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OCR for page 234
1 1 Growth
ENERGY AND PROTEIN REQUIRE MENTS
FOR GROWING DAIRY HEIFERS
Since the publication of the last National Research
Council review of nutrient requirements of dairy cattle
(National Research Council, 1989), several articles on use
of accelerated growth programs for heifers and their effects
on milk production have been published (rammers et al.,
1999; Radcliff et al., 1997; Van Amburgh et al., 1998a,
1998b). In addition, there have been several reports of
studies on protein requirements of heifers (Pirlo et al.,
1997; Tomlinson et al., 19971. This renewed interest in
rearing heifers is largely due to the costs of raising replace-
ment animals and the impact of the growing period on
lifetime milk production. These economic imperatives
underscore the importance of accurate prediction of heifer
nutrient requirements. Energy and protein requirements
for growth are estimated from the energy and protein
content of the tissue deposited during growth (National
Research Council, 19961. The amount of energy required
for growth is calculated from the net energy deposited.
The amount of protein that must be consumed daily to
achieve the target growth rate is the sum of 1) rumen
degradable protein (RDP) required for microbial growth
that can be achieved given the level of ruminally available
carbohydrates, and 2) rumen undegradable protein (RUP)
required to supplement the microbial protein produced to
support the energy allowable average daily gain (ADG).
Preston (1982) indicated that protein requirements for
growth could be expressed as a ratio of dietary crude pro-
tein (CP) to dietary total digestible nutrients (TDN). How-
ever, this approach does not account for differences in
RDP and RUP requirements, and in mature body size.
Tomlinson et al. (1997) reported a growth response when
RUP was added to heifer diets. A growth response also
was evident when RUP was added to low energy, but not
high energy, diets fed to heifers less than 385 days old
(Bethard et al., 19971. Heifers responded to both supple-
mental TDN and CP when the basal diet contained 90
percent of National Research Council-predicted require-
ments (Pirlo et al., 19971. Accurate estimation of dietary
requirements for protein should be based on ruminal and
tissue requirements in varied production environments
(National Research Council, 1996; Van Amburgh et al.,
1998a).
Terminology
In this section on growth, several terms are used which
are less familiar to those in the dairy industry than to those
who work primarily with growing animals. In the 1989
publication on requirements of dairy cattle (National
Research Council, 1989), all calculations were done on a
full body weight (BW or FBW) basis. In this publication,
the terms shrunk body weight (SBW) and empty body
weight (EBW) also are used. These terms permit better
description of biologic functions than reliance on live
weight alone. For example, SEW, which is defined as 96
percent of FEW, is equivalent to an animal's weight after
an overnight fast without feed or water. It is used to com-
pute NEM requirements, which are measured as fasting
heat production (National Research Council, 19841.
Shrunk body weight also is used in calculations to deter-
mine the amount of net energy available for growth in the
diet (NEFG) and target shrunk weight gain (SWG). Empty
body weight (weight without ingesta), which is 89.1 percent
of SEW or 85.5 percent of BW, was used to develop the
equation to predict the energy required for SWG because
net energy requirements are a function of the proportion
of fat and protein in the empty body tissue gain (EBG)
(Garrett et al., 19591. Empty body gain is 96 percent of
SWG.
Growth Requirements and Composition of Gain
The strong relationship between weight and height (Hei-
nrichs and Losinger, 1998) makes it possible to use linear
measurements to describe dimensional changes as an ani-
234
OCR for page 235
Growth 235
mat matures (Hoffman, 1997; Kertz et al., 1998; Lammers
et al., 19991. Although these measurements have several
useful field applications, skeletal growth cannot be directly
used to compute energy and protein requirements for
growth for two reasons: 1) net energy for gain (NEG) is
defined as the energy content of the tissue deposited during
growth, and 2) most of the data relating stature and weight
are from Holsteins so that the system would be unworkable
for other breeds. It is a function of the proportion of fat
and protein in EBG (Garrett et al., 1959~. Simpfendorfer
(1974) summarized data on the body composition of grow-
ing cattle from birth to maturity and found that 95.6-98.9
percent of the variation in chemical composition was associ-
ated with differences in the weights of cattle of similar
mature sizes. If an animal is fed a diet containing adequate
energy, the percentage of protein diminishes and the per-
centage of fat increases in the empty body as the animal
matures (National Research Council, 1996~. Chemical
maturity is achieved when weight gain contains little addi-
tional protein (National Research Council, 1996~. Previous
subcommittees on beef and dairy nutrition (National
Research Council, 1984,1989,1996) adopted the equation
developed by Garrett (1980) to predict the energy content
of weight gain. Garrett's data set included 72 comparative
slaughter experiments conducted at the University of Cali-
fornia between 1960 and 1980 with approximately 3,500
cattle (predominantly British breed beef steers) fed a vari-
ety of diets. The Garrett equation describes the relationship
between retained energy (RE) and EBG for a given EBW.
The same data were used to derive the relationships
between FEW, SEW, and EBW and to describe the com-
position of ingesta-free BW gain at a particular stage of
growth of cattle (National Research Council, 1996~.
Because the weight at which cattle reach a given chemi-
cal composition varies depending on mature size and gen-
der, body composition may differ among animals of similar
weights (National Research Council, 1996~. Following the
approach adopted in the 1984 Nutrient Requirements of
Beef Cattle (National Research Council, 1984) and in the
1989 Nutrient Requirements of Dairy Cattle (National
Research Council, 1989), recently developed systems to
predict animal requirements have used a size scaling
approach to account for these effects (National Research
Council, 1996~. The size-scaling approach adopted in the
Australian system (Commonwealth Scientific and Indus-
trial Research Organization ECSIRO], 1990) involves calcu-
lation of the relationship between an animal's current
weight and a standard reference weight. The standard ref-
erence weight is defined as the weight at which skeletal
development is complete and the empty body contains 25
percent fat corresponding to a body condition score (BCS)
of 3 on a 0 to 5 scale. To facilitate ration balancing, standard
reference weights for different breeds are provided in a
table in the CSIRO system (19901.
Oltjen et al. (1986) developed a simulation model of
growth and body composition based on differential equa-
tions describing whole body DNA accretion and protein
synthesis and degradation. He assumed that the difference
between net energy available for gain and that required
for protein synthesis deposited as fat. By using the ratio
between the animal's current weight and its mature weight,
it was possible to adjust for differences in mature size.
In the model developed by the Institut National de la
Recherche Agronomique (INRA) system (Institut National
de la Recherche Agronomique, 1989), the amounts of pro-
tein and lipid retained daily are predicted considering the
type, live weight, and daily live weight gain of the animal.
The INRA approach to prediction of energy and protein
requirements involves use of allometric relationships
between EBW and live weight, between lipid content (kg)
and EBW, and between protein content and fat-free body
mass. The coefficients in the INRA equations are the
parameters obtained by fitting data on live weight and
age to the Gompertz equation (Taylor, 1968~. The French
system includes initial and final weights and growth curve
coefficients for six classes of bulls, two classes of steers,
and two classes of heifers for finishing cattle, and two
classes each for male and female growing cattle. The
amount of lipid deposited daily is proportional to the daily
live weight gain raised to the power 1.8 (BWi81. Daily
protein accretion is calculated from the gain in the fat-free
body mass because protein content of fat-free gain varies
little with type of animal, growth rate, or feeding level
(Garrett, 19871.
The mature weights of dairy cattle vary from 400 kg for
small breeds to more than 680 kg for large breeds. Because
of the considerable variation in mature size within and
among breeds, this committee decided that it was necessary
to consider mature size in estimating growth requirements.
In the previous publication on the nutrient requirements of
dairy cattle (National Research Council, 1989), size effects
were taken into account by including requirements for
small, medium, and large breeds in the nutrient require-
ment tables. However, the equations used to compute the
net energy and protein content of gain were not adjusted
to account for the effect of mature weight.
The National Research Council Nutrient Requirements
of Beef Cattle (1996) adopted the size scaling system devel-
oped by Fox et al. (1992) with refinements published by
Tylutki et al. (19941. This system is used to account for
differences in mature size of cattle (Equations 11-1 and
11-2) with further modifications made to adapt it for use
with dairy heifers (except for pre-ruminant calves) (Fox et
al., 19991. As in the CSIRO (1990) and INRA (1989) sys-
tems, it is assumed in this model that the chemical composi-
tion of gain is similar among animals at the same proportion
of mature BW. The size scaling equation in the beef growth
OCR for page 236
236 Nutrient Requirements of Dairy Cattle
model (National Research Council, 1996) is similar to the
approach adopted by CSIRO (19901.
The equations of Garrett (1980), with the adjustments
for mature size shown in Equations 11-2 and 11-5, are
used to compute the energy content of gain at various
stages of growth and rates of gain. These equations were
chosen because: a) they were developed from a large,
robust data set (Garrett, 1980), b) they have been used with
success in previous National Research Council publications
(National Research Council, 1984, 1989, 1996), and c) they
accurately described the net energy and protein content
of Holstein heifers (Fox et al., 1999) using the adjustments
for mature body size in Equations 11-2 and 11-5.
EQSBW = SBW x (478/MSBW) (11-1)
RE, Meal = 0.0635 x EQEBW075
x EQEBGi 097 (11-2)
where EQEBW is 0.891 x EQSBW and EQEBG is 0.956
x SWG.
In this growth model, EQSBW is the weight at which
the standard reference animal has the same energy content
of gain as the dairy heifer being evaluated. An analysis of
the California data set indicated that the mature SBW for
the animals in the serial slaughter studies averaged 478 kg.
Equation 11-2, which describes the energy content of gain
at a particular weight for the California data base (National
Research Council, 1996), is used in the current model to
describe the growth curve of dairy heifers. As a result, the
standard reference animal is assumed to have a mature
weight of 478 kg (National Research Council, 19961. In
Equation 11-2, energy content of gain increases with
weight and rate of growth. If we assume that the average
Holstein has a full BW (FBW) of 677 kg or SBW of 650
kg, the relationship between this animal and the standard
reference animal can be determined using Equation 11-
1. The ratio of the reference SBW to the mature SBW
(478/650) is used to determine that the standard reference
animal weighs 73.5 percent as much as the Holstein at
chemical maturity. Assuming an average SBW of 650 kg,
Equation 11-1 indicates the standard reference animal
weighs 478/650 = 73.5 percent as much at maturity, and
therefore weighs 73.5 percent as much as this Holstein at
the same stage of chemical maturity. For example, the
"size-scaled" weight of a Holstein heifer with an SBW of
300 kg (313 FBW) and a mature SBW of 650 kg (677
FBW) is 300 x (478/650) = 221 kg. This value is then
adjusted to an empty body basis (221 x 0.891 = 197 kg)
and used in Equation 11-2 to compute her net energy
requirement. For a 300 kg SBW Holstein heifer with a
mature weight of 800 kg, the size-scaled weight is 300 x
(478/800) = 179 kg, with an EBW of 159 kg. The size-
scaled weight of a Jersey heifer weighing 300 kg SBW with
a mature weight of 400 kg is 300 x 478/400 = 359 kg with
an EBW of 320 kg, which is used in Equation 11-2 to
compute her net energy requirement. Although these three
heifers weigh the same amount (300 kg SBW), the Jersey
heifer is at 75 percent of her mature weight, while the
average and large Holstein heifers are at 46 percent and
38 percent of their respective mature weights. When these
size-scaled weights are used in Equation 11-2 with a rate
of gain of 0.7 kg (EBG = 0.7 x 0.956 = 0.669), the
Jersey heifer will have the highest net energy content of
gain, followed by the average and large mature size Hol-
stein heifers (3.09, 2.15, and 1.83 Meal, respectively). The
validation by Fox et al. (1999) showed that this size scaling
approach can be used for dairy heifers.
Given the relationship between energy retained and pro-
tein content of gain, protein content of SWG (net protein
for gain, NPg) is computed from the following equation
(National Research Council, 1984, 19961:
NPg, g/d = SWG x (268 — (29.4
x (RE/SWG)~) (11-3)
The retained protein predicted in Equation 11-3 is adjusted
for mature size because the RE used in that equation is
based on EQEBW. The absorbed protein requirement is:
MPGrowth = NPg / (0.834— (EQSBW x 0.001141)
If EQSBW is ~ 478 kg, then EQSBW = 478 kg.
(11-4)
To develop feeding programs and evaluate heifer perfor-
mance, daily gain must be predicted from the diet being
fed. This is accomplished by substituting EQSBW for SBW
and the net energy available for growth (NEFG) for RE
in the Garrett (1980) equation (Equation 11-5) to pre-
dict SWG:
SWG = 13.91 x NEGrowthDiet09~6
x EQSBW-06837 (11-5)
Actual SWG and NEGrowthDiet can be substituted into
Equation 11-3 to compute the protein required for the
observed SWG and NEFG. Equation 11-4 can then be
used to compute the MP required for the observed SWG
to evaluate whether protein requirements have been met.
Evaluation of Model Predictions of Energy and Protein
Requirements for Growth of Dairy Heifers
Table 11-1 shows the net energy requirements of heifers
of different mature sizes (65O, BOO, and 400 kg) growing at
different rates (0.6, 0.8, and 1.0 kg/day). Several important
relationships are shown in this table. First, as BW increases,
the energy content of the gain increases and protein con-
tent of the gain decreases, because more energy is depos-
ited as fat. Second, as SWG increases, energy content of
the gain increases and protein content of the gain decreases
because the gain contains a higher proportion of fat as
OCR for page 237
Growth 237
TABLE 11-1 Relationship Between Mature Size and
Growth Requirementsa
Mature weight Live Body Weight During Growth (kg)
650 kg Holstein 200 250 300 350 400 450 500
800 kg Holstein 246 308 369 431 493 554 616
400 kg Jersey 139 173 208 242 277 312 346
SWG (kg/day)
0.6
0.8
1.0
NEG required, Mcal/db
1.34 1.58 1.81 2.03 2.25 2.46 2.66
1.83 2.17 2.48 2.79 3.08 3.37 3.64
2.34 2.77 3.17 3.56 3.94 4.30 4.65
Net protein required for growth, g/dc
122 114 108 101 95 89 83
161 151 141 132 124 115 107
199 187 175 163 152 142 131
Metabolizable protein required for growth, g/dd
182 183 185 187 190 194 199
241 241 243 245 248 253 259
299 299 300 302 305 310 316
0.6
0.8
1.0
0.6
0.8
1.0
aThe body weights are full, not shrunk, body weights. The weights within the
same column are at the same stage of growth.
bNEG requirement is computed from Equation 11-2: Retained energy (RE), Meal
= 0.0635 EQEBW075 EQEBGi097, where EQEBWis equivalent empty body weighs
arid EQEBG is 0.956 X SWG.
CNet protein in the gain is computed from Equation 11-3: NPg (g/d) = SWG
X (268 - (29.4 X (RE/SWG)))
~Metabolizable protein required is computed from Equation 11-4: MPGrowth
= NPg / (0.834 - (EQSBW X 0.00114)); If EQSBW is > 478 kg, then EQSBW
= 478 kg.
growth rate increases. Third, as animals increase in weight,
metabolizable protein required does not decrease as rap-
idly as net protein required, because the efficiency of pro-
tein absorption declines. As energy intake above mainte-
nance increases, it is assumed that the rate of protein
deposition becomes limiting, and excess energy is depos-
ited as fat. The fat dilutes the body content of protein, ash,
and water, which are deposited at nearly constant ratios
to each other at a given age (Garrett, 19871. The carcasses
of Holstein heifers growing from 344 to 388 kg SBW that
gained either 0.8 or 1.2 kg/d contained 12.1 or 18.5 percent
body fat in the SBW (Radcliff et al., 19971. Holstein heifers
grown to 321 kg SBW (334 kg FBW) deposited 1.93 Mcal/d
(2.58 Mcal/kg SBG) when grown at 0.75 kg/d compared
to 2.75 Mcal/d (3.67 Me al/kg SBG) when the heifers grew
at 0.95 kg/d (Waldo et al., 19971.
The equations used to predict energy and protein
retained during growth were validated using data from
experiments with Holstein heifers that were serially slaugh-
tered (Fortin et al., 1980; Anrique et al., WOO, as described
by Fox et al., 19991. Although these animals were fed diets
that were pelleted and contained less fiber than usually is
fed to growing animals, the energy retained for the
observed daily gain can be used to validate this model. Plots
of observed and predicted values and plots of residuals of
data on composition of gain of Angus and Holstein heifers
showed that the composition of gain for beef and dairy
breeds was similar when the size scaling approach was
used. The slope and intercept of the regression describing
the composition of gain of the Holstein heifers was similar
to the regression for the combined data set. The r2 was
0.86 when observed and predicted data on RE of Holstein
heifers were regressed using the equations from Nutrient
Requirements of Dairy Cattle (National Research Council,
1989) with a bias of—11 percent. The r2 was 0.96 for the
model presented here, with a bias of—4 percent. When
similar regressions were performed to evaluate prediction
of RP in Holstein heifers, the r2 was 0.91 for the 1989
equations and 0.71 for the model presented here, with
biases of—13 and—10 percent, respectively. The bias for
the 1989 National Research Council equations was non-
uniform, with under prediction of RP at lower BW. These
results indicate the present model can be used to predict
RE and RP for dairy heifers. We suggest, however that
more research is needed to account for factors influencing
RP, as indicated by the lower r2 and higher bias in predict-
ing RP compared to RE.
Information from 32 Holstein heifers fed alfalfa or corn
silage diets at two rates of ADG (0.78 and 0.99 kg/d) from
181 to 334 kg of FEW (Waldo et al., 1997) was used
to evaluate the prediction of EBW and EBG. The EBW
averaged 89 percent of SBW compared to 89.1 percent in
the Garrett (1980) data-base, which was used to develop
this model. The EBG averaged 87.4 percent of SWG com-
pared to 95.6 percent in the Garrett (1980) data-base. In
Holstein steers at the same stage of growth as the heifers
in the trials conducted by Waldo et al. (1997) (< 400 kg
SBW), EBW was 89 percent of SBW and EBG averaged
95.7 percent of SWG (Abdalla et al., 19881. These values
are nearly identical to those used in this model.
Based on these evaluations of the model, errors in pre-
dicting net energy and protein requirements and SWG
may occur due to one or more of the following factors:
· Using an incorrect MSBW.
· Short-term, transitory effects of previous nutrition.
· Variation in the NEM requirement.
· Variation in the ME value assigned to the feed because
of variations in feed composition and extent of ruminal or
intestinal digestion.
· Variation in NEM and NEG derived from the ME
because of variation in end products of digestion and their
metabolizability.
· Variations in gut fill.
Although ionophores are commonly fed to replacement
heifers, the computer model accompanying this publication
includes no adjustments for ionophores for several reasons.
The relative importance ofthe various effects of ionophores
such as changes in intake, protein sparing, influence on
ruminal pH, increased energetic efficiency of the ruminal
microbes and reduced problems with protozoa! pathogens
has not been fully elucidated. The effects of ionophores
OCR for page 238
238 Nutrient Requirements of Dairy Cattle
vary with diet, animal condition, environmental conditions,
and the types of ionophore used. The model may not
predict accurately when ionophores are fed unless the user
adjusts either intake or the digestibility of nutrients in
the ration.
SETTING TARGET GROWTH RATES
Growth rates of replacement heifers affect economic
returns on dairy farms (Cady and Smith, 19961. Inadequate
size at first parturition may limit milk production and con-
ception rate during first lactation (Hoffman et al., 19961.
Excess energy intake, however, can have negative effects
on mammary development by affecting the mammary
parenchyma (ductular epithelial tissue) (Harrison et al.,
1983; Foldager and Serjsen, 19871. There was an interac-
tion between protein and energy because, when adequate
amounts of metabolizable protein were supplied to animals
receiving high-energy diets, fewer effects on mammary
development were evident (Radcliff et al., 19971. Follow-
up research showed that heifers fed diets high in energy
and protein decreased age at first parturition and milk
production at first lactation (Radcliff et al., 2000) but milk
production was not reduced in the first lactation in other
heifers raised on an accelerated (0.9 kg ADG/day) growth
program (Abeni et al.,20001. Because puberty is associated
with BW and weight is not linearly related to growth,
parenchyma tissue growth may be truncated before full
ductal development occurs if excess energy is consumed
before puberty (Van Amburgh et al., 19911. Excessive
energy intake, indicated by over-conditioning from 2 to 3
months of age until after conception, can reduce first lacta-
tion milk production (Van Amburgh et al., 1998b). Numer-
ous data are available to support the concept of a genetically
determined threshold age and weight at which heifers
attain puberty (National Research Council, 19961. ;[oubert
(1963) proposed that heifers would not attain puberty until
they reached a given degree of physiologic maturity, which
is similar to the "target weight" concept proposed by
Lamond (19701. Simply stated, the concept is to feed heif-
ers to attain a pre-selected or target weight at a given
age to achieve optimum first lactation performance while
controlling the costs of rearing replacements. Heifers of
beef breeds usually attain puberty at about 60 percent of
mature weight, while dual purpose and dairy heifers reach
puberty at a younger age at about 55 percent of mature
weight (National Research Council, 19961.
Optimum growth rates for heifers to minimize replace-
ment costs while maximizing first lactation milk production
have been described recently (Ferguson and Otto, 1989;
Hoffman, 1997; Van Amburgh et al., 1998b). The Nutrient
Requirements of Beef Cattle (National Research Council,
1996) equations to predict target weights, modified and
evaluated by Fox et al. (1999), are used to predict target
weights for dairy heifers. Further modifications included
in this version of Nutrient Requirements of Dairy Cattle,
compared to those outlined by Fox et al. (1999), are that
the target weights after first and third calving were set to
82 and 100 percent of mature weight respectively, instead
of 85 percent and 96 percent.In the following equations,
calving weights are weights after parturition. The equations
to predict target weights and rates of gain are as follows:
Target weight first bred
= Mature SBW x 0.55 (11-6)
Target age for 1st pregnancy
= Target first calving age — 280 (11-7)
Target SWG before 1st pregnancy
= (Target weight first bred—current SBW)/
(Target age for 1st pregnancy— current age) (11-8)
Target 1st calving weight
= Mature SBW x 0.82
(11-9)
Target 2nd calving weight
= Mature SBW x 0.92 (11-10)
Target 3rd calving weight
= Mature SBW x 1.00
First pregnant SWG
= (Target 1st calving weight
(11-11)
—Target weight first bred)/280 (11-12)
1st lactation SWG
= (Target 2nd calving weight
— Target 1st calving weight)/ (11-13)
Calving interval
2nd lactation SWG
= (Target 3rd calving weight
—Target 2nd calving weight)/
Calving interval
Where calving interval (CI) is in days.
(11-14)
For all target rates of gain, Equation 11-2 is used to
compute the NEG requirement and Equations 11-3 and
11-4 are used to compute the protein requirement for
growth. Observed weights can be substituted for the previ-
ous target weight and divided by days left to reach the
next target weight to determine SWG required to achieve
the next target weight. The NEG required to reach the
target weight can then be calculated. The target ADG will
be small when the actual weight is close to the target
weight. For pregnant animals, weight gain due to growth
of the gravid uterus should be added to predicted daily
shrunk weight gain (SWG) as follows:
ADGpreg = 665 x (CBW/45) if
DaysPreg ~ 190 (11-15)
OCR for page 239
Growth 239
Where CBW = expected calf birth weight (kg).
For pregnant heifers, weight of fetal and associated uter-
ine tissue and fluids should be subtracted from SEW to
compute growth requirements. The conceptus weight
(COO) can be calculated as follows:
CW= (18 + ((DaysPreg— 190) x 0.6651)
x (CBW/45) (11-16)
When evaluating requirements and rations with the
accompanying computer model, the user must choose
whether to use the target gains predicted by the model
using the system described above or to enter desired rates
of gain (for example, 500g/day) to determine nutrient
requirements. The only difference between these two sys-
tems is the rate of gain used to calculate the requirements;
all the other computations are similar.
Evaluation of Target Weight Equations
The NEG required for growth of replacement heifers
can be calculated from published data (Van Amburgh et
al., 1998a). This study involved 273 Holstein heifers fed
from an average of 77 d of age through the first lactation.
Average mature weight of the herd determined at all stages
of lactation was 641 kg. The weight after weaning (calves
were weaned at 6-8 wk and there was a 3-wk transition
period) was 84 kg, average age at first calving was 687 d,
and calving interval was 431 d. Targets computed with the
model presented are shown in Table 11-2. Average BW
and SWG observed in this experiment compared well with
model predicted values. The SWG before first calving aver-
aged 0.82 kg/d compared to a target of 0.87 kg/d; weight
at first pregnancy was 370 kg vs. the target of 352 kg; the
SWG during first pregnancy averaged 0.63 kg/d vs. a target
of 0.62 kg/d; weight post first calving averaged 533 kg vs.
a target of 526 kg; first lactation SWG averaged 0.136 kg/
d vs. a target of 0.148 kg/d; and the weight after the second
TABLE 11-2 Calculation of Target Weights and Daily
Gain Using the Data Set of Van Amburgh et al. (1998a)
Target
Input variables and calculations of target
641 X 0.55 = 352 kg
= 687 d
687 - 280 = 407 d
Target first pregnant weight, kg
Target first calving age, days
Target age at first pregnancy, days
Target SWG before conception, kg
(352 - 84) / (407 - 77) = 0.87 kg/d
Target weight post-f~rst calving, kg 641 X 0.82 = 526 kg
Target SWG after first conception, kg (526 - 352) / 280 = 0.62 kg/d
Target weight post-second calving, kg 641 X 0.92 = 590 kg
Calving interval, days = 431 d
Target SWG after first calving, kg
Target weight post-third calving, kg 641 X 1 = 641 kg
Target SWG after second calving, kg (641 - 590) / 431 = 0.118 kg/d
(590 - 526) / 431 = 0.148 kg/d
calving was 592 kg (projected from 40 wk of lactation SEW
and SWG) compared to a target of 590 kg.
Using the data from Table 11-2, the target growth rates
and energy and protein requirements are calculated using
the data from Van Amburgh et al. (1998a). This example
outlines the calculations performed by the model.
Recent studies have provided target weights and growth
rates for Holstein heifers (Hoffman, 1997; Kertz et al.,
19981. The target postpartum weight for the Van Amburgh
study (1998a) (526 kg) agrees with the actual weight of
533 kg, and both of these weights are within the ranges
suggested by Hoffman (1997) (515-558 kg). The data of
Kertz et al. (1997, 1998) indicated that postpartum weight
of replacement heifers should be 77 percent of mature
BW, compared to 83 percent in the study of Van Amburgh
et al. (1998a) and the target of 82 percent in this model.
The target weight at conception of 352 kg is within the
range proposed by Hoffman (19971. The target daily gain
before conception in this study (0.87 kg/d), which was set
for animals calving at 22.5 months of age, agrees with the
upper range of 0.84 kg/d suggested by Hoffman (1997) for
animals calving at 24 months of age. The target ADO in
the study by Van Amburgh et al. (1998a) (0.87 kg/d) was
between the standard and accelerated ADO reported by
Lammers et al. (1999) (0.70 and 1.01 kg/d, respectively),
and is within the range suggested by Kertz et al. (1998)
(0.82-0.93 kg/d). Thus, this model appears to give target
weights and growth rates within the ranges suggested by
recent research with Holstein cattle (Table 11-31.
MAINTENANCE REQUIREMENT
EFFECTS ON GROWTH
The growth rate of heifers depends on the net energy
available after maintenance requirements have been met.
Data collected on growth of dairy heifers on farms in Wis-
cousin indicated that environment had a substantial effect
on heifer growth (Hoffman et al., 19941. The National
Research Council (1996) provided a summary of the effects
of environment on maintenance requirements of cattle.
The maintenance model published by the National
Research Council (1996) was adapted by this committee,
with modifications for dairy heifers based on Fox and
Tylutki (19981.
The maintenance requirement for energy was defined
in Nutrient Requirements of Beef Cattle (National Research
Council, 1996) as the intake of feed energy that results in
no net loss or gain of energy from the tissues of the animal's
body. This energy is required for essential metabolic pro-
cesses, body temperature regulation and physical activity.
To predict the amount of feed intake required for these
purposes in diverse situations, the maintenance require-
OCR for page 240
240 Nutrient Requirements of Dairy Cattle
TABLE 11-3 Application of Equations to Predict Energy and Protein Requirements, Using Target Weights and
Daily Gains from Table 11-2 (Van Amburgh et al., 1998a)
Variable
Calculation of requirement
NEG required for target SWG for growth before first conception:
Mean target SBW
EQSBW
EQEBW
EQEBG
NEG required
NEG required for target SWG for heifer growth during first pregnancy:
Mean target SBW
EQSBW
EQEBW
EQEBG
RE (or NEG
required) during
pregnancy
NEG required for target SWG during first lactation:
Mean target SBW
EQSBW
EQEBW
EQEBG
NEG required
NEG required for target SWG during second lactation:
Mean target SBW
EQSBW
EQEBW
EQEBG
NEG required
(352 + 84) / 2 = 218 kg
(478/641) X 218 = 163 kg
163 X 0.891 = 145 kg
0.87 X 0.956 = 0.83 kg/d
0.0635 X 145°75 X 0.83~°97 = 2.16 Mcal/d
(352 + 526) / 2 = 439 kg
(478/641) X 439 = 327 kg
327 X 0.891 = 292 kg
0.956 X 0.62 = 0.59 kg/d
0.0635 X 292°7s X o.59l°97 = 2.51 Mcal/d
(526 + 590) / 2 = 558 kg
(478/641) X 558 = 416 kg
416 X 0.891 = 371 kg
0.956 X 0.148 = 0.141 kg/d
0.0635 X 371°75 X 0.1411°97 = 0.63 Mcal/d
(590 + 641) /2 = 616 kg
(478/641) X 616 = 459 kg
459 X 0.891 = 409 kg
0.956 X 0.118 = 0.113 kg/d
0.0635 X 409°7s X 0.1131°97 = 0.53 Mcal/d
ment must be partitioned into the energy required for basal
metabolism, physical activity, and temperature regulation.
Basal Maintenance Requirement
Fox and Tylutki (1998) defined the maintenance require-
ment for dairy heifers in a thermoneutral environment
with minimal activity as follows:
NEM = (0.086 x SBW075
x COMP) + ad
(11-17)
Where COMP = compensatory effect for previous plane
of nutrition, and ad = maintenance adjustment for previ-
ous temperature effect (Meal/d/kg SBW075).
The coefficient of 0.086 for dairy heifers is based on
calorimetric data (Haaland et al., 1980; 1981) and compara-
tive slaughter studies (Fox and Black, 1984). Approximately
10 percent of this requirement is for activity (Fox and
Tylutki, 1998). Fox and Tyltuki (1998) presented a more
complicated model to account for variation in heat stress.
Adjustment for Previous Temperature
The ad value is used to adjust for the effect of the
previous temperature on metabolic rate. The National
Research Council (1981) concluded that the temperature
to which the animal had been exposed previously (Prev-
Temp) has an effect on the animal's current basal metabolic
rate. A temperature of 20°C is thermoneutral because it
has no effect on basal metabolic rate. The studies of Young
(1975a,b) were used to describe how the NEM requirement
of cattle adapted to a given thermal environment is related
to the previous ambient air temperature.
ad = 0.0007 x (20—PrevTemp) (11-18)
The current temperature (Temp) affects how much
energy is required to respond to the current effects of cold
or heat stress. On average, temperatures move slowly from
one season to the next, but can fluctuate widely from day
to day. To avoid a model that is too sensitive to temperature
effects, we recommend using the average mean daily tem-
perature over the previous month to which the animals
have been exposed as the value for PrevTemp. The recom-
mended input for current temperature is the average daily
temperature for the previous week. To account for local
environmental effects, it is best to measure these tempera-
tures in the animal's environment (barn, outside lot, etc.).
Adjustment for Previous Plane of Nutrition
Recent summaries of the literature (CSIRO, 1990;
National Research Council, 1996) documented the effect
of restricted feeding on fasting heat production. Sheep and
cattle kept in drought conditions averaged 16 percent lower
OCR for page 241
Growth 241
fasting metabolism than those with access to adequate feed
supplies (CSIRO, 19901. These changes in basal metabolic
requirement are due to changes in the activity of ionic
pumps, metabolite cycling, and, most importantly, alter-
ations in the size and metabolic activity of visceral organs
(National Research Council, 1996~. The National Research
Council (1996) concluded that the requirement for metab-
olism of fasted animals was reduced by an average of 20
percent in published studies. Clearly, the extent and dura-
tion of undernutrition, as well as the plane of nutrition
during the period of repletion, affect this average. An
assumption made in the current model is that the BCS
reflects the previous plane of nutrition. A change of 10
percent in the energy requirement for fasting metabolism
is predicted for each increase or decrease in condition
score from the average of 3. For example, animals with a
BCS of 2 and 4 would have a basal metabolic requirements
equal to 90 and 110 percent of the requirements of an
animal with a BCS of 3.
COMP = 0.8 + ((BCS — 1) X 0.05) (11-19)
Adjustment for the Direct Effects of Cold Stress
The following series of equations are used to compute
the energy required to maintain a normal body tempera-
ture during cold stress.
SA = 0.09 x SBW067 (11-20)
HP = (MEI — NEFP) / SA (11-21)
EI = (~7.36 - (0.296
x WINDSPEED)
+ (2.55 X HAIRDEPTH))
x COAT) x 0.8 (11-22)
Where SA = surface area (m2), HP = heat production
(Mcal/m2/d), MEI = metabolizable energy intake (Mcal/d),
NEFP = net energy available for production, Mcal/d, EI
= external insulation value (°C/Mcal/m2/d), WIND-
SPEED = wind speed (kph), HAIRDEPTH = hair depth
(cm), and COAT = adjustment factor for external insula-
tion. COAT is a discrete variable that is used to describe
the insulation value of the coat with a choice of 4 codes;
1 = clean and dry, 2 = some mud on lower body, 3 =
wet and matted, and 4 = covered with wet snow or mud.
When the COAT variable equals 1, no change is made in
the effectiveness of the insulation provided by the coat,
but, when the COAT variable is equal to 2, 3, or 4, the
coat insulation is 0.8, 0.5 or 0.2 times that of the clean,
dry coat.
INS = TI + EI (11-23)
Where I = insulation value (°C/Mcal/m2/d), and TI
tissue (internal) insulation value (0C/Mcal/m2/d) and is
2.5 for newborn calf,
6.5 for 1-mo old calf,
5.1875 + (0.3125 X BCS) for yearlings, and
5.25 + (0.75 X BCS) for adult cattle.
LCT = 39 — (INS x HP x 0.85) (11-24)
MECs = SA x (LCT—Tc) / INS (11-25)
NEMCs = km x MEcs (11-26)
DMI for maintenance = NEM / NEMa (11-27)
Where LCT = animal's lower critical temperature (°C),
MECs = metabolizable energy required for cold stress
(Mcal/d), NEMCs = net energy required for cold stress
(Mcal/d), km = diet NEM/diet ME, NEM = net energy
required for maintenance adjusted for acclimatization and
cold stress, and NEMa = net energy value of diet for mainte-
nance (Meal/kg).
Adjustment for the Direct E~ects of Heat Stress
The NEM requirement increases when temperature
increases above thermoneutral because of the energy cost
of dissipating excess heat (National Research Council,
19961. Because of the diff~culty in accounting for the com-
plex interactions involved in predicting the upper critical
temperature, a panting index (NEM multiplier of 1.07 if an
animal has rapid, shallow breathing or 1.18 if open mouth
panting is evident) is used to adjust for the energy cost to
dissipate excess heat. A more complex model was devel-
oped Fox and Tylutki (1998) to account for the effects of
humidity and temperatures above thermoneutral on the
maintenance requirement.
Model Evaluation
The effects of temperature, relative humidity, wind, and
hair coat condition on maintenance energy requirements
are shown in Table 11-4. The effects of acclimatization are
TABLE 11-4 Multipliers Used to Adjust the
Maintenance Energy Requirement to Reflect Various
Environmental Conditionsab
—1. 1°C —12°C —23°C
Hair Coat Code 1c 3c 1c 3c 1c 3c
Wind velocity (kph)
1.6 1.17 1.41 1.37 1.90
16 1.33 1.70 1.80 2.27 2.26 2.84
1.74 2.39
aTemperature values reflect current temperature (Temp).
bValues given are net energy maintenance requirement (NEM) required for these
conditions divided by the maintenance requirement without stress.
CHair coat code: 1 = dry and clean, 2 = mud on lower body (values not shown),
and 3 = wet and matted.
OCR for page 242
242 Nutrient Requirements of Dairy Cattle
accounted for by using the average temperature for the
previous month for PrevTemp. Current environmental
effects on energy requirements are computed by determin-
ing heat loss relative to heat production, based on current
temperature, internal and external insulation, wind, and
hair coat depth and condition. This calculation becomes
important when the animal is in an environment below
the model's lower critical temperature. No effect is evident
at 20°C, but when the hide is dirty and it is—12°C with
a 16 kph wind, the maintenance requirement is nearly
three times as high as the requirement of a clean animal
in a thermoneutral environment without wind. The mainte-
nance requirement multiplier of 1.17 at —1.1°C with a
clean and dry hair coat reflects the adjustment for acclima-
tization, because in this environment the animals are above
their lower critical temperature. Energy intake also affects
cold stress because increased ME intake results in a larger
heat increment that can be used to alleviate cold stress.
Table 11-5 shows the predicted impact of the environ-
ment on the performance of heifers from 8 weeks to calving
(Fox and Tylutki, 19981. At a thermoneutral temperature
(20°C), the revised model yields the same maintenance
requirement as the National Research Council (1989)
requirements. In Table 11-5, the "northern" environment
category has mean monthly temperatures similar to the
those in the north central and northeastern United States,
while "southwest" reflects mean monthly temperatures
found in the southwestern United States. In situation 1,
the animal's coat is clean and dry, while in situation 2 the
coat is moderately matted. In situation 3, the hair coat is
moderately matted from April through November and the
animal is housed in a lot with 10 cm of mud from November
through March. Situation 4 is the same as situation 1 except
that there is a 16 kph wind. The specific effects of tempera-
ture and hair coat insulation are shown in Table 11-4.
The energy available for growth depended on interactions
among DMI, heat increment, and animal insulation, vari-
ables that were influenced by environmental temperature,
wind, and animal heat production and loss. When environ-
mental stress delayed puberty, age at first calving was
increased. Weight at first calving was decreased if environ-
mental stress occurred after conception.
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Calving age, mo 20.3 21.1 28.5 28.5 25.9 20.7 20.7 22.4 20.7
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CMean monthly temperatures similar to the southwestern region of the United States.
Average daily gain.
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Representative terms from entire chapter:
nutrient requirements
