Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol83.Issue1.Jan2000:
Animal Feed Science and Technology
83 (2000) 31±47
Effective rumen degradability and intestinal
indigestibility of individual amino acids in
solvent-extracted soybean meal (SBM) and
xylose-treated SBM (SoyPass1)
determined in situ
O.M. Harstad*, E. Prestlùkken
Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N - 1432 AÊs, Norway
Received 2 February 1999; received in revised form 30 August 1999; accepted 22 September 1999
Abstract
The study comprised two samples of solvent-extracted soybean meal (SBM) and two samples of
xylose-treated SBM (SoyPass1). The main objectives were to determine effective rumen
degradability (ERD) and intestinal indigestibility of their individual amino acids (AA) in situ.
The relative contribution of Lys was on average 17% lower and of Arg 7% lower in SoyPass1 than
in SBM (p < 0.05). Manufacturing of SoyPass1 increased significantly the relative contribution of
Ile, Leu, Val and Gly, but these effects were small in magnitude. Effective rumen degradabilities of
total AA (TAA) calculated at a rumen outflow rate of 8% hÿ1, was as low as 29% for SoyPass1
compared to 53% for SBM. The corresponding values for crude protein (CP) were 27 and 52% for
SoyPass1 and SBM, respectively. In SBM, Arg, Glu and Lys had higher (p < 0.05) ERD than TAA,
whereas Ser, Phe, Leu, Gly, Thr, Tyr, Ile, Cys, Val, Ala and Met showed lower (p < 0.05) ERD than
TAA. In SoyPass1, ERD of Lys and Cys did not differ significantly from TAA. With these
exceptions, variation in ERD among AA in SoyPass1 was as in SBM. However, the differences
between individual AA and TAA were much smaller than in SBM. Intestinal indigestibility of TAA
measured on original feed (OF) was 1.8 and 2.0% for SBM and SoyPass1, respectively (p > 0.05).
For CP, the corresponding values were 2.0% for SBM and 2.3% for SoyPass1. Pre-incubating the
samples in the rumen for 16 h, numerically decreased intestinal indigestibilities of all individual
AA, but the effect was significant for only 5 AA. There were significant differences in intestinal
indigestibilities among AA, but the differences were small in magnitude. From the results obtained,
it was concluded that, for SBM and SoyPass1, TAA in the protein fraction digested in the intestine
*
Corresponding author. Tel.: 47-64-94-80-00; fax: 47-64-94-79-60.
E-mail address: odd.harstad@ihf.nlh.no (O.M. Harstad).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 1 4 - 5
32
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
(PDI) can be predicted accurately by using proportion AA-N: N in rumen undegraded protein
(RUP) of 0.85, and ERD and intestinal indigestibility as for CP. For SoyPass1, this way of
prediction of individual AA would result in only small errors, at least for those AA which are
regarded as limiting in milk production. In contrast, for SBM satisfactory prediction of individual
AA absorbed in the intestine requires determination of ERD on individual basis. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: Amino acid profile; Lys; Met; Protein; Nylon bag technique; Mobile nylon bag technique
1. Introduction
Solvent-extracted soybean meal (SBM), which is a commonly used protein supplement
to high-producing dairy cows, is palatable with a well-balanced amino acid (AA)
composition. However, SBM protein is extensively degraded in the rumen. Highproducing dairy cows need significant amounts of rumen undegraded feed protein (RUP)
which is digested post-ruminally to meet their AA requirement. Treatment of SBM with a
xylose-containing calcium lignosulfonate have increased the proportion of RUP in SBM
considerably (Windschitl and Stern, 1988; Walts and Stern, 1989; Nakamura et al., 1992).
In diets, where SBM is the major contributor of RUP, Met turns out to be the first limiting
AA (Maiga et al., 1996; Schingoethe, 1996). The AA profile of RUP in untreated SBM
can be different from that of the original feed (Crooker et al., 1986; Susmel et al., 1989;
Erasmus et al., 1994; Cozzi et al., 1995; Vanhatalo et al., 1995; Maiga et al., 1996;
O'Mara et al., 1997; Van Straalen et al., 1997; Zebrowska et al., 1997), making prediction
of absorbed AA uncertain. In the experiments conducted with SBM, rumen degradability
of individual AA is determined at one or two rumen incubation times only. As far as we
know, the only exceptions are Varvikko et al. (1983) (one cow only), Susmel et al. (1989)
and Cozzi et al. (1995) with untreated SBM. Varvikko et al. (1983) and Weisbjerg et al.
(1996) determined rumen degradation of AA after three incubation times with
formaldehyde-treated and xylose-treated SBM (SoyPass1), respectively. Therefore,
information about effective rumen degradability (ERD) of individual AA is limited.
Likewise, more information is needed on the intestinal indigestibility of individual AA in
RUP of SBM (O'Mara et al., 1997). The study of Weisbjerg et al. (1996) with SoyPass1
did not include the control of untreated SBM. Thus, the effect of xylose treatment of
SBM on ERD and intestinal indigestibility of individual AA has not previously been
examined in situ.
The main objectives of our research were to determine ERD and intestinal
indigestibility of individual AA of SBM and SoyPass1. A preliminary report on part
of this study has already been published (Prestlùkken and Harstad, 1996).
2. Material and methods
2.1. Experimental feeds
Two samples of solvent-extracted soybean meal (SBM) from different batches and two
samples of SoyPass1 made from the same batches as SBM, respectively, were examined.
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
33
The feeds were manufactured commercially at the same plant (Denofa A/S, Fredrikstad,
Norway). SoyPass1 was manufactured by adding Xylig (Borregaard Lignotech,
Sarpsborg, Norway) to SBM under heat and elevated moisture (US Patent No.
4,957,748, 18 September 1990). Xylig is a product rich in xylose produced from wood.
2.2. Animals and diets
We planned to use the same three animals to carry out the in situ measurements of both
batches of the experimental feeds. Unfortunately, one of the animals used on batch one,
experienced health problems unrelated to the experiment, and was removed from the
study. Therefore, three different animals were used on batch two. All six experimental
animals were multiparous non-lactating dairy cows of the Norwegian Red Cattle breed,
fitted with a rumen cannulae (Bar Diamond, Parma, ID, US) and a T-shaped PVC
duodenal cannulae located 50±80 cm distal to pylorus. They were housed in tie-stalls and
fed a standardized diet at maintenance, consisting of 4 kg grass hay per day and 1.8 kg
concentrate mixture per day (175 g CP kgÿ1 DM). The ration was offered in two equal
meals at 06:00 and 15:00 h. The metabolism unit used was authorized for animal
experiments by the Norwegian Animal Research Authority.
2.3. In situ measurements
The in situ procedures applied to measure rumen degradability and intestinal
indigestibility of crude protein (CP) and individual amino acids (AA) were, as described
by Madsen et al. (1995) and Prestlùkken (1999). One exception was the pore size of the
nylon bags used to measure intestinal indigestibility of CP and AA. In the present study,
nylon bags with pore size of 15 mm (ZBF AG, CH 8803, Ruschlicon, Switzerland) were
used instead of 11 mm as recommended (Madsen et al., 1995). The intestinal
indigestibility measurements were on the original feeds (OF) and their rumen undegraded
feed residues after 16 h of rumen incubation.
2.4. Chemical analyses
Chemical composition of the experimental feeds and AA content of their residues after
washing, rumen or intestinal incubation were carried out as described by Prestlùkken
(1999). Feed crude protein (N 6.25) degradation in the digestive tract was calculated on
basis of N determined by the Dumas method (AOAC, 1990) using the Leco combustion
system (LECO CHN-1000 analyser; Leco, MI).
2.5. Calculations and statistical analysis
The kinetics of in situ CP and AA degradation in the rumen were calculated according
to the following exponential model: D(t) a b(1 ÿ exp (ÿct)), where D(t) is the
percentage degradation of CP or AA at time t; a the soluble fraction; b the potential
degradable fraction, and c the fractional degradation rate of b. The non-linear parameters
were obtained by use of the PROC NLIN procedure of SAS (SAS, 1990). Effective rumen
34
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
degradation of CP or AA was calculated as: a (b c)/(c kp) assuming a rumen
outflow rate (kp) of 8% hÿ1. Within feedstuff, ERD and intestinal indigestibility of CP
and individual AA were compared by use of the Duncan multiple range test (SAS, 1990).
The effect of rumen incubation on the proportion of AA-N and individual AA in the
protein residues were tested with linear regression analysis (PROC REG) (SAS, 1990).
Intestinal digestibilities of rumen undegraded AA as well as CP were calculated
according to the following general equation (Hvelplund et al., 1992).
TD UDNÿTU=UDN
where TD is the true intestinal digestibility of rumen undegraded protein fraction
(g 100ÿ1 g); UDN the fraction of rumen undegraded dietary protein (g gÿ1) original feed
protein fraction, and TU the fraction of truly indigestible protein in the feed (g gÿ1)
original feed protein fraction
The amount of each AA digested in the intestine was calculated on the basis of their
content in the feed, ERD and intestinal digestibility. The amount of total and individual
AA digested in the intestine was also predicted based on the assumption that ERD and
intestinal indigestibility of individual AA was as for CP, and that AA constituted 85% of
CP in RUP. Differences between SBM and SoyPass1 in rumen and intestinal degradation
characteristics of CP and AA were tested using PROC GLM (SAS, 1990) with feed and batch
as main effects and animal as random effect. The significance level was p < 0.05, unless
stated otherwise.
3. Results and discussion
3.1. Feed chemical composition
The differences in chemical composition and in AA profile between the two batches of
SBM as well as of SoyPass1 were relatively small (Table 1). The variation of AA-N of
total N from 81.1 to 86.2% in the two batches of SBM was within the range cited in the
literature (O'Mara et al., 1997). The two batches of SBM were similar in AA composition
(Table 1), and in accordance with that observed in the studies of Susmel et al. (1989),
Maiga et al. (1996) and O'Mara et al. (1997). However, in other studies with SBM
(Erasmus et al., 1994; Cozzi et al., 1995; Zebrowska et al., 1997), the AA profile differed
from that found in our experiment.
Xylig, which contains mainly carbohydrate components and minerals, diluted the
content of CP and fat in SoyPass1, as expected. The xylose treatment increased the
measured NDF content by 9%-units. This substantial increase of NDF in SoyPass1
may be due to elevated N content in NDF resulting from the Maillard reaction caused
when SBM is heated with added xylose (Windschitl and Stern, 1988; Van Soest, 1994).
The NDF content of 22.2 and 21.4% of DM in batches 1 and 2 of SoyPass1, respectively,
agree well with the corresponding value of 20.1% found in the study of Weisbjerg et al.
(1996). The treatment of SBM with xylose had no systematic effect on the proportion of
AA-N. The average value of 82.4% for SoyPass1 was slightly >80.4% obtained with
SoyPass1 in the study of Weisbjerg et al. (1996). The relative contribution of Lys was, on
35
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
Table 1
Chemical composition, content of amino acid- N (AA-N), essential AA (EAA), non essential AA (NEAA) and
individual AA in the two batches of solvent-extracted soybean meal (SBM) and xylose-treated SBM (SoyPass1)
Batch 1
Batch 2
SBM
SoyPass
SBM
SoyPass1
g 100ÿ1 g DM
Ash
Crude protein
Crude fat
Crude fibre
NDF
6.7
52.0
1.6
5.8
13.6
6.9
47.6
1.4
5.6
22.2
7.2
50.6
2.4
7.4
12.7
6.9
46.5
2.0
7.5
21.4
g 100ÿ1 g AA
EAA
Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Tyr
Val
49.0
7.8
2.8
4.8
7.8
6.4
1.4
5.1
4.0
4.1
4.8
48.0
7.2
2.7
4.8
7.9
5.3
1.4
5.2
4.1
4.2
5.2
49.1
7.7
2.9
5.0
7.7
6.3
1.3
5.3
4.1
3.8
5.0
48.3
7.2
2.8
5.1
7.9
5.3
1.3
5.4
4.2
3.8
5.3
51.0
4.0
11.7
1.5
18.7
4.3
5.3
5.6
52.0
4.4
11.8
1.4
19.2
4.4
5.2
5.6
51.0
4.3
11.3
1.7
18.6
4.4
5.3
5.5
51.7
4.5
11.4
1.6
18.9
4.4
5.4
5.5
81.1
81.5
86.2
83.3
NEAA
Ala
Asp
Cys
Glu
Gly
Pro
Ser
g 100ÿ1 g N
AA-N
1
average, 17% lower and of Arg 7% lower in SoyPass1 compared with SBM (p < 0.05)
(Table 1). Lys is usually the most sensitive AA to be affected by methods used to protect
proteins from ruminal degradation (Windschitl and Stern, 1988). It is often lost at levels
5±15 times higher than other AA (Dakowski et al., 1996). Lys may be one of the first
limiting AA in milk protein synthesis (Schingoethe, 1996) and is, therefore, of particular
interest. As far as we know, there are no results published on the effect of treating SBM
with xylose and heating on its content of Lys. However, negative effects on Lys content,
even greater than those found in the present study, are reported from experiments with
formaldehyde treated SBM (Crooker et al., 1986), roasted soybeans (Faldet et al., 1992),
moist heat treated Canola meal (Moshtaghi Nia and Ingalls, 1995) and toasted rape seed
meal (Dakowski et al., 1996). Manufacturing of SoyPass1 increased significantly the
relative contribution of Ile, Leu, Phe, Val and Gly, but these effects were small in
magnitude (Table 1).
36
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
3.2. Rumen degradation characteristics
Rumen degradation characteristics of protein fractions and individual AA are given in
Table 2. There were small, but significantly (p < 0.05) higher ERD of TAA than CP; 1.1
and 1.8%-units for SBM and SoyPass1, respectively. This is in contrast to Susmel et al.
(1989) who observed for SBM ERD, calculated with an outflow rate of 7% hÿ1, of 50 and
54% for TAA and CP, respectively. Weisbjerg et al. (1996) found also for SoyPass1 ERD
of TAA as much as 4%-units higher than for CP. Thus, it is uncertain if ERD of CP can be
used to predict ERD of TAA for SBM and SoyPass1.
Solvent-extracted soybean meal showed greater variation in ERD among AA than
SoyPass1. In SBM, Arg, Glu and Lys had higher (p < 0.05) ERD than TAA, whereas Ser,
Phe, Leu, Gly, Thr, Tyr, Ile, Cys, Val, Ala and Met showed lower ERD than TAA (Table
2). The difference between Arg and Met, which showed the highest and lowest ERD
values, respectively, was as high as 12.6%-units. Susmel et al. (1989) found also that Arg,
Glu and Lys were the three AA in SBM, which showed the highest ERD. However, in
contrast to our results, Met showed higher ERD and Pro lower ERD than average in the
study of Susmel et al. (1989). Moreover, in their experiment, ERD of Ser, Phe, Ile and
Leu did not show lower ERD than the average as observed in our study (Table 2).
The change in AA profile from original feed (OF) to RUP reflects the effect of rumen
exposure on the extent of rumen degradation of individual AA. Thus, any conclusions on
the effects of rumen exposure on AA profile also apply to rumen degradation of
individual AA. A fall in proportion results in higher degradation than average, whereas an
increase in proportion will result in lower than average degradation. For some AA, their
proportion in feed residues changed dramatically after rumen incubation for >24 h, and
sometimes in a direction opposite to that observed in incubations of
83 (2000) 31±47
Effective rumen degradability and intestinal
indigestibility of individual amino acids in
solvent-extracted soybean meal (SBM) and
xylose-treated SBM (SoyPass1)
determined in situ
O.M. Harstad*, E. Prestlùkken
Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N - 1432 AÊs, Norway
Received 2 February 1999; received in revised form 30 August 1999; accepted 22 September 1999
Abstract
The study comprised two samples of solvent-extracted soybean meal (SBM) and two samples of
xylose-treated SBM (SoyPass1). The main objectives were to determine effective rumen
degradability (ERD) and intestinal indigestibility of their individual amino acids (AA) in situ.
The relative contribution of Lys was on average 17% lower and of Arg 7% lower in SoyPass1 than
in SBM (p < 0.05). Manufacturing of SoyPass1 increased significantly the relative contribution of
Ile, Leu, Val and Gly, but these effects were small in magnitude. Effective rumen degradabilities of
total AA (TAA) calculated at a rumen outflow rate of 8% hÿ1, was as low as 29% for SoyPass1
compared to 53% for SBM. The corresponding values for crude protein (CP) were 27 and 52% for
SoyPass1 and SBM, respectively. In SBM, Arg, Glu and Lys had higher (p < 0.05) ERD than TAA,
whereas Ser, Phe, Leu, Gly, Thr, Tyr, Ile, Cys, Val, Ala and Met showed lower (p < 0.05) ERD than
TAA. In SoyPass1, ERD of Lys and Cys did not differ significantly from TAA. With these
exceptions, variation in ERD among AA in SoyPass1 was as in SBM. However, the differences
between individual AA and TAA were much smaller than in SBM. Intestinal indigestibility of TAA
measured on original feed (OF) was 1.8 and 2.0% for SBM and SoyPass1, respectively (p > 0.05).
For CP, the corresponding values were 2.0% for SBM and 2.3% for SoyPass1. Pre-incubating the
samples in the rumen for 16 h, numerically decreased intestinal indigestibilities of all individual
AA, but the effect was significant for only 5 AA. There were significant differences in intestinal
indigestibilities among AA, but the differences were small in magnitude. From the results obtained,
it was concluded that, for SBM and SoyPass1, TAA in the protein fraction digested in the intestine
*
Corresponding author. Tel.: 47-64-94-80-00; fax: 47-64-94-79-60.
E-mail address: odd.harstad@ihf.nlh.no (O.M. Harstad).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 1 1 4 - 5
32
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
(PDI) can be predicted accurately by using proportion AA-N: N in rumen undegraded protein
(RUP) of 0.85, and ERD and intestinal indigestibility as for CP. For SoyPass1, this way of
prediction of individual AA would result in only small errors, at least for those AA which are
regarded as limiting in milk production. In contrast, for SBM satisfactory prediction of individual
AA absorbed in the intestine requires determination of ERD on individual basis. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: Amino acid profile; Lys; Met; Protein; Nylon bag technique; Mobile nylon bag technique
1. Introduction
Solvent-extracted soybean meal (SBM), which is a commonly used protein supplement
to high-producing dairy cows, is palatable with a well-balanced amino acid (AA)
composition. However, SBM protein is extensively degraded in the rumen. Highproducing dairy cows need significant amounts of rumen undegraded feed protein (RUP)
which is digested post-ruminally to meet their AA requirement. Treatment of SBM with a
xylose-containing calcium lignosulfonate have increased the proportion of RUP in SBM
considerably (Windschitl and Stern, 1988; Walts and Stern, 1989; Nakamura et al., 1992).
In diets, where SBM is the major contributor of RUP, Met turns out to be the first limiting
AA (Maiga et al., 1996; Schingoethe, 1996). The AA profile of RUP in untreated SBM
can be different from that of the original feed (Crooker et al., 1986; Susmel et al., 1989;
Erasmus et al., 1994; Cozzi et al., 1995; Vanhatalo et al., 1995; Maiga et al., 1996;
O'Mara et al., 1997; Van Straalen et al., 1997; Zebrowska et al., 1997), making prediction
of absorbed AA uncertain. In the experiments conducted with SBM, rumen degradability
of individual AA is determined at one or two rumen incubation times only. As far as we
know, the only exceptions are Varvikko et al. (1983) (one cow only), Susmel et al. (1989)
and Cozzi et al. (1995) with untreated SBM. Varvikko et al. (1983) and Weisbjerg et al.
(1996) determined rumen degradation of AA after three incubation times with
formaldehyde-treated and xylose-treated SBM (SoyPass1), respectively. Therefore,
information about effective rumen degradability (ERD) of individual AA is limited.
Likewise, more information is needed on the intestinal indigestibility of individual AA in
RUP of SBM (O'Mara et al., 1997). The study of Weisbjerg et al. (1996) with SoyPass1
did not include the control of untreated SBM. Thus, the effect of xylose treatment of
SBM on ERD and intestinal indigestibility of individual AA has not previously been
examined in situ.
The main objectives of our research were to determine ERD and intestinal
indigestibility of individual AA of SBM and SoyPass1. A preliminary report on part
of this study has already been published (Prestlùkken and Harstad, 1996).
2. Material and methods
2.1. Experimental feeds
Two samples of solvent-extracted soybean meal (SBM) from different batches and two
samples of SoyPass1 made from the same batches as SBM, respectively, were examined.
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
33
The feeds were manufactured commercially at the same plant (Denofa A/S, Fredrikstad,
Norway). SoyPass1 was manufactured by adding Xylig (Borregaard Lignotech,
Sarpsborg, Norway) to SBM under heat and elevated moisture (US Patent No.
4,957,748, 18 September 1990). Xylig is a product rich in xylose produced from wood.
2.2. Animals and diets
We planned to use the same three animals to carry out the in situ measurements of both
batches of the experimental feeds. Unfortunately, one of the animals used on batch one,
experienced health problems unrelated to the experiment, and was removed from the
study. Therefore, three different animals were used on batch two. All six experimental
animals were multiparous non-lactating dairy cows of the Norwegian Red Cattle breed,
fitted with a rumen cannulae (Bar Diamond, Parma, ID, US) and a T-shaped PVC
duodenal cannulae located 50±80 cm distal to pylorus. They were housed in tie-stalls and
fed a standardized diet at maintenance, consisting of 4 kg grass hay per day and 1.8 kg
concentrate mixture per day (175 g CP kgÿ1 DM). The ration was offered in two equal
meals at 06:00 and 15:00 h. The metabolism unit used was authorized for animal
experiments by the Norwegian Animal Research Authority.
2.3. In situ measurements
The in situ procedures applied to measure rumen degradability and intestinal
indigestibility of crude protein (CP) and individual amino acids (AA) were, as described
by Madsen et al. (1995) and Prestlùkken (1999). One exception was the pore size of the
nylon bags used to measure intestinal indigestibility of CP and AA. In the present study,
nylon bags with pore size of 15 mm (ZBF AG, CH 8803, Ruschlicon, Switzerland) were
used instead of 11 mm as recommended (Madsen et al., 1995). The intestinal
indigestibility measurements were on the original feeds (OF) and their rumen undegraded
feed residues after 16 h of rumen incubation.
2.4. Chemical analyses
Chemical composition of the experimental feeds and AA content of their residues after
washing, rumen or intestinal incubation were carried out as described by Prestlùkken
(1999). Feed crude protein (N 6.25) degradation in the digestive tract was calculated on
basis of N determined by the Dumas method (AOAC, 1990) using the Leco combustion
system (LECO CHN-1000 analyser; Leco, MI).
2.5. Calculations and statistical analysis
The kinetics of in situ CP and AA degradation in the rumen were calculated according
to the following exponential model: D(t) a b(1 ÿ exp (ÿct)), where D(t) is the
percentage degradation of CP or AA at time t; a the soluble fraction; b the potential
degradable fraction, and c the fractional degradation rate of b. The non-linear parameters
were obtained by use of the PROC NLIN procedure of SAS (SAS, 1990). Effective rumen
34
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
degradation of CP or AA was calculated as: a (b c)/(c kp) assuming a rumen
outflow rate (kp) of 8% hÿ1. Within feedstuff, ERD and intestinal indigestibility of CP
and individual AA were compared by use of the Duncan multiple range test (SAS, 1990).
The effect of rumen incubation on the proportion of AA-N and individual AA in the
protein residues were tested with linear regression analysis (PROC REG) (SAS, 1990).
Intestinal digestibilities of rumen undegraded AA as well as CP were calculated
according to the following general equation (Hvelplund et al., 1992).
TD UDNÿTU=UDN
where TD is the true intestinal digestibility of rumen undegraded protein fraction
(g 100ÿ1 g); UDN the fraction of rumen undegraded dietary protein (g gÿ1) original feed
protein fraction, and TU the fraction of truly indigestible protein in the feed (g gÿ1)
original feed protein fraction
The amount of each AA digested in the intestine was calculated on the basis of their
content in the feed, ERD and intestinal digestibility. The amount of total and individual
AA digested in the intestine was also predicted based on the assumption that ERD and
intestinal indigestibility of individual AA was as for CP, and that AA constituted 85% of
CP in RUP. Differences between SBM and SoyPass1 in rumen and intestinal degradation
characteristics of CP and AA were tested using PROC GLM (SAS, 1990) with feed and batch
as main effects and animal as random effect. The significance level was p < 0.05, unless
stated otherwise.
3. Results and discussion
3.1. Feed chemical composition
The differences in chemical composition and in AA profile between the two batches of
SBM as well as of SoyPass1 were relatively small (Table 1). The variation of AA-N of
total N from 81.1 to 86.2% in the two batches of SBM was within the range cited in the
literature (O'Mara et al., 1997). The two batches of SBM were similar in AA composition
(Table 1), and in accordance with that observed in the studies of Susmel et al. (1989),
Maiga et al. (1996) and O'Mara et al. (1997). However, in other studies with SBM
(Erasmus et al., 1994; Cozzi et al., 1995; Zebrowska et al., 1997), the AA profile differed
from that found in our experiment.
Xylig, which contains mainly carbohydrate components and minerals, diluted the
content of CP and fat in SoyPass1, as expected. The xylose treatment increased the
measured NDF content by 9%-units. This substantial increase of NDF in SoyPass1
may be due to elevated N content in NDF resulting from the Maillard reaction caused
when SBM is heated with added xylose (Windschitl and Stern, 1988; Van Soest, 1994).
The NDF content of 22.2 and 21.4% of DM in batches 1 and 2 of SoyPass1, respectively,
agree well with the corresponding value of 20.1% found in the study of Weisbjerg et al.
(1996). The treatment of SBM with xylose had no systematic effect on the proportion of
AA-N. The average value of 82.4% for SoyPass1 was slightly >80.4% obtained with
SoyPass1 in the study of Weisbjerg et al. (1996). The relative contribution of Lys was, on
35
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
Table 1
Chemical composition, content of amino acid- N (AA-N), essential AA (EAA), non essential AA (NEAA) and
individual AA in the two batches of solvent-extracted soybean meal (SBM) and xylose-treated SBM (SoyPass1)
Batch 1
Batch 2
SBM
SoyPass
SBM
SoyPass1
g 100ÿ1 g DM
Ash
Crude protein
Crude fat
Crude fibre
NDF
6.7
52.0
1.6
5.8
13.6
6.9
47.6
1.4
5.6
22.2
7.2
50.6
2.4
7.4
12.7
6.9
46.5
2.0
7.5
21.4
g 100ÿ1 g AA
EAA
Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Tyr
Val
49.0
7.8
2.8
4.8
7.8
6.4
1.4
5.1
4.0
4.1
4.8
48.0
7.2
2.7
4.8
7.9
5.3
1.4
5.2
4.1
4.2
5.2
49.1
7.7
2.9
5.0
7.7
6.3
1.3
5.3
4.1
3.8
5.0
48.3
7.2
2.8
5.1
7.9
5.3
1.3
5.4
4.2
3.8
5.3
51.0
4.0
11.7
1.5
18.7
4.3
5.3
5.6
52.0
4.4
11.8
1.4
19.2
4.4
5.2
5.6
51.0
4.3
11.3
1.7
18.6
4.4
5.3
5.5
51.7
4.5
11.4
1.6
18.9
4.4
5.4
5.5
81.1
81.5
86.2
83.3
NEAA
Ala
Asp
Cys
Glu
Gly
Pro
Ser
g 100ÿ1 g N
AA-N
1
average, 17% lower and of Arg 7% lower in SoyPass1 compared with SBM (p < 0.05)
(Table 1). Lys is usually the most sensitive AA to be affected by methods used to protect
proteins from ruminal degradation (Windschitl and Stern, 1988). It is often lost at levels
5±15 times higher than other AA (Dakowski et al., 1996). Lys may be one of the first
limiting AA in milk protein synthesis (Schingoethe, 1996) and is, therefore, of particular
interest. As far as we know, there are no results published on the effect of treating SBM
with xylose and heating on its content of Lys. However, negative effects on Lys content,
even greater than those found in the present study, are reported from experiments with
formaldehyde treated SBM (Crooker et al., 1986), roasted soybeans (Faldet et al., 1992),
moist heat treated Canola meal (Moshtaghi Nia and Ingalls, 1995) and toasted rape seed
meal (Dakowski et al., 1996). Manufacturing of SoyPass1 increased significantly the
relative contribution of Ile, Leu, Phe, Val and Gly, but these effects were small in
magnitude (Table 1).
36
O.M. Harstad, E. Prestlùkken / Animal Feed Science and Technology 83 (2000) 31±47
3.2. Rumen degradation characteristics
Rumen degradation characteristics of protein fractions and individual AA are given in
Table 2. There were small, but significantly (p < 0.05) higher ERD of TAA than CP; 1.1
and 1.8%-units for SBM and SoyPass1, respectively. This is in contrast to Susmel et al.
(1989) who observed for SBM ERD, calculated with an outflow rate of 7% hÿ1, of 50 and
54% for TAA and CP, respectively. Weisbjerg et al. (1996) found also for SoyPass1 ERD
of TAA as much as 4%-units higher than for CP. Thus, it is uncertain if ERD of CP can be
used to predict ERD of TAA for SBM and SoyPass1.
Solvent-extracted soybean meal showed greater variation in ERD among AA than
SoyPass1. In SBM, Arg, Glu and Lys had higher (p < 0.05) ERD than TAA, whereas Ser,
Phe, Leu, Gly, Thr, Tyr, Ile, Cys, Val, Ala and Met showed lower ERD than TAA (Table
2). The difference between Arg and Met, which showed the highest and lowest ERD
values, respectively, was as high as 12.6%-units. Susmel et al. (1989) found also that Arg,
Glu and Lys were the three AA in SBM, which showed the highest ERD. However, in
contrast to our results, Met showed higher ERD and Pro lower ERD than average in the
study of Susmel et al. (1989). Moreover, in their experiment, ERD of Ser, Phe, Ile and
Leu did not show lower ERD than the average as observed in our study (Table 2).
The change in AA profile from original feed (OF) to RUP reflects the effect of rumen
exposure on the extent of rumen degradation of individual AA. Thus, any conclusions on
the effects of rumen exposure on AA profile also apply to rumen degradation of
individual AA. A fall in proportion results in higher degradation than average, whereas an
increase in proportion will result in lower than average degradation. For some AA, their
proportion in feed residues changed dramatically after rumen incubation for >24 h, and
sometimes in a direction opposite to that observed in incubations of