Effective rumen degradability and intestinal
indigestibility of individual amino acids in
solvent-extracted soybean meal (SBM) and
xylose-treated SBM (SoyPass
1)
determined in situ
O.M. Harstad
*, E. Prestlùkken
Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N - 1432 AÊ s, 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 SoyPass1than in SBM (p< 0.05). Manufacturing of SoyPass1increased 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 SoyPass1and 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 SoyPass1was 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
Animal Feed Science and Technology 83 (2000) 31±47
*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).
(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. High-producing 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.
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 kgÿ1DM). 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 15mm (ZBF AG, CH 8803, Ruschlicon, Switzerland) were
used instead of 11mm 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 (N6.25) 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)ab(1ÿexp (ÿct)), where D(t) is the
percentage degradation of CP or AA at time t; a the soluble fraction; b the potential
degradable fraction, andcthe fractional degradation rate ofb. The non-linear parameters
were obtained by use of thePROC NLINprocedure of SAS (SAS, 1990). Effective rumen
degradation of CP or AA was calculated as: a(bc)/(ckp) 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 100ÿ1g); 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 usingPROC GLM(SAS, 1990) with feed and batch
as main effects and animal as random effect. The significance level wasp< 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
average, 17% lower and of Arg 7% lower in SoyPass1compared 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).
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
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 SoyPass1ERD
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 <24 h. This was observed for Ile, Leu, Met, Thr, Gly and Pro in SBM. The two longest incubation intervals were, therefore, omitted from the regression analyses presented in Table 3. In SBM, incubation up to 24 h significantly affected the proportion of 14 out of the 17 AA
studied. In SoyPass1
, only Arg, Leu and Thr were influenced (p< 0.05) by rumen
incubation. Crooker et al. (1986) determined the AA profile in OF and RUP of SBM after rumen incubation for 12 h. Their results showed a similar degradation pattern to that observed in the present study. The exceptions were Met and Pro which showed equal, and lower, rumen degradability than the average, respectively. Erasmus et al. (1994) compared AA profile in OF and the rumen residues after 16 h of incubation and observed
that for SBM, only His and Lys decreased after rumen exposure (p< 0.05), i.e. had higher
degradability than the average. This is in accordance with our result for Lys, but not for His which was not significantly affected by rumen incubation (Tables 2 and 3). Moreover, in the study of Erasmus et al. (1994), none of the AA proportions increased significantly after rumen incubation. However, 11 of the AA were affected numerically in the same way as in our study. The most pronounced deviations were observed for Ala, Cys and Glu, which were only negligibly affected by rumen exposure in the study of Erasmus et al. (1994), but were significantly affected in our study. In contrast, the results of Maiga et al. (1996) with SBM were in agreement with our results for Ala, Cys and Glu. Proportions of Arg and Glu, and to a lesser extent Lys, decreased after rumen incubation for 12 h, whereas Met, Thr, Ala, Cys and Tyr showed the greatest increase in proportion.
Table 2
Rumen degradation characteristics of crude protein (CP), total amino acids (TAA), essential AA (EAA), non-essential AA (NEAA) and individual AA of solvent-extracted soybean meal (SBM) and xylose-treated SBM (SoyPass1)
Protein-fraction Degraded after different periods (h) in rumen (g 100ÿ1g) Degradation characteristicsa
0b,c 2c 4c 8c 16c 24c 48c 72c ac bc cc ERDc,d
CP SBM 15.0 31.1 33.7 47.0 66.8 79.4 96.8 99.2 17.4 82.4 5.89 52.2 de
SoyPass1 9.2 10.6 13.0 18.6 25.6 42.8 81.9 89.3 3.3 96.7 2.59 26.9 e
SEM 0.12 0.89 1.45 1.53 1.79 3.26 2.71 1.77 0.81 0.88 0.29 1.19
TAA SBM 14.0 31.9 35.7 49.5 68.1 79.7 96.9 99.2 17.7 82.2 6.18 53.3 c
SoyPass1 8.4 11.9 16.4 22.5 28.7 43.7 82.3 89.5 5.2 94.8 2.65 28.7 bc
SEM 0.46 1.08 0.78 1.45 1.51 3.59 2.66 1.80 0.89 0.95 0.32 1.22
EAA SBM 14.7 32.2 36.0 49.9 68.0 79.8 96.9 99.4 18.2 81.7 6.14 53.5 c
SoyPass1 8.2 12.2 16.3 23.2 28.7 44.1 82.7 89.7 5.2 94.8 2.68 28.9 bc
SEM 0.49 1.07 0.79 1.46 1.53 3.58 2.65 1.79 0.90 0.93 0.33 1.23
NEAA SBM 13.1 31.6 35.4 48.9 68.3 79.7 96.9 99.0 16.9 82.8 6.24 53.1 cd
SoyPass1 8.6 11.5 16.6 21.5 28.6 43.3 81.7 89.2 5.0 95.0 2.62 28.4 cd
SEM 0.42 1.11 0.80 1.46 1.48 3.59 2.68 1.80 0.89 0.98 0.31 1.20
Arg SBM 17.8 37.8 41.2 55.5 73.4 84.0 97.7 99.6 22.1 77.5 7.07 58.4 a
SoyPass1 10.6 14.7 19.0 26.1 32.4 47.5 84.5 90.7 7.9 92.1 2.80 31.7 a
SEM 0.75 1.12 0.82 1.43 1.41 3.51 2.22 1.63 1.04 1.18 0.29 1.13
His SBM 18.8 33.6 36.7 49.4 68.5 80.2 97.0 99.4 20.9 79.1 5.90 54.1 c
SoyPass1 10.9 16.7 20.2 24.8 30.2 47.0 84.8 90.7 8.5 91.5 2.73 31.7 a
SEM 0.59 1.09 0.76 1.56 1.78 3.45 2.46 1.66 0.78 0.77 0.32 1.34
Ile SBM 11.7 26.6 30.7 43.7 63.8 76.2 96.3 99.3 13.8 86.2 5.59 49.1 g
SoyPass1 6.8 8.5 12.1 17.9 25.1 40.4 79.9 88.2 2.4 97.6 2.53 25.4 g
SEM 0.49 1.12 0.81 2.29 1.66 3.65 3.12 2.04 0.85 0.85 0.32 1.24
Leu SBM 12.0 28.9 32.3 44.2 63.9 76.5 96.4 99.4 15.1 84.9 5.57 49.8 g
SoyPass1 7.3 11.3 15.1 19.7 25.2 40.3 80.0 88.7 3.8 96.2 2.50 26.6 ef
SEM 0.45 1.18 0.72 1.56 1.67 3.73 3.09 1.99 0.87 0.87 0.32 1.30
Table 2 (Continued)
Protein-fraction Degraded after different periods (h) in rumen (g 100ÿ1g) Degradation characteristicsa
0b,c 2c 4c 8c 16c 24c 48c 72c ac bc cc ERDc,d
Lys SBM 15.5 33.9 40.6 55.5 68.8 80.7 97.0 99.2 20.4 78.9 6.61 56.0 b
SoyPass1 4.6 8.8 15.0 27.1 28.9 43.2 83.6 89.9 3.3 96.8 2.79 28.2 cd
SEM 0.59 1.15 1.23 1.60 1.33 3.60 2.56 1.74 0.84 1.02 0.32 1.32
Met SBM 8.5 21.8 25.6 41.1 60.9 73.5 95.9 99.2 9.5 90.5 5.43 45.8 i
SoyPass1 5.8 7.0 9.9 20.0 26.5 41.2 81.7 88.7 0.94 99.1 2.67 25.5 g
SEM 0.38 1.29 1.17 1.37 2.12 4.05 3.11 1.90 0.94 0.94 0.36 1.51
Phe SBM 11.7 28.3 31.9 46.9 66.2 78.3 96.7 99.4 14.5 85.4 6.0 50.9 f
SoyPass1 8.5 10.1 12.9 20.7 26.0 41.0 80.8 88.5 3.5 96.5 2.55 26.7 ef
SEM 0.11 1.02 0.82 1.47 1.64 3.65 2.88 1.98 0.64 0.69 0.31 1.27
Thr SBM 12.5 27.9 30.3 44.2 63.6 76.2 96.3 99.3 14.5 85.5 5.55 49.3 g
SoyPass1 6.9 11.1 15.8 22.8 28.5 44.2 82.9 89.4 4.2 95.8 2.71 28.4 cd
SEM 0.85 1.18 0.79 1.36 1.62 3.79 2.86 1.82 1.08 1.08 0.34 1.36
Tyr SBM 12.0 27.3 30.8 44.5 63.4 76.4 96.2 99.0 14.4 85.6 5.56 49.3 g
SoyPass1 10.0 11.0 14.8 19.9 26.9 42.3 81.2 88.4 4.6 95.4 2.54 27.6 de
SEM 0.16 0.92 0.71 2.15 1.75 3.72 2.98 1.94 0.67 0.67 0.31 1.23
Val SBM 9.0 24.0 26.7 40.6 61.4 74.4 96.0 99.1 10.6 89.4 5.42 46.5 i
SoyPass1 4.8 11.4 13.7 17.7 24.9 41.5 80.6 88.7 2.45 97.5 2.56 25.9 gf
SEM 0.25 1.08 0.70 1.92 1.88 3.86 3.18 1.94 0.70 0.70 0.31 0.26
Ala SBM 10.0 23.4 26.2 39.2 60.5 73.2 95.8 99.1 10.8 89.2 5.24 45.8 i
SoyPass1 9.6 12.3 16.6 21.1 26.4 43.0 81.5 89.1 5.4 94.6 2.56 28.2 cd
SEM 0.05 1.16 0.85 1.71 1.91 4.05 3.19 1.84 0.44 0.44 0.32 1.47
Asp SBM 13.5 32.2 35.9 49.5 68.8 80.2 97.1 99.5 17.4 82.3 6.31 53.6 c
SoyPass1 8.4 11.6 16.0 22.2 28.8 42.2 81.0 89.4 5.0 95.0 2.6 28.2 cd
SEM 0.44 1.13 0.92 1.39 1.42 3.68 2.76 1.84 0.90 1.00 0.31 1.23
Cys SBM 10.5 24.9 29.5 44.4 61.8 75.2 96.1 99.2 12.7 87.3 5.51 48.1 h
SoyPass1 6.9 11.6 15.4 24.9 31.0 41.6 83.3 90.0 4.8 95.2 2.70 28.8 bc
SEM 0.45 1.01 1.04 1.36 1.55 3.28 2.86 1.71 0.87 0.87 0.30 1.21
Glu SBM 14.8 36.4 41.3 55.1 73.9 84.2 97.8 99.6 19.7 79.6 7.49 58.1 a
SoyPass1 9.8 11.9 18.1 21.9 30.2 44.8 82.2 89.8 6.0 94.0 2.67 29.4 b
SEM 0.36 1.22 0.90 1.50 1.37 3.37 2.36 1.76 0.82 1.04 0.26 1.11
Gly SBM 12.5 28.9 32.2 44.3 64.1 76.0 95.7 97.0 15.6 83.8 5.57 49.7 g
SoyPass1 7.1 12.0 16.7 21.9 28.4 42.8 80.8 87.8 5.0 95.0 2.57 28.0 cd
SEM 0.42 1.12 0.77 1.47 1.53 3.66 2.89 1.83 0.91 0.85 0.33 1.27
Pro SBM 12.7 32.1 34.9 49.4 68.7 80.4 97.0 99.2 16.6 83.0 6.36 53.3 c
SoyPass1 9.2 11.1 15.3 21.1 27.8 43.7 82.6 89.4 4.6 95.4 2.65 28.2 cd
SEM 0.68 1.18 0.80 .50 1.96 3.79 2.58 1.81 1.19 1.30 0.30 1.17
Ser SBM 12.6 29.9 33.4 46.9 66.7 78.3 96.7 99.0 15.9 84.0 5.96 51.5 ef
SoyPass1 6.5 9.5 15.1 18.9 26.7 41.7 81.5 88.9 3.03 97.0 2.60 26.6 ef
SEM 0.54 1.24 1.02 2.38 1.38 3.72 2.78 1.87 0.97 1.01 0.32 1.25
aa, Water soluble and rapidly degradable fraction (g 100ÿ1g);b, insoluble, but degradable fraction (g 100ÿ1g);c, degradation rate of thebfraction (% hÿ1); ERD,
effective rumen degradability calculated with an outflow rate (k)8% hÿ1; SEM, standard error of LS means. bWater solubility.
cSoyPass1differ (
p< 0.05) from SBM for all protein fractions and individual AA.
dMeans with different letters within a column and feed differ (p< 0.05).
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Table 3
Proportion of amino acid N (AA-N) of total N (g 100ÿ1g), and individual AA (g 100ÿ1g AA) in rumen undegraded protein after washing only (0 h), or after incubation in the rumen for different periods for solvent-extracted soybean meal (SBM) and SoyPass1
Ala SBM 4.3 4.6 4.7 4.9 5.0 5.3 5.5 5.1 4.5 (0.06) 0.04 (0.00) 0.92 *
SoyPass1 4.4 4.4 4.4 4.5 4.5 4.5 4.5 4.5 4.4 (0.03) 0.00 (0.00) 0.08
Asp SBM 11.4 11.3 11.3 11.3 11.1 11.0 9.5 8.0 11.4 (0.03) ÿ0.02 (0.00) 0.92 *
SoyPass1 11.5 11.6 11.6 11.5 11.5 11.8 12.0 11.4 11.5 (0.05) 0.01 (0.00) 0.29
Cys SBM 1.6 1.7 1.7 1.7 1.8 1.9 1.9 1.6 1.7 (0.02) 0.01 (0.00) 0.88 *
SoyPass1 1.5 1.5 1.5 1.5 1.5 1.6 1.4 1.4 1.5 (0.03) 0.00 (0.00) 0.23
Glu SBM 18.3 17.2 16.9 16.3 15.1 14.2 12.1 10.9 17.7 (0.20) ÿ0.16 (0.02) 0.95 *
SoyPass1 18.7 18.9 18.6 19.0 18.5 18.5 18.6 17.8 18.8 (0.12)
ÿ0.01 (0.01) 0.17
Gly SBM 4.4 4.5 4.5 4.7 4.8 5.1 9.6 17.6 4.4 (0.03) 0.03 (0.00) 0.97 *
SoyPass1 4.4 4.4 4.4 4.4 4.4 4.4 4.7 5.3 4.4 (0.02) 0.00 (0.00) 0.21
Pro SBM 5.4 5.2 5.3 5.2 5.1 5.0 5.3 5.6 5.3 (0.03) ÿ0.01 (0.00) 0.83 *
SoyPass1 5.2 5.3 5.3 5.3 5.3 5.2 5.0 5.3 5.3 (0.02)
ÿ0.00 (0.00) 0.12
Ser SBM 5.5 5.6 5.7 5.7 5.7 5.8 6.5 7.6 5.6 (0.03) 0.01 (0.00) 0.68 *
SoyPass1 5.6 5.7 5.6 5.7 5.7 5.7 5.7 5.8 5.6 (0.03) 0.00 (0.00) 0.01
aRegression analysis with AA-N of total N and individual AA as the dependent variables and time of ruminal incubation (0±24 h) as independent variable for SBM
and SoyPass1. *(p< 0.05).
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(2000)
31±47
O'Mara et al. (1997) compared AA profile in intact SBM with the AA profile in the RUP fraction after incubation for 8 and 12 h. With the exception of Pro, the individual AA showed the same degradation pattern as in the present study. However, Ala increased less in the study of O'Mara et al. (1997) than in our study. Cozzi et al. (1995) and Vanhatalo et al. (1995) compared the profiles of essential AA of intact SBM with those of the residues after washing or rumen incubation for 8, 12, 16 and 24 h, and 10 h, respectively. As in our study, Arg and Lys had higher rumen degradation than average. However, in their studies, His also showed a significantly higher rumen degradation than the average, which does not agree with our results. The other essential AA reported by Cozzi et al. (1995), (Ile, Leu, Met, Phe, Thr, Val) showed no change, or only a tendency toward a lower proportion, after rumen incubation, indicating a higher extent of degradation than the average. This is in contrast to our results (Tables 2 and 3) and the results of Vanhatalo et al. (1995). Zebrowska et al. (1997) and Van Straalen et al. (1997) determined rumen degradation of individual AA in SBM after incubation for 16 and 12 h, respectively. Their results showed a similar degradation pattern to that observed in the present study. The exception was Val, which had an average rumen degradability in the study of Zebrowska et al. (1997), but a lower degradability than the average in our study (Tables 2 and 3) and in the study of Van Straalen et al. (1997). Based on literature values, Rulquin and VeÂrite (1993) found that the concentration of Arg tends to decrease in the residues after rumen incubation (9±16 h), i.e. show higher degradability than average, and that branch-chained AA (Leu, Ile and Val) tend to increase, i.e. show lower degradation than average after rumen incubation. Arg is known to be very sensitive to fermentation, whereas peptide bounds with branch-chained AA are highly resistant to hydrolysis (Rulquin and VeÂriteÂ, 1993). The effect of rumen exposure on individual AA degradability obtained in sacco are not consistent. There are discrepancies between experiments, which partly may arise from individual subjective interpretation and methodological differences (Rulquin and VeÂriteÂ, 1993). However, the majority of the experiments indicate that, in highly degradable protein sources, like SBM, Arg, Glu and probably Lys have higher extents of rumen degradation than average, whereas Met and the branch-chained AA (Leu, Ile and Val) are degraded less extensively than average. Although our results, and those of Maiga et al. (1996), O'Mara et al. (1997), Van Straalen et al. (1997) and Zebrowska et al. (1997), indicate that Thr, Tyr, Cys and Ala in SBM have a lower extent of rumen degradation than average, the findings for Cys and Ala are not consistent for SBM (Erasmus et al., 1994).
The ERD of SoyPass1 for TAA was approximately half of that for untreated SBM
(28.7 vs. 53.3%) (Table 2). For most of the AA, the rumen escape fraction increased
between 50 and 70%. This effect was attributed to the reduction of the solublea-fraction,
and to the reduction in the rate of degradation of the potentially degradableb-fraction.
Solvent-extracted soybean meal and SoyPass1 showed the same degradation pattern in
relation to the mean value of TAA, except for Lys and Cys. However, the differences between the individual AA and TAA were much lower than in SBM, but were still statistically significant for some AA (Table 2). The difference between Arg and Ile, which showed the highest and lowest degradability values, respectively, was only 6.3%-units. Thus, the treatment of SMB had a relatively greater effect on AA with high compared to low ERD before treatment.
Lys, which was degraded to a greater extent than TAA in SBM (Table 2), showed a
lower extent of rumen degradation than TAA in SoyPass1
, although this was not statistically significant. Lys is the primary AA involved in the Maillard reaction, which is responsible for the decrease in protein degradation after xylose treatment (Windschitl and Stern, 1988). It is, therefore, not surprising that the treatment of SMB with xylose and heating had a specific protecting effect on Lys. In the study of Weisbjerg et al. (1996), Lys
in SoyPass1was also degraded in the rumen to the same extent as TAA (51.5 vs. 50.9%).
However, in their study, Met had 2.1%-units higher ERD than TAA, which is in contrast to our result (Table 2). A smaller level of variation in rumen degradability among AA for high RUP protein sources, such as treated SBM, is consistent with published findings (see, O'Mara et al., 1997). However, the effect of treatment on reducing the rumen degradability of Lys in our experiment was greater than seen in experiments with formaldehyde treated SBM (O'Mara et al., 1997).
In the literature, 8, 12 or 16 h incubation times are most commonly used in experiments to investigate the influence of rumen exposure on the AA profile. The AA profile in the residues after a single rumen incubation time may be different from that of RUP based on ERD of individual AA (Tables 2 and 3). Hence, caution must be observed when the AA profile in the residue of a single incubation point is used as a predictor for the AA profile in RUP reaching the small intestine.
3.3. Intestinal indigestibility of feed protein fractions
Intestinal indigestibility of CP and AA of OF protein and protein residues after incubation in the rumen for 16 h are shown in Table 4. Intestinal indigestibility of TAA
was lower than of CP in both, SBM and SoyPass1
, but this difference was relatively small in magnitude and not statistically significant (Table 4). Zebrowska et al. (1997) determined intestinal digestibility of rumen undegraded CP and AA in SBM after 16-h incubation and observed values of 99% for both, CP and TAA. Moreover, in the study of Weisbjerg et al. (1996), the difference in intestinal digestibility between CP and TAA was
also not significant for SoyPass1
. Thus, CP intestinal digestibility seems to be a good
predictor of intestinal AA digestibility for both, SBM and SoyPass1.
Total tract indigestibility of CP of SBM, as low as 1±2%, (Table 4) is in agreement with earlier results in our laboratory (Volden and Harstad, 1995) as well of others (Erasmus et al., 1994; Vanhatalo et al., 1995; O'Mara et al., 1997; Van Straalen et al., 1997; Zebrowska et al., 1997). Likewise, there were only small and non-significant effects of rumen pre-incubation on protein total tract indigestibility (Table 4). This is in agreement with other studies using SBM (Volden and Harstad, 1995). Although the treatment of SBM numerically increased total tract indigestibility of CP, TAA and individual AA, the effects were not significant. Intestinal indigestibility of 2% of TAA measured on intact
SoyPass1
is <6%, found in the study of Weisbjerg et al. (1996). Use of bags with pore
size of 9mm in the study of Weisbjerg et al. (1996), compared with 15mm in our study,
may explain at least a part of this difference.
There were some statistically significant differences in indigestibility among individual AA, but most of these were small in magnitude. The exceptions were Arg and Glu, which
had lower indigestible fractions and Gly, which showed a higher indigestible fraction than TAA. Total tract indigestibility of individual AA in SBM reported in the literature are not consistent (Erasmus et al., 1994; O'Mara et al., 1997).
In the study of Dakowski et al. (1996), the intestinal digestibility of Lys in rapeseed meal was more negatively affected by heat treatment than TAA. In the present study, we also expected a specific negative effect of treatment on the intestinal
digestibility of Lys in SoyPass1
due to the use of Lys in the Maillard reaction. However, as shown in Table 4, the effect of treatment on intestinal indigestibility of Lys was not greater than the average effect. In the study of Weisbjerg et al. (1996), the intestinal
digestibility of Lys in SoyPass1
did not differ from TAA digestibility. Thus, it seems that
the manufacturing of SoyPass1
has no negative influence on the intestinal digestibility of Lys.
Table 4
True indigestibility of crude protein (CP), total amino acids (TAA), essential AA (EAA), non-essential AA (NEAA) and individual AA of original feed protein (I-OF) and feed protein residues after incubation in the rumen for 16 h (I-16) measured with the mobile nylon bag technique in solvent-extracted soybean meal (SBM) and xylose-treated SBM (SoyPass1)
Protein-fraction SBMa SoyPass1a SEM Contrast
I-OF I-16 I-OF I-16 feed (F) incubation (I) FI
aMeans with different letters within a column differ (p< 0.05). *(p< 0.05).
3.4. Protein value of the rumen undegraded fraction
The amount of total and individual AA digested in the intestine, both measured and predicted, is shown in Table 5. Xylose treatment of SBM increased the measured amount
of TAA digested in the small intestine by 80 g kgÿ1DM, or 40% (Table 5).
There were no significant differences between the measured and predicted TAA digested in the small intestine (Table 5). The differences between predicted and measured
values were, respectively, 2.6% for SBM and 3.1% for SoyPass1
. Thus, the hypothesis that feed content of absorbable TAA may be predicted on the basis of measurements on
CP, and use of the constant of 0.85 for TAA in RUP holds for SBM and SoyPass1
. This is in agreement with the conclusion of Weisbjerg et al. (1996), based on results for 15
concentrates. Moreover, for SoyPass1
, prediction resulted in only small errors for most of the individual AA. Measured disappearance of Lys and Met agreed well with those calculated. The AA that showed the greatest deviation from predicted values were Arg
and His. For SoyPass1
, prediction would result in even smaller errors if the proportion of
Table 5
Measured and predicted amount of total amino acids (TAA), essential AA (EAA), non-essential AA (NEAA) and individual AA digested in the intestine from the rumen undegraded protein fraction (RUP) measured in situ
Protein-fractiona SBM SoyPass1 SEM Contrastsb
predictedc measured predictedc measured 1 2 3
TAA 199.7 194.6 281.2 272.7 5.1
EAA 99.5 96.7 137.5 133.3 2.5 *
NEAA 100.2 98.0 143.7 139.4 2.6 *
Arg 16.0 14.0 21.1 19.8 0.4 * *
bProbability of contrasts:p< 0.05. 1, SBM vs. SoyPass1; 2, measured vs. calculated; and 3, interaction. cThe predicted values are based on the assumptions that effective rumen degradability and intestinal
indigestibility of individual AA were as for crude protein, and that the AA constituted 85% of RUP fraction (g kgÿ1DM).
*p< 0.05.
AA-N actually found in the original feed (0.824 in average) was used instead of the factor of 0.85. In contrast, prediction would lead to a bias for some of the AA in SBM, with predicted values giving an overestimation of as much as 13% for Arg, and Glu and an underestimation of 10±13% for Val and Met.
From the results obtained in this study, it can be concluded that, for SBM and
SoyPass1, TAA in RUP digested in the small intestine can be predicted accurately by
using a proportion AA-N : N in RUP of 0.85, and ERD and intestinal indigestibility as
for CP. For SoyPass1, this way of predicting individual AA would result in only small
errors, at least for those AA which are regarded as limiting for milk production. In contrast for SBM, satisfactory prediction of individual AA absorbed in the intestine requires determination of ERD on an individual basis.
Acknowledgements
We gratefully acknowledge M. Henne, M. Bratberg and R. évstegaard for technical assistance.
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