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OCR for page 13
ENERGY REQUIREMENTS OF
LAC TAT I N G A N D P R E G N A N T C OWS
Energy Units
Energy requirements for maintenance and milk produc-
tion are expressed in net energy for lactation KNELL units.
The net energy for lactation system (Moe and Tyrrell,
1972) uses a single energy unit KNELL for both maintenance
and milk production because metabolizable energy (ME)
was used with similar efficiencies for maintenance (0.62)
and milk production (0.64) (Moe and Tyrrell, 1972) when
compared with directly measured fasting heat production
(Flats et al., 19651. The energy values of feed are also
expressed in NED units. Thus in the tables in Chapter 14
and in the computer model, one feed value KNELL is used
to express the requirements for maintenance, pregnancy,
milk production, and changes in body reserves (not growth)
of adult cows.
ENERGY VALUES OF FEEDS
The method used to obtain and express feed energy
values in this edition is substantially different from that
used in previous versions. In the 6~ revised edition of the
Nutrient Requirements of Dairy Cattle (National Research
Council, 1989), foodstuffs were assigned total digestible
nutrient (TDN) values that had been determined experi-
mentally using similar feeds. The concentrations of digest-
ible energy (DE), ME, and NED for each foodstuff were
then calculated from the TDN value using Equations 2-1,
2-2, and 2-3. Equations 2-1 and 2-2 assume intake is the
same for the independent and dependent variables (e.g.,
both at one times maintenance or 1X). Equation 2-2
was derived with cows fed at 3 times maintenance (3X),
and questions have been raised (Vermorel and Coulon,
1998) about its accuracy when used to convert DEN to
MEN. Equation 2-3 converts TONE to NEW assuming
an 8 percent reduction in digestibility at 3X maintenance.
Energy
DE (Meal/kg) = 0.04409 X TDN(%)
ME (Meal/kg) = 1.01 x DE (Meal/kg) 0.45
NEL (Meal/kg) = 0.0245 X TDN(%) 0.12
The problems with this approach are:
(2-1)
(2-2)
(2-3)
· Most of the experimentally determined TDN values
currently available in feed composition tables are from
experiments conducted many years ago; however, other
composition data have been updated. The TDN values in
the table may not correspond to the feed with the nutrient
composition given in Table 15-1.
· A published TDN value is only appropriate when the
nutrient composition of the feed is essentially the same as
that for the feed used in the digestibility trial.
· For many feeds, TDN cannot be measured directly
because the feed cannot comprise a major portion of the
diet. Calculating TDN using the difference method can
lead to inaccurate (because of associative effects) and
imprecise estimates of TDN.
· Very few ME and NED values of individual foodstuffs
are available; rather ME and NED values of mixed diets
are measured. The equations used to convert TDN to ME
and NED were derived for complete diets, and the TDN
for many foodstuffs are outside of the range for TDN
values of the diets used to generate the equations, and the
equations may not be linear over a wide range of TDN.
· A constant discount of 8 percent as calculated in Equa-
tion 2-3 assumes all cows are consuming at 3X mainte-
nance. Based on the normal distribution of milk production
among herds, the mean energy intake for a herd may range
from 2 to more than 4X maintenance.
Because of these problems, the TDN values at 1X mainte-
nance (TDXlx) in Table 15-1 and in the software dictionary
were calculated from composition data rather than being
experimentally determined. In addition, NED values are
calculated based on actual intake and the digestibility of
the entire diet. In Table 15-1, NED values for individual
13
OCR for page 14
14 Nutrient Requirements of Dairy Cattle
feeds are shown assuming intake at 3 and 4X maintenance
and a total diet TANG of 74 percent. The NED of diets
formulated using the NED values in Table 15-1 may be
different than the NED of diets formulated by the computer
model because intake and digestibility discount (estimated
from total diet TDX~X) may be different from those
assumed in Table 15-1.
Estimating TDN of Feeds at Maintenance
A summative approach was used to derive the TENS
values in Table 15-1. In this approach, the concentrations
(percent of dry matter) oftruly digestible nonf~ber carbohy-
drate (NFC), CP, ether extract (EE), and NDF for each
feed are estimated (Weiss et al., 1992) using Equations 2-
4a, 2-4b, 2-4c, 2-4d, 2-4e. Ether extract does not represent
a nutritionally uniform fraction and therefore does not have
a constant digestibility across feedstuffs. Fatty acids (FA)
are a uniform fraction with a true digestibility of 95 tolOO
percent when diets contain 3 percent or less EE (Palm-
quist, 19911. A value of 100 percent digestibility was cho-
sen. FA content of feed can be estimated as FA = EE
1 (Allen, 20001. A more accurate approach would be to
measure FA directly; however, limited data prevented the
inclusion of FA data in Table 15-1. In all equations listed
below, measured FA or EE 1 can be used to represent
the FA fraction.
Truly digestible NFC (tdNFC)
= 0.98 (100 F(NDF NDICP)
+ CP + EE + Ash]) x PAF
Truly digestible CP for forages (tdCPfl
= CP x exp[ - 1.2 x (ADICP/CP)]
Truly digestible CP for concentrates (tdCPc)
= F1 (0.4 x (ADICP/CP)~] x CP (2-4c)
Truly digestible FA (tdFA)
= FA Note: If EE <1, then FA = 0 (2-4d)
Truly digestible NDF (tdNDF)
= 0.75 x (NDFn L)
x F1 (L/NDFn j0 667] (2-4e)
In Equations 2-4a, 2-4b, 2-4c, 2-4d, 2-4e, NDICP =
neutral detergent insoluble N x 6.25, PAF = processing
adjustment factor (see below), ADICP = acid detergent
insoluble N x 6.25, FA = fatty acids (i.e., EE 1), L
= acid detergent lignin, and NDFn = NDF NDICP.
All values are expressed as a percent of dry matter (DM).
Note: Digestible NDF can be obtained using a 48-hour
rumen in vitro assay. The in vitro NDF digestibility is
entered into the model when the software is used and that
value is used to calculate digestible NDF at maintenance.
Equations 2-4a, 2-4b, 2-4c, 2-4d, and 2-4e are based on
true digestibility, but TDN is based on apparent digestibil-
ity; therefore, metabolic fecal TDN must be subtracted
from the sum of the digestible fractions. Weiss et al. (1992)
determined that, on average, metabolic fecal TDN
equalled 7. The TENS is then calculated using Equation
2-5.
TANS (%) = tdNFC + tdCP
+ (tdFA x 2.25) + tdNDF 7 (2-5)
Equations 2-4 and 2-5 were used to calculate TENS,
for most, but not all, foodstuffs in Table 15-1. Different
equations are used to estimate TDN for animal protein
meals and fat supplements (see below).
EFFECT OF PROCESSING ON NFC DIGESTIBILITY
Physical processing, and heat and steam treatment of
feeds usually does not greatly change their composition as
measured by conventional feed testing assays but often
increases the digestibility of starch (see Chapter 131. To
account for the effect of processing and some other non-
chemical factors on starch digestibility, an empirical
approach was used. Based on in viva digestibility data (see
Chapter 13), a processing adjustment factor (PAF) was
developed (Table 2-11. Expected true digestibility of NFC
at 1X maintenance is about 0.98 and 0.90 at 3X ma~nte-
nance (approximately the feeding level used in the digest-
ibility studies) (Tyrrell and Moe, 1975; Van Soest, 19821.
(2-4a) TABLE 2-1 Processing Adjustment Factors (PAF)
for NFCa
(2-4b) Feedstuff
PAF
Bakery waste
Barley grain, rolled
Bread
Cereal meal
Chocolate meal
Cookie meal
Corn grain, cracked dryb
Corn grain, groundb
Corn grain, ground high moistures
Corn and cob meal, ground high moistures
Corn grain, steam flaked
Corn silage, normal
Corn silage, mature
Molasses (beet and cane)
Oats grain
Sorghum grain, dry rolled
Sorghum grain, steam-flaked
Wheat grain, rolled
All other feeds
1.04
1.04
1.04
1.04
1.04
1.04
0.95
1.00
1.04
1.04
1.04
0.94
0.87
1.04
1.04
0.92
1.04
1.04
1.00
a See Chapter 13 for details on how values were calculated. For feeds not shown,
PAF = 1.0.
b Mean of several experiments, actual PAF depends on particle size. Finer grinding
will increase PAF.
CMean density of 0.36 kg/L; PAF should be negatively correlated with density.
dMean density of 0.36 kg/L; PAF should be negatively correlated with density.
OCR for page 15
Energy 15
The PAF was calculated by dividing in viva starch digest-
ibility of different feeds by 0.90. The PAF is used only for
NFC. The PAF adjustment will result in overestimation
of energy values in some feeds when fed at maintenance,
but NED values when fed at 3 times maintenance should
be correct.
ANIMAL PROTEIN MEALS
Animal products contain no structural carbohydrates;
however, certain animal products contain substantial
amounts of neutral detergent insoluble residue. Because
this material is not cellulose, hemicellulose, or lignin, the
above equations cannot be used. For those feeds, TDN1x
was estimated using Equation 2-6.
TDN1x (%) = CPdigest x CP + FA
x 2.25 + 0.98(100 - CP
Ash EE) - 7 (2-6)
Where CPdigest = estimated true digestibility of CP
(Table 2-2) and FA = EE 1. The CPdigest values are
from Table 15-2 assuming an intake of 2 percent of body
weight (BW). The method used to obtain those values is
explained in Chapter 5.
TABLE 2-2 True Digestibility Coefficients of CP
Used to Estimate TDN1x Values of Animal-Based
Feedstuffs
Feedstuff
Blood meal, batch dried
Blood meal, ring dried
Hydrolyzed feather meal
Hydrolyzed feather meal with viscera
Fish meal (Menhaden)
Fish meal (Anchovy)
Meat and bone meal
Meat meal
Whey
FAT SUPPLEMENTS
The TDN1x values of different fat supplements were
calculated from measured fatty acid digestibility. Partial
digestion coefficients (Table 2-3) of fatty acids from supple-
TABLE 2-3 True Digestibilities at Maintenance
(assumed 8 percent increase in digestibility compared
with 3X maintenance) of Fatty Acids from Various
Fat Sources
Fat Fat type Mean % SD N
Calcium salts of fatty acids Fatty acids
Hydrolyzed tallow fatty acids Fatty acids
Partially hydrogenated tallow Fat plus glycerol
Tallow Fat plus glycerol
Vegetable oil Fat plus glycerol
0.86 0.11 15
0.79 0.08 9
0.43 0.13 9
0.68 0.13 10
0.86
mental fat sources were determined indirectly by differ-
ence F(additional fatty acid intake during fat supplementa-
tion minus additional fecal fatty acid output during fat
supplementation)/(additional fatty acid intake during fat
supplementation); Grummer, 1988]. Assumptions associ-
ated with this method are that endogenous lipid remains
constant, and digestibility of fatty acids in the basal diet
does not change when supplemental fat is fed. For fat
sources containing triglycerides (tallow, partially hydroge-
nated tallow, and vegetable oil), ether extract was assumed
to contain 90 percent fatty acids and 10 percent glycerol,
and the glycerol was assumed to be 100 percent digestible
at 1X. In the experiments used to determine fat digestibil-
ity, cows were fed at approximately 3X maintenance.
Therefore, the original values were divided by 0.92 to
adjust values to TDN1x. After adjusting digestibility for
intake (Table 2-3), digestible fat was multiplied by 2.25 to
convert to TDN1x (Equations 2-7a and 2-7b).
For fat sources that contain glycerol:
TDN1x (%) = (EE x 0.1) + [FAdigest
x (EE x 0.9) x 2.25] (2-7a)
For fat sources that do not contain glycerol:
TDN1x (%) = (EE x FAdigest) x 2.25 (2-7b)
where FAdigest = digestibility coefficients for fatty acids
(Table 2-31.
True Digestibility
o 876 Estimating DE of Feeds
0.78
0.81
0.94
0.95
0.80
0.92
1.00
Crampton et al. (1957) and Swift (1957) computed that
the gross energy of TDN is 4.409 Mcal/kg. Because nutri-
ents have different heats of combustion (e.g., 4.2 Mcal/kg
for carbohydrates, 5.6 Mcal/kg for protein, 9.4 Mcal/kg for
long chain fatty acids, and 4.3 Mcal/kg for glycerol; May-
nard et al., 1979), the gross energy value of TDN is not
constant among feeds. The gross energy of TDN of a feed
that has a high proportion of its TDN provided by protein
will be greater than 4.409. Conversely the gross energy of
TDN of a feed with a high proportion of its TDN provided
by carbohydrate or fat will be less than 4.409. Therefore,
the calculation of DE as 0.04409 x TDN (percent) as in
the previous edition (National Research Council, 1989)
was abandoned. Digestible energy was calculated by multi-
plying the estimated digestible nutrient concentrations
(Equations 2-4a through 2-4e) by their heats of combus-
tion, as shown in Equations 2-8a, 2-8b, 2-8c, and 2-8d.
Since DE is based on apparent digestibility and Equations
2-4a through 2-4e are based on true digestibility, a correc-
tion for metabolic fecal energy is needed. The heat of
combustion of metabolic fecal TDN was assumed to be
4.4 Mcal/kg; metabolic fecal DE = 7 x 0.044 = 0.3
Mcal/kg.
OCR for page 16
16 Nutrient Requirements of Dairy Cattle
For most feeds:
DELI (Meal/kg) = (tdNFC/100)
x 4.2 + (tdNDF/100) x 4.2 + (tdCP/100) (2-8a)
x 5.6 + (FA/100) x 9.4 - 0.3
For animal protein meals:
DElX (Meal/kg) = (tdNFC/100) x 4.2
+ (tdCP/100) x 5.6 + (FA/100)
x 9.4 - 0.3
For fat supplements with glycerol:
DElX (Meal/kg) = 9.4 x (FAdigest x 0.9
x (EE/100)) + (4.3 x 0.1 x (EE/100)) (2-8c)
For fat supplements without glycerol:
DElX (Meal/kg) = 9.4 x FAdigest
x (EE/100)
In the above Equations, 2-8a through 2-8d, tdNFC,
tdNDF, tdCP, and FA are expressed as percent of DM.
In Equation 2-8b protein digestibilities are from Table
2-2. For Equations 2-8c and 2-8d, fatty acid digestibilities
(FAdigest) are from Table 2-3. Because the method used
to estimate those values already accounts for the difference
between apparent and true digestibility, the 0.3 adjustment
is not needed in Equations 2-8c and 2-8d.
Estimating DE at Actual Intake
The digestibility of diets fed to dairy cows is reduced
with increasing feed intake (Tyrrell and Moe, 1975). This
reduces the energy value of any given diet as feed intake
increases. This is particularly important in today's high
producing dairy cows where it is not uncommon for feed
intake to exceed 4 times maintenance level of intake. The
rate of decline in digestibility with level of feeding has
been shown to be related to digestibility of the diet at
maintenance (Wagner and Loosli, 1967). Diets with high
digestibility at maintenance exhibit a greater rate of depres-
sion in digestibility with level of feeding than diets with
low digestibility fed at maintenance. Previous National
Research Council reports (National Research Council,
1978, 1989) used a constant depression of 4 percent per
multiple of maintenance to adjust maintenance energy val-
ues to 3X maintenance energy values. Using this method
of discounting, the percentage unit decline in TDN for a
diet containing 75 percent TENS would be 3 percentage
units per multiple of maintenance, while the depression
for a diet containing 60 percent TENS would be 2.4 units.
The differences in rate of depression in digestibility are
generally negligible for diets having maintenance TDN
values of 60 percent or less.
Figure 2-1 shows the relationship between digestibility
at maintenance and the percentage unit decline in digest-
ibility per multiple of maintenance feeding from literature
reports (Brown, 1966; Colucci, et al., 1882; Moe et al.,
4.5
~ 4
.' 3.5
~ ~2
._ v
0' 2 5
2
1.5
(2-8b) 0' 0.5
a)
O
55 60 65 70
Maintenance TDN
75 80
FIGURE 2-1 The relationship between feeding level expressed
as multiples of maintenance and the unit decline in diet TDN
per multiple of maintenance where TDN percentage unit decline
(2-8d) = 0.18 x - 10.3, r2 = 0.85.
1965; Tyrrell and Moe, 1972; 1974; 1975; Wagner and
Loosli, 1967). It was apparent that the rate of decline in
digestibility with level of feeding was a function of the
maintenance digestibility of the diets fed: TDN percentage
unit decline = 0.18 x TENS10.3 (r2 = 0.85). Because
DE, not TDN, is used to calculate ME and NED, this
equation was converted so that a percent discount, not a
TDN percentage unit discount, was calculated:
Discount= L(TDN~X L(0.18 x TENS)
10.34) x Intake)~/TDN~x (2-9)
where TENS is as a percent of dry matter and is for the
entire diet, not the individual feed, and intake is expressed
as incremental intake above maintenance (e.g., for a cow
consuming 3X maintenance, intake above maintenance =
2). For example, for a cow consuming a diet that contains
74 percent TENS at 3X intake, digestibility would be
expected to be 0.918 times the value obtained at
maintenance.
Based on Equation 2-9, a diet with a TENT of 57.2
would exhibit no depression in digestibility with level of
intake. Based on Figure 2-1, the discount for diets with
60 percent or less TENT is negligible; therefore, for diets
with 60 percent or less TENT the discount was set to 1.0
(i.e., no discount was applied). Furthermore, a maximum
discount was set so that discounted diet TDN could not
be less than 60 percent. Data on effects of intake much
greater than 4X maintenance are lacking. Vandehaar (1998)
suggested that the effect of intake on digestibility is not
linear, but rather the digestibility discount increases at a
decreasing rate as feed intake increases. The possibility of
a nonlinear response was one reason the minimum dis-
counted TDN was set at 60 percent. Data are needed on
the effects of very high intake on digestibility. The data
in Figure 2-1 were generated with diets not containing
supplemental fat. It was assumed that increasing TENT
by increasing dietary fat above 3 percent would not affect
OCR for page 17
Energy 17
the digestibility discount. Therefore the TUNE value, used
only for the discount calculation, does not include TDN
provided by dietary fat in excess of 3 percent. Diets with
TUNE of 62, 67, 72, and 77 percent would exhibit a 0.9,
1.8, 2.7, and 3.6 percentage unit decline in TDN, respec-
tively, per multiple of maintenance feeding. The percent
decline in digestibility in the respective diets would be
1.5, 1.8, 3.8, and 4.7 percent. This adjustment is used
continuously across all levels of feeding as contrasted to
constant adjustment to 3X level of feeding used in the 1989
National Research Council report. The DELI for each feed
was determined and then multiplied by the discount factor
obtained using Equation 2-9 to calculate DE at productive
levels of intake (DEp).
Estimating ME at Actual Intake
Equation 2-2 was derived to convert DE into ME when
cows were fed at production levels of intake. Therefore
ME at production levels of intake (MEp) should be calcu-
lated from DEp. Equation 2-2 was developed with diets
containing about 3 percent ether extract, but because the
efficiency of converting DE from fat into ME is approxi-
mately 100 percent (Andrew et al., 1991; Romo et al.,
1996), Equation 2-2 underestimates ME of high fat diets.
A theoretical approach was used to adjust ME values of
feeds with more than 3 percent EE. Assuming a feed
with 100 percent EE has ME = DE and subtracting that
equation from Equation 2-2 (1.01 X DE 0.45) and
dividing by the change in EE concentration (100 - 3)
yields the expression: 0.000103 X DE + 0.00464 change
in ME per increase in EE content (percentage unit). The
DE term was assumed to be negligible; therefore, MEp
values of feeds with more than 3 percent EE were
increased by 0.0046 per percentage unit increase in EE
content above 3 percent (Equation 2-10~. For feeds with
less than 3 percent EE, Equation 2-2 is used to calcu-
late MEp.
MEp (Meal/kg) = F1.01 x (DEp) 0.45]
+ 0.0046 X (EE 3) (2-10)
where DEp is Mcal/kg and EE is percent of DM.
For fat supplements, MEp (Meal/kg) = DEp (Meal/kg).
Estimating NED at Actual Intake
The use of Equation 2-3 to estimate NED has been
criticized because it results in essentially equal efficiencies
of converting DE to NED for all feeds (Vermorel and Cou-
lon, 1998~. Using Equation 2-3, a feed with 40 percent
TDN (DE = 1.76 Mcal/kg) has an efficiency of converting
DE to NEW of 0.49 and for a feed with a TDN of 90
percent (DE = 3.97 Mcal/kg), the efficiency is 0.53. That
range in efficiencies is less than would be expected among
feeds when DE is converted to NED. To overcome this
problem, an equation derived by Moe and Tyrrell (1972)
to convert MEp to NED at production levels of intake (NEIL)
was chosen to replace the previous TDN-based NED
equation.
NEW (Meal/kg) = t0.703 X MEp (Meal/kg)]
0.19 (2-11)
A modification was made to adjust for improved metabolic
efficiency of fat. The average efficiency of converting ME
from fat to NED is 0.80 Esd = 0.05; N = 3; (Andrew et al.,
1991; Romo et al., 1996~. The same approach as discussed
above to adjust MEp for fat content was used to account
for increased efficiency of converting ME from fat to NED.
The resulting term was: (0.097 X MEp + 0.19~/97 increase
in NED per percentage unit increase in feed EE content
above 3 percent (Equation 2-12~. For feeds with less than
3 percent EE, Equation 2-11 is used to calculate NEIL.
NEIL (Meal/kg) = 0.703 X MEp 0.19
+ (~0.097 X MEp
+ 0.19~/97] X FEE 3] ~ (2-12)
where MEp is Me al/kg and EE is percent of DM.
For fat supplements, NEIL (Meal/kg) = 0.8 X MEp
(Meal/kg).
Estimating Net Energy of Feeds for Maintenance and
Gain
The equations used to estimate the net energy for main-
tenance (NEM) and net energy for gain (NEG) used for
beef cattle (National Research Council, 1996) were
retained. The NEM and NEG content of feeds assumed dry
matter intake at 3 times maintenance and are calculated
by multiplying DEN (described above) by 0.82 to obtain
ME (National Research Council, 1996~. That ME value
is then converted to NEM and NEG using the following
relationships (Garrett, 1980~:
NEM = 1.37 ME 0.138 ME2
+ 0.0105 ME3 - 1.12 (2-13)
NEG = 1.42 ME 0.174 ME2
+ 0.0122 ME3 - 1.65 (2-14)
where ME, NEM, and NEG are expressed in Mcal/kg.
Those equations are not appropriate for fat supplements.
For those feeds, MEp = DEp, and the same efficiency
(0.80) of converting ME to NED was used to convert ME
to NEM. The efficiency of converting ME to NEG was set
at 0.55 for fat supplements. The method used to calculate
feed energy values for calves weighing less than 100 kg is
described in Chapter 10.
OCR for page 18
18 Nutrient Requirements of Dairy CattIe
Comparison of New NET Values with Values from
1989 Edition
For foodstuffs in Table 15-1, NED values were calculated
using the approach outlined above for cows fed at 3X
maintenance and compared with values in Table 7-1 in the
previous edition of the Nutrient Requirements of Dairy
Cattle (National Research Council, 19891. The mean NED
value for all feeds listed in Table 15-1 is 2 percent lower
than the mean NED value for the same feeds in the 6
revised edition of Nutrient Requirements of Dairy Cattle
(National Research Council, 19891. Although on average
the values are similar, some marked differences exist. In
general, forages, especially lower quality forages, have
lower NED values, high protein feeds have higher NED
values, and starchy concentrates have values similar to
those in the previous edition (National Research Council,
19891. The NED for cottonseeds is about 16 percent lower
and the value for roasted soybeans is about 25 percent
higher than in the previous edition. In the previous edition,
cottonseeds had more NED than roasted soybeans; how-
ever, cottonseed has much more NDF (50 vs. 22 percent),
more lignin (13 vs. 3 percent), and less CP (23 vs. 43
percent). The NDF in cottonseed hulls, which provide
most of the NDF in whole cottonseeds, has a low digestibil-
ity. These differences in composition and fiber digestibility
imply that soybeans should provide more energy than cot-
tonseeds. Because of differences in the ability of soybeans
and cottonseeds to stimulate chewing and rumination, in
low fiber diets, cottonseed may reduce negative associative
effects and appear to have more energy than soybeans.
Diets including whole cottonseeds and roasted soybeans
were included in the evaluation of the software model
(Chapter 161. Although data are very limited, estimated
NED provided by those diets did not deviate greatly from
estimated NED expenditures.
Using two different methods, the NED values for feeds
in the 6~ revised edition of the Nutrient Requirements of
Dairy Cattle (National Research Council, 1989) were
found to be about 5 percent (Weiss, 1998) and 5 to 7
percent (Vermorel and Coulon, 1998) too high. When NED
values were calculated as described above and applied to
the data set of Weiss (1998), the overestimation of feed
energy was reduced from 5 percent to 1.2 percent. Dhiman
et al. (1995) conducted an experiment with cows fed differ-
ent ratios of alfalfa silage and concentrate (ground high
moisture ear corn and soybean meal) for the entire lacta-
tion. Based on the nutrient composition of their feeds
and calculated energy balance, NED values for the diets
calculated using Equation 2-12 ranged from + 5.6 percent
to 7.3 percent with a mean bias of O percent. For the
four diets used by Tyrrell and Varga (1987), the calculated
NED values (Equation 2-11) ranged from 1.3 to 5.1 percent
higher than measured values (mean bias was 2.8 percent).
For the four diets used by Wilkerson and Glenn (1997),
the calculated values ranged from 7 percent lower to 1.2
percent higher than measured values (mean bias was 3.5
percent).
Precautions
The energy values for feeds and diets are based mostly
on chemical characteristics of the feed and assume that
feed characteristics limit energy availability. Composition
of the total diet and dry matter intake have marked
effects on digestibility and subsequent energy values. Diets
that do not promote optimal ruminal fermentation will
result in an overestimation of energy values. For example,
if digestibility of diets is constrained by a lack of ruminally
available protein or by low pH caused by feeding diets
with insufficient fiber (or excess NFC), calculated energy
values will be overestimated. Positive associative effects
are not considered. In a situation where a fibrous feed is
added to a diet with insufficient fiber, the energy value of
that feed may appear to be higher than values calculated
with Equation 2-12 because of overall improved ruminal
digestion.
ENERGY REQUIREMENTS
Maintenance Requirements
Measured fasting heat production (Flats et al., 1965) in
dry non-pregnant dairy cows averaged 0.073 Mcal/kg
BW0 75, and estimated fasting heat production using regres-
sion analysis suggested an identical value. Because these
measurements were made with cows housed in tie stalls
in metabolic chambers, a 10 percent activity allowance was
added to account for normal voluntary activity of cows that
would be housed in drylot or free stall systems, such that
the maintenance requirement for NED is set at 0.080 Meal/
kg BW075 for mature dairy cows.
Cows of similar size and breed may vary in their mainte-
nance requirements, even under controlled activity condi-
tions, by as much as 8 to 10 percent (Van Es, 19611. The
National Research Council (1996) used a net energy main-
tenance value of 0.077 Mcal/kg075 empty body weight
(EBW) for British beef cattle breeds with adjustments to
maintenance requirements based on breed and/or geno-
type. Assuming an empty body mass of 85 percent of live
weight, the implied maintenance requirement on a live
weight basis would be 0.065 Mcal/kg075. A breed adjust-
ment factor of 1.2 was used for Holsteins and Jerseys by
the National Research Council (1996), which would then
adjust the maintenance requirement to 0.079 Mcal/kg075,
which is nearly identical to the current value of 0.080 Meal/
kg BW075 used in this report.
OCR for page 19
Energy 19
It has been suggested that maintenance requirements
among beef cattle breeds varies with milk production. Very
few direct comparisons have been made of the effect of
dairy cattle breed on energy metabolism. Tyrrell et al.
(1991) compared nonlactating and lactating Holstein and
Jersey cows. Although actual milk yields were greater for
Holstein cows than for Jersey cows, energy output in milk
as a function of metabolic weight was similar, and there
was no evidence to suggest that energy requirements for
maintenance or production differed between breeds.
Lactation Requirements
The NE required for lactation KNELL is defined as the
energy contained in the milk produced. The NED concen-
tration in milk is equivalent to the sum of the heats of
combustion of individual milk components (fat, protein,
and lactose). Reported heats of combustion of milk fat,
protein, and lactose are 9.29, 5.71, and 3.95 Mcal/kg,
respectively. Frequently, milk fat and protein but not milk
lactose are measured. Milk lactose content is the least
variable milk component and is essentially a constant 4.85
percent of milk and varies only slightly with breed and
milk protein concentration.
Milk crude protein, when estimated as N times 6.38,
contains approximately 7 percent nonprotein nitrogen
(NPN) (DePeters et al., 19921. Urea N accounts for about
50 percent of NPN in milk; and ammonia, peptides, cre-
atine, creatinine, hippuric acid, uric acid, and other N-
containing components make up the remainder of NPN
in milk (DePeters et al., 19921. Based on the average com-
position and the heats of combustion of individual NPN
constituents, the heat of combustion for NPN is 2.21 kcal/
g crude protein. Where total and not true protein is deter-
mined, the coefficient (weighted average of the different
N compounds in milk) for milk crude protein is 5.47 kcal/
g. This value is slightly higher than the coefficient of 5.31
determined by regression analysis of milk energy on milk
fat, protein, and lactose (Tyrrell and Reid, 19651. Where
individual components are measured directly, NED concen-
tration in milk is calculated as:
NED (Meal/kg) = 0.0929 x Fat % + 0.0547
x Crude Protein %
+ 0.0395 x Lactose % (2-15)
When only fat and protein in milk are measured and
the lactose content of milk is assumed to be 4.85 percent,
the NED concentration of milk is calculated as:
NED (Meal/kg) = 0.0929 x Fat % + 0.0547
x Crude Protein % + 0.192 (2-16)
If milk true protein rather than crude protein is mea-
sured, the coefficient in the equation above should be
changed from 0.0547 to 0.0563, which reflects the relative
proportions of true protein and NPN and their energy
values discussed above.
The Gaines formula (Gaines, 1928) for 4 percent fat-
corrected milk (4 percent FCM, kg/d = 0.4 x milk, kg/d
+ 15 x fat, kg/d) has been used for more than 70 years
as a means to correct milk yields to a constant energy
basis. The Gaines formula is based on an assumed NED
concentration of 0.749 Mcal/kg of milk when milk contains
4 percent fat. The 1989 National Research Council report
used a value of 0.74 Mcal/kg, but based on measured heats
of combustion (Moe and Tyrrell, 1972), the actual coeff~-
cient is 0.749/kg of FCM when calculated using the Gaines
equation. The Gaines formula, which is based on volume
of milk and total yield of fat, underestimates the energy
value of milk when milk fat content is less than 3 percent.
When milk fat is the only milk constituent measured, NED
concentration can be calculated using the Tyrrell and Reid
(1965) formula:
NED (Meal/kg of milk) = 0.360
+ L0.0969(fat %~] (2-17)
The feed energy requirements for production of individ-
ual milk components have not been defined. The NED
system in this edition is based on yield of total energy in
milk and does not account for many of the differences
in metabolic transactions or the substrates required for
synthesis of individual milk components. The measured
calorimetric inefficiency of use of ME for milk includes
losses associated with metabolic transactions for conversion
of absorbed nutrients into milk components, the energy
required for nutrient absorption, and increased rates of
metabolism in visceral tissues required for support of
increased milk production. Theoretical calculations of
energy requirements for production of individual milk
components have been made (Baldwin, 1968; D ado et al.,
19931. These estimates only account for energy losses in
metabolic transactions associated with production of indi-
vidual milk components. Theoretical efficiencies for use of
ME for milk fat, protein, and lactose synthesis as estimated
from Mertens and D ado (1993) were 81, 89, and 77 per-
cent, respectively, each well above the 64 percent mea-
sured calorimetric efficiency for use of dietary ME for
milk energy production (Moe and Tyrrell, 19721. Metabolic
models that incorporate changes in visceral metabolism,
transport, resynthesis of metabolites, and other energy
costs (Baldwin et al., 1987) account for most ofthis discrep-
ancy, but it is still difficult to assign these costs to produc-
tion of individual milk components. It is envisioned that
future net energy requirements for milk will be centered
more on substrate requirements for production of individ-
ual milk components rather than a more general require-
ment for total milk energy output.
OCR for page 20
20 Nutrient Requirements of Dairy Cattle
Activity Requirements
The energy required for maintenance includes a 10 per-
cent allowance for activity, which should provide sufficient
energy for the usual activity of lactating cows that are fed
in individual stalls or drylot systems. At similar production,
grazing cattle expend more energy than animals fed in
confinement because: 1) the distance between the milking
center and pasture is usually greater than the distance
between the milking center and most confinement housing
areas; 2) grazing cattle may have to walk where elevations
change; and 3) grazing cattle spend more time eating than
do confinement fed cattle. The increase in energy require-
ment for grazing cattle is largely a function of the distance
walked, topography of the pasture, and BW. Heat produc-
tion increases 0.00045 Mcal/kg BW for every kilometer a
cow walks horizontally (Agricultural Research Council,
1980; Bellows et al., 1994; Coulon et al., 19981. Because
no net work is actually done, increased energy required
for physical activity is reflected in increased heat produc-
tion and by definition is equivalent to NED required for
maintenance. Thus in NED units, the energy required for
excessive walking was set at 0.00045 Mcal/kg per kilometer
walked. Excessive walking was defined as the distance a
grazing cow travels between the pasture and the milking
center. For a grazing 600-kg cow walking 0.5 km to and
from the milking parlor 2 times per day (2 km total), the
extra NED allowance is 0.54 Mcal or about a 5 percent
increase in maintenance requirements.
Based on data generated with growing cattle (Holmes
et al., 1978; Havstad and Malechek, 1982), the increased
eating activity associated with grazing compared with stall-
fed cattle required 0.003 Mcal of ME/kg BW per day or
approximately 0.002 Mcal of NE/kg BW. That value was
for cattle consuming only pasture and should be reduced
to reflect the amount of concentrate fed. In this edition,
it is assumed that the diet for grazing lactating cows would
be 60 percent pasture (dry basis). Therefore the activity
allowance for eating act by grazing lactating cows (Meal
of NELL is calculated as 0.0012/kg of BW. For good quality,
high yielding pastures, we assumed that energy expended
walking within a paddock would be similar to that of cows
housed in free stall barns. The total increase in the daily
energy requirement for maintenance of cows grazing rela-
tively flat, high yielding pasture should be increased
0.00045 Mcal of NE/kg BW per km of distance between
the pasture and milking center plus 0.0012 Mcal per kilo-
gram BW. For example, a 600-kg cow grazing a flat pasture
(comprised 60 percent of total diet) approximately 0.5 km
from the milking center and milked twice daily will walk
2 km/d to and from the milking center. The maintenance
energy requirement should be increased by 2 x 0.00045
x 600 = 0.54 Mcal for walking and 0.0012 x 600 = 0.7
Mcal for eating activity or approximately 1.2 Mcal of NED/
day (approximately a 12 percent increase in maintenance
requirement).
The energetic cost for cows grazing hilly topography is
higher than that for cows grazing relatively flat pastures.
The actual cost for a specific situation is difficult to quantify,
because the change in elevation usually will not be known,
and cows will walk both up and down hills. The Agricultural
Research Council (1980) estimated that 0.03 Mcal of NED
per kg BW is required for a cow to walk 1 vertical km.
The committee used a qualitative system to adjust for
topography. A 'hilly' pasture system was defined as one in
which cows moved a total of 200 m of vertical distance
(50 m hill walked 4 times each day). Using the Agricultural
Research Council (1980) value, the energy requirement for
maintenance of cows grazing a hilly location was increased
0.006 Mcal of NE L/kg BW. That adjustment is in addition
to the increases in energy requirements for walking from
the pasture to the milking center and for eating. Using the
previous example for a cow that is milked twice daily and
is grazing a hilly pasture located 0.5 km from the milking
center, maintenance requirements would be increased
(0.00045 x 600 x 2) + (0.0012 x 600) + 0.006 x 600
= 4.9 Mcal NE/day or an increase in maintenance of
about 50 percent. As milk yield increases, appetite and the
amount of energy expended gathering food would also
increase, but this effect is not included in activity require-
ment calculations.
The time spent grazing is dependent on the amount of
forage consumed and the relative availability of herbage.
Where abundance of herbage is low, cows spend more
time to consume the same amount of forage. Forage intake
is dependent on milk production of cows and the amount
of supplemental grain that is fed with the pasture. In a
review (CSIRO, 1990), it was estimated that grazing activity
increased energy requirements relative to maintenance by
20 percent on flat terrain and by as much as 50 percent
on hilly pasture. They proposed a system to account for
increased energy costs associated with grazing based on
forage intake and digestibility, terrain, and herbage avail-
ability. This system was included in the National Research
Council's Nutrient Requirements of Beef Cattle (19961;
however, the proposed equation has not been evaluated.
Evaluation of that equation suggested that a 600-kg milking
cow, consuming 15 kg of DM from good quality pasture
(65 percent DM digestibility) with moderate to good avail-
abilitY of forage (2 to 3 metric tons/hectare), increased
NED requirements by 4 to 4.4 Mcal/d.
For growing heifers on pasture, energy requirements
should be increased to cover increased eating activity and
walking. The same energy costs used for lactating cows
were used for heifers (NEM values assumed to be equiva-
lent to NELL. The energy required for walking by heifers
was set at 0.00045 Mcal of NE M/kg BW per kilometer
walked. The distance heifers walk each day will vary
OCR for page 21
Energy 21
depending on availability of forage and placement of water.
Havstad and Malechek (1982) reported that grazing beef
heifers walked 3.9 km per day when forage supply was
adequate. The committee assumed the average growing
heifer would walk approximately twice as much when graz-
ing as when housed in confinement (an increase of approxi-
mately 2 km/d). Therefore, the NEM requirement for walk-
ing for grazing heifers was set at 0.00045 x 2 = 0.0009
Mcal/kg BW per day. The energy associated with eating
activity was the same as that used for lactating cows except
pasture was assumed to provide 80 percent of the diet
(0.0016 Mcal NEM x BOO). The total adjustment for the
daily energetic cost (NEM, Mcal/day) of grazing for growing
heifers is (0.0016 x BW) + (0.0009 x BOO). The same
equation as that used to estimate energy required for walk-
ing in hilly pasture for lactating cows was used for heifers.
For hilly pastures, maintenance requirements should be
increased an additional 0.006 Mcal of NE M/kg BW per day.
For example a 300-kg heifer grazing a hilly pasture would
require (0.0009 x 300) + (0.0016 x 300) + (0.006 x
300) = 2.6 Mcal of ME for activity (or an increase in
maintenance requirement of about 40 percent).
The energy requirements for activity given above are
based on many assumptions and very limited data. Accurate
information on walking distances, topography, pasture
yields, etc., for a specific situation is very difficult to quan-
tify. The actual energy required for activity under specific
circumstances could vary greatly from those calculated with
the above equations. The previous edition of the Nutrient
Requirements of Dairy Cattle (National Research Council,
1989) stated that maintenance energy should be increased
by 10 percent with good quality, high yielding pastures.
Based on available data, that value is probably too low.
The value probably ranges from about 10 (flat pasture
located close to the milking center) to more than 50 (hilly
pasture located far from the milking center) percent of
maintenance energy.
Environmental Effects
For lactating cows in cold environments, the change in
energy requirement is probably minimal because of the
normally high heat production of cows consuming large
amounts of feed. Even with the increased use of naturally
ventilated free stall housing systems, it is unlikely that cows
will require increased intake of energy to counteract cold
environments if they are kept dry and are not exposed
directly to wind. Young (1976) summarized experiments
with ruminants in which an average reduction in DM
digestibility of 1.8 percentage units was observed for each
10°C reduction in ambient temperature below 20°C. Much
ofthis lowered digestibility under cola stress maybe related
to an increased rate of passage of feed through the digestive
tract (Kennedy et al., 19761. Because of the effects of low
temperature on digestibility, under extremely cold weather
conditions, feed energy values could possibly be lower
than expected.
Mild to severe heat stress has been estimated (National
Research Council, 1981) to increase maintenance require-
ments by 7 to 25 percent, respectively (for a 600-kg cow,
this equates to between 0.7 and 2.4 Mcal of NEL/day);
however, insufficient data are currently available to quan-
tify these effects accurately. Heat stress induces behavioral
and metabolic changes in cattle (West, 19941. Some
changes, such as panting, increase energy expenditures,
while other changes (reduced dry matter intake, selective
consumption, reduced activity, and reduced metabolic
rate) will reduce heat production. An equation to adjust
maintenance requirement based on environmental factors
related to heat stress (ambient temperature, relative
humidity, radiant energy, and wind speed) has been devel-
oped (Fox and Tylutki, 1998), but it has not been suff~-
ciently validated. Because of limited data, no adjustments
for heat stress have been included in the calculation of
maintenance requirements of adult cattle in this version.
Users, however, should be aware of the effects heat stress
has on maintenance requirement and may wish to make
dietary adjustments to account for those effects.
Pregnancy Requirements
Estimates of the energy requirements for gestation dur-
ing the last 100 days of pregnancy are from Bell et al.
(19951. The energy required for gestation is assumed to
be O when the day of gestation is less than 190 and the
maximum gestation length is set to 279 days (longer gesta-
tion periods result in no change in energy requirements).
Bell et al. (1995) serially slaughtered Holstein cows at
various stages of gestation and generated a quadratic equa-
tion to describe the energy content of the gravid uterus.
The first derivative of that equation yields the daily change
in energy content. The subcommittee assumed that energy
requirements for gestation would depend on birth weight
of the calf; therefore, an adjustment relative to the mean
birth weight of Holstein calves (45 kg) was included in the
Bell et al. equation. Efficiency of ME use by the gravid
uterus was assumed to be 0.14 (Ferrell et al., 19761. There-
fore, the ME requirement for gestation is described as:
ME (Meal/d) = L(0.00318 x D 0.0352)
x (CBW/4514/0.14 (2-18)
where D = day of gestation between 190 and 279, and
CBW is calf birth weight in kilograms. To convert ME to
NED an efficiency of 0.64 was used; therefore, the NED
requirement for pregnancy is:
NED (Meal/d) =
F(0.00318 x D 0.0352)
x (CBW/4514/0.218 (2-19)
OCR for page 22
22 Nutrient Requirements of Dairy Cattle
where D = day of gestation between 190 and 279, and
CBW is calf birth weight in kilograms.
Tissue Mobilization and Repletion During Lactation and
the Dry Period
The growth model (Chapter 11) computes growth
requirements until females reach their mature weight.
However, changes in body composition during lactation
and the dry period primarily reflect depletion and repletion
of tissues when diets provide insufficient or excess energy.
The body tissues involved (primarily internal and external
fat depots) are commonly called body reserves.
Optimum management of energy reserves is critical to
economic success with dairy cows. When cows are too fat
or thin, they are at risk for metabolic disorders and diseases,
decreased milk yield, low conception rates, and difficult
calving (Ferguson and Otto, 19891. Overconditioning is
expensive and can lead to calving problems and lower dry
matter intake during early lactation. Conversely, thin cows
may not have sufficient reserves for maximum milk produc-
tion and often do not conceive in a timely manner.
The dairy cow mobilizes energy from body tissue to
support energy requirements for milk production during
early lactation and replates mobilized tissue reserves during
mid and late lactation for the subsequent lactation. As
this is a normal physiological process that occurs in all
mammals, it should be expected that all cows will mobilize
energy stores in early lactation. There have been a number
of experiments in which amounts of energy mobilized from
tissue during early lactation were measured (Andrew et
al., 1994, 1995; Komaragiri and Erdman, 1997, 1998; Chil-
lard et al., 1991; Gibb et al., 19921. In addition, experiments
with bST (Tyrrell et al., 1988; Brown et al., 1989; McGuffey
et al., 1991) clearly demonstrate that the initial increase
in milk production associated with bST relies on partial
mobilization of energy stores. In both early lactation and
during a 4- to 6-week period after bST injection, increases
in DMI lag behind the increase in milk production. Under
these circumstances body tissue is mobilized as a source
of energy and to a lesser extent a source of protein to
support nutrient requirements for milk production.
Changes in BW of cows may not reflect true changes
in stores of tissue energy. In experiments where stores of
body energy were measured by slaughter analysis, stores
of energy differed by as much as 40 percent, and there
was little or no change in BW from calving to 5 to 12 weeks
postpartum (Andrew et al., 1994; Gibb et al., 19921. As
feed intake increases, gastrointestinal contents (gut filly
increase. The average gut fill in dairy cows is approximately
15 percent of BW. French workers (Chillard et al., 1991)
suggested a 4 kg increase in gut fill for each kilogram
increase in DMI. Data from more recent experiments using
both direct and indirect measurements of gut fill suggest
gut fill increases 2.5 kg for each kilogram increase in dry
matter intake (Komaragiri and Erdman, 1997, 1998; Gibb
et al., 19921. Because tissue mobilization during early lacta-
tion occurs at the same time that feed intake is rapidly
increasing, decreases in body tissue weight are masked by
increases in gut fill such that changes in BW do not reflect
changes in tissue weight. After peak milk production, feed
intake declines and gut fill decreases, such that increases
in BW underestimate true changes in body tissue weight.
The energy value of a kilogram of true body tissue that
is lost or gained is dependent on the relative proportions
of fat and protein in the tissue and their respective heat
of combustion. On average, fat-free mass contains 72.8
percent water, 21.5 percent protein, and 5.7 percent ash
(Andrew et al., 1994, 1995; Komaragiri and Erdman, 1997,
1998; Chilliard et al., 1991; Gibb et al., 19921; nearly identi-
cal to the respective values of 72.91, 21.64, and 5.34 percent
reported by Reid (19551.
This committee chose to use the National Research
Council (1996) body reserves model with modifications by
Fox et al. (1999) to predict body composition based on
body condition score (BCS; see section below) of cows of
different body sizes and amounts of body reserves. Body
condition score (BCS) measurements can be made readily
on farms, and BCS is correlated with body fat and
energy contents.
Equations relating BCS with body composition were
developed from data using a nine point BCS scale (1 to 9
scoring system, BCS(9~) on 106 mature cows of diverse
breed types, mature weights and BCSs. The resulting equa-
tions that describe relationships between BCS(9) and
empty body percentage of fat (Equation 2-2O, protein;
Equation 2-21, water) and ash were linear. The BCS
accounted for 65, 52, and 66 percent of the variation in
body fat, body protein, and body energy, respectively
between individual animals.
Proportion of empty body fat
= 0.037683 X BCS(9) (2-20)
Proportion of empty body protein
= 0.200886 - 0.0066762 X BCS(9) (2-21)
Equations 2-20 and 2-21 use BCS on a 1 to 9 scale (i.e.,
BCS(9~; however, a 1 to 5 scale is commonly used for
dairy cattle (Wildman et al., 1982; Edmonson et al., 1989;
Figure 2-2~. In the model, users input BCS on a 1 to 5
scale, and the program internally converts those to the 1
to 9 scale as
BCS(9) = ((Dairy BCS 1) X 2) + 1 (2-22)
Equations 2-20 and 2-21 are used to estimate the compo-
sition of body tissue gain or loss, which is then used to
calculate the energy supplied or required for changes in
body reserves. Regression analysis on slaughter data from
OCR for page 23
23
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OCR for page 24
24 Nutrient Requirements of Dairy Cattle
25 cows at various stages of lactation (Andrew et al., 1991)
suggested a heat of combustion for body fat and protein
of 9.2 and 5.57 Mcal/kg, respectively. These values are
similar to the values of 9.4 and 5.55 Mcal/kg reported for
growing steers (Garrett, 19871. The committee chose 9.4
and 5.55 Mcal/kg for body fat and protein. To determine
the total energy contained in 1 kg of reserves, the heats
of combustion are multiplied by the estimated proportions
of fat and protein:
Total reserves energy (Mcallkg)
= Proportion empty body fat X 9.4
+ proportion of empty body protein X 5.55 (2-23)
The amount of energy per kilogram of BW for different
BCS are shown in Table 2-4. Reserve energy when used
to support milk production has an efficiency of 0.82. There-
fore NED provided by body reserves is:
NED from body reserve loss (Meal/kg)
= Reserve energy (Equation 2-23) x 0.82 (2-24)
The measured efficiency of use of dietary ME for body
tissue energy deposition was 0.60 percent in nonlactating
cows and 0.75 in lactating cows (Moe et al., 19711. If the
efficiencies of ME used for milk production and BW gain
by lactating animals are 0.64 and 0.75, respectively, the
amount of NED required for 1 kg of gain in reserves during
lactation is:
NED (Meal/kg gain)
= Reserve energy (Equation 2-23
x (0.64/0.751) (2-25)
In nonlactating cows, the efficiency term in the previous
equation is (0.64/0.601. Because digestibility is decreased
when large amounts of feed are consumed by cows, the
feed required for tissue gain during the dry period would
be less than projected because of greater digestibility of
any given diet when cows are fed at maintenance. The
NED provided by loss of reserves or needed to replenish
reserves is shown in Table 2-4 for cows with different BCS.
To estimate the amount of energy provided by or
required for a one-unit change in BCS, change in BW
relative to change in BCS must be calculated. The mean
change in empty BW (EBW) per one-unit change in BCS
(5-point scale) is 13.7 percent (Fox et al., 19991. The EBW
is calculated es 0.851 x shrunk BW; shrunk BW = 0.96
x BW; therefore, EBW = 0.817 x BW. The BCS 3 (5-
point scale) was set as the base (1.001; the relative EBW
(or BW) can be calculated at other BCS (Table 2-41. For
example, a 600-kg cow with a BCS of 3 (EBW of 513 kg)
would be expected to weigh 518 kg (600 x 0.863; Table
2-4) at a BCS of 2. The amount of tissue energy required
per kilogram gain in EBW (Table 2-4) is calculated as the
energy provided by fat and protein at the next higher BCS
(weighted by EBW at next higher BCS), subtracted from
the energy provided by fat and protein at the current BCS
(weighted by EBW at the current BCS), divided by EBW at
next higher BCS minus EBW at current BCS. To calculate
energy provided per kilogram of EBW loss, the same equa-
tion is used except values at current BCS are subtracted
from values at next lower BCS.
This model was validated with the data of Otto et al.
(1991), as described by Fox et al. (19991. In this study,
body composition and BCS of 56 Holstein cows selected
to represent the range in dairy body condition scores 1 to
5 were determined. Body fat at a particular condition score
in Holstein cows was predicted with an r2 of 0 95 and a bias
of1.6 percent. The relationship between BW change and
BCS in these Holstein cows was 84.6 kg/BCS (r2 = 0.961.
This value of 84.6 kg/BCS compared well to 80 kg predicted
by the model and 82 kg in the data previously mentioned
TABLE 2-4 Empty Body (EB) Chemical Composition at Different Body Condition Scores (BCS), Relative EB
Weight (EBW), and NED Provided by Live Weight (LOO) Loss and NED Needed for LW Gaina
% of EB Energy, Mcal Mcal
EBW Mcal/kg NE/kg of NE/kg of
BCS Fat Protein Ash Water (% of BCS 3) EBW changed LW lossC LW gains
1.0 3.77 19.42 7.46 69.35 72.6 5.14 ... 3.60
1.5 7.54 18.75 7.02 66.69 79.4 5.72 (5.14) 3.44 4.01
2.0 11.30 18.09 6.58 64.03 86.3 6.41 (5.72) 3.83 4.50
2.5 15.07 17.42 6.15 61.36 93.1 6.98 (6.41) 4.29 4.90
3.0 18.84 16.75 5.71 58.70 100.0 7.61 (6.98) 4.68 5.34
3.5 22.61 16.08 5.27 56.04 106.9 8.32 (7.61) 5.10 5.84
4.0 26.38 15.42 4.83 53.37 113.7 8.88 (8.32) 5.57 6.23
4.5 30.15 14.75 4.43 50.71 120.6 9.59 (8.88) 5.95 6.73
5.0 33.91 14.08 3.96 48.05 127.4 (9.59) 6.43 ...
aEmpty body weight = 0.817 x live weight.
bTissue energy contained in 1 kg of EBW gain going to next higher 0.5 BCS. Values in parentheses are tissue energy contained in 1 kg of EBW loss going to next lower
0.5 BCS.
CValues were calculated by converting tissue energy per kilogram of EBW into tissue energy per kilogram of BW (EBW X 0.855) and then converting to dietary NED
using an efficiency of 0.82 for converting tissue energy from live weight loss to dietary NED, and an efficiency of 1.12 for converting dietary NED to tissue energy for live
weight gain.
OCR for page 25
Energy 25
TABLE 2-5 Energy Provided by or Needed to Change Body Condition Score (BCS) of Cows of Different Live
Weights and BCS
Live weight (kg)
BCS 400 450 500 550 600 650 700 750
Mcal of NET provided by a loss of one BCSa
230 259 288 317 346 375 404 432
245 276 307 338 368 399 430 460
257 289 321 353 385 417 450 482
266 299 332 365 399 432 465 498
Mcal of NET needed to gain one BCSb
287 323 359 395 431 467 502 535
298 335 372 410 447 484 522 559
306 344 382 421 459 497 535 574
312 351 390 429 468 507 546 585
a Represents the NED provided by mobilization of reserves when moving to next lower score. For example, a 400-kg cow in BCS 3 will provide 245 Mcal of NED when
BCS decreases one unit.
b Represents the NED required to replenish reserves when moving to the next higher score. For example a 600-kg cow in BCS 3 will require 459 Mcal of NED to increase
BCS one unit.
in this chapter. Although the evaluation strongly supports
the use of this model, further validation with other data
sets should be conducted.
This model predicts energy reserves to be 5.47 Mcal/kg
live weight loss from BCS 3.0 to BCS 2.0. The mean value
of tissue energy is 6 Mcal/kg (Gibb et al., 1992; Andrew
et al., 1994; Komaragiri and Erdman, 1997; Tamminga,
1981) and that is the value used in the 1989 edition
(National Research Council, 19891. The predicted energy
content of weight loss ranged from 4.36 Mcal/kg at BCS
1.5 to 7.59 Mcal/kg at BCS 4.5 compared to CSIRO (1990)
values of 3.0 and 7.1, respectively. Protein in the weight
loss from BCS 3 to BCS 2 was predicted to be 68 g/kg,
compared to 135, 138, and 160g/kg weight loss for the
CSIRO (1990), AFRC (1993), and National Research
Council (19891.
Body Condition Scoring
Body condition scoring (BCS), although subjective
nature, is the only practical method of evaluation of body
energy stores in dairy cows. In the U.S., the most common
systems of BCS use a f~ve-point scale originally proposed
by Wildman et al. (1982) with a BCS of 1 being extremely
thin and a score of 5 being extremely fat. This system
included a combination of both visual appraisal and manual
palpation to score individual cows. Edmonson et al. (1989)
suggested a BCS chart system using a 5-point scale based
on visual appraisal of only 8 separate body locations. Analy-
sis of variation due to cows and to individuals assessing
BCS suggested that visual appraisal of two key locations
(between the hooks and between the hooks and pins) had
the smallest error due to assessor and accounted for the
greatest proportion of variation due to individual cows.
Figure 2-2 shows the suggested BCS chart based on these
two key areas.
Loss of BCS is expected during earlylactation when a
cow is mobilizing body fat in support of energy needs for
lactation. Typical observed changes in BSC range from
0.5 to 1.0 condition score units during the first 60 days
postpartum. A 1-unit decrease in BCS for a cow weighing
650 kg at calving (BCS 4) would provide 417 Mcal of NED
(Table 2-51. That amount of NED is sufficient to support
564 kg of 4 percent fat-corrected milk.
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Representative terms from entire chapter:
dairy cattle
