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OCR for page 7
Companson of New
Protein Systems for
Ruminants
INTRODUCTION
Several new theoretical protein systems have been
proposed that have potential application to feeding ru-
minants. These new systems require several additional
concepts that the current National Research Council
(NRC) systems, such as that for dairy cattle (1978), do
not. Dietary intake crude protein (Ilk is either degraded
(DIP) in the rumen, with partial or total conversion to
bacterial and protozoa! crude protein (BCP), or passed
from the rumen as undegradec! intake protein (UIP).
Microbial growth in the rumen requires either DIP,
which may include either dietary nonprotein nitrogen
(NPN), or a net ruminal influx of endogenous urea as
crude protein (RIP) from either saliva or across the ru-
men wall. Production of BCP associated with microbial
growth is related to energy fermented in the rumen and
is expressed most commonly as a function of apparently
fermented organic matter (FOM). Excess DIP increases
the concentration of ruminal ammonia and increases
the ruminal efflux of ammonia as crude protein (REP)
by absorption and passage. Production of BCP repre-
sents both a protein requirement and a subsequent
source of protein for the tissue needs of the cow. Effi-
ciency of ruminal utilization of protein is 1.0 when DIP
exactly meets the BCP need. When DIP equals BCP
need, RIP must equal REP. The theoretical efficiency of
tissue utilization of protein is maximum when BCP and
UIP exactly meet the cow's tissue need. The theoretical
efficiency of producing milk is maximum when both ef-
ficiencies in rumen and tissue utilization are maximum,
i.e., neither DIP nor UIP is excessive.
The new concepts require that ruminal undegrada-
bility (UIPIP) must be specified in addition to a total
tissue protein requirement. As higher milk production
requires more total protein and available DIP exceeds
that converted to BCP, more undegradable protein
7
sources increase the efficiency of N use. A similar situa-
tion prevails in the rapidly growing animal.
Objectives of this paper are (1) to present a compara-
ble tabulation of factors used in five U. S. and five Euro-
pean factorial systems that are static or partly static sys-
tems; (2) to calculate, as an example, minimal dietary
protein and optimal UIPIP based on factors for a 600-kg
cow producing from 10 to 40 kg of milk per day; and (3)
to compare the expected flow of N into the small intes-
tine and into the sinks of milk, urine, and feces. Papers
previously published (Verite et al., 1979; Waldo, 1979;
Chalupa, 1980a; Verite, 1980, Waldo and Glenn, 1982)
have compared factors of some systems. Yerite et al.
(1979) compared the protein concentration in dry mat-
ter (DM) required for milk production from 15 to 35 kg,
and Geay (1980) compared protein required for growth
based on several systems. Waldo and Glenn (1982) com-
pared the distribution of dietary protein and N to milk,
urine, and feces in five European systems.
FACTORS IN AVAILABILITY OF
ABSORBED PROTEIN
Factors from 10 systems are compared in Tables 1 and
2. The current NRC dairy system (Swanson, 1977, 1982;
NRC, 1978) is included as a reference. Four new U.S.
systems have been proposed. These systems will be
called Burroughs (Burroughs et al., 1971, 1974, 1975a,
b; Trenkle, 1982), Satter (Roffler and Satter, 1975a,b;
Satter and Roffler, 1975; Satter, 1982), Chalupa
(1975b, 1980a), and Cornell (Fox et al., 1982; Van Soest
et al., 1982~. Two new European systems the ARC
system in Great Britain (Roy et al., 1977, ARC, 1980)
and the PDI grele system in France (Verite et al.,
19793 are official proposals within each country.
Kaufmann (1977b, 1979) has proposed a system in Ger
OCR for page 8
~ Ruminant Nitrogen Usage
many, and Landis (1979) has proposed a system in
Switzerland. Haselbach (1980) and Schurch (1980) also
presented discussions relative to the proposal of Landis.
Danfaer (1979) has outlined many factors in a model of
protein utilization from Denmark. Danfaer et al.
(1980), Madsen et al. (1977), and Molter and Thomsen
(1977) also presented data from Denmark that will be
used for some values not specified in the model of Dan-
faer. Danfaer does not propose a system but gives some
factors in protein utilization. The Cornell system intro-
duces dynamic factors.
The new systems require specification of several new
factors to describe availability of protein at the intes-
tine. The division of IP into DIP and UIP fractions must
be specified. The proportional production of BCP from
DIP (BCPDIP) must be specified. Production of BCP
must be related to dietary energy, which frequently is
expressed as either FOM or apparently cligested organic
matter (DOM). The division of BCP into nucleic acid N
as crude protein equivalent (NCP) and bacterial and
protozoa! true protein (BTP) must be specified. If theo-
retical urinary and fecal N excretion are to be calcu-
lated, the digestible nucleic acid N as crude protein
equivalent (DNP) must be specified.
Intake Protein per Unit of Dry Matter
The required IP concentration in the dietary DM
(IPDM) in the newer systems is still variable and directly
related to milk production as in the NRC system based
on total protein or crude protein (CP) (Table 1~. How-
ever, in the newer systems, high milk production can be
sustained with less IP if UIPIP also is increased, and dry
cows in low production can be fed less IP if UIPIP is
decreased.
Undegraded and Degraded Intake Protein per
Unit of Intake Protein
All of the new systems consider the dietary IP to be
divided into undegraded (UIP) and degraded (DIP)
fractions, with the proportional division represented by
UIPIP and DIPIP. This division is most generally con-
sidered continuously variable (Table 1~. The Chalupa
and ARC systems place all proteins into four classes hav-
ingUIPIPofO.20 + 0.10,0.40 + 0.10,0.60 + 0.10,
and > 0.70. The Cornell system defines an indigestible
intake protein (IIP) fraction in IP. The Cornell system
also further subdivides DIP into soluble and potentially
degradable subfractions and includes a dynamic degra-
dation of the potentially degradable subfraction.
The proper division of IP into UIP and DIP is the ma-
jor new input required for these new systems to be effec
tive in practice. The derivations or sources of these data
are not always specified. Burroughs et al. (1975b) have
an extensive tabulation of feedstuff degradabilities for
their system. Satter is collecting in vivo data for com-
mon dairy feeds used in the north central United States.
Chalupa (1980a) has accepted the ARC tabulation of
feeds into four classes. The PDI system (Demarquilly et
al., 1978) uses an extensive tabulation of solubility and
in vitro fermentability. Verite and Sauvant (1981) pro-
posed equations for calculating digestible protein reach-
ing the intestine from IP and protein of concentrates sol-
uble in salt solution. The other systems propose neither a
source of undegradability data nor an analytical
method for obtaining the data.
Crude Bacterial Protein per
Unit of Degraded Intake Protein
Six systems assume no loss or gain of protein in the
production of BCP from DIP (BCPDIP), or BCPDIP =
1.00, but the ARC and Chalupa systems assume BCP-
DIP of dietary urea to be 0.80 (Table 1~. The Satter sys-
tem assumes an RIP equivalent to 12 percent of dietary
IP and 90 percent utilization of ruminal ammonia, or
bacterial and protozoa! crude protein/ruminally avail-
able nitrogen as protein (BCPRAP); if degradability =
0.7,then the netinfluxisO.12 - 0.7~1.0 - 0.9) = 0.05
for BCPDIP = 1.05. The Danfaer model assumes
BCPDIP = 0.90. The Cornell system proposes a range
of BCPDIP from 0.5 to 0.9. Such low efficiencies in-
crease implied protein requirement by increasing esti-
mates of ammonia absorption and urinary excretion.
It seems unrealistic to assume that degradation of pro-
tein can be optimized for high milk production so that
conversion of DIP to BCP fully attains 1.00, even
though this is the goal of any ideal protein system. Wa-
ter passage from the rumen will elute some ammonia
that must be replaced. The dynamic model of Baldwin
et al. (1977a) indicates that one-fourth of ammonia
leaves the rumen by passage and three-fourths by ab-
sorption in a 40-kg sheep fed a 22.5 percent CP alfalfa
hay at 37.9 g of DM/h. Kaufmann (1977a) found duode-
nal N (g/100 g of feed N) = 34.2 + 1032.711P (percent
of dietary DM) in 45 observations on lactating dairy
cows; this equation implies a gain of total N in the ru-
men below 15.7 percent dietary IP and a Toss of total N
above 15.7 percent. Hogan (1975) described protein
reaching the intestines (gig IP) = 0.33 + 0.18 DOM
intake with r = 0.96 using sheep; assuming that DOM
= 0.67 DM, this equation implies a gain of protein in
the rumen below 14.2 percent IP and ~ loss of protein
above 14.2 percent IP. Oyaert and Bouckaert (1960) de-
scribed the percentage of protein N intake absorbed in
OCR for page 9
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OCR for page 11
the rumen = - 20.8 ~ 1.62 NH3 - N (mg/100 ml of
rumen fluid) with r = 0.91 for n = 10 diets fed to sheep;
this equation implies a gain of protein in the rumen be-
low 13 mg NH3 - N/100 ml and a loss above 13 mg
NH3 - N/100 ml.
Crude Bacterial Protein per
Unit of Fermented Organic Matter
The most common expression of BCP to microbial en-
ergy fermentation is as a function of FOM (BCPF'OM).
Five systems assume proportional BCPFOM that range
from 0.15 to 0.25 (Table 1~. The Satter, PDI, and Lan-
dis systems relate BCP to DOM (BCPDOM) and specify
no proportions for BCPFOM. The Cornell system is dy-
namic for this factor. Thomas (1973), in his summary,
calculated a mean of 0.20 for 27 diets fed to sheep and
cattle; Kaufmann (1977a) calculated a mean of 0.20 for
11 diets fed to dairy cows. Diet does affect this factor.
McMeniman et al. (1976) calculated means of 0.1375 for
diets with high concentrates and 0.1962 for diets with
fresh or dried forages. Chamberlain and Thomas
(1980a) present a range from 0.0625 to 0.1375 for diets
consisting of only hay-crop silages.
Fermented Organic Matter per
Unit of Digested Organic Matter
When BCP is based on FOM, it is necessary to assume
a proportional FOM per unit of DOM (FOMDOM).
These proportions range from 0.65 to 0.68 except in the
Burroughs system, for which 0.52 is used (Table 1~. The
Cornell system is dynamic for this factor.
Crude Microbial Protein per
Unit of Digestible Organic Matter
The eight fully static systems assume proportional
BCP per unit of DOM (BCPDOM) that range from
0.0975 to 0.153 (Table 1~; excluding the low 0.0975 for
the Chalupa system and the high 0.153 for the Danfaer
model narrows the range from 0.12 to 0.135.
Digested Organic Matter per Unit of Dry Matter
Because BCP is a function of DOM and IF usually is
specified as a proportion of dietary DM, some specifica-
tion of the proportional DOM per unit of DM
(DOMDM) must be made. No system describes this rela-
tionship well. For subsequent calculations in the latter
sections of this chapter when no value is specified, a
value of 0.67 will be used; taken from the analyses of
Tyrrell and Moe (197S) on the data of Wagner and
Comparison of New Protein Systems for Ruminants I}
Loosli (1967~. Diets containing from 25 to 75 percent
concentrate and being consumed from 2.82 to 4.05
times maintenance had total digestible nutrients (TDN)
from 66 to 68 percent. Increasing the percentage of con-
centrate increased intake, but digestibility depression
offset the expected increase of digestibility.
True Bacterial Protein per
Unit of Crude Microbial Protein
All systems, except the Landis system, split the BCP
into BTP and NCP components with the proportional
division represented by BTPBCP and NCPBCP. All sys-
tems specify 0.80 for BTPBCP and 0.20 for NCPBCP
except the Danfaer model, which specifies 0.85 ant!
0.15, respectively (Table 1) .
Digestible Bacterial Protein per
Unit of True Bacterial Protein
All systems, except the Landis system, specify digest-
~ble bacterial true protein (DBP) per unit of BTP
(DBPBTP). These proportions range from 0.70 to 0.90
with 0.80 most frequently used (Table 1~.
Digestible Bacterial Protein per
Unit of Crude Bacterial Protein
All new systems specify a proportional DBP per unit
of BCP (DBPBCP) with the range from 0.56 to 0.72 (Ta-
ble 1) . All of the new proportions are below the 0.75 that
is assumed in the present NRC system.
Digestible Nucleic Acid Nitrogen per
Unit of Crude Nucleic Add Nitrogen
Only three systems specify any rate for NCP. The
Danfaer model assumes a proportional 0.85 for digest-
ible nucleic acid N as protein equivalent (DNP) per unit
of NCP (DNPNCP). The Chalupa system assumes
DNPNCP = 1.00. Kaufmann (1977b) describes his sys-
tem as having a NCPBCP of 0.10 that has a digestibility
of 0.85 and another NCPBCP of 0.10 that has a digest-
ibility of 0. For a greater equivalence to the Danfaer
model, the Kaufmann system is redescribed in Table 1
as having the full NCPBCP of 0.20 that has a digestibil-
ity of 0.425. This description gives the same distribution
of nucleic acid N as the original Kaufmann system.
Specification of the cligestibility of nucleic acid N is nec-
essary to compare the theoretical urinary and fecal ex-
cretion of N with ire vivo results. It is also unreasonable
to expect that the nucleic acid N will be more digestible
than the bacteria that contain it.
OCR for page 12
12 Ruminant Nitrogen Usage
Digestible Undegraded Protein per
Unit of Undegraded Intake Protein
All systems specify proportional digestible unde-
graded intake protein (DUP) per unit of UIP (DUPUIP)
with the range from 0.70 to 0.90 (Table 1~. The PDI
system assumes variable digestibility as specified in their
equation 5 (Verite et al., 1979~. Substitution of their
equation 4 into their equation 5 gives a true digestibility
of undegradedN = t(0.65 - 0.143) x insolubleNin-
take]/0.65 x insoluble N intake = 0.78 for a mean; this
mean is also equal to the mean of their variable range
from 0.60 to 0.95. The difference between this mean
and their variable digestibilities is that their variable di-
gestibilities include all of the residual error of a particu-
lar feed associated with the derivation of the constants
describing fecal N output.
Fecal Metabolic Protein
Fecal metabolic protein is the most variable factor in
the systems (Table 1~. Fecal metabolic protein either is
not specified as a separate factor or is specified as a sepa-
rate factor that is a function of DM intake (DMI), indi-
gestible dry matter intake (IDMI), or indigestible or-
ganic matter intake (IOMI). The units are either as
absorbed (FPA) or net (FPN) protein. The ARC and Sat-
ter systems do not specify any FPA or FPN as a separate
factor. The Cornell system mentions it as a separate fac-
tor but does not specify an equation. The PDI system
specifies FPA as 0.057 per unit of IOMI. The NRC sys-
tem specifies FPA as 0.068 per unit of IDMI or as 0.030
per unit of DMI with slightly less accuracy. The Cha-
lupa system specifies FPN as 0.03 per unit of DMI. How-
ever, it considers two-thirds of this to be undigested bac-
terial cells that are accounted for as indigestible
bacterial protein and indigestible nucleic acid protein
equivalent in this publication. All other systems specify
FPA as a function of DMI with factors ranging from
0.012 to 0.026. The Burroughs system specifies the FPA
as a reduction of absorbed protein (AP) from feed. All
systems specifying FPA may use that FPA as a reduction
of AP from feed.
In viva data on lactating cows fed forage-concentrate
diets may be used for comparing with the fecal meta-
bolic protein specifications of these systems. Boekholt
(1976) found that digestible protein (DP) as a percent-
age of dietary dry matter or DP (percent of DM) =
0.833 x IP(percentofDM) - 3.31,withr2 = 0.95,sy.x
= 0.469, and n = 362 for dairy cattle whose mean milk
production wasl8.9 + 5.2kg/day~asastandarddevia-
tion) and IP (percent of DM) was 16 + 2.3 percent. This
equation implies a fecal metabolic protein fraction of
0.033 gig of dietary DM. Waldo and Glenn (1982) per
formed a similar analysis on the data of Conrad et al.
(1960) and found DP (percent of DM) - 0.861 x IP
(percent of DM) - 2.86, with r2 - 0.92, sy.x - 0~743,
and n = 177 for dairy cattIe whose milk production was
11.8 + 3.1 kg/day and IP (percent of DM) was 15.3 +
2.8. This equation implies a fecal metabolic protein of
0.029 g/g of dietary OM. That these proportions could
round to 0.030 is support for the slightly less accurate
estimate of the NRC system, but as FPA rather than
FPN. At 15 percent dietary IP, these equations imply
that 57 percent of the fecal N arises from this source and
that 19 to 22 percent of dietary IP is required to meet this
need. It seems realistic to include a factor for fecal meta-
bolic protein, since it has so much quantitative impor-
tance.
FACTORS IN THE REQUIREMENT FOR
ABSORBED PROTEIN
No factors other than those already used in the NRC
system are required in the new protein systems. The to-
tal protein requirement includes that for fecal metabolic
protein, maintenance, and production. The mainte-
nance requirement may include fecal ~netabolic pro-
tein, urinary endogenous protein, and surface protein.
The production requirement is the sum of one or more of
four factors lactation, conceptus, weight change, and
growth (including surface material).
Maintenance
FECAL METABOLIC PROTEIN
Fecal metabolic protein is considered differently in
the systems (Table 2~. The ARC and Satter systems do
not specify any FPA or FPN as a separate factor. The
Cornell system cloes not specify how the fecal metabolic
protein fraction is considered. The Burroughs system
has specified F PA as a reduction from AP available from
feed. The Kaufmann and Landis systems specify F PA as
a component of total requirement independent of main-
tenance; the model of Danfaer also seems to in.clude
FPA as a component of total requirements. The inclu-
sion of F PA either as a feed reduction factor or fully con-
sidered as a component of total requirement supplies the
full requirement for fecal N. The NRC system includes a
part of the fecal metabolic protein in the maintenance
requirement an`1 the remainder in the production re-
quirement. The Chalupa system specifies one-third of
total fecal metabolic protein in maintenance. The PDI
system includes only part of total fecal metabolic pro-
tein as a component of the requirement; the remaining
requirement for fecal N excretion must be met by reduc-
ing assumed urinary N excretion.
OCR for page 13
URINARY ENDOGENOUS PROTEIN
Neither the PDI nor Landis systems specify this factor
(Table 2~. All other systems specify an endogenous uri-
nary protein equivalent either in units of absorbed
(UPA) or net (UPN) protein. This requirement is usually
calculated as a power function of body weight near
0.75.
SURFACE PROTEIN
No specification is made in the Landis system and a
zero specification is made in the Burroughs, Satter, Cor-
nell, Danfaer, and Kaufmann systems (Table 2~. All
other systems specify a surface protein requirement in
units of absorbed (SPA) or net (SPN) protein. The SPN is
less than 5 percent of the total maintenance for the Cha-
lupa and NRC systems. The SPN represents about 20
percent of the maintenance requirement of the ARC sys-
tem. Because the PDI system uses the SPA required to
give N retention equal to hair and scurf loss as its total
maintenance requirement, its SPA is relatively higher
than all others.
TOTAL
The total maintenance requirement as AP is in Table
2 for comparative purposes. The total maintenance re-
quirements are extremely variable, ranging from 100 to
395 g of AP. Unfortunately, these are not equivalent be-
cause some include fecal metabolic protein and some do
not. The relatively low requirement of the Burroughs
system can be accounted for partially by the deduction
of fecal metabolic protein from available AP. Similarly,
the relative low requirements of the Danfaer, Kauf-
mann, and Landis systems are accounted] for by their
consideration of fecal metabolic protein as a separate
component of total requirement. No equivalent factors
can account for the lowest requirement in the ARC sys-
tem; however, the failure to include a fecal metabolic
protein factor probably contributes to its smallness.
Production
LACTATION
The lactation protein requirement as absorbed (LPA)
units is the assumed protein concentration or lactation
net protein requirement as net (LPN) units divided by
the assumed efficiency (LPNLPA) (Table 2~. The most
commonly assumed efficiency is 0.70. The efficiency of
Burroughs is highest at 0.95 and of Danfaer is lowest at
0.56 (Table 2) . The LPA requirement for 30 kg of milk is
in Table 2. These requirements range from 990 to 1,920
Comparison of New Protein Systems for Ruminants 13
g of LEA, with the major cause of differences being dif-
ferences in efficiency. The ARC system has the second
lowest requirement for milk along with the lowest re-
quirement for maintenance and no reduction of avail-
able AP by fecal metabolic protein.
CONCEPTUS
The conceptus protein requirement as absorbed
(YPA) units for the last 2 months of pregnancy varies
from 107 to 205 g (Table 2~. A frequent requirement is
about 160 g. Five systems have not described a require-
ment for the conceptus.
WEIGHT CHANGES IN LACTATION
Six systems rlo not specify a factor for weight change.
When weight change is specified as retained protein in
net (RPN) units in the NRC, ARC, Oanfaer, and Satter
systems, the proportions range from 0.112 to 0.225. The
validity of the NRC and ARC systems assuming a differ-
ent proportion for gain and loss when the units are de-
fined as RPN seems questionable. The efficiency for
weight change is the same as for lactation in the ARC
and Satter systems.
GROWTH
Six systems have proposed the proportional gain as
protein (Table 2~. Burroughs et al. (1974) assume the
proportional retained protein as net (RPN) units in live-
weight gain (G) declined from 0.150 at 150 kg of live-
weight to 0.110 at 500 kg for finishing steers and heifers
of early maturing breeds. Chalupa (1975b) adopted
these same data. The ARC (1980) assume proportional
RPN in empty body weight gain (EBWG) declined from
0.181 at 50 kg of empty body weight (EBW) to 0.140 at
500 kg for steers of an average size with 0.6 kg EBWG/
day. Proportional RPN is changed by a factor of 0.90 for
smaller breeds and 1.10 for larger breeds. Proportional
RPN is changed by a second factor of 0.90 for heifers and
1.10 for bulls. Proportional RPN is changed by a third
factor of 0.013 subtracted from 1.0 for each 0.1 kg of
EBWG greater than 0.6 and 0.013 addec] to 1.0 for each
0.1 kg of EBWG less than 0.6. The PDI (Verite et al.,
1979) system assumes proportional RPN in G to decrease
from 0.186 to O. 135 with maturity; the proportion var-
ies with liveweight, G. breed, and sex. Robelin and
Daenicke (1980) extend the PDI system by giving a set of
equations for describing the proportional RPN as con-
tinuous functions of liveweight and G within very early
maturing steers, early maturing bulls, and late matur-
ing bulls. Fox et al. (1982) describe the retention of RPN
as a function of EBW for steers of medium frame size.
OCR for page 14
14 Ruminant Nitrogen Usage
This steer of medium-frame size is considered a refer-
ence animal with an equivalent weight equal to its
actual weight. Eight other frame sizes and two other
sexes are specified that require adjustment factors for
converting their actual weight to equivalent weight;
these equivalent weights, theoretically, have the same
body composition. Adjustment factors for steers are
1.25 for smallest frame, 1.00 for medium frame, and
0.83 for largest frame. Adjustment factors for heifers are
1.56 for smaldest frame, 1.25 for medium frame, and 1.04
for largest frame. Adjustment factors for bulls are 1.04
for smallest frame, 0.83 for medium frame, and 0.69 for
largest frame. The NRC (1978) requirement for dairy
cattle is in Table 2. The NRC (1984) requirement for
beef cattle calculates RPN as a function of the energy
concentration of gain for steers. Composition of gain
of medium-frame heifers is assumed equivalent to
medium-frame steers weighing 15 percent more. Com-
position of gain of bulls and large-frame steers was as-
sumed equivalent to medium-frame steers weighing 15
percent less. Liveweight, daily gain, breed or frame
size, and sex are the four most important factors affect-
ing the protein energy ratio in growing and fattening
cattle. The functional change in protein and fat deposi-
tions with increasing energy deposition remains some-
what controversial. The proposals range from linear
changes in energy deposited as fat and protein (Tyrrell
et al., 1974; Geay, 1984) to an asymptotic maximal de-
position of protein (Byers, 1982b) and to a maximal pro-
tein (reposition followed by a decrease (Anrique, 19764.
The efficiencies of converting retained protein as ab-
sorbed (RPA) units to RPN, or RPNRPA, range from
0.45 (NRC, 1978) to 0.75 (ARC, 1980) in Table 2. The
NRC (1984) requirements for beef cattle assume an effi-
ciency of 0.66.
Data on sheep are not specific in the various models.
As a consequence they are not covered in this discussion.
Comments on gain and concepts applying to it would be
appropriate for sheep in lieu of more definite data.
DYNAMIC MODELS
Dynamic models have been proposed that describe
protein utilization for the entire animal. Other dynamic
models describe ruminant digestion of dietary crude
protein and carbohydrates, while others describe nitro-
gen metabolism in the ruminant without any reference
to energy. Some of these models are considered prelimi-
nary. Generally, the models are not published in full
detail so that direct communication with the authors is
required for enough detail to use, compare, or challenge
them.
Two dynamic models for specifying protein require-
ments for ruminants are being developed in the United
States. At Michigan, Fox et al. (1976) introduced a net
protein system. Bergen et al. (1979) calculated the up-
per limit of ruminal microbial protein synthesis. Bergen
et al. (1982) describe the efficiency of microbial protein
synthesis in relation to specific growth rate, growth
yield, and maintenance in rumen bacteria. They dem-
onstrate an increase in ribonucleic acid/protein ratio as
specific growth rate increases in anaerobic bacteria.
Such a large difference in this ratio must raise questions
about the constancy of the ratio of nonammonia nitro-
gen and amino nitrogen entering the small intestine or
apparently absorbed in the small intestine. Johnson and
Bergen (1982) describe the effects of diet on the fraction
of organic matter digestion occurring in the rumen and
efficiency of microbial protein production. Wailer et al.
(1982) describe their progress toward a dynamic model
of protein requirement for the ruminant that considers
economics as well as nutrition and emphasizes the alge-
bra and linear programming necessary to consider the
uncertainty of feed composition and least cost formula-
tion.
At Cornell, Van Soest et al. (1982) propose a rumen
submodel for nitrogen utilization that describes the out-
put of protein by using the following inputs: soluble pro-
tein; three true protein subfractions based on the degra-
dability rates (B~, rapid; Be, intermediate; and Be,
slow); bound protein; nonstructural carbohydrate, po-
tentially digestible organic matter; rates of digestion for
each protein, nonstructural carbohydrate and poten-
tially digestible organic matter subfractions; and rates
of passage for liquids and solids. Fox et al. (1982) com-
plete the total model by describing the factors in the cal-
culation of requirements for growth (Table 2~.
The nitrogen flux within the rumen as REP loss of
ammonia by absorption and passage and as RIP gain of
urea from saliva or blood are very important. Nolan et
al. (1976) describe the nitrogen dynamics on a three pool
model of rumen ammonia, plasma urea, and cecal am-
monia in a sheep eating about 22 g air dry feed/in that
contained 18.7 percent CP. When mean dietary N in-
take was 16.3 g/d, mean rumen ammonia N was 20.9
mg/100 ml, mean plasma urea N was 18.1 mg/100 ml,
and total flux of rumen ammonia was 15.0 go/. Of this
total flux 28.7 percent was recycled, and 71.3 percent
was irreversible loss via influx and efflux. The influx
sources, as a percentage of total, were: dietary ant] en-
dogenous sources, 61.9; blood urea, 6.9; and from cecal
ammonia but not via blood urea, 2.5. The efflux losses,
as a percentage of total, were: absorbed, 44.4, micro-
bial protein synthesized into tissue, 20.6; and cecal am-
monia from rumen microbes, 6.3. Only 40 percent of
rumen bacterial N came from ammonia N. and only 20
percent of urea degraded in the intestinal tract was de-
gracled in the rumen. Mazanov and Nolan (1976) de
OCR for page 15
Comparison of New Protein Systems for Ruminants 15
scribe the nitrogen dynamics in a nine-part model using
the above data combined with data from lower N in-
takes. When mean dietary N intake was 14. I6 g/d, total
flux of ammonia N was 9.11 g/d. Of this total flux, 19.2
percent was recycled. The influx sources, as a percent-
age of total, were: dietary amino N. 67.0; urea, 13.2;
and dietary ammonia N. 0. 6. The efflux losses, as a per-
centage of total, were: microbial N not recycled, 31.3;
and ammonia N absorbed or passed, 49.5.
Baldwin et al. (1977a, proposed a model of ruminant
digestion that uses 12 chemical inputs: lignin, cellulose,
hemicellulose, pectin, starch, soluble carbohydrate, or-
ganic acids, lipids, ash, insoluble protein, soluble pro-
tein, and NPN. The model uses one physical input: frac-
tion retained on 1-mm sieve. This model emphasizes the
importance of ammonia passage as a loss of N from the
rumen. Baldwin and Denham (1979) present another
model of N metabolism in the rumen that emphasizes
the difference in affinity of the two major enzymes for
ammonia. Glutamic dehydrogenase is constitutive and
has a low affinity for ammonia (Km = 5 mM); glu-
tamine synthetase is induced at low ammonia concen-
trations and has a high affinity for ammonia (Km = 0.2
mM). Such a difference may explain why microbial
growth is not limited until concentrations fall below 3 to
5 mg/100 ml, but microbial fermentation of the carbo-
hydrates in some diets is limited at concentrations below
20 to 25 ma/ 100 ml, a critical point in comparing in vitro
and in vivo results. The dietary differences in ruminal
methylamine concentration (Hill and Mangan, 1964)
may affect the competitive uptake of ruminal ammonia
by bacteria.
Black et al. (1980-1981) describe a model of rumen
function that uses these chemical inputs: beta-hexose
(lignin, cellulose, and hemicellulose); alpha-hexose
(pectin and starch), soluble carbohydrate (including
glycerol), total fatty acids, inorganic sulfur; ash; protein
(true protein and free amino acids); NPN (including nu-
cleic acids); potential degradability of beta-hexose; and
potential degradability of protein. The mode] has one
physical input: modulus of fineness of diet. Other mod-
eling inputs are: feed intake; time feeding; time rumi-
nating; and reduction in maximum rate or degradation
of beta-hexose, alpha-hexose, and protein due to diet.
Endogenous inputs are: true protein, NPN, and inor-
ganic sulfur. Beever et al. (1980, 1981) did a sensitivity
analysis for 22 variables that could not be set with confi-
dence. Six variables with a high sensitivity, i.e., a
change in protein flow greater than 40 percent from the
possible range in input variable, were: potential degra-
dability of protein, fractional outflow rate of water,
fractional outflow rate of microbes, energy required for
microbial maintenance, salivary flow, and proportion
of rumen ammonia available for microbial growth.
Faichney et al. (1980) found predictions of this model to
be closer to observations in one data set than predictions
from the ARC and PDI systems.
COMPARISON AND CHALLENGE OF
SYSTEMS WITH IN VI VO DATA
A comparison and challenge of implications of the
systems with in vivo data from lactating cattle is inform-
ative after their assumptions and calculations are under-
stood. For these comparisons and challenges we have
calculated IF as a percentage of DM, optimum UIPIP,
either the sum of BTP and UIP or the sum of BCP and
UIP reaching the small intestine, fecal N as a percentage
of dietary N. urinary N as a percentage of dietary N. and
milk N as a percentage of dietary N for a 600-kg cow
producing 10, 20, 30, and 40 kg milk/day with degrada-
bility optimal. These predicted data then are compared
with expected in viva data on protein reaching the small
intestine (Tamminga and van Hellemond, 1977;
Journet and Verite, 1979; Bohr et al., 1979) and in vivo
data on the distribution of N in feces, urine, and milk
(Conrad et al., 1960; Boekholt, 1976~. Some additional
data and assumptions are required because BCP pro-
duction is a function of FOM and fecal metabolic pro-
tein is a function of DMI, IDMI, or IOMI. No attempt
was made to compare and challenge the Cornell system
because it contains several dynamic relationships.
Energy Standards
Except for the ARC and PDI systems, the new protein
systems are published without any specific statement of
or reference to an energy standard. Production of BCP is
related to energy fermented in the rumen, which is more
frequently FOM. Fecal metabolic protein is related to
some dietary component, most frequently dietary DM.
These or other required energy variables must be speci-
fied for a complete system. The energy requirements
and the DM intakes used in these comparisons and chal-
lenges of protein feeding systems and their sources are in
Table 3. Chalupa (1980a) used metabolizable energy as
the energy unit, but energy requirements were not fully
elaborated, so TDN is used as the energy requirement
for the Burroughs, Chalupa, NRC, and Satter systems.
Assumptions about concentrations of energy in dietary
DM vary as well as the assumptions about absolute
amounts of either. In going from 5 to 40 kg of milk, en-
ergy concentrations increase 85 percent in the PDI sys-
tem, 33 percent in the Kaufmann system, and 65 per-
cent in the Landis system. When energy concentration is
not specified, we have assumed it to be constant (based
on the proposed maximum of Tyrrell and Moe, 1975)
with DOMDM = 0.67 as discussed earlier for TDN.
OCR for page 16
16 Ruminant Nitrogen Usage
TABLE 3 Dry Matter Intakes and Energy Standards When Energy
Concentration Varied as Used in Comparison and Challenge of Protein Systems
PDI ~KaufmannC Landisf
NRC° ARCb DanfaerC
Dry Dry Dry Dry Dry Dry
Milk Matter Matter Matter Matter Matter NEL Matter
(kg) (kg) (kg) (kg) UFL (kg) SE (kg) (MJ) (kg)
5 8.6 7.2 7.5 7.1 12.3 4375 9 51.2 11.5
10 10.9 9.4 9.8 9.3 13.7 5750 11 66.9 13.0
15 13.2 11.7 12.1 11.5 15.1 7125 13 82.6 14.5
20 15.4 14.1 14.4 13.7 16.5 8500 15 98.3 16.0
25 17.7 16.4 16.7 16.1 17.9 9875 17 114.0 17.5
30 20.0 18.8 19.0 18.6 19.2 11250 19 129.7 19.0
35 22.2 21.3 21.3 21.0 20.6 12625 20 145.4 20.5
40 24.5 23.6 23.6 23.5 21.9 14000 21 161.1 22.0
a Calculated from total digestible nutrients for maintenance of the mature, lactating, 600-kg cow and
production of milk with 3.5 percent fat (NRC, 1978) by dividing by .67. Used for the NRC, Burroughs,
Chalupa, and Satter systems.
Calculated from megajoules of metabolizable energy for maintenance of a 600-kg cow with 0 live-
weight change and production of milk with 3.68 percent fat while being fed a diet with metabolizab~lity
or q = .60 (ARC, 1980) by dividing by 11.
Calculated as Scandinavian feed energy (FE) units from Madsen et al. (1977) (Table 3) starting from
N in microbial net protein divided by 16 g N per FE divided by digestibility or .60 divided by efficiency
or .71; then 16.S FE = 19 kg dry matter from Danfaer et al. (1980, p. 12~.
From Verite et al. (1978, Table 12.3~. UFL = the French net energy unit and is the total requirement
for a 600-kg cow consuming good quality forage and producing milk with 4.0 percent fat.
'From Kaufmann (1977b, 1979). SE = starch equivalent unit. Data arelinearly interpolated and
extrapolated from the data in Table 2 (Kaufmann, 1979~.
fFrom Landis (1979~. NEL = net energy for lactation. Data are linearly interpolated and extrapolated
from data in Table 2.
Such different energy assumptions contribute to differ-
ences among the protein systems.
While the use of TDN is questioned by many, the
available data for alternatives are not as numerous. Of
even more importance is the fact that in use many of the
alternative energy terms are derived from TDN or an
estimate of TDN. Thus, we do not feel that TDN is, in
fact, an improper base.
Additional Assumptions
Several additional assumptions that were required in
one or more of the systems and their bases are in Table 4.
Where the disposition of NCP is not described, its digest-
ibility was assumed to be 0.85, and the excretion of di-
gested fraction was assumed to be via urine.
Minimum Dietary Intake Protein Percentage
Dietary IP percentages required in nine systems,
when undegradability is optimal, are compared (Figure
3) . Differences among the systems are smaller (from 9 to
13.2 percent IP) at 10 kg of milk but become larger (11 to
17.4 percent IP) at 40 kg of milk. The Danfaer model
requires the highest IP percentage at every milk yield.
Presumably, this higher requirement is primarily a
result of a lower assumed efficiency of milk production.
The Burroughs, ARC, and Satter systems require a
much lower IP percentage than other systems at higher
milk production. The probable causes of their low re-
quirements are the highest efficiency for converting AP
to milk assumed in the Burroughs system; the second
lowest AP requirement for lactation plus a low AP re-
quirement for maintenance with no separate fecal
metabolic protein requirement in the ARC system; and
no fecal metabolic protein requirement as a function of
DM intake either alone or as a component of mainte-
nance in the Satter system.
Optimum Undegradability
Optimum IP undegradabilities required when IP per-
centage is minimum are compared (Figure 4~. Differ-
ences among the systems arelarge (7 to 41 percent at 10
kg of milk) and remain large (20 to 55 percent at 40 kg of
milk). The undegradability of many common diets for
dairy cows is considered to be near 0.30 (Satter and Rof-
fler, 1975~. The ARC and Burroughs systems do not re-
quire an undegradability as high as 0.30 at 40 kg of milk
per day. These low undegradability requirements are
OCR for page 17
Comparison of New Protein Systems for Ruminants 17
TABLE 4 Additional Assumptions of Protein i
and Energy Relationships
Assumption
Systemsa
Proteins'
CBPDIP= 1.00 N
DNPCNP = 85c A, P. B. S _
LNPLMP= .60 L E 14
Energyd at
DM = TDN/.67e N. C, S LIZ,
11 MJ ME/kg DMf A O
19 kg DM = 16.5 FE. D
AM = DM x .9 p
DE - ME/.82'' A
DONI = DM x .67 D '0
DOM = UFL x .732i P
DOM = NEL/9.31i L
1 kgDOM = 900 SEE K
19 MJ ME/kg DOM/ A
IOM = 0M - DOM P
aA, ARC; B. Burroughs; C, Chalupa; D, Danfaer; K, Kaufmann;
L, Landis; N. NRC; P. PDI; and S. Satter.
b CBPDIP, crude bacterial protein/degraded intake protein;
DNPCNP, digestible nucleic acid bacterial protein/crude nucleic acid
bacterial protein; LNPLMP, lactation net protein/lactation metabo-
lizable protein.
'From Danfaer (1979).
~DM, dry matter; TDN, total digestible nutrients; ME, metaboliz-
able energy; FE, Scandinavian feed energy unit; OM, organic matter;
DE, digestible energy; DOM, apparently digested organic matter;
UFL, French net energy unit; NEL, Swiss net energy unit; SE, starch
equivalent; IOM, indigestible organic matter.
From analyses of Tyrrell and Moe (1975) on data of Wagner and
Loosli (1967).
fFrom ARC (1980, see p. 112).
"From Danfaer et al. (1980, see p. 12).
From ARC (1980, see p. 136).
iFrom INRA (1978, see p. 589); and ARC (1980, see Table 4.7). ME
= 2.73 UFL and DOM = ME/3.72 so DOM = UFL x (2.73/3.72)
= UFL x .732.
Calculated from Landis (1979~. .135 CBPDOM/.0145 CBPNEL
= 9.31.
From Kaufmann (1977b).
From ARC (1980, see p. 136~.
related to the low protein percentages, and their causes
as discussed earlier. The Chalupa system always
requires an undegradability greater than 0.30. This
high unclegradability results primarily from the low
BCPDOM.
A plot of the UIPIP as a function of concentration of
IF (Figure 5) indicates a great diversity among the sys-
tems. The differences are largely caused by assumptions
about changes of energy concentration and dry matter
intake for meeting the additional energy needs for high
milk procluction. If increasing energy requirements are
met by increasing energy concentration more than DM
intake, as in the Kaufmann, Landis, and PDI systems,
then protein concentration varies more than UIPIP. If
~6
o
/
No/ / A
1 0 20 30
M I LK (kg/day)
FIGURE 3 Intake protein percentage in dry matter as a
function of milk production. A, ARC; B. Burroughs; C, Cha-
lupa; D, Danfaer; K, Kaufmann; L, Landis; N. NRC; P. PDI;
and S. Satter.
increasing energy requirements are met by increasing
DM intake more than energy concentration, as in the
ARC, Burroughs, Chalupa, Danfaer, and Satter sys-
tems, then UIPIP varies more than protein concentra-
tion.
Protein Reaching the Small Intestine
IN VIVO REFERENCE DATA
Three data sets (Tamminga and van Hellemond,
1977, Journet and Ferrite, 1979; Bohr et al., 1979) are
available that describe protein flowing into the duode-
num of the lactating cow. Tamminga and van Helle-
mond (1977) observed amino acid N (g/day) = 32.3
DOM (kg/day) - 8.63, with r2 = 0.90. Their organic
matter intakes ranged from 4.7 to 14.6 kg/day, N intake
ranged from 140 to 430 g/day, and digestible IF ranged
from 11.2 to 23.1 percent of DOM in 49 observations.
Rohr et al. (1979) observed amino acid N (g/day) =
31.42 DOM (kg/day) - 40.56, with r2 = 0.8S. Their
organic matter intakes ranged from 8.88 to 15.14 kg/
day, N intake ranged from 205 to 413 g/day, and crude
protein ranged from 12.9 to 15.6 percent of dietary DM
in 21 observations. These two equations indicate that
DOM is a primary determinant of protein entering the
small intestine. Journet and Verite (1979) observed non-
ammonia N (g/day) = 23.85 DOM (kg/day) + 0.60 in
vitro nondegradable N (g/day) + 8. 6, with R2 = 0.886
OCR for page 18
IS Ruminant Nitrogen Usage
60:
50
Be 40
-
a,
6 30
cr
LL
of
10:
o 1
B
0 10 20
MILK (kg/day)
30 40
FIGURE 4 Undegradability of dietary intake protein as a
function of milk production. A, ARC; B. Burroughs; C, Cha-
lupa; D, Danfaer; K, Kaufmann; L, Landis; P. PDI; and S.
Satter.
in equation 2 with lactating cows. Their DOM intakes
ranged from 4.3 to 12.2 kg/clay, and nondegradable N
intakes ranged from 40 to 266 g/day in 42 observations.
The equation of Tamminga and van Hellemond always
gives a greater expectation than the equation of Bohr et
al. (1979) because Tamminga and van Hellemond sam-
pled posterior but Rohr et al. (1979) sampled anterior to
the pancreatic and bile ducts.
SYSTEM COMPARISONS
First, one type of predicted flow into the small intes-
tine of true protein (STP) was calculated as the sum of
BTP plus UIP without endogenous protein for each sys-
tem. Another type of predicted flow into the small intes-
tine of crude protein (SCP) was calculated as the sum of
BCP plus UIP without endogenous protein for each sys-
tem. Second, three expecter] protein flows into the small
intestine were calculated for each system based on DOM
intake and UIP intake, if required, in the three equa-
tions just discussed. These two types of estimates of pro-
tein flow will be called predicted for the two former
and expected for the three latter. Comparisons of the
predicted protein flow, as STP, and expected protein
flow, as amino nitrogen, are in Figures 6 and 7, compar-
ison of predicted protein flow, as SCP, and expected
protein flow, as nonammonia N. are In Figure 8. Pre-
dicted flows into the small intestine from the ARC, Bur
roughs, and Satter systems were less than expected flows
in all three comparisons. This difference probably
results from their low AP requirement and their low IF
concentration in the DM. The predicted flow in the
Landis system was always less than the expected flow,
and an explanation for this is not clear. The predicted
flow from the NRC was highest and generally greater
than expected in the two comparisons with expected
flow based on DOM. This high predicted flow for the
NRC system probably results from no subtraction of
NCP. The predicted flow in the Danfaer model was next
highest. This probably resulted from having the highest
AP requirement and the highest IF concentration in the
Dot. The predicted flows of the Kaufmann and PDI sys-
tems were similar to the expected flows. The predicted
flow for the Chalupa system was similar to the expected
flow based on DOM but decreased relative to expected
flow when undegradable protein became a partial basis
of expectation. This difference probably resulted from
the high undegradability and the low microbial protein
production per unit of DOM.
Fecal Crude Protein Equivalent Excretion
Relative to Crude Protein Percentage
Fecal crude protein (F P) equivalent was calculated as
the sum of indigestible bacterial protein (IBP), indigest-
ible nucleic acid crude protein (INP) equivalent, indi
60
50 _
an 40
6 30
tr:
C'
LU
He
TIC
20 _
10 _
K '
Lo So
AD
B
O _I I
8 10
PROTEIN (%dm)
D /
1 1 1 1
12 14 16 18
FIGURE 5 Undegradability of dietary intake protein as a
function of intake protein percentage in dry matter. A, ARC;
B. Burroughs; C, Chalupa; D, Danfaer; K, Kaufmann; L,
Landis; P. PDI; and S. Satter.
OCR for page 19
Comparison of New Protein Systems for Ruminants 19
gestible undegraded dietary protein (IUP), and fecal
metabolic protein as absorbed (FPA) or net (FPN) units.
The FP excretion, as a percentage of dietary IP, is ex-
pressed as a function of IP as a percentage of dietary DM
(Figure 9~. Reference curves are plotted from the analy-
sis (Waldo and Glenn, 1982) of the data of Conrad et al.
(1960) and Boekholt (1976~. The ARC, Burroughs, Cha-
lupa, and Satter systems and the Danfaer model predict
fecal excretions lower than expected from the data of
Conrad et al. (1960) or Boekholt (1976~. The probable
causes of these low excretions are the use of zero fecal
metabolic protein in the ARC and Satter systems as a
function of dietary DM and a relatively low fecal meta-
bolic protein in the Chalupa, Danfaer, and Burroughs
systems. The use of zero fecal metabolic protein pro-
duces a relatively constant percentage output of N in-
take in the feces, and use of a low fecal metabolic protein
produces a curve with less slope than expected. The PDI
system predicts a fecal output in the general range of
that expected from the data of Conrad et al. (1960) and
Boekholt (1976), but it declines more rapidly as concen-
tration increases; the more rapid decline occurs because
fecal metabolic protein actually decreases due to lower
indigestible OM as milk production and protein concen-
tration increase. The NRC system predicts a fecal excre-
tion essentially equal to that expected from Boekholt
4 _
3
-
~2 ~
c,
a:
-
1
A
N
EXPECTED (kg/day)
FIGURE 6 Protein flow into small intestine predicted from
the system versus that expected based on the digestible organic
matter of the system and the equation of Tamminga and van
Hellemond (1977~. A, ARC; B. Burroughs; C, Chalupa; D,
Danfaer; K, Kaufmann; L, Landis; N. NRC; P. PDI; and S.
Satter.
N
3 _
-
-
y
-
~2
LU
1
- ~:
0 1 2 3 4
EXPECTED (kg/day)
FIGURE 7 Protein flow into small intestine predicted from
the system versus that expected based on the digestible organic
matter of the system and the equation of Bohr et al. (1979~. A,
ARC; B. Burroughs; C, Chalupa; D, Danfaer; K, Kaufmann;
L, Landis; N. NRC; P. PDI; and S. Satter.
(1976) and slightly higher than expected from the data
of Conrad et al. (1960~. The Kaufmann and Landis sys-
tems predict fecal excretions most similar to those which
occur because their assumptions for fecal metabolic pro-
tein and digestibility are similar to those in the data of
Conrad et al. (1960) and Boekholt (1976~.
Fecal Crude Protein Equivalent Excretion
Relative to Milk Production
The FP excretion, as a percentage of dietary IP, is ex-
pressed as a function of milk production in Figure 10.
Two reference points for these data are 37.5 percent
from Boekholt (1976) and 33 percent from the analysis
(Waldo and Glenn, 1982) of the data of Conrad et al.
(1960~. Basically, the same comments apply to Figure 10
as were made for Figure 9. The Satter system and the
ARC system, to a lesser degree, predict low outputs that
are nearly constant because they assume zero fecal
metabolic protein per unit of feed DM. The Chalupa,
Danfaer, and Burroughs systems predict low outputs
that decrease gradually with increasing milk production
because they assume a minimal fecal metabolic protein.
The PDI system predicts an output in the expected
range, but its predicted output declines rapidly because
this fecal metabolic protein output actually declines
with increasing milk production. The NRC system pre
OCR for page 20
20 Ruminant Nitrogen Usage
/
////
o, ~
1 _
1
0 1
2 3 4
EXPECTED (kg/day)
FIGURE 8 Protein flow into small intestine predicted from
the system versus that expected based on the digestible organic
matter plus undegraded protein intake of the system and the
equation of Journet and Verite (1979) . A, ARC; B. Burroughs;
C, Chalupa; D, Danfaer; K, Kaufmann; L, Landis; P. Pl)I;
and S. Satter.
diets more fecal output than expecter] because it assumes
lower digestibility. The Kaufmann and Landis systems
predict fecal output that follow the expected curve (Fig-
ure 9) but are slightly higher than expected.
Urinary Crude Protein Equivalent
Excretion Relative to Milk Production
Urinary crude protein (UP) equivalent was calculated
as the algebraic sum of rumen efflux of crude protein
(REP) equivalent or a rumen influx of crude protein
(RIP) equivalent; digestible nucleic acid crude protein
(DNP); maintenance protein as absorbed (MPA3 units
that is free of any fecal metabolic N. if possible; and the
protein difference of LPA minus LPN. If necessary, fe-
cal metabolic N was subtracted to balance the system.
Possibly, the tissue utilization of nucleic acids should be
considered based on the finding of a 47 percent retention
of activity in the tissues of the ruminating lamb by Raz-
zaqueetal. (1981~.
The UP excretion as a percentage of dietary IP is ex-
pressed as a function of milk production (Figure 11~.
Two reference points for these data are 35.7 percent
from Boekholt (1976) and 38.6 percent from the data of
Conrad et al. (1960~. The Satter system predicts a uri-
nary excretion greater than expected primarily because
it assumes a low efficiency of milk production. The Dan
faer system predicts a urinary excretion greater than ex-
pected because it assumes a low efficiency for milk pro-
duction and assumes an efflux of N as ammonia from the
rumen to the blood. The ARC and Burroughs systems
did not predict high urinary excretions as might be ex-
pected in order to balance low fecal excretions. Their
predicted urinary excretions were similar to those of
Boekholt and Conrad; their low dietary IP were ac-
counted for by their high efficiencies of producing milk
from AP. The PDI system is the only one that predicted
an increasing UP excretion as milk production in-
creased, and these excretions were generally lower than
those of Boekholt and Conrad. This increasing urinary
N excretion seems to result from the decreasing fecal
metabolic N excretion at high milk production. The
Chalupa system predicts UP excretions that are consis-
tent with those of Boekholt and Conrad. The NRC sys-
tem predicts low UP excretions that result from an as-
sumption of zero DNP. The Landis system predicts a
relatively low UP excretion because no DNP fraction is
included. The Kaufmann system predicts a low UP ex-
cretion because the digestibility of nucleic protein
equivalent is only one-half of the more common assump-
tion.
Milk Nitrogen Output Relative to Milk Production
Output of milk protein in net (LPN) units as a per-
centage of dietary IP was expressed as a function of milk
60
50:
~ 30
o
A:
UJ 20
10
X it_
PROTEIN (% DM)
FIGURE 9 Fecal protein as a function of intake protein per-
centage in dry matter. A, ARC; B. Burroughs; C, Chalupa; D,
Danfaer; K, Kaufmann; L, Landis; N. NRC; P. POI; S. Sat-
ter; X, Boekholt (1976); and Y. Conrad et al. (1960).
OCR for page 21
Comparison of New Protein Systems for Ruminants 21
production (Figure 12~. Two reference points for these
data are 24.9 percent from Boekholt (1976) and 21.7
percent from the data of Conrad et al. (1960~. In all
systems milk protein is assumed equal to requirement as
LPN units. The high fractional output for the ARC and
Burroughs systems is primarily a function of the low
protein intake. All of these systems predict a higher out-
put of dietary IP in milk than either the mean of 24.9
percent from Boekholt (1976) when mean milk produc-
tion was 18.9 kg/day or the mean of 21.7 percent from
the data of Conrad et al. (1960) when the mean milk
production was 11.8 kg/day. Increasing milk produc-
tion to the average (25 kg/day) assumed here and opti-
mizing degradability both will increase the fractional
output of dietary IP into milk. It seems overly optimistic
to assume that outputs greater than 40 percent can be
obtained easily.
CRITICAL COMMENTS ON OMISSIONS
OF SOME SYSTEMS
Comparison and analysis of these systems as described
earlier emphasize three important points that fre-
quently are overlooked but should receive more empha-
sis. First, a fecal metabolic protein fraction is needed for
FP excretion to correspond to in vivo data. Second, this
fecal metabolic protein fraction should be considered ei-
ther a separate component of total requirement or a feed
reduction component and not be included in mainte
60-
50t
40 '
L
K ~_
10 _
O
O JO
1 1 1
20 30 40
M l ~ K (kg/day)
FIGURE 10 Fecal protein as a function of milk production.
A, ARC; B. Burroughs; C, Chalupa; D, Danfaer; K, Kauf-
mann; L, Landis; N. NRC; P. PDI; S. Satter; X, Boekholt
(1976~; and Y. Conrad et al. (1960~.
so_
so
- -
~ 40 _
._
-
z
~ 30 _
o
CL
~ 20 _
CC
10 _
O
D.
0 10
20 30 40
M I LK (kg/day)
FIGURE 11 Urinary protein as a function of milk produc-
tion. A, ARC; B. Burroughs; C, Chalupa; D, Danfaer; K,
Kaufmann; L, Landis; N. NRC; P. PDI; S. Satter; X,
Boekholt (1976); and Y. Conrad et al. (1960).
nance per se for simplicity as has been done in some cases
(or ignored in others). Third, specification of the DM
intake and DOM, or other energy components, are an
integral part of any complete protein system.
Fecal metabolic protein is an important component
of the protein requirement of the ruminant. Fecal meta-
bolic protein represents about 57 percent of the total EP
and about 20 percent of the IP requirement at 15 per-
cent dietary IP for the negative intercept from either the
equation of Boekholt (1976) or the equation (Waldo and
Glenn, 1982) based on the data of Conrad et al. (1960)
as its estimate. The failure to include a fecal metabolic
protein factor in a protein feeding system will result in
underestimation of requirements for IP percentage in
dietary DM and for undegraclability of dietary protein.
The fraction of dietary nitrogen excreted in the feces
will be underestimated, and the fractional FP excretion
as a function of IP concentration will not have the char-
acteristic in viva hyperbolic curvature.
Fecal metabolic protein is most commonly related to
DMI except for the PDI systems where it is related to
IOMI and the NRC system where it is related to IDMI.
The PDI equation (Verite et al., 1979) is based on sheep
and has an R2 = 0.74; the equations of Boekholt (1976)
and the data of Conrad et al. (1960) are based on lactat-
ing cattle and have r2 = 0.95 and 0.92, respectively.
Fecal metabolic protein is more highly correlated with
DM than IOMI. Three g of FMP/100 g of DMI is ~ good
simple interim proportion. Fecal metabolic protein is a
OCR for page 22
22 Ruminant Nitrogen Usage
60
50
~ 40
He
o
CL
ye
30
20
10
o
ON Lip X
P y
1 1
0 10
20 30 40
MILK (kg/day)
FIGURE 12 Milk protein as a function of milk production.
A, ARC; B. Burroughs; C, Chalupa; D, Danfaer; K, Kauf-
mann; L, Landis; N. NRC; P. PDI; S. Satter; X, Boekholt
(1976~; and Y. Conrad et al. (1960~.
function of DM intake, maintenance protein is a func-
tion of body weight, and production protein is a func-
tion of milk output. Fecal metabolic protein is consid-
ered most simply either as a separate component of the
total requirement along with maintenance and produc-
tion as used by Danfaer (1979), Kaufmann (1979), and
Landis (1979) or as a feed reduction component as used
by Burroughs et al. (1975b). When the units are consid-
ered as SPA, there is little conceptual difference be-
tween these methods of accounting. Operationally, this
is much simpler than either having the fecal metabolic
protein for a part of dietary DM included in mainte-
nance and the remainder accounted for in the produc-
tion requirement as in the NRC (1978) system or having
one-third of the total fecal metabolic protein require-
ment per unit of DM in maintenance (Chalupa, 1980a).
No AP system is complete until all of the integral en-
ergy components required in the system are described.
The BCP requirement per se and its contribution to the
animal's need for AP are a function of the energy fer-
mentecl in the rumen; generally, this component is ap-
parently FOM. The fecal metabolic protein require-
ment is related to another feed component; generally,
this component is dietary DM. The relationship be-
tween these two components or the digestible energy
concentration in the diet thus is needed. The assumption
made here is that digestible organic matter, TDN, or
energy digestibility must be asymptotic at about 67 per-
cent based on the analyses of Tyrrell and Moe (1975) of
the data of Wagner and Loosli (1967~. This assumption
of a constant energy concentration is different from the
PDI assumption where energy concentration is 85 per-
cent greater for high milk production than for low milk
production. The relative changes of concentration ver-
sus undegradability of protein are affected largely by
the relative changes of digestibility and intake of en-
ergy, respectively, in requirements for higher produc-
tion.
Representative terms from entire chapter:
metabolic protein
