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ELSEVIER Livestock Production Science 40 (1994) 139-155
LIVESTOCK
PRODUCTION
SCIENCE
The Dutch protein evaluation system: the DVE/OEB-system
S. Tamminga a, W.M. Van Straalen b, A.P.J. Subnel c'*, R.G.M. Meijer c, A. Steg a,
C.J.G. Wever e, M.C. Blok e
"Department of Animal Nutrition, Agricultural University, Haagsteeg 4, 6708 PM, Wageningen, Netherlands
bCLO-institute for Animal Nutrition "'De Schothorst", P.O. Box 533, 8200 AM, Lelystad, Netherlands
CResearch Station for Cattle, Sheep and Horse Husbandry (PR), Runderweg 6, 8219 PK, Lelystad, Netherlands
dResearch Institute for Livestock Feeding and Nutrition (IWO-DLO), P.O. Box 160, 8200 AD, Lelystad, Netherlands
eNational Reference Centre of Livestock Production, Runderweg 2, 8219 PK, Lelystad, Netherlands
fCentral Bureau for Livestock Feeding, Runderweg 6, 8219 PK, Lelystad, Netherlands
Received 13 August 1993; accepted 1 February 1994
Abstract
In 1991 a new protein evaluation system replaced the Digestible Crude Protein (DCP) system in the Netherlands: the DVE/
OEB-system. The system was mainly developed with the aim to prevent avoidable losses of nitrogen, by feeding according to
more exactly defined requirements of dairy cows. A second aim was to predict milk protein production more accurately.
Protein requirements for maintenance, milk protein production, growth, mobilisation, metabolic losses in the digestive tract
and gestation are expressed in DVE, the sum of digestible feed and microbial true protein available in the small intestine.
In the system each feed has a DVE-value composed of the digestible true protein contributed by feed protein escaping rumen
degradation ( 1 ), microbial protein synthesized in the rumen (2) and a correction for endogenous protein losses in the digestive
tract (3). Each feed also has a degraded protein balance (OEB) reflecting the difference between the potential microbial protein
synthesis based on degraded feed crude protein and that based on energy available for microbial fermentation in the rumen.
The framework of the new system is based on what are considered strong elements of other recently developed protein
evaluation systems. Additionally new elements are introduced, including undegraded starch (USTA), fermentation products
(FP) in ensiled feeds, the role of energy balance in protein supply and the way in which requirements change in the course of
lactation. Data within the framework of the system are mainly of Dutch origin. This is particularly true for the regression
equations developed to predict the protein values of forages and protein values of a number of by-product ingredients.
Keywords: Dairy cattle; Protein Evaluation; Nitrogen loss; Milk protein
1. Introduction
In the Netherlands dairy rations are formulated
according to the energy-standards in a net energy sys-
tem, the VEM-system (Van Es, 1975, 1978). Until
1991 the Digestible Crude Protein system (DCP, the
*Corresponding author
0301-6226/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved
SSDIO301-6226(94)OOO12-V
difference between CP (NX 6.25) ingested with the
ration and CP excreted in the feces) was used to express
protein requirements for dairy cattle as well as the pro-
tein value of feeds (CVB, 1990).
Protein that really can be utilised is only that part of
the ingested CP which is digested in and subsequently
absorbed from the small intestine (SI) as amino acids.
The DCP-system is a poor predictor of the amount of
140
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
true protein absorbed from the SI, because it does not
indicate to which degree the CP in a feedstuff is
degraded in the rumen, nor does it take into account
microbial protein synthesis in the rumen. These are
important limitations, because CP that is degraded in
the rumen and lost as ammonia (NH3) and urea can
not be utilised by the animal. Because no ruminal N-
transactions are incorporated in the DCP-system, it is
hardly possible to improve the efficiency of N-utilisa-
tion in dairy cows with this system.
In many countries more sophisticated systems
describing the digestion and metabolism of N in a more
detailed way than the DCP-system does, were intro-
duced in practice (INRA, 1978; ARC, 1984; NKJ-NJF,
1985; NRC, 1985; Ausschuss for Bedarfsnormen,
1986). After their first introduction some of the systems
were updated already (Vtrit6 et al., 1987; AFRC,
1992).
The objectives of this study were to develop a system
that:
(a) Describes digestion and metabolism of N in dairy
cows in detail,
(b) Identifies and quantifies the losses of N due to an
inappropriate intake of feed N.
Principles of already existing systems were used to
develop the framework of the DVE/OEB system,
which describes digestion and metabolism of N under
Dutch circumstances. Together with information on the
digestive behaviour of a wide variety of feeds used in
Dutch dairy diets, such a system should make it pos-
sible to feed protein more accurately according to the
real demands of the dairy cow and prevent unnecessary
losses of nitrogen (N).
2. The prevention of losses of N
For a system which describes and quantifies the
losses of N in a ruminant animal, information on the
sites and moments in the digestion and metabolic proc-
esses at which N losses occur is needed. In Table 1
such an example for the Dutch dairy cow is given
(Tamminga, 1992).
The annual input of N in the Dutch dairy cow (pro-
duction level: 6250 kg/year) is around 175 kg. When
the roughage part of the basal ration mainly contains
grass-products it is slightly higher, when on the other
Table 1
The N-losses (kg N per cow and year) in the Dutch dairy cow
producing 6250 kg of milk (kg/year) (Tamminga, 1992)
Form Input Losses
Output Output Output Output
milk tissues faeces urine
Feed 175
Rumen loss 25
Nucleic acids 15
Undigested 25
Endogenous 25 15
Maintenance 1 6
Milk 33 24
Growth 3 - 3
Total 33 4 50 88
hand maize-silage is the main part of the basal diet, it
is slightly lower. Only about 20% of the 175 kg of
ingested N becomes recovered as milk protein or is
deposited as protein in lean tissue.
Dutch practices of feeding dairy cows result in
annual N losses from the rumen of around 25 kg,
because degraded CP and energy are usually unbal-
anced (Demeyer and Tanuninga, 1987; Sniffen and
Robinson, 1987; Van Straalen and Tamminga, 1990).
Often there is a surplus of rumen degraded protein and
breakdown of CP and microbial protein synthesis do
not always occur at the same moment. Consequently,
a shortage of feed N in the rumen may also occur
occasionally.
Fecal excretion is also an important loss (Charmley
et al., 1988) and amounts to about 50 kg of N a year.
Half of this originates from undigested feed CP and
microbial CP. The other half is due to metabolic losses
(enzymes, epithelial cells and mucus ). Part of the met-
abolic losses appear in the feces as bacterial CP result-
ing from microbial activity in the hind gut. Metabolic
losses need to be replaced. The process of resynthesis
is therefore considered to be associated with N losses
and believed to cause an elevated N excretion in the
urine (Tamminga, 1992). Table 1 shows that about
65% of the N that is lost, is excreted in the urine, but
only a small proportion of the loss is a consequence of
the losses in maintenance and growth. These latter
losses are difficult to avoid.
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
141
Part of the microbial CP will also be lost in the urine,
because it is not true protein (amino acids), but nucleic
acids. The animal's tissues and organs do not utilise
nucleic acids as well as they utilise amino acids (Arms-
trong and Hutton, 1975). An important additional uri-
nary N loss is associated with the synthesis of milk
protein. Average efficiencies for utilization of absorbed
true protein are assumed to be 0.67 for maintenance,
0.50 for growth (NRC, 1985 ) and 0.64 for the synthesis
of milk protein (V6rit6 et al., 1987).
Reducing these losses succesfully in practice
requires first of all a protein evaluation system based
on a detailed, preferably dynamic description of the N-
metabolism in the dairy cow. The system should also
include a proper description of the protein value of
feeds (Van Straalen and Tamminga, 1990), including
microbial protein supplied by each feed. Additionally,
a correct formulation of the requirements of true protein
at every moment in lactation is needed.
3. Modern protein evaluation systems
It was chosen to develop a
system
based on the prin-
ciples already formulated in existing modern protein
evaluation systems. The protein value for feeds and the
requirements for dairy cows are both expressed as the
amount of true protein truly digested in and absorbed
from the small intestine of the animal: DVE. Other
systems use comparable units viz. MP (AFRC, 1992),
PDI (INRA, 1978; V6rit6 et al., 1987), AAT (Madsen,
1985; Hvelplund and Madsen, 1990), AP (NRC,
1985) and AAS (Ausschuss fiir Bedarfsnormen,
1986).
It was difficult to decide which of the systems was
most appropriate under Dutch circumstances. In liter-
ature many comparisons between different protein
evaluation systems have been reported (Madsen, 1979,
1980, 1985; Jarrige and Alderman, 1987; Waldo and
Glenn, 1984; Orskov and Miller, 1988; Van der Honing
and Alderman, 1988), but they all remain rather
descriptive. Van Straalen et al. (1993a) evaluated
which system could be used best under Dutch circum-
stances. Their conclusion was, that of the modern sys-
tems the PDI-system was the most accurate in
predicting milk protein production. An additional
advantage of the PDI system is that it well tested and
widely used in practice.
Table 2
List of abbreviations
AAN
NAAN
BRE
%BRE
CASH
CFAT
CP
CPM
D
DCP
DOM
DVBE
%DVBE
DVE
DVME
DVMFE
FOM
MREN
MREE
MVRAS
OEB
%RRE
S
STA
U
UM
USTA
%USTA
VRAS
%VRAS
:Nitrogen present in amino acids
:Non amino-acid-N
:Undegraded feed CP
:Fraction of undegraded feed CP in total feed CP
:Crude inorganic matter
:Crude fat
:Crude protein
:Metabolic crude protein
:Unsoluble but potentially degradable fraction in
nylon bag incubations
:Digested Crude Protein
:Digested Organic Matter
:Digested degraded feed CP
:Digestion in small intestine of the undegraded feed
protein
:True protein digested in the small intestine
:Rumen synthesised microbial protein digested in the
small intestine
:Endogenous protein losses in digestion
:Fermentable Organic Matter
:Microbial protein synthesised in the lumen based on
available nitrogen
:Microbial protein synthesised in the rumen based on
available energy
:Maximum value of VRAS
:Degraded protein balance
:Fraction of undegraded feed CP in total feed CP
after long term rumen incubation
:Soluble fraction in nylon bag incubations
:Starch
:Undegradable fraction in nylon bag experiments
:Indigested Dry Matter
:Undegraded Starch
:Fraction of Undegraded Starch
:Digestible fraction of Crude Ash
:Digestion coefficient of Crude Ash
The Dutch system was therefore developed with the
French PDI-system as a basis. If considered appropri-
ate, elements of other systems were incorporated. For
instance for expressing maintenance requirements, the
approach in the AP-system (USA) was followed. To
get a clear impression of the N-losses in the rumen, the
concept of the Scandinavian PBV-value
(PBV = protein balance in the rumen) was accepted.
A list of abbrevations used in the text is given in
Table 2.
142 S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
4. The supply of true protein to the small intestine
Different components contribute to the DVE value:
( 1 ) Undegraded feed CP digested in and absorbed from
the small intestine as amino acids: DVBE
(2) Microbial CP digested in and absorbed from the
small intestine as amino acids: DVME
(3) Endogenous losses resulting from digestion:
DVMFE
The DVE-value of a feedstuff is then formulated as:
DVE = DVBE + DVME - DVMFE (1)
5. Digestible undegraded feed protein (DVBE)
To quantify the DVBE-value of a feedstuff, infor-
mation is needed on the total amount of CP as well as
on the ratio AAN/total-N. Furthermore the degradation
and digestion of the AAN must be estimated.
5.1. Undegraded feed crude protein (BRE)
The fraction of feed CP escaping degradation in the
rumen is estimated from the U, S and D-fraction result-
ing from incubation of a feed in nylon bags in the rumen
(Van Straalen and Tamminga, 1990). The size of the
U-fraction is determined after long term ( 10-14 days)
rumen incubations. The size of the actually degraded
fraction is subsequently estimated from the potentially
degradable fraction (D), the rate of degradation (ko)
and the rate of passage (kp) (Robinson et al. 1986). It
should be pointed out that the size of the potentially
degradable fraction is not derived from the estimated
asymptote of the degradation curve, as is done in the
model of ~3rskov and McDonald (1979), a model often
used to describe nylon bag incubation data. Based on
international and Dutch data, passage rates (kp) of
4.5% for roughages and 6% for concentrates were
adopted. The %BRE-values for feeds were mainly
derived from compiled Dutch and international data
(Van Straalen and Tamminga, 1990). For feeds on
which no data were available the %BRE value was
estimated by comparison with feeds of a similar nature
and a comparable chemical composition. If no infor-
mation was available a %BRE value of 35% was
assumed.
The amount of BRE (g/kg) in individual feeds is
estimated as:
BRE= 1.11 × (%BRE/100) ×CP
(BRE and CP in g/kg; %BRE in %)
(2)
The factor 1.11 in formula (2) is taken from the
French PDI-system.
The %BRE-values of roughages were mainly
derived from data obtained in Dutch trials (Meijer,
1990; Tamminga et al.; 1991; Bosch et al., 1991; Van
Vuuren et al., 1992; De Visser, unpublished). For fresh
grasses, grass silages and hays, multiple regression
equations, in which chemical composition (CP, DM)
and day of harvest (DH) were identified as explaining
variables for %BRE, were developed (Van Straalen
and Tamminga, 1990; Tamminga et al., 1991; CVB,
1991a):
%BRE=a+bl XCP+b2 ×DH+b3 ×DM
a, bl, b2, b3: regression coefficients
CP (N × 6.25): in g/kg DM
DH: days of harvest after April
1 st
DM: dry matter content (g/kg)
(3)
R 2 varied from 0.73 for fresh grasses to 0.80 for hays.
Values for the regression coefficients are given by CVB
(1991a). Because of observed discrepancies between
the estimated DVE value and production responses in
practice after feeding ensiled feeds, grass silages in
particular, for this category of feeds it was additionally
assumed that 5% of the S fraction is also washed out
of the rumen before being degraded.
5.2. Percentage of amino acids in undegraded feed
crude protein
Results of nylon bag incubation studies were used to
estimate the percentage of amino acid N (AAN) in
undegraded dietary CP. Differences in AAN in residues
from nylon bags incubated in the rumen for different
lengths of time were found to be small for concentrate
ingredients (Vrrit6 et al., 1987; Hvelplund and Hes-
selholt, 1987). For roughages more variable results
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155 143
were reported (Rook et al, 1984; Hvelplund, 1987; Hof
et al., 1990; Van Straalen et al., 1993b).
Most systems have accepted an AAN/N-ratio of 1.0
(ARC, 1984; NRC, 1985; Vtrit6 et al., 1987). In the
Nordic AAT/PBV system, a value of 0.65 was
accepted for roughages and 0.85 for concentrates
(Madsen, 1985). In the DVE-system, the estimation
of the percentage of amino acids in undegraded feed
CP is not specified, but taken into account in the esti-
mation of the intestinal digestion of CP.
c, b4, bs: regression coefficients
CP (N × 6.25): in g/kg DM
DH: Days after April 1st
Values for the regression coefficients are given by
CVB (1991a).
6. Microbial protein digestible in the small
intestine (DVME)
5.3. Digestion of undegraded feed crude protein
(%DVBE)
In the DVE system the estimated intestinal digestion
of undegraded feed CP is based on results of mobile
nylon bags passing the digestive tract (Van Straalen
and Tamminga, 1990). Because the intestinal digestion
of non-amino acid-N (NPN) is low, and the percentage
of amino acids in the undegraded feed CP digested in
the small intestine is high (Tamminga and Oldham,
1980), the true digestion of amino acids is given as
%DVBE. For feeds of which no direct information was
available, %DVBE was estimated on the basis of infor-
mation of comparable feeds. Feeds with a high cell wall
content were given a value of 50%. Products of which
information was completely lacking, were given a
value of 75%. For roughages insufficient information
was available of trials in which the mobile nylon bag
technique had been used. The %DVBE is therefore
calculated from the %BRE and the indigestible CP
fraction after long term rumen incubation (%RRE):
%DVBE = 100× (%BRE- %RRE)/%BRE (4)
The amount of DVBE is then calculated as:
DVBE=CP × (1.11 × %BRE/100)
× (%DVBE/100) (5)
(DVBE and CP in g/kg DM; other values in %.)
For roughages (grasses, grass silages, hays) %RRE
is estimated from the chemical composition and day of
harvest (CVB, 1991a):
To estimate microbial growth, the DVE-system uses
the organic matter (OM) available for fermentation by
the rumen microbes under anaSrobic conditions as
found in the rumen, like in the PDI-system. It is called
fermentable organic matter (FOM). FOM is calculated
from the apparently digested organic matter (DOM),
but DOM is corrected for the amounts of crude fat
(CFAT), undegraded feed CP (BRE), undegraded
starch (USTA), and end products of fermentation
(FP) in ensiled feeds.
USTA values are based on rumen escape values
determined with nylon bag incubations (Tamminga et
al., 1990; Nocek and Tamminga, 1991 ) and if relevant,
corrected with a factor 0.75 to account for the observed
negative effects of pelleting. To compensate for differ-
ences observed between in vivo and in sacco values, it
was further assumed that 10% of the starch fraction that
is washed out of nylon bags prior to rumen incubation,
escapes from rumen degradation (Nocek and Tam-
minga, 1991).
The correction for fermentation end products in
ensiled feeds is based on the assumption that from the
most important fermentation end products lactic acid
and alcohols, rumen microbes can extract the equiva-
lent of about 50% of the energy (ATP) extractable
from carbohydrates. Hence, DOM is corrected for 50%
of the fermentation end products in ensiled products.
The way in which the DOM fraction is corrected is
shown in the following equation:
FOM = DOM-CFAT-CP × (%BRE/100)-STA
× (%USTA/100) - 0.50 × FP (7)
(%BRE and %USTA in %; other parameters in g/kg).
%RRE= c +b4 ×CP+b5 ×DH
(6)
Values for CP, DOM, CFAT, %BRE, STA and
%USTA are given by CVB (1991b) as far as the con-
144 S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
centrates and industrial by-products are concerned. For
roughages values are also listed in CVB (1991a).
Equations to calculate the FP-content of ensiled feeds
were derived from Steg et al., (1990).
6. I. Microbial protein production in the rumen
In the French PDI system microbial protein produc-
tion is based on FOM (Vrrit6 et al., 1989) and is
calculated to be 145 g of microbial CP per kg FOM. In
the DVE-system a value of 150 g/kg FOM was
adopted. This slightly higher value was chosen
because, except for maize and milocorn, the PDI sys-
tem, does not account for undegradable starch. More-
over, the French values were derived from a set of data
in which the level of intake was relatively low. From
work by e.g. Robinson et al. (1987) it is known that a
higher intake stimulates the efficiency of microbial pro-
tein synthesis positively.
6.2. Amino acids in microbial crude protein and its
true digestion
Based on data from Dutch trials (S. Tamminga,
unpublished) as well as literature, a value of 0.75 was
accepted for the AAN/N ratio in microbial CP and a
true digestion of 85% was chosen for AAN. At the
same level of FOM, only a minor difference exists
between the French and Dutch estimation of digestible
microbial protein (DVME). The latter is calculated as:
accordingly. In rations of average composition, loss of
metabolic crude protein (CPM) equals 50 g/kg UDM
(CVB, 1991a).
UDM intake can be separated in indigestible organic
matter and indigestible inorganic matter. In the DVE
system the digestible inorganic matter (VRAS) is cal-
culated from the crude inorganic matter (CASH) as:
VRAS = %VRAS / 100 X CASH
(%VRAS in %; CASH in g/kg DM)
(9)
Each feedstuff has a maximum amount of VRAS
(MVRAS). The introduction of MVRAS prevents
overestimation of VRAS, for instance due to a large
but variable proportion of sand in an individual batch
of a particular feedstuff. More detailed information on
MVRAS for different feeds is given in CVB ( 1991a
and 1991b).
The UDM is calculated as:
UDM = 1000-DOM-VRAS
(all values in g/kg)
(lO)
Based on a net loss of metabolic protein of 50/kg
UDM and an efficiency of resynthesis of 0.67, the
requirement of DVE for metabolic protein losses
(DVMFE), and used as a correction factor for the pro-
tein value of each feedstuff, is calculated as:
DVME = FOM X 0.150 X 0.75 X 0.85
(all values in g/kg)
(8)
DVMFE = 0.075 × UDM
(11)
7. Endogenous losses in digestion (DVMFE)
Endogenous CP lost in the digestive process exists
of digestive enzymes, bile, desquamated epithelial cells
and mucus. Although it originates from the animal
itself, its magnitude is considered to depend more on
characteristics of the feed than of the animal. The DVE,
required to compensate for endogenous losses, called
DVMFE, is not restricted to endogenous protein itself
but also includes amino acids lost in its resynthesis.
DVMFE is considered to be directly related to the
undigested DM and the DVE-value of feeds is corrected
8. The degradable protein balance (OEB)
The OEB value, like the PBV value in the AAT/
PBV system (NKJ-NJF, 1985), shows the
(im)balance between microbial protein synthesis
potentially possible from available rumen degradable
CP (MREN) and that potentially possible from the
energy extracted during anaerobic fermentation in the
rumen (MREE). It also reflects the difference between
PDIN and PDIE in the French system (V~rit6 et al.,
1987).
When positive, the OEB-value gives the loss of N
from the rumen. When OEB is negative, microbial pro-
s. Tamminga et al. / Livestock Production Science 40 (1994) 139-155 145
tein 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. Contrary to the PBV
value, in the DVE system, the OEB value is recom-
mended not to become negative. The risk of a shortage
of N for the microbes is considered too high. In that
case the calculated values of DVME may not be
achieved. This risk is particularly apparent at higher
levels of feed intake, normally found in early lactation,
combined with infrequent feeding.
OEB = MREN - MREE
(all values in g/kg)
MREN is calculated as:
(12)
MREN= CPx ( 1-1.11 x %BRE/100) (13)
(MREN and CP in g/kg; %BRE in %).
The maximum synthesis of microbial CP based on
energy is calculated as:
(hair, scurf, skin secretions) divided by the efficiency
of utilisation for maintenance:
DVE-M = (2.75 X BW °5 +0.2
X BW °'6)/0.67)
(15)
(DVE-M in g/day; BW= body weight in kg)
9. 2. Milk protein production (D VE-P)
Modern protein evaluation systems developed till
now, use a constant efficiency factor to express the
utilisation of absorbed true protein for milk protein
production. The PDI-system uses a value of 0.64. Ini-
tially this value was also chosen for the DVE-system.
However, production trials performed under Dutch cir-
cumstances revealed that this efficiency was variable
and dependent on the DVE/NEL-ratio (Subnel and
Meijer, 1993; Van Straalen et al, 1993a), and level of
production (Subnel and Meijer, 1993). Based on this
finding, an equation was derived (Subnel and Meijer,
1993), by which a direct estimation of DVE-require-
ment for production of milk protein (DVE-P in g/day)
can be made:
MREE = FOM X 0.15
(FOM in g/kg)
(14) DVE-P = 1.396 X GRP + 0.000195 x GRP 2 (16)
(DVE-P in g/day); GRP: Milk protein production in
g/day)
9. Protein requirements in the DVE-system
Dairy cattle require protein for maintenance, for ges-
tation, for growth and for milk production. In the DVE
system the requirements are corrected for protein that
is mobilised from or stored in body reserves. As was
explained earlier, in the DVE-system the requirement
for metabolic losses in the digestive tract is taken into
account in the DVE-value of each individual feedstuff.
As a result maintenance requirements do not have to
account for metabolic losses from the digestive tract
and the approach chosen by NRC (1985) was fol-
lowed.
9.1. Maintenance (DVE-M)
The DVE-requirement for maintenance is calculated
as the DVE-requirements for losses in urine and body
9.3. Growth and mobilisation (DVE-GM)
Requirements for growth and the amount of protein
that becomes available from mobilised body reserves
depend on the actttal energy balance of the animal. This
balance is calculated as the intake of net energy (VEM)
minus net energy required for processes mentioned
above. When the balance is positive, energy, part of
which is protein, is stored in body reserves. When the
balance is negative, i.e. when energy is mobilised, part
of that energy will become available as amino acids
which can be used for metabolic processes.
In the DVE system it is assumed that 10% of the
energy in body reserves is present in protein (A.J.H.
Van Es, unpublished; Waldo et al., 1991 ). Therefore
in body reserves each 6.9 MJ (the equivalent of 1000
VEM), contain about 0.7 MJ in protein, which, under
the assumption of 24 MJ/kg of protein, is the equiva-
lant of 29 g of protein. Restoring body reserves in dairy
146
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
cattle, is assumed to be possible with an efficiency of
50% (NRC, 1988). Because of the absence of meta-
bolic losses in digestion and an appropriate amino acid
composition, protein from body reserves is expected to
be used more efficiently for milk protein production
than DVE absorbed from the small intestine (80% ver-
sus 64%). In a negative energy balance situation, the
mobilised energy is also assumed to be used for milk
production with an efficiency of 80% (Van Es, pers.
comm.). This means that per 6.9 MJ negative energy
balance 36 g of body protein is mobilised, the equiva-
lent of 36× (80/64)=45 g DVE. For animals in a
positive energy balance each 6.9 MJ, will require 57
(29/0.5) g of DVE for restoring body reserves.
9.4. Gestation (DVE-G)
For the DVE-requirements for gestation, the NRC
appraoch was followed. From day 141 till day 281 after
conception, DVE is required for the foetus and extra
maternal tissues. Like in the NRC approach, the effi-
ciency is assumed 50% (NRC, 1985).
DVE-G (g/day) =
(34.375 × exp (8.537 - 13.1201 ) × exp ~ - o.oo262- × o~ _ 0.00262 × D
0.50 (17)
(D = days after conception between 141 and 281.)
10. Discussion
10.1. Validation of modern protein evaluation
systems
Validation of new protein evaluation systems has not
been performed on a large scale. Some comparisons
were either rather theoretical or were made with sys-
tems already abandoned for use in practice. Many
experiments to evaluate the effect of protein feeding on
protein production were carried out in the past, but only
a limited number of these were used to validate protein
evaluation systems (Jarrige and Alderman, 1987). Dif-
ferences between predicted and observed milk produc-
tion varied between systems and experiments (Vik-
Mo, 1985; MacRae et al., 1988; Sloan et al., 1988;
Garnsworthy, 1989; Broderick et al., 1990; Cody et al.,
1990; Robinson et al., 1991; Susmel et al., 1991). Yet
it became also apparent from such evaluations that pro-
tein intake estimated according to new systems, usually
shows a better relationship with milk protein produc-
tion than CP or DCP intake does (Thuen and Vik-Mo,
1985; Vik-Mo, 1985; Bricenco et al., 1988). The var-
iation still observed in such comparisons probably
results from differences in experimental conditions
(design, type of feedstuff), production level and type
of animals used (Van Straalen et al., 1993a). It also
became apparent that the optimum dietary CP content
is variable due to differences in true protein supply and
requirement (Waldo and Glenn, 1984; Alderman,
1987).
A large data set of Dutch milk production trials was
used to make a comparison between the CP, DCP, MP,
AAT/PBV, PDI, AAS and the AP-system (Ketelaar,
1986; Van Straalen et al., 1993a). Milk protein pro-
duction predicted by the different systems was com-
pared with the protein production realised in feeding
trials. The accuracy with which milk protein output was
estimated was generally improved when the CP- or
DCP-system was replaced by a modern system. A large
part of the remaining error of prediction could be
explained by the protein/energy ratio in the diet. Of
the modem systems, the PDI-system was more accurate
in predicting the milk protein production than (in fol-
lowing order) the AAT, AAS, AP and MP-systems.
The overestimated milk protein production in the
AAT and AAS system appeared mainly the result of an
assumed (too) high efficiency of utilisation of
absorbed protein for milk protein production. The main
reason for overestimation in the AP-system was an
overestimated AP-supply. In the MP-system not only
the MP-supply was overestimated, maintenance
requirements appeared underestimated at the same
time.
The PDI-system was finally chosen as the basis of
the DVE/OEB-system, but elements of other systems
(NRC, 1985; NKJ-NJF, 1985) were also incorperated
in it. Examples are N-losses from the rumen, estima-
tions of maintenance requirements and requirements
for gestation. Although the framework was taken from
already existing systems, the DVE/OEB-system uses
data mainly originating from Dutch research, particu-
larly with regard to the protein values of roughages.
Some elements in the recently developed protein eval-
uation systems are still somewhat uncertain because of
a lack of documentation. They are discussed below.
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
147
10.2. Digested undegraded feed crude protein
(DVBE)
A first point of concern is the nylon bag incubation
method used to estimate the contribution of undegraded
feed CP. This has become the almost universally
adopted method. Applying this method for measuring
CP degradation in feeds low in CP, fibrous roughages
in particular, easily leads to contamination with micro-
bial N of the residues. Using the normal washing pro-
cedure this contamination is difficult to wash out of the
bags (Kennedy et al., 1984). Microbial contamination
is however of more theoretical than of practical impor-
tance. Feeds low in CP, even if they are heavily con-
taminated with microbial N, do not contribute much to
the intestinal supply of rumen undegraded true protein.
The estimated effective rumen escape is based on
the ratio between rate of disappearance through deg-
radation and rate of total disappearance from the rumen,
the latter based on a (usually) fixed rate of passage.
Rate of passage was shown to vary with level of feed
intake (Madsen, 1986) and type of diet (Clark et al.,
1992). A high passage rate shifts the site of digestion
from the rumen to the lower gut. This is not only the
case with protein but also with energy yielding sub-
strates enabling microbial growth. An underestimated
rumen escape due to a high rate of passage is therefore
likely to be counterbalanced by a decreased ruminal
microbial synthesis as well as a decreased intestinal
digestion.
Different values for the rate of passage (kp) have
been adopted in different protein evaluation systems.
The Nordic system uses an outflow rate of 8% per hour
(Madsen and Hvelplund, 1985). The French PDI sys-
tem (Vrrit6 et al., 1987) uses 6% for all feeds, despite
their claim that 4.5% was more appropiate for rough-
ages. Reviewing data from literature, Tamminga and
Ketelaar (1988) concluded that values of 5% for con-
centrates and 3% for roughages looked appropriate.
These latter values seem low compared to what was
adopted in most other systems and as a compromise,
the DVE-system uses 6% as a mean kp-value for con-
centrates and 4.5% for roughages.
Rate of degradation also varies, not only among
feeds, but also with diet composition. Concentrate rich
diets usually cause a low ruminal pH, which may
reduce the rate of CP degradation (Vik-Mo and Lind-
berg, 1985; Clark et al., 1992). Because a high pro-
portion of concentrates in the diet usually coincides
with or maybe even causes a lower rate of passage
(Owens and Goetsch, 1986), effective CP escape may
not change. So, although rate of CP degradation in the
rumen is a more dynamic process than simulated by
nylon bag incubations, intestinal supply of absorbed
protein per kg of feed ingested is probably less variable
due to compensating mechanisms. Fixed figures for CP
escape in individual feeds as used in the DVE and other
protein evaluation systems seem therefore justified, at
least at present.
In the PDI-system, the prediction of the amount of
CP (NAN) entering the small intestine was based on
multiple regression analysis of duodenal flow data from
in vivo experiments and published in international lit-
erature. The main body of data originated from trials
with sheep. In the equation developed to predict the
amount of BRE entering the small intestine, a regres-
sion coefficient of I. 11 appeared for the amount of feed
CP escaping rumen degradation, based on nylon bag
incubation studies. At first sight this suggests that the
nylon bag method underestimates the amount of feed
CP escaping degradation. Other in vivo observations
(Aitchison et al., 1986; Oosting, 1993) do suggest
however that nylon bag incubations underestimate rate
of degradation, at least that of cell walls. It should be
realized, that in a multiple regression equation, regres-
sion coefficients are not entirely independant of each
other. Explanations are than that the flow of microbial
CP into the small intestine is underestimated, that the
contribution of endogenous CP is underestimated or
that, because part of it is flushed out with the fluid, feed
CP leaves the rumen at a faster rate than other feed
ingredients (Tammingaet al., 1989). Lack of solid data
prevent drawing a firm conclusion, the reason why the
regression factor was maintained in the DVE system,
rather than to increase passage rates to values which
seem physiologically unrealistic.
During the development of the DVE system a dis-
crepancy between the DVE-value according to the
DVE-system and observed production responses
occurred for ensiled roughages. This difference was
not apparent in non-fermented (dry or fresh) feeds.
The causes for this discrepancy were not clear. A factor
of importance may be microbial CP, formed during the
ensiling process. This microbial CP, a large part of
which can be washed out immediately in nylon bag
incubations, may leave the rumen at a fast rate since it
148
S. Tamminga et al. /Livestock Production Science 40 (I 994) 139-155
can easily be washed out of the rumen with the fluid
phase and thus partly escape ruminal degradation. For
ensiled feeds it was therefore adopted that 5% of the
N-fraction that will normally be washed out is escaping
degradation in the rumen.
Another point of concern is the AAN/total N ratio
in feed CP escaping rumen degradation. Nylon bag
studies performed to determine the AAN/N ratio in
undegraded feed CP, showed little variation for con-
centrates (Vtrit6 et al., 1987;, Hvelplund and Hessel-
holt, 1987), but for roughages more variable results
were reported. For ryegrass (Hvelplund, 1987) and for
grass silage (Rook et al., 1984) it was found that the
degradation of CP in the rumen is followed by a slight
reduction in the AAN/N ratio in the undegraded CP,
compared to the CP in feed. Van Straalen et al. (1993b)
on the other hand, found a rise in the AAN/N ratio in
the undegraded CP compared to the feed CP. This rise
might be due to the fact that NPN is more degradable
in the rumen than AAN. Hofet al. (1990) observed an
initial rise in AAN/N followed by a decrease. This does
suggest that two NPN fractions are present in rough-
ages, one, probably associated with the cell contents,
which can easily be washed out and one which is quite
resistant against washing out of nylon bags, possibly
because this fraction is associated with the cell walls.
This also points out the importance of the length of
incubation time in such studies.
According to Vtrit6 et al. (1987), AAN/N in nylon
bag incubation residues was on average 0.85 in all
feeds. In the Nordic system it is assumed that of the
undegraded feed CP entering the small intestine and
originating from concentrates the AAN/N ratio is 0.85,
undegraded feed CP originating from roughages is
assumed to have an AAN/N ratio of only 0.65. The
lower value for roughages was justified based on a
comparison of data from nylon bag incubations and
data of duodenal flow measurements (Hvelplund and
Madsen, 1985). At first sight this assumption seems
fair, but it may also be assumed that the major part of
non-amino acid-N (NAAN) present in roughages, par-
ticularly in silages, is soluble and washed out of nylon
bags (Hof et al., 1990; Van Straalen et al., 1993b).
Hvelplund and Madsen (1985) derived their value
from multiple regression calculations in which the duo-
denal flow of Non-ammonia-N (DNAN) and that of
amino acid N (DAAN) was related to carbohydrates
fermented (DCHO) and N escaping degradadion
(UN) in the rumen. DNAN and DAAN estimates were
on the same set of data, hence, the ratio between the
regression coefficients when estimating DAAN and
DNAN from DCHO and UN should give an indication
of the AAN/N ratio in microbial and undegraded feed
CP respectively. The ratio between the regression coef-
ficients obtained for UN originating from roughage rich
(R) and concentrate rich (C) diets was 0.59 and 0.86
respectively. However, the ratio for DCHO originating
from R and C diets were 0.74 and 0.57 respectively,
suggesting that microbial CP originating from C diets
has a much lower AAN/N ratio than those originating
from R diets, which is difficult to rationalize. This
observation emphasizes the danger of drawing conclu-
sions on individual regression coefficients obtained
from multiple regression equations.
Despite that part of the feed CP escaping degradation
in the rumen is not AAN, most systems assume 100%
of the total undegraded feed-CP being AAN. According
to Vtrit6 et al. (1987) this is justified because unde-
graded feed CP really entering the duodenum has a
higher AAN/N ratio than residues from nylon bag
incubations. This opinion could be challenged,
because, when using AAN/N ratios for microbial CP,
undegraded concentrate CP and undegraded roughage
CP of 0.75; 0.85 and 0.65 respectively, this would sug-
gest an AAN/N ratio in CP flowing into the small
intestine of around 0.75. Ratios observed in vivo are
usually lower (Hvelplund and Madsen, 1985). This
also indicates a high contribution of NPN in endoge-
nous secretions.
The NRC (1985) reported data based on regression
analysis and found a mean value of 0.80 for the true
absorption of AAN entering the duodenum. In the
French system the digestion of undegraded feed CP is
given per category of feeds, and calculated from the
amount of undegraded total CP entering the duodenum
and the undigested CP. It varies between 0.6 and 0.95
(INRA, 1978). A good relationship was observed
between the calculated digestion and the digestion
measured by the mobile nylon bag technique (Vtrit6
et al., 1987).
Van Bruchem et al.(1989) estimated an overall true
digestion of AAN passing into the proximal duodenum
and terminal ileum of 0.85 in sheep fed diets of whole
roughage or roughage-mixed with concentrates. In
most diets part of the undegraded feed CP in the duo-
denum originates from roughage. For cows fed a diet
S. Taraminga et al. / Livestock Production Science 40 (1994) 139-155
149
of pure haylage Hvelplund (1984) found a digestion
of 0.61. According to Hvelplund and Madsen (1990),
digestion of AAN in this fraction is lower than that of
AAN from protein supplements because in roughages
the undegraded CP is linked to fibre and thus more
resistant to digestion in the small intestine.
In the DVE system the intestinal digestion of unde-
graded feed AAN is based on measurements with the
mobile nylon bag method (Van Straalen and Tam-
minga, 1990). A limitation of this method is that it
measures the digestion of the total N rather than of
AAN. This approach seems however justified because
AAN appears to have a much higher intestinal digestion
than NPN (Oldham and Tamminga, 1980).
For roughages insufficient information was available
from mobile nylon bag experiments.%DVBE was
therefore calculated from the undegraded residue after
long rumen incubations as given by Eq. (4). This was
based on a linear relationship between the size of the
truly undegradable fraction (after two weeks of rumen
incubation) and the undigested fraction after 16 hours
of rumen incubation followed by intestinal digestion in
mobile nylon bags (Tamminga and Ketelaar, 1988),
observed for concentrate ingredients. Further research
is needed to establish a similar relationship for rough-
ages.
10.3. Microbial protein digested in the small intestine
(DVME)
In the Nordic AAT/PBV system microbial protein
synthesis is related to the carbohydrates digested
(DCHO). Microbial protein synthesis in the DVE-sys-
tem is related to the FOM, like in the French PDI-
system. The differences between the two approaches
are small (Hvelplund and Madsen, 1990).
When calculating FOM from DOM, theoretically the
latter should also be corrected for the OM fermented in
the hindgut and for the fecal excretion of endogenous
and dietary fat. A further correction should be made
for the amount of apparently undigested CP (unde-
graded feed CP, microbial CP and endogenous CP). It
is assumed that the positive and negative influences on
FOM as mentioned above largely compensate each
other.
The full potential of microbial CP yield in the rumen
from the energy released during fermentation is only
achieved when the microbes leave the rumen at a pas-
sage rate equal to their division rate (Hvelplund and
Madsen, 1990). Normally this is not the case and the
amount of microbial CP entering the small intestine
remains below potential. Clearance of microbes from
the rumen is influenced by dilution rate (Van Soest,
1982). A lower passage rate compared to division rate
increases the proportion of substrate lost in mainte-
nance of the microbial population (Hvelplund and
Madsen, 1990). Factors influencing the ruminal out-
flow rate of microbes, divide the maintenance costs
over a greater or lesser microbial yield (Kennedy et al.,
1976; Allen and Harrison, 1979; Harstad and Vik-Mo,
1985; Meyer et al., 1986).
The microbial eco-system in the rumen to a large
extent depends on cross-feeding between microbial
species. It can be argued that cross-feeding circum-
stances become sub-optimal when maximum feed
intake is approached and that net microbial growth,
strongly favoured by a rapid passage rate, becomes
reduced.
Sources of variation in microbial CP flow to the
duodenum were reviewed by Hvelplund and Madsen
(1990). They include the recycling of NH3 (NRC,
1985; 1988; Nolan and Stachiw, 1979), protozoal pre-
dation (Coleman, 1975), the quality of the degraded
feed CP (McAllen et al., 1988), and specific require-
ments for amino acids or peptides (Russell et al.,
1983), branched chain volatile fatty acids (Russell and
Hespell, 1981) or minerals (Durand and Komisarczuk,
1988). The influence of each single factor is however
not yet known (Hvelplund and Madsen, 1990).
In most systems microbial yield is only related to the
DMI or OM digestion (Nocek and Russell, 1988).
Some of the factors influencing microbial yield, are
included in the Cornell Net Carbohydrate and Protein
System, CNCPS (Fox et al., 1992; Russell et al., 1992;
Sniffen et al., 1992). In this system it is assumed (Rus-
sell et al., 1992) that dietary NDF-content and the rum-
inal concentrations of NH 3 and peptides have a
significant influence on microbial growth. Different
types of microbes use different N-sources for growth.
In the CNCPS it is assumed that the amount of carbo-
hydrates or CP digested in the rumen is influenced by
their relative rates of degradation and passage. Ruminal
passage rates are influenced by DMI, particle size, bulk
density and type of feed (forage or concentrates) (Snif-
fen et al., 1992).
Because losses of NH3 from the rumen through pas-
150
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
sage and absorption, are considered inevitable, the PDI-
system (Verit6 et al., 1987) assumes that a maximum
of 90% of degraded feed N can be used for microbial
protein synthesis; the MP system (AFRC, 1992)
assumes that feed N quickly degraded (QDN) can be
captured with an efficiency of 80%. The DVE-system,
like the AAT/PBV system, assumes that the N from
degraded feed CP that can not be used immediately for
microbial protein synthesis is compensated by recy-
cling of urea. The maximum efficiency of utilisation of
feed N by rumen microbes is therefore assumed to be
100%.
Microbial CP is a mixture of protozoal and bacterial
CP. Although variable, the protozoal contribution to
the total microbial CP is considered relatively small
(Harrison and McAllen, 1980).
Like N in feed, N in microbes is only partly present
as AAN, and the ratio AAN/N seems variable. Varia-
tion in the AAN/N ratio in microbes as summarized
for the different protein evaluation systems, reflect the
variation found in bacterial preparations. As summa-
rized by Hvelplund and Madsen (1990), variation
could be due to diet, due to time of isolation compared
to feeding and due to feeding regime. Indications for
influence of diet are given by Hvelplund (1986).
In the French PDI-system the AAN/N ratio in micro-
bial CP is given as 0.8. The ARC (1980) gives a value
of 0.81, also calculated by Storm (1982) based on 41
published reports in literature. NRC (1985) has
adopted the value of 0.8, the Nordic countries 0.7
(Madsen, 1985) and Germany also 0.7 (Rohr, 1987).
In the DVE-system a ratio of 0.75 is assumed.
The true digestion of microbial AAN in the French
system is 80%. The true digestion of microbial protein
was reported 87% by Tas et al. ( 1981 ), 81% by Storm
and Orskov (1983), 85% by Storm et al. (1983a) and
85% by Hvelplund (1985). These figures suggest a
fairly constant digestion of amino acids in microbial
CP. In the DVE-system a value of 0.85 was chosen.
10.4. Endogenous losses in digestion (DVMFE)
In reviews (Boekholt, 1976; ARC, 1984; NRC,
1985; Owens, 1987), excretion of metabolic fecal N
(MFN) was calculated between 20 and 30 g of CP per
kg DM intake. MFN does however not represent true
metabolic losses from the gut. The regulation of quan-
tity and composition of endogenous CP losses from the
gut is not well documented, but the quantity is assumed
to be at least related to the DM (NRC, 1988; Swanson,
1982; Van Bruchem et al., 1987; 1989) or OM (V6rit6
et al., 1987) passing the intestinal tract. Part of the
metabolic excretions are re-absorbed from the small
intestine. In the hindgut part of it is converted into
microbial CP or absorbed as NH3 after microbial deg-
radation. In the opposite direction, transfer of urea from
the blood to the hindgut and a subsequent capture by
microbes also occurs (ARC, 1984; Tamminga, 1992).
Endogenous CP losses have to be replaced by resyn-
thesis. The French PDI-system and the Nordic AAT/
PBV-system includes them in their maintenance
requirement, while the NRC system considers them as
a seperate requirement. The DVE system was mainly
introduced with the aim to control avoidable N losses
to the environment. Because these losses can be manip-
ulated by selecting feed ingredients, causing low
endogenous losses, it was decided to follow the NRC-
approach.
Metabolic losses vary with the quality of the diet
(Tamminga, 1992). The NRC (1985) suggests a value
of 30 g of CP per kg of DM ingested at a digestion of
the DM of 67%. This implies a (fecal) CP excretion
of 90 g per kg of undigested DM. This approach does
not take into account that part of the MFN is in fact
undigested microbial CP. In rations of average com-
position this amount is estimated at about 40 g per kg
of undigested DM (CVB, 1991a). These losses have
to be corrected for. The total loss of metabolic CP is
therefore assumed to be around 50 g per kg of undig-
ested DM. This value is comparable to values found by
V6rit6 et al. (1987) who found the following relation-
ship to estimate metabolic CP (CPM) losses:
CPM = 0.0289 × FOM + 0.216 × BRE + 0.060
× UDM
(FOM, BRE and UDM in g/kg)
From this equation it appears that with each kg of
fecally excreted organic matter, about 60 g of CP is
lost. With an average OM/DM ratio in the feces of
85%, this adds up to 51 g of MCP per kg UDM. Assum-
ing an efficiency for synthesis of 67% (NRC, 1985),
the DVE-requirement to replace these losses is calcu-
lated as 75 g per kg UDM.
S. Tamminga et al. / Livestock Production Science 40 (1994) 139-155
151
10.5. The degraded protein balance ( OEB)
Compared to the French PDI-system (V6rit6 et al.,
1987), the value PDIN is used in a different way in
both the AAT/PBV-(NKJ-NJF, 1985) and the DVE-
system. In these systems it is called protein balance in
the rumen (PBV or OEB) and reflects the losses of N
not captured in the rumen. This was done to visualize
the losses of N in dairy cattle diets to those who for-
mulate rations in practice. In the DVE-system the OEB
value should not be negative. In the AAT/PBV system
a negative value of PBV is allowed. Kristensen et al.
(1988) and Hvelplund et al. (1987) showed that in
early lactation, values below - 300 g PBV/day reduce
production, and hence a value around 0 is recom-
mended. Hvelplund and Madsen (1990) concluded
that the PBV value of a ration can be allowed below
zero when the AAT supply is above requirement,
because the N from the surplus of absorbed amino acids
can be recycled to the rumen. This could be of impor-
tance in early lactation, but may still result in rumen
NH 3 levels low enough to impair feed intake and diges-
tion (Oldham, 1984). In late lactation there is ample
N for recycling. Based on results of V6rit6 and Geay
(1987), Hvelplund and Madsen (1990) calculated an
allowance of around - 10 gr PBV/SFU (Scandinavian
Feed Unit) in early lactation and - 15 PBV/SFU in
mid-lactation for the Nordic system. V6rit6 et al.
(1987) tolerate an even more negative value for dry
cows. The (lack of) influence of a negative value of
OEB in the DVE system has yet to be demonstrated in
production trials, but at present a negative OEB is not
recommended for dairy cows.
10.6. D VE-requirements
Different systems use different protein requirements
due to differences in diets, protein values of the feeds,
types of animals, production levels and type of trials
from which values have been derived (N-balances and
feeding trials (INRA, 1978) versus factorial
approaches (ARC, 1980 and 1984; NRC, 1985)).
For maintenance, the French system uses a require-
ment of 3.25 g PDI per kg metabolizable body weight
(MBW), a value also used in the Nordic system (Mad-
sen, 1985). The NRC gives requirements according to
Eq. (16). Although all systems use a constant effi-
ciency of N-utilisation for milk production it is known
that the efficiency decreases with increasing ratio of
protein and energy (DVE/NEL) in the diet (Webster,
1987; Van Straalen et al., 1993a; Subnel and Meijer,
1993). Subnel and Meijer (1993) showed in addition
to the DVE/NEL-ratio the level of production is impor-
tant.
Analysis of a large number of feeding trials at INRA
showed that the efficiency varies between 0.58 and
0.69. When PDI-intake decreased, generally protein
production decreased and efficiency increased, both in
a curvilinear manner. The efficiency-factor of 0.64 used
in the French system was taken at a point above which
little or no extra production of milk protein due to extra
intake of PDI is found (V6rit6 et al., 1987), and is
called the optimum efficiency. Initially the factor 0.64
was also chosen in the DVE-system, but based on
Dutch production trials a new requirement formula was
derived in which the effect of level of production on
efficiency is incorperated. This part of the system will
be discussed in a seperate paper (Subnel et al., 1993).
The new DVE-system was accepted in practice.
Wether the chosen parameters in the system are well
enough adjusted to the Dutch circumstances is being
tested in several production trials. The exact level of
OEB at which minimal losses of N from the rumen
emerge has theoretically been established at zero.
Wether this value can be achieved in pratice without
any loss of protein production is being evaluated in
seperate production trials.
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R~sum6
Tamminga, S., Straalen, W.M. Van, Subnel, A.P.J., Meijer, R.G.M., Steg, A., Wever, C.J.G. et Blok, M.C., 1994. Le syst~me d'6valuation des
prot6ines des ruminants: Le syst~me DVE/OEB. Livest Prod. Sci., 40:139-155 (en anglais).
En 1991, un nouveau syst~me d'6valuation du taux prot6ique a remplac6 le syst~me DCP aux Pays-Bas: Le Syst&ne DVE/OEB. Ce syst~me
a 6t6 d6velopp6 afin de pr6venir les laertes non-necessaires d'azot6 pour ajuster exactement le r6el besoin de la vache laiti~re et de predire plus
exactement la production des prot6ines du lalt.
Les besoins en prot6ines pour l'entretien, la production laiti~res, la croissance et la gestation sont exprim6s en DVE, concemant les aliments
digestibles et les prot6ines microbiennes dans l'intestin gr~le.
Pour chaque mati6re premiere, la valeur de la DVE donne la quantit6 de prot6ines disponsibles consistant en prot6ines by-pass ( 1 ), les
prot6ines synth6tis6s par les microorganismes du rumen (2), et une correction pour les prot6ines endog~nes perdues par les processes de
digestion (3).
Pour chaque mati~re premiere, la balance des prot6ines non d6gradables refl6te la diff6rence entre la synth6se prot6ique microbiennes
disponsible bas6e sur la d6gradation des prot6ines et l'6nergie disponsible du6 au proc6d6 de fermentation du rumen.
Le syst~me DVE/OEB est bas6 sur ce qui est consid6r6 comme les meilleurs 616ments des syst~mes modemes d'6valuation prot6iques des
autres pays.
Des nouveaux 616ments sont la f6cule r6sistante ~t fermentation dans le rumen (USTA), les produits de fermentation des silages (FP), la
relation entre la balance d'6nergie et la disponibilit6 des prot6ines dans l'intestine et la diff6rence des besoins d6pendant de la production des
prot6ines de lait.
Le syst~me a 6t6 contruit en utilisant principalement les donn6es des recherches N6erlandaises, particuli~rement pour les valeurs prot6iques
fourragi~res et sous-produits.
Zusammenfassung
Tamminga, S., Straalen, W.M. Van, Subnel, A.P.J., Meijer, R.G.M., Steg, A., Wever, C.J.G. und Blok, M.C., 1994. Das Niederl~indische
Eiweissbewertungssystem: Das DVE/OEB System. Livest Prod. Sci., 40:139-155 (anf englisch)
Das DVE/OEB System wurde 1991 an stelle des bis dahin gebr~uchlichen dcp-Systems eingefiihrt als neues Eiweissbewertungssystem.
Dieses System wurde entwickelt, um unn0tige Stickstoffveduste zu vermeiden dutch eine genauere Anpassung der Fiitterung an die wirklichen
Bedarfsnotmen und um die Milcheiweissproduktion genauer voraussagen zu kSnnen. Der Eiweissbedarf fiir Erhaltung, Milcheiweissproduktion,
Wachtstum and Schwangerschaft wird ausgedriickt in DVE, verdauliches Futter- und Mikrobeneiweiss des Diinndarms.
Der DVE-gehalt eines jeden Futtermittels repr~,isentiert das verfiigbare Eiweiss, berechnet ans der Summe aas bestiindigem Eiweiss ( 1 ) and
microbiellem Eiweiss (2) vermindert um endogene Eiweissveduste in Verdauugsproze (3).
Die unbestiindige Eiweissbilanz (OEB) eines jeden Futtermittels spiegelt den Unterschied zwischen einer m0glichen mikrobiellen Eiweiss-
synthese, basierent auf abbanbarem Eiweiss und verfiigbarer Energie, und die Fermentationsprozessen im Pansen wider.
Das DVE/OEB-System beruht auf was andere L~lnder die festen Elemente der modemem Eiweissbewertungssysteme bezeichnen. Neue
Elemente sind best~dige St~rke (USTA), Fermentationsprodukte in Silagen (FP), Energiebilanz bei tier Eiweissversorgung and der Eiweiss-
Verwertung in abh~ingigkeit der Milchproduktionsmange. Es wurde aufgebaut aus Daten mit haupts~ichlichem Urspnmg in der holl~ndischen
Forschung under besonderer Bem'cksichtigung von Eiweissgehalten in Grundfuttermitteln and einige indusaielle Nebenprodukte.
