Using the DVE/OEB model to determine optimal
conditions of pressure toasting on horse beans
(
Vicia faba
) for the dairy feed industry
P. Yu
*, J.O. Goelema, S. Tamminga
Department of Animal Nutrition, Wageningen Agricultural University, Zodiac,Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Received 18 January 2000; received in revised form 27 April 2000; accepted 22 June 2000
Abstract
The effects of pressure toasting (100, 118 and 1368C for 3, 7, 15 and 30 min) of horse beans on
potential ruminant protein nutritional values were evaluated by the new Dutch protein evaluation system: the DVE/OEB model. The items assessed in this experiment were: (a) rumen bypass protein (BCP); (b) rumen bypass starch (BSt); (c) fermented organic matter (FOM); (d) truly absorbed bypass protein (ABCP); (e) microbial protein synthesized in the rumen based on available energy (E_MP); (f) microbial protein synthesized in the rumen based on available N (N_MP); (g) true protein supplied to the small intestine (TPSI); (h) truly absorbed rumen synthesized microbial protein (AMP); (i) endogenous protein losses (ENDP); (j) truly digested protein in the small intestine (DVE) and (k), degraded protein balance (OEB). Pressure toasting signi®cantly increased
BCP, BSt, TPSI, ABCP, DVE (P<0:001) and decreased FOM, E_MP, AMP, N_MP and OEB
(P<0:001) with increasing temperatures and times. The values of BCP, BSt, TPSI, ABCP and
DVE at 1368C/15 min were increased by 213.0, 83.0, 66.1, 246.1 and 90.1% and the values of
FOM, E_MP, AMP, N_MP and OEB at 1368C/15 min were decreased by 28.7, 30.9, 29.0, 49.0 and
69%, respectively, over the raw horse beans. The results indicated that although pressure toasting reduced microbial protein synthesis due to reducing FOM, TPSI didn't decrease but increased substantially because BCP more than enough to compensate for the decrease in microbial protein. Therefore the net absorbable DVE in the small intestine was highly increased. The OEB values
were signi®cantly reduced (P<0:001) but were not negative. Results indicated that microbial
protein synthesis might not be impaired due to the suf®cient N supplied in the rumen, but the high
positive OEB values in the most treatments except 1368C/15 min (The OEB values: 31.9 g/kg DM)
86 (2000) 165±176
*Corresponding author. Present address: Department of Animal and Poultry Science, University of
Sasakatchewan, 51 Campus Drive, Saskatoon, SK, Canada S7N 5A8. Tel.:1-306-966-4132; fax:1-306-966-4151.
E-mail address: yupe@sask.usask.ca (P. Yu).
indicated that there were large losses of N in the rumen. It was concluded that pressure toasting at high temperature was effective in shifting protein degradation from rumen to the intestines and in
increasing the DVE values without reaching negative OEB values. The treatments of 1008C for 7,
15 or 30 min, 1188C for 3, 7, 15 or 30 min and 1368C for 3 or 7 min were not suf®cient to reduce
N-loss in the rumen due to the too high OEB values. But pressure toasting at 1368C/15 min might be
optimal treatments for horse beans due to the very lower OEB values. Additional study is required concerning the effects of optimal pressure toasting of horse beans on animal performance.
#2000 Published by Elsevier Science B.V.
Keywords:Horse bean; Protein evaluation; DVE/OEB model; Optimal pressure toasting; Cows
Nomenclature
ABCP truly absorbed bypass protein in the small intestine (g/kg DM)
AMP truly absorbed rumen synthesized microbial protein in the small intestine (g/kg DM)
BCP bypassing rumen microbial degradation of feed protein (g/kg DM) %BCP fraction of bypassing rumen degradation of feed protein
BSt bypassing rumen microbial fermentation of feed starch (g/kg DM) %BSt fraction of bypassing rumen degradation of feed starch
Cfat crude fat (g/kg DM)
D insoluble but potential degradation fraction in the in sacco incubations (%) DOM digested organic matter (g/kg DM)
DVE truly digested protein in the small intestine (g/kg DM) dASH digestibility of inorganic matter (%)
dBCP digestibility of bypass protein in the small intestine (%) ENDP endogenous protein in the small intestine (g/kg DM)
E_MP microbial protein synthesized in the rumen based on available energy (g/kg DM)
FOM organic matter fermented in the rumen (g/kg DM) Kd the rate of degradation ofDfraction (%/h) Kp passage rate (%/h)
N_MP microbial protein synthesized in the rumen based on available nitrogen (g/kg DM)
OEB degraded protein balance (g/kg DM)
S soluble fraction in the in sacco incubation (%) T0 lag time in which no degradation takes place (h) TPSI true protein supplied to the small intestine (g/kg DM)
U undegradable fraction in the in sacco incubation (%) UASH undigested inorganic matter (g/kg DM)
UDM undigested dry matter (g/kg DM) UOM undigested organic matter (g/kg DM)
1. Introduction
Horse beans (Vicia faba),also called faba beans (Petterson and MacKintosh, 1994), have high protein (25±30%) and starch contents (30±40%) (Tamminga et al., 1990; Petterson and MacKintosh, 1994), are well suited agronomically to the ecological and climatic conditions of many countries (Cros et al., 1992; Benchaar et al., 1994) and appear to be potentially useful protein supplements in ruminal diets.
However their rapid and extensive degradation by rumen microbes, resulting in imbalance between feed breakdown and microbial protein synthesis and causing unnecessary N-loss from rumen, make them unsuitable and/or inef®cient to be used in the unprocessed form in ruminal diets. Studies have shown that protein degradability of horse bean was 85±90% (Van Straalen and Tamminga, 1990; Aguilera et al., 1992; Cros et al., 1992). Thus there were little protein remaining to bypass the rumen to the small intestine. But protein becomes available to the animal only after digestion in and absorption from the small intestine (Hvelpund et al., 1992).
Not only is protein degradability high in horse beans but also the starch degradability. The study indicated that ruminal starch degradability of horse beans was 76±78% (Tamminga et al., 1990). In high producing dairy cows, glucose can also be a limiting nutrient (Nocek and Tamminga, 1991; Van Bruchem, 1991). If the non-structural dietary carbohydrates (starch) are quantitatively degraded in the rumen, the animal has to rely for its glucose supply mainly on glucogenic precursors such as propionic acid and glucogenic AA. Under such conditions, productivity increases if a part of the dietary non-structural dietary carbohydrates bypasses the reticulo-rumen. It is advantageous under such conditions to have more starch escape degradation in the rumen and provide a source of glucose in the small intestine (Nocek and Tamminga, 1991) to achieve a higher milk production. Such an advantage may also be true in growing meat animals (Tudor, 1990).
If horse beans are to be used more ef®ciently in high yielding dairy cows or young growing ruminants, the extent of protein and starch degradation in the rumen must be reduced without altering their intestinal digestibilities.
Pressure toasting (Yu, 1995) reduced the rumen protein degradation and increased BCP. But the optimal processing conditions have not yet been found.
To fully and accurately evaluate the above nutritive values in quantitative of raw and pressure toasted horse beans in dairy cows, a proven evaluation method must be used. The in sacco and mobile bag techniques which are internationally accepted methods (Tamminga and Jansman, 1993), together with the newly developed Dutch protein evaluation system: the DVE/OEB model (Tamminga et al., 1994) were employed.
2. Materials and methods
2.1. Feedstuffs
Horse beans were obtained from the Dutch commercial company. The chemical compositions of raw horse beans are present in Table 1.
2.2. Pressure toasting
Horse beans were pressure toasted at three different temperatures (100, 118 and 1368C) for 3, 7, 15 and 30 min in an incomplete block design. All treatments were carried out in duplicate resulting in 22 treatments in total divided into A and B series as shown in the Table 1. The treatments of 1008C/3 min and 1368C/30 min were dropped due to no expected signi®cant difference between the raw and 1008C/3 min and the risk of overheating, respectively.
Processing was carried out at Wageningen Feed Processing Center (WFPC) using a laboratory scale pressure toaster as described by Van der Poel (1990). After toasting, horse beans were dried at 358C/18 h in the oven, allowed to cool down to ambient temperature and then coarsely ground through a 3 mm screen (Hammer Mill AEG TYP AM80N2).
2.3. Animals and diets
Four lactating Holstein±Friesian cows ®tted with a large rumen cannula with an internal diameter of 10 cm for measuring rumen degradability were housed at the tie stall at the experimental station in Wageningen Agricultural University. All cows received daily about 16 kg of DM of a diet consisting of a commercial pelted concentrate (6.5 MJ
Table 1
The conditions of pressure toasting treatments of A and B series of horse beans Treatments Series A Series B
NEL and 120 g DVE/kg) and hay (55% of total DM intake, 853 g DM/kg, 5.4 MJ NEL and 62 g DVE/kg) according to Dutch lactating dairy cow feed requirements.
Four lactating Dutch dairy cows, ®tted with a T-piece cannula in the proximal duodenum, housed on a tie-stall and fed pelted commercial concentrate and hay to Dutch feeding standards (CVB, 1996), were used to determine intestinal digestion by the mobile bag technique at the research institute of IVVO (The Netherlands).
All the cows were individually fed twice daily at 08:00 h and 16:00 h. Water was always available. A 14 days period of adaptation was allowed.
The animal used in these experiments were cared for in accordance with the guidelines Dutch Animal Care and Use.
2.4. Rumen incubation
Ruminal degradation characteristics of horse beans in the rumen of 4 lactating dairy cows were determined using the in sacco method. Incubation of all treatments in the rumen were with 5.5 g DM in coded nylon bags (10 cm17 cm) with the pore size of approximately 40mm (Nylot, Switzerland). The rumen incubations were performed according to the `gradual addition/all out' schedule. Incubations were carried out for 24, 12, 8, 4 and 2 h, bags were inserted at 17:00, (next day) 05:00, 09:00, 13:00, 15:00 and all were removed at 17:00 h. The 48 h rumen incubations were carried out from 20:00 until 20:00 h 2 days later. All treatments were randomly allocated over all cows and the whole incubation period.
After incubation, the bags were removed from rumen and rinsed under a cold stream of tap water to remove excess ruminal contents and microbes on the surface to stop microbial activity. The bags were washed with cool water without detergent in a commercial washing machine for 55 min without spinning and subsequently dried at 608C for 24 h. The 0 h incubation samples were only put in the washing machine under the same conditions. Dry samples were stored in a cool room (48C) until analysis. The residues were pooled according to feed treatment and incubation time and then ground through a 1 mm screen and analyzed for DM, ash, St and N.
2.5. Intestinal digestion
bags were stored atÿ208C until all the bags had been recovered. These bags were thawed and washed in a washing machine for 2 h at 408C without spinning. The residues were freeze dried, weighed and pooled according to feed treatments and analyzed for N, DM and ash after pooled residues were ground using a 1 mm mesh.
2.6. Chemical analysis
Laboratory samples of the feeds, rumen residues and mobile bags residues of all treatments of horse beans were prepared by grinding to pass a 1 mm mesh. DM was determined by drying at 1058C to constant weight (AOAC, 1984). Ash was determined by ashing at 5508C to constant weight (AOAC, 1984). St was determined according to the NIKO method (Brunt, 1992). N was analyzed by Kjeldahl digestion and distillation (Gerhardt Vadopest 6, Germany) and CP content was obtained as N6:25 (Boer, 1995).
2.7. The DVE/OEB model
2.7.1. Rumen protein and starch degradation characteristics
Rumen degradation characteristic, BCP and BSt in the rumen were determined by the in sacco method (Tamminga and Jansman, 1993). In this technique, the results were calculated using the NLIN (non linear) procedure of the statistical package SAS (SAS, 1991) using iterative least squares regression (Gauess±Newton method) by the following the ®rst order kinetics equation: R t UDexpÿKd tÿT0 (érskov and McDonald, 1979; Tamminga et al., 1994) (1), where,R(t) stands for residue (in %) of the amount of incubated material afterth of rumen incubation;UandDin %; T0 in h; Kd in %/h.
BCP were calculated as: %BCPUDKp/(KpKd); (2). BCP1:11CP
%BCP=100, (3), where, Kp of 6%/h was adopted based on international data (Tamminga et al., 1994); BCP and CP in g/kg DM; The factor 1.11 in the formula was taken from the French PDI-system (INRA, 1978), the regression coef®cient of in vivo on in sacco degradation data.
BSt were calculated as: %BStDKp= KpKd 0:1S, (4); BStSt g=kg %BSt=100, (5), where: Kp of 6%/h was adopted based on international data
(Tamminga et al., 1994); BSt and St in g/kg, DM For the factor 0.1 in the formula (4), it was assumed that for starch 10% of S escape rumen fermentation (Tamminga et al., 1994).
2.8. Microbial protein synthesis in the rumen
FOM in the rumen was calculated as: FOMDOMÿCFatÿBCPÿBStÿFP, (6), where, DOM, CFat, BCP, BSt in g/kg DM; FP is the fermentation products for conserved forages (g/kg DM) not for legume seeds.
Subsequently E_MP was estimated as: E_MP0:15FOM, (7), where, E_MP in g/ kg DM, the factor 0.15 means that per kg FOM, 150 g of microbial protein CP is assumed to be synthesized. TPSI was calculated as: TPSIBCP0:75MP, (8), where, factor 0.75 means that 75% of microbial N is present in AA, the remaining part of N in nucleic acids.
2.9. Intestinal digestion of feed and microbial protein
The previously discussed BCP and TPSI did not give exact enough information on the amount of AA absorbable from the small intestine. A correction is needed for protein losses due to incomplete digestion and resulting from endogenous excretion. True digesti-bility of microbial protein is assumed to be 85% (Egan et al., 1985) and, therefore, the amount of AMP can be estimated as: AMP0:850:750:15FOM, (9), where, AMP in g/kg DM. For feed ingredients, ABCP is calculated as: ABCP dBCP=100BCP, (10). In DVE/OEB model, ENDP in the intestine is related to the amount of DM excreted in the feaces. According to DVE/OEB, 75 g of absorbed protein per kg DM in feacal excretion is required to compensate for endogenous losses. Therefore ENDP is estimated as: ENDP75UDM, (11), where, UDM and ENDP in g/kg DM; UDMUOM UASH (12), where, UOMOMÿDOM; UASHASH-ASHdASH, dASH for both horse beans are 50% (CVB, 1996).
The DVE value was estimated as: DVEABCPAMP-ENDP, (13), where, DVE in g/kg DM.
2.10. The degraded protein balance
The OEB value is balance between microbial protein synthesis from rumen degradable CP and that from the energy extracted during anaerobic fermentation in the rumen. There-fore, the OEB value was estimated as: OEBN_MP-E_MP, (14), where, N_MPCP ÿBCPCP-1:11%BCP/100; E_MP0:15FOM; all parameters in g/kg DM. When OEB is positive, it indicates the loss of N from the rumen. When negative, microbial protein synthesis may be impaired, because of a shortage of N in the rumen. The optimum OEB value in a ration is, therefore, zero or slightly above (Tamminga and Jansman, 1993).
2.11. Statistical analysis
Statistical analyses were carried out using the SAS (1991). Analysis of variance was by using Proc GLM of SAS. Comparison of means were carried out by using the Student± Newman±Keuls test (Steel and Torrie, 1980) when the effect of treatment was signi®cant (P<0:05).
3. Results
3.1. Chemical compositions
Table 2
Effect of pressure toasting on nutritional values (e.g. DVE and OEB) of horse beans in lactating dairy cows, calculated according to the new Dutch DVE/OEB modela
Raw Temperature (8C) SEMb
100 118 136
7 min 15 min 30 min 3 min 7 min 15 min 30 min 3 min 7 min 15 min
Chemical compositions
DM (g/kg) 887.10 d 902.65 ab 903.05 ab 902.45 ab 906.45 a 902.35 ab 901.30 ab 900.45 ab 904.00 ab 899.45 b 893.15 c 1.26 Ash (g/kg, DM) 35.80 35.85 36.00 35.85 36.00 36.05 36.20 36.15 36.35 36.15 36.20 0.10 St (g/kg, DM) 322.60 335.43 334.90 345.87 336.38 333.78 338.89 333.09 332.80 339.18 326.64 5.65
N(g/kg, DM) 39.32 40.08 40.49 40.52 40.42 40.41 39.98 40.01 39.83 39.77 39.91 0.38
Rumen degradation characteristics of crude protein (CP)
S(%) 64.20 a 61.41 b 58.23 c 54.36 d 51.82 e 48.57 f 41.21 g 38.11 h 34.23 i 30.98 j 31.27 j 0.59 Kd_st (%/h) 4.86 4.51 5.18 4.66 4.84 4.73 3.60 3.87 4.08 3.87 3.44 0.34 %BSt 29.01 f 31.85 ef 31.58 ef 32.87ef 35.40 ed 37.83 d 42.51 c 44.37 c 44.60 c 48.28 b 53.09 a 1.01 BSt (g/kg DM) 93.50 e 106.84 d 105.80 d 113.59 d 119.06 cd 126.28 c 144.01 b 147.69 b 148.38 b 163.74 a 173.46 a 3.19 FOM (g/kg, DM) 651.01 a 631.48 ab 613.40 ab 592.10 b 597.16 b 592.27 b 464.70 c 530.53 cd 516.73 cd 493.10 de 464.70 e 9.85 E_MP (g/kg, DM) 97.65 a 94.73 ab 92.01 ab 88.82 b 89.58 b 88.84 b 81.07 c 79.58 cd 77.51 cd 73.97 de 69.71 e 1.48 TPSI (g/kg, DM) 120.46 g 119.69 g 125.27 fg 131.98 ef 141.04 e 137.82 e 155.05 d 158.64 d 170.36 c 184.24 b 200.07 a 2.50 AMP (g/kg, DM) 62.26 a 60.39 ab 58.16 b 26.62 b 57.10 b 56.64 b 51.68 c 50.74 cd 49.42 cd 47.15 de 44.44 e 0.95 ENDP (g/kg, DM) 13.01 13.36 14.22 14.56 13.12 13.14 13.97 14.08 14.06 13.45 13.42 0.57 ABCP (g/kg, DM) 40.14 f 42.71 f 49.23 f 58.57 e 65.73 e 64.35 e 86.06 d 90.45 d 103.70 c 120.27 b 138.93 a 2.56 N_MP (g/kg, DM) 198.56 a 201.83 a 196.78 a 187.86 ab 178.77 b 181.35 b 155.60 c 151.11 c 136.68 dv 119.80 e 101.62 f 3.93 DVE (g/kg, DM) 89.39 g 89.74 g 93.67 fg 100.63 ef 109.72 e 107.85 e 123.77 d 127.10 d 139.05 c 153.97 b 169.94 a 2.49 OEB (g/kg, DM) 100.91 ab 107.10 a 104.77 ab 99.05 ab 89.20 b 92.51 ab 74.53 c 71.53 c 59.18 d 45.84 e 31.92 f 3.66
3.2. Quantitative evaluation of raw and pressure toasting horse beans
The effects of pressure toasting on protein degradation and digestion and microbial protein synthesis and digestion of horse bean in dairy cows are presented in Table 2. Pressure toasting had no signi®cant effects onU(CP), T0, dBCP DOM, UOM, UASH, UDM and ENDP (P>0:05), but had signi®cant effects onS,D, %BCP, %BSt, BCP, BSt, FOM, E_MP, TPSI, AMP, ABCP, DVE, N_MP, OEB (P<0:01) and Kd (P<0:05).
Pressure toasting signi®cantly reducedS, increasedD, reduced Kd without affectingU, resulting in decreasing rumen degradability of CP and St thus increasing BCP 3.1 times (from 47.2 in the raw to 147.8 g/kg DM in 1368C/15 min) and BSt 1.9 times (from 93.5 in the raw to 173.5 g/kg DM in 1368C/15 min), compared with the raw, respectively.
FOM was reduced gradually and varied from 651.0 in the raw to 464.7 g/kg in 1368C/ 15 min due to increasing BCP and BSt, resulting in decreasing E_MP. Though E_MP decreased, TPSI was increased from 120.5 in the raw to 200.1 g/kg DM in the 1368C/ 15 min. Based on the assumption of true digestibility of microbial protein as 85%, AMP reduced from 62.3 in the raw to 44.4 g/kg DM in 1368C/15 min.
For ENDP, pressure toasting did not signi®cantly change its content, averaging 13.7 g/kg DM.
Pressure toasting did not signi®cantly affect digestibility of BCP, averaging 90.2%. ABCP in the small intestine was increased signi®cantly from 40.1 in the raw to 138.9 g/kg DM in 1368C/15 min.
The DVE value was increased with increasing temperatures and times as shown in Fig. 1. Compared with the raw, it was increased 1.9 times from 89.4 in the raw to 169.4 in 1368C/15 min.
3.3. Degraded protein balance
As to the OEB value, it was reduced with increasing temperatures and times as shown in Fig. 2. Compared with the raw (100.9 g/kg DM), it reduced 3.2 times in 1368C/15 min but not to the level of negative.
4. Discussion
Input data from in sacco, mobile bag techniques were from dairy cows. Consequently the data generated by the model, though of signi®cance in the dairy cows, are best regarded as characteristics of the test material.
Protein evaluation results by the DVE/OEB model indicated that though pressure toasting reduced microbial protein synthesis due to a reduction in FOM and a reduction in rumen protein degradation, the DVE value did not decrease but increased markedly. This was due to the fact that BCP was increased more than enough to compensate for the com-puted decrease in microbial protein production. Therefore, the net absorbable DVE value in the animal was substantially increased. The largest increase was found in 1368C/15 min. The OEB value shows the (im)balance between microbial protein synthesis from available rumen degradable CP and potential energy from anaerobic fermentation in the rumen. When the OEB value is positive, it indicates the N-loss from the rumen. When negative, microbial protein synthesis is predicted to be impaired because of a shortage of N in the rumen. The optimum OEB value in a ration is therefore zero or slightly above
Fig. 2. Effect of pressure toasting on the OEB value of horse beans in dairy cows (OEBdegraded protein balance).
(Tamminga et al., 1994). The margin for safety is to allow for asynchrony Ð a factor important in feeding supplements to grazing animal or feeding an ingredient separately of the main basal feed.
Present study showed that raw horse beans had a high OEB value, which indicated an imbalance between feed N degradation and utilization and indicated a potentially large N-loss from rumen. Pressure toasting signi®cantly reduced the OEB values but did not cause them to become negative. Pressure toasting at 1368C/15 min might cover the optimal treatment range for horse bean in terms of treating to achieve target values for potential net absorbable protein in the small intestine while holding any N-loss in the rumen to a low level.
When combining with a roughage or another supplement, the OEB value, if positive, will be reduced only by the presence of rapidly fermentable low N substrate. Roughage with a negative OEB would bene®t from addition of higher OEB supplements. If OEB is negative, the overall effect of a high ABCP may not be bene®cial until other material raises OEB to zero or slightly above zero. The fermentable OM such as degradable starch may improve microbial protein in such a case.
All the results reported here are output from a model with inputs based on in sacco, mobile bag techniques measurements. The challenge is to apply the predictions and evaluate them in an animal performance experiment. However, the number of such studies in this area available to challenge the model is limited. Part of reason is that the information on DVE and OEB values of each feedstuffs, or data from which these are derived is limited.
5. Conclusion
It was concluded that pressure toasting was effective in shifting protein degradation from rumen to intestine and increased the DVE value with increasing temperatures and times but did not cause the OEB value to become negative.
However, pressure toasting of horse beans at 1008C (7, 15 and 30 min), 1188C (3, 7, 15 and 30 min) and 1368C (3 and 7 min) did not fully prevent unnecessary N-loss from rumen due to their high OEB values, though it reduced rumen degradation of protein and increasing true absorbed protein in the small intestine. Pressure toasting at 1368C/15 min might be an upper to the optimal treatment range due to its high DVE without producing negative OEB value affecting microbial protein production.
Further studies are required concerning the effects of optimal pressure toasting of horse beans on animal performance.
Acknowledgements
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