of acid detergent insoluble nitrogen (ADIN). Thus, ADIN may provide information about the history of heating and the nitrogen availability of heat-treated feedstuffs (van Soest and Mason, 1991). The expander treatment reduced the ruminal degradation of protein (Table 4) to a much higher extent than it reduced the degradation of DM (Table 3). This means that the treatment had a specific effect on the ruminal degradation of protein. No adequate references were found in the literature dealing with expander treatment of oats, whereas the only reference concerning the effect of expander treatment of barley was Arieli et al. (1995). They found that the expander treatment reduced the rate of nitrogen degradation,

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but increased the proportion of potential nitrogen degraded in the rumen. Their results are, however, confusing since potential nitrogen degradability was as low as 59% in the control and as high as 115% in the expanded sample, whereas the potential degradability of DM was 88 and 89% in the control and the expanded sample, respectively. These results indicate some problems for the NLIN procedure in SAS to fit the data for nitrogen disappearance to the exponential function. In a recent study of McNiven et al. (1995), EPD in barley was reduced from 76 to 55% by flame roasting. In the study of McNiven et al. (1994), flame roasting at 1688C reduced the rumen degradation of protein in barley and oats with 32 and 36% units, respectively. Fiems et al. (1990), using steam-flaked barley, did not calculate EPD. However, by assuming a rumen outflow rate of 8% hÿ1, EPD in barley was reduced from 80 to 56% in their study. In another study, Weisbjerg et al. (1996) found that heat treatment of barley reduced EPD from 86 to 67%. The mechanisms behind the protection of protein against ruminal degradation in heattreated barley and oats are complex. However, it is likely that chemical reactions occurring during heat processing are responsible for the reduction in ruminal degradation. Reactions that might occur during heat processing have recently been reviewed by Voragen et al. (1995). Heat treatment of protein will result in denaturation of protein and probably transform the proteins to a more resistant structure. In addition, heat processing can result in formation of cross-linkages between amino acids and reducing sugars (the Maillard reaction), or between proteins (iso-peptide bonds). These reactions will probably make the feed protein more resistant against degradation in the rumen. Peisker (1992) suggested that protein can be bound physically rather than chemically into a matrix of heat- treated starch and protein. Furthermore, McAllister et al. (1993) suggested that variation in the protein±starch matrix could be a major factor responsible for differences in ruminal digestion of cereals. Differences in the arrangement of the protein±starch matrix might explain the differences in ruminal degradation of protein and DM that can be seen between barley and oats. In barley, the proteins form a rather rigid matrix in which starch granules are embedded. In contrast, in oats, the proteins and starch appear as spherical bodies in a rather loose arrangement (Fulcher, 1986). In addition, barley and oats differ greatly in terms of composition of their protein fractions. In oats, the content of soluble albumins and globulins is high, whereas in barley, the more insoluble prolamins and globulins dominate (Hoseney, 1994). These differences in the protein±starch matrix, and in the content of the different protein fractions, may also explain why oats responded to higher treatment intensities than barley (Fig. 1). Both in the present study with expander treatment and in the study of McNiven et al. (1994) with flame roasting, barley seemed to be more readily affected by heat treatment than oats. In addition, the ruminal degradation of barley protein seemed to reach a point at which any additional increase in treatment intensity did not result in a further decrease in ruminal degradation of protein. In contrast, in oats, the ruminal degradation of protein was even decreased at the highest treatment intensity (Table 4). Nocek (1988) recommended the correction of the contamination of microbial protein in the nylon bag residues. Varvikko (1986) claimed that especially in cereals this is important. Erasmus et al. (1994), however, found in 12 different feedstuffs, on average only 3.9% microbial contamination in residues after 16 h rumen incubation. In their

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study, the nylon bags were washed for 10 min in a washing machine. In the present study, the bags were washed for 3  10 min in a washing machine, making microbial contamination probably of even less importance. Moreover, no appropriate data for correction of microbial contamination were available. Thus, correction for microbial contamination was not done. The risk for microbial contamination should, however, be studied more closely in future projects. 4.2. Ruminal degradation in expander-treated SBM and RSM According to NRC (1989), heating SBM at 120, 130 or 1408C reduces ruminal degradation of protein from 65% in the unheated meal to 41, 29 or 18%, respectively, whereas ruminal degradation of protein was reduced from 72 to 30% in protected RSM. Even though no precise description of the processing methods is given, this confirms that heat processing is commonly accepted as a method for altering ruminal degradation of protein in SBM and RSM for ruminants. Expander treatment of SBM reduced EPD considerably (Table 4), whereas the treatment had only a minor effect on EPD in RSM. No references have been found that deal with the expander treatment of SBM as presented in this paper. However, Waltz and Stern (1989), who evaluated various methods for protecting soybean protein from degradation by rumen bacteria, found that the rumen degradation of expeller-processed SBM and extruded SBM was reduced compared with that of solvent-extracted SBM, with the expeller-processing being more efficient than extruding. Titgemeyer and Shirley (1997) found higher estimates of rumen undegraded protein in different expellerprocessed SBMs compared to solvent-extracted SBM, whereas Faldet et al. (1991) found higher estimates of rumen-undegraded protein both in expeller-processed and roasted SBM compared to solvent-extracted SBM. Deacon et al. (1988), however, found that the extrusion of solvent extracted SBM had no effect on the ruminal degradation of protein. Furthermore, they found no reduction in ruminal degradation of protein by extruding solvent extracted RSM (canola meal). In contrast, Sommer et al. (1996) reported that expanding RSM at 120 or 1308C considerably reduced rumen degradation of protein. By heating solvent-extracted canola RSM in a vacuum tumble drier at 1258C or 1458C for 10, 20 or 30 min, McKinnon et al. (1991) almost halved the rumen degradation of protein compared with the untreated control meal. The heat±moisture treatment of RSM reduced the rumen degradation of protein 10% in the study of Vanhatalo et al. (1995). Mir et al. (1984) reported that dry-heating at 1108C for 2 h or at 1208C for 20 min had no effect on the rumen degradation of protein in SBM. In contrast, the rumen degradation of protein in RSM was decreased by heating. The findings in the present study do not support their hypothesis that rapeseed proteins are denatured by heat more easily than the soybean proteins. In RSM, the expander treatment caused only a minor reduction in EPD, even at 1908C, whereas the treatment of SBM led to a 10% unit reduction in EPD at a temperature as low as 1308C (Table 4). However, when discussing the effect of heat treatment it is important to emphasise that protein in SBM and RSM already had been toasted following the solvent-extraction process. Therefore, it can be difficult to achieve any additional effects on protein degradation in the rumen through further processing. Hence, to predict the effect of heat treatment, the processing history of the feedstuff

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17

should be known. In addition to processing temperature and time, the processing history should include moisture content, site and temperature of steam/water added, pressure, energy input, and if possible some information about variety and growing conditions. 4.3. Intestinal digestibility Several of the reactions responsible for the reduction in ruminal degradation may also reduce intestinal digestibility of protein. Therefore, as discussed by Satter (1986), the challenge when heat-treating feedstuffs is to identify processing conditions that reduce the rumen degradability of protein without reducing intestinal digestibility. The effect on intestinal digestibility of rumen-undegraded protein by heat-treating cereals with expanders, or similar HTST methods, is not well documented. In the present study, there was no increase in indigestible protein between untreated and expanded barley (Table 5). In oats, the content of indigestible protein tended to increase at the hard expander treatment compared with the untreated. The increase in content of indigestible protein was, however, small compared to the dramatic drop in ruminal degradation. The practical implication when calculating the digestibility of rumen-undegraded protein, as described by Hvelplund et al. (1992) is, therefore, negligible. However, also using the mobile bag technique, McNiven et al. (1994) found a considerable reduction in intestinal digestibility of barley and oats by flame roasting at 1688C. The risk for over-protecting protein in cereals by heat-processing should therefore be taken seriously. In SBM, the content of indigestible protein initially was low, and decreased by the expander treatment (Table 5). This finding indicates that HTST processes such as the expander treatment do not over-protect SBM protein. Although there was a tendency to increased content of indigestible protein at the hard treatment, the same conclusion must be drawn for RSM. However, several examples exist where severe heat treatment reduced intestinal digestibility of protein in SBM or RSM (McKinnon et al., 1991; Moshtaghi Nia and Ingalls, 1995; Dakowski et al., 1996). The most interesting result shown in Table 5 is that the content of indigestible protein was lower after rumen pre-incubation in most of the feedstuffs. This means that the intestinal digestibility of rumen undegraded protein increases with ruminal preincubation. Similar effects of rumen pre-incubation have been shown by Hvelplund et al. (1992) and Volden and Harstad (1995). The mechanism is not known, but microbial degradation of components inhibiting the enzymatic digestion of protein in the small intestine is one plausible explanation to the observed effect. Furthermore, entrance of intact feed to the small intestine is not physiological. Thus, the digestibility of rumen undegraded protein should always be determined on residues from rumen pre-incubation. Madsen et al. (1995) recommended the use of residues after 16 h rumen pre-incubation. 4.4. Effect of particle loss on ruminal degradation of protein Particle loss from the nylon bags can result in an overestimation of ruminal degradation (Michalet-Doreau and Ould-Bah, 1992). Dewhurst et al. (1995) seriously doubted that the nylon bag technique is suitable for studies of concentrate ingredients with a high content of either soluble constituents or unfermentable `fines' which can pass out of the bags.

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Assuming that the particles lost from the nylon bags are degraded at the same rate and to the same extent as material left in the bags, ruminal degradation can be corrected for particle loss as described by Weisbjerg et al. (1990) and Madsen et al. (1995). However, in feedstuffs where particle size distribution varies, the assumption may be questioned (Madsen et al., 1995). The loss of particles only concerns the fine particles (MichaletDoreau and Ould-Bah, 1992). If these particles are degraded more rapidly than the larger ones left in the nylon bags, correction for particle loss according to Weisbjerg et al. (1990) will underestimate ruminal degradation. Nevertheless, taking the assumption as valid, the present study showed that there was considerable particle loss in barley and oats, particularly in the latter (Table 6). The high loss of fines could be associated with the grinding procedure prior to the nylon bag incubations. Especially in oats, grinding will cause a fracture of the seed kernels, leaving starch and protein as a fine powder which can be lost through the pores of the nylon bags. The expander treatment reduced particle loss, especially in oats (Table 6). This led to a considerable decrease in EPDcorr in the untreated oats compared to the uncorrected EPD value (Table 4), whereas EPDcorr and EPD were similar at the hard treatment. The reduction in EPDcorr, however, was still significant for all treatment intensities. In barley, correction for particle loss did not influence the calculated EPD value at any of the treatment intensities (Table 6). These findings are in contrast to Weisbjerg et al. (1996), who found with barley that correction for particle loss reduced the calculated effect of heat treatment on EPD from more than 20 to only 3% units. In SBM, RSM and the protein mixture, correction for particle loss increased EPDcorr (Table 6) compared to uncorrected EPD value (Table 4), whereas no differences between EPDcorr and EPD were observed in barley and the cereal mixture. These findings are attributed to the shift of ruminal outflow rate (k) from 8 to 5% hÿ1 when correcting for particle losses (Madsen et al., 1995). In barley and the cereal mixture, the decrease in rumen outflow rate compensated for the particle loss, making EPDcorr and EPD similar. In SBM, RSM and the protein mixture, the influence of the reduction in ruminal outflow rate is higher than the reduction in Acorr, making EPDcorr higher than EPD. 4.5. Ruminal degradation of feed mixtures versus individual feedstuffs Formulation of feed mixtures is based on the assumption that individual feedstuffs give an additive contribution to the nutritive value according to their inclusion ratio. In the present experiment, the calculated CP contents of the two feed mixtures were 197 (cereal mixture) and 363 (protein mixture) g kgÿ1 DM, respectively, whereas the corresponding measured CP contents were 200 and 355 g kgÿ1 DM (Table 1). Nevertheless, these results only indicate that the inclusion ratio of each feedstuff component is correct. Whether or not nutritive characteristics of feed mixtures such as ruminal degradation of protein can be estimated in a similar manner, has received limited attention. Furthermore, it seems that the possibilities for interactions (positive or negative) between feedstuffs when a feedstuff mixture is exposed to a certain treatment usually are neglected when calculating the nutritive value of the mixture. In the present experiment, the EPD measured was 4±5% units lower than the calculated EPD both in the untreated and expanded mixtures (Table 7). These findings illustrate the

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19

difficulties in assessing the protein value obtained on individual feedstuffs composed the feed mixtures. Vik-Mo and Lindberg (1985), investigating degradability of protein in different feedstuffs in the rumen, found good agreement between ruminal disappearance of N in barley and SBM and in a mixture of barley and SBM. Their results, and the findings of Murphy and Kennelly (1987) comparing measured and estimated crude protein degradabilities in four concentrate mixtures of either barley and canola meal, or barley and corn gluten meal, indicate that ruminal degradation of protein in mixtures can be estimated from measured values in single feedstuffs. However, in a recent study, van Straalen et al. (1997) estimated the disappearance of N and amino acids after washing in a washing machine and after 12 h rumen incubation, to be lower than the measured disappearance. Furthermore, Chapoutot et al. (1990) showed that calculated DM degradation was lower than that measured in different mixtures of barley, maize, lupine and corn gluten feed, especially at the shorter rumen incubation times. The assumption that ruminal degradation of the single ingredients reflects the degradation of the concentrate mixture, therefore may not be valid. Based on the measured values for EPD of each individual feedstuff, the predicted reduction in EPD by the expander treatment was approximately 20 and 10% units in the cereal mixture and the protein mixture, respectively (Table 7). The measured reduction in EPD by expanding the complete mixture was 20 and 4% units in the two mixtures, respectively. These results show that at least for the cereal mixture, the reduction in protein degradation was achieved by expanding individual feedstuffs as well as by expanding feedstuff mixtures. Furthermore, the agreement between the EPD values of the expanded feed mixtures and the mixtures of expanded individual feedstuffs, was good, especially for the cereal mixture. These results indicate no interactions with regard to the ruminal degradation of protein between feedstuffs when expanding the complete mixture as a whole, compared to expanding each individual feedstuff. Therefore, the expander technique presented can be carried out on individual feedstuffs as well as on feed mixtures. It must, however, be emphasised that the statements presented here are based on limited material and do not allow a detailed discussion of the topic. In the calculation of degradability it was assumed that the feedstuffs behaved uniformly in the nylon bags as individual feedstuffs and as parts of a feed mixture. This assumption may be questioned. The calculations were based on simple first-order degradation kinetics. Several alternative models describing nutrient digestion in the rumen exist (Martens, 1993). A model including a lag phase or second-order kinetics might have increased the precision and fit in additivity. Furthermore, protein (actually N) was the only pool of nutrient considered. A precise description of degradation rates and pools of protein and carbohydrates as proposed, for example, by Sniffen et al. (1992), would have added useful information to the discussion. The important question regarding additivity when assessing nutritive value of individual feedstuffs to feed mixtures, should be studied more closely in the future. 5. Conclusions The results show that the expander treatment efficiently reduced ruminal degradation of protein, especially in barley and oats and in a feedstuff mixture based on barley and

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oats. Less pronounced reduction in ruminal degradation of protein was observed with SBM and a feedstuff mixture based on SBM and RSM. It had no effect on the ruminal degradation of protein in RSM. The expander treatment had no severe negative effect on the intestinal digestibility of protein in any of the feedstuffs. The risk of over-protecting the protein by the expander treatment, even at temperatures as high as 1708, therefore seems to be minimal. The effect of the expander treatment on the ruminal degradation of protein was similar for individual feedstuffs and feed mixtures. This result indicates that there is no need for expanding each ingredient separately, and that a feed mixture can be expanded as a whole. Particle loss of protein in the washing procedure of the nylon bags was high in barley and particularly oats. Corrections for loss of particles should be done routinely when determining protein degradation in feedstuffs with high amounts of fines which can be lost from nylon bags. The expander treatment reduced the loss of particles, especially in oats. Although, reduction in particle loss reduced the effect of expander treatment in oats, the reduction in EPD was still significant at all treatment intensities. Acknowledgements The author gratefully acknowledge Dr. O.M. Harstad for assistance in planning of the experiments, Ms. T. Gjefsen for technical assistance in conducting the experiments, Ms. I. Parker and Mr. J. Rekkedal for laboratory assistance and Drs. N.P. Kjos, M.A. McNiven and H. Volden for a critical review of the manuscript. The research work was financially supported by Norske Felleskjùp, Oslo. References AOAC, 1980. Official Methods of Analysis, 13th edn., Association of Official Analytical Chemists, Washington, DC. Arieli, A., Bruckental, I., Kedar, O., Sklan, D., 1995. In sacco disappearance of starch nitrogen and fat in processed grains. Anim. Feed Sci. Technol. 51, 287±295. Bach Knudsen, K.E., 1997. Carbohydrate and lignin contents of plant materials used in animal feeding. Anim. Feed Sci. Technol. 67, 319±338. Broderick, G.A., Wallace, R.J., érskov, E.R., 1991. Control of rate and extent of protein degradation, In: Tsuda, T., Sasaki, Y., Kawashima, R. (Eds.), Physiological Aspects of Digestion and Metabolism in Ruminants, Academic Press, San Diego, CA, pp. 541±592. Campling, R.C., 1991. Processing cereal grains for cattle ± A review. Livest. Prod. Sci. 28, 223±234. Chapoutot, P., Giger, S., Sauvant, D., Jeantet, S., 1990. Etude de l'additivite de la deÂgradation in sacco de la matieÁre seÁche des meÂlanges simples d'aliments concentreÂs, Reprod. Nutr. Dev., Suppl. 2, pp. 169s± 170s. Cone, J.W., ClineÁ-Theil, W., Malestein, A., van't Klooster, A.T., 1989. Degradation of starch by incubation with rumen fluid. A comparison of different starch sources. J. Sci. Food Agric. 49, 173±183. Dakowski, P., Weisbjerg, M.R., Hvelplund, T., 1996. The effect of temperature during processing of rape seed meal on amino acid degradation in the rumen and digestion in the intestine. Anim. Feed Sci. Technol. 58, 213±226. Deacon, M.A., de Boer, G., Kennelly, J.J., 1988. Influence of jet-sploding and extrusion on ruminal and intestinal disappearance of canola and soybeans. J. Dairy Sci. 71, 745±753.

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