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Effect
of
Wheat Silage Maturity on Digestion
and Milk Yield in Dairy
Cows
ABSTRACT
The effect of wheat crop maturity on
diet digestibility and lactational perfor-
mance by high yielding dairy cows was
measured in an 8-wk lactation experi-
ment under commercial dairy herd con-
ditions. Friesian cows (n
=
168) were fed
7
kg of DM from either early
or
late cut
wheat silage (harvested at middle flower-
ing or at the end of the milk stage). Each
diet contained
33%
NDF, 18.5 percent-
age units of which was from forage.
Feed intake
(22
kg/d of DM) and DM
digestibility
(63%)
of the two diets were
similar. Dietary NDF digestibility was
higher in the early cut silage
(45.7)
than
in the late cut silage
(41.3%).
Although
DM from the two silages was similarly
degraded in the rumen, degradability of
NDF was
24%
higher in the early cut
silage. Yields of milk and milk energy in
the cows receiving the early cut silage
were higher than those of cows receiving
the late cut silage by
3.2
kg/d and
.85
McaVd, respectively. Apparently, NDF
content is an inaccurate predictor of
energy content of wheat silage.
(Key
words:
fiber quality, wheat silage,
dairy cows)
INTRODUCTION
A
strong positive correlation exists between
feed
intake and milk yield in dairy cows
(26).
Although feed intake can
be
predicted from a
model that assumes a correlation between die-
tary
NDF content and rumen fill
(13),
this
prediction may
be
improved by consideration
Received April 22,
1993.
Accepted August
5,
1993.
IRnanciaJ
assistance to
the
tbt
author
from
the
kraeli
Dairy
Board
is
acknowledged.
1994
J
Dairy
Sci 77:237-243
237
A.
ARIEL11
and
G.
ADIN
Department
of
Animal Science
Faculty
of
Agriculture
The
Hebrew
University
of
Jerusalem
Rehovot
76100,
Israel
of a correction factor for forage quality
(29).
According to Waldo and Jorgensen
(26),
high
quality forage is characterized by high feed
intake, digestibility, and utilization.
A
supply
of high quality forage, which may
be
achieved
by early harvesting
(a),
is particularly impor-
tant for the high yielding cow
(20).
Advancing maturity of forage is associated
with decreasing NDF degradability in
the
ru-
men
(18).
When decrease in fiber quality was
compensated by increasing dietary shelled corn
content, thereby formulating diets that
provided similar dietary NDF, alfalfa forage
maturity had little effect on diet intake and
utilization
(9).
However, regression analysis
suggests that, at constant dietary NDF, ad-
vanced alfalfa maturity adversely affects milk
yield
(IO).
In
diets formulated
to
provide similar con-
centrations of dietary NDF,
an
increase in
NDF degradability, attained by manipulating
the relationship between forage and concen-
trate
ingredients, was associated with higher
yields of milk and milk protein
(14).
Because
during maturation NDF content in most
forages increases
as
degradability decreases,
no information exists on the effect of NDF
degradability on
milk
yield when NDF concen-
tration and source remain constant. In wheat,
NDF
content remains quite constant during the
reproductive maturation process
(27)
because
starch
content, which seems to match the in-
crease
in lignocellulose formation, increases.
The objective of
this
study was to assess the
performance of high yielding dairy cows fed
wheat silage at two stages of maturity.
MATERIALS AND
METHODS
Cow9
Israeli-Friesian cows (n
=
168)
were
as-
signed to two dietary treatments for
2
mo.
Only potentially high yielding cows from a
238
ARlELI
AND
ADIN
commercial herd at Kibbutz Netiv Halamed
Hei were
used.
Cows were evenly assigned
between treatments according to initial milk
yield, lactation number, and DIM and were
kept under similar conditions of space, roof
area, shade, and water supply. The diets con-
tained ensiled wheat forage cut at two stages
of
maturity.
At the beginning of the experi-
ment, milk yield was 31.2 kg of 3.5% FCM
(SE
=
.7)
in cows receiving the early cut silage
(early treatment) and 31.8
kg
(SE
=
.7)
in the
cows receiving the late cut silage
(late
treat-
ment).
Initial
DIM for these treatments were
119 and 129
(SE
=
8),
respectively. Early cut
silage was fed to 59 multiparous and 25
primiparous cows; the late cut silage was fed
to 61 multiparous and 23 primiparous cows.
Some cows were removed from the experimen-
tal
treatments in accordance with routine com-
mercial herd considerations. The number of
cows was held constant; cows were replaced
with cows with comparable yield
traits.
The
number of cows that remained during the en-
tire experimental period included
50
mul-
tiparous and 23 primiparous cows
for
the early
cut silage and
54
multiparous and 20
primiparous cows in the late cut silage. Cows
were milked at 0430, 1230, and 1930 h. Daily
milk yield and composition were recorded ev-
ery 2 wk.
Dieta
Wheat forage of the cultivar ‘Ariel’ was
harvested at two stages of maturity. Forage for
the early cut silage was harvested at a middle
flowering stage after 129 d postemergence and
was wilted to 30% DM. Eleven days later,
forage for the late cut silage was gathered at
the
milk
stage, when DM was 31.5%.
Wheat silage and vetch hay served
as
the
main sources of forage for both diets (Table 1).
Complementary ingredients were calculated
using a least-cost linear program (Gavish,
Giva’t Brenner, Israel) to supply 1.73 Mcal of
NE&g of DM, 16.5% CP with
68
gkg of
ruminally undegraded CP, and 33% NDF with
18.5%
NDF from forage ingredients (Table 2)
and were provided
as
a concentrate mix. Intake
of whey, supplied for ad libitum intake via the
drinking water, was monitored by flow meters.
The diets were offered at
O600
h through a
mixer that automatically recorded data for
loading and unloading. Daily consumption by
each treatment was summarized.
Orts
from
each treatment, which usually were
4%
of the
diet offered, were also
recorded
every morn-
ing. Once a week, the diets and
orts
from each
treatment were sampled for DM, CP, and fiber
fraction analyses, and the data were used to
calculate net DMI and dietary nutrient content.
During wk
0,
4,
and
8,
cows were scored
for body condition by the same trained
in-
dividual using a scoring system described else-
where
[@);
1
=
extremely thin to
5
=
ex-
tremely fat].
Digestibility
Trial
Feed intake and diet digestibility were
measured using a two-marker method in 10
TABLE
1.
Dietary ingredients.
WlY Late
treatment
treatment
Wheat
silage
(early)
Wheat
silage
(lac)
Vetch hay
BlWd
Whole
cottonseed
Sorghum
grain
Barley
grain
corn
grain
Tapioca
Rye
Corn
gluten
meal
pcathcr
meal
soybean
mtal
cottonseed
meal
Rapesaed
meal
Wheat
bran
Wheat
middling
Hydrolized vegetable oil
Rotemd
fat
NaCl
Calcium
salt
Vitamin
mix1
Minerals2
UW
Soy
hulis
Total
-
(96
of
DM)
-
30.5
1
3.45
7.71
8.25
9.17
2.37
6.84
.68
4.33
3.15
2.42
.68
3.83
.so
1.96
4.79
4.79
.4
1
.46
.27
.82
.18
1.19
1
.os
.I8
...
100.0
...
33.17
3.06
7.65
8.21
9.52
2.41
7.26
.54
2.09
1.72
2.45
.68
3.86
1.18
2.00
4.86
4.90
.36
36
.32
.91
.18
.73
1.09
...
100.0
‘Daily vitamin intake:
18000
IU
of
vitamin
A,
36,000
IU
of
vitamin
D,
and
217
ILJ
of
vitamin
E.
2Daily
mineral
intake:
2.5
mg
of
Se,
.435
g
of
Mn,
.425
g
of
Zn,
.ll
g
of
CU.
.212
g
of
Fe,
.005
g
of
I,
and
.OU2
mg
of
Co.
WHEAT
SILAGE
MATURITY
AND
MILK
YIELD
239
TABLE
2.
Chcmical
composition.
DM
OM
CP
NDF
ADF
NEL
(%
of
DM)
(Mcavkg)
Early
silage 30.1 91.8 6.5 53.7 35.7 1.49l
Late silage 37.9 93.4 6.4 53.0 35.5 1.49'
Vetch
hay
88.6 91.8 16.0
50.0
34.1 1.30
Whole
cottonseed
92.0 85.0 21.7 48.1 34.4 2.07
Bread
82.8 85.0 14.7 2.7
0
1.75
5.0 93.0 14.0
0
0
1.88
Concentrate
(early)
88.0 93.0 23.5 23.6
7.7
1
.85
Concentrate
(late)
88.5 93.0 25.3 24.5 8.7 1.88
calculated
according
to
Conrad
et
al.
(6).
multiparous cows per treatment on
30
d of the
experimental period. Each cow received 32 g
of Cr-mordanted marker (1.7 g of
Cr)
orally
(23)
for 10 consecutive d after the morning
milking. Fecal grab samples were taken during
the last
3
d of marker feeding
three
times per
24-h cycle. Samples were stored and later ana-
lyzed for Cr and indigestible NDF (12).
In
those 20 cows, rumen fluid also was sampled
by stomach tube during the last week of the
experimental
period
3
h after the morning
feeding and frozen immediately for further
analysis.
For in situ incubations of silage,
TMR,
and
feces, polyester bags were suspended in the
rumen of
two
rumen-cannulated
dairy
cows,
which were in midlactation and were main-
tained on a concentrate diet
(34%
NDF). One
cow
served
for the determination of silage
degradability and the other to determine die-
tary
and fecal indigestible NDF content during
the digestibility
trial.
Dry
milled samples
(5
g)
of the two silages were weighed into 12-
x
6-cm
polyester bags with 45-p mean pore size.
Bags in four replicates were introduced
serially
into the rumen and retained for 96,48, 36,
24,
12,
9,
6,
or
3
h. Disappearance at 0-h incuba-
tion was evaluated
by
immersion of bags in
water at 39°C for
1
h. The rumen-incubated
polyester bags were removed together and im-
mediately
Msed
with cold tap water. Amounts
of residual organic and nitrogenous matter,
NDF, and ADF were
measured
after
the bags
were dried for 48 h at 60°C.
A similar protocol was
used
to determine
TMR
and feces concentrations of indigestible
NDF after 192 h of incubation.
Kinetics of the degradation of OM, nitroge-
nous matter, and fiber fractions in the rumen
were determined
as
described by ehskov and
McDonald (17). Data were fitted to the ex-
ponential equation P
=
A
+
B
(1
-
ea), where
P
=
degradation after
t
hours, and
A,
B,
and
C
were calculated for each feedstuff by an itera-
tive minimal least squares program using the
Marquardt algorithm. The effective degradabil-
ities
(D)
of OM, CP, and fiber fractions
in
the
rumen were calculated
as
D
=
A
+
[(BC)/(C
+
k)], assuming that the rate of particulate out-
flow from the rumen,
k,
is
4%h.
In
vitro DM digestibility was assessed for
the two silages
as
described by Tilley and
Terry
(2).
Analy8es
Chemical analyses were performed
on
dry
1-mm milled samples. The DM was assayed
after drying
at
105'C for 12
h
except
in
silages, which were
dried
at 6O'C for
48
h. The
OM
was determined after ashing at 600'C for
2 h. The CP was analyzed by using a Kjeldahl
(Tecator, Hoganiis, Sweden) autoanalyzer. Fi-
ber components (NDF and
AD-
were deter-
mined according
to
the method of Goering and
Van Soest
(7).
Chromium
in
dried, blended
feed and in feces samples was determined
following acid digestion by atomic absorption
spectrophotometry. The
VFA
in centrifuged
rumen fluid were assessed by gas chromatogra-
phy on .15 Carbowax 20M (Applied Science
Laboratories Inc., State College,
PA),
and
NH3
N
was determined by the phenol procedure
(4).
Journal
of
Science Vol. 77,
No.
1,
1994
240
ARIEL1
AND
ADIN
TABLE 3. Fitted exponential constants1 for the degradability and the effective degradability
of
nutrients
in
the
two
silages.
DM
OM
CP
NDF
ADF
1.22
MY
A%
28.23 26.58 69.21
0
B,
%
49.65 53.25 9.84 82.01 77.45
c,
nl
.029
,028
,207
.022
.024
D,
%
43.7 42.7 76.7 29.4 30.2
r*
.99
.99 .93 .99 .99
4%
31.62 31.70 69.84 3.4
5.3
Late
B, 42.16 44.20 7.53 85.15 72.21
c.
/h
.023 ,022 ,373 .013 .016
D,
%
42.8 42.1 76.1 23.7 26.5
9
.99
.90
.89 .99 .98
~ ~
1A.B.C
=
Fitted
exponential constants
for
nutrient degradability;
D
=
effective degradability
of
nutrient
at
a
rumen
outflow rate
of
4%h.
Statistical
Analyses
Analysis of variance
was
used
to examine
differences
between
diets in milk yield and
yield traits using
ANOVA
of the general linear
models procedure
(19).
Because of a significant
interaction between yield and number of
calv-
ings, cows were grouped by
parity.
In
primiparous cows, analysis of yield
used
DIM
and initial yield
as
covariates;
in
multiparous
cows, yield during the previous lactation
also
was considered.
Digestibility and intake means were ana-
lyzed for significance by Student’s
t
test. Sig-
nificance was declared at
P
<
.05
unless other-
wise indicated.
RESULTS
Predicted parameters of rumen degradation
of nutrients in the two silages and their effec-
tive degradabilities are presented in Table
3.
The high coefficient
of
determination
(.89
to
.99;
P
<
.001)
for rumen degradation of DM,
OM, CP, NDF, and ADF in both silages agrees
with the exponential model
(17).
Although
DM, OM, and CP in the two silages were
similarly degraded in the rumen, degradabili-
ties
of
NDF
and
ADF
were
24
and
14%
higher, respectively, in the early cut silage.
In vitro digestibility
of
DM also was similar
in the early cut
(60.9%)
and late cut
(58.1%)
silages. Average feed intakes of the two treat-
ments, based on the double marker approach
(23.5
kg/d of DM,
SE
=
1.4,
and
23.1
kg/d
of
DM,
SE
=
1.8,
for the early and late treat-
ments, respectively) agree well with the overall
average feed intake,
21.9
kg/d of DM and
22.0
kg/d of DM in these cows, respectively. Ap-
parent digestibilities
of
DM, OM, and CP were
similar
(64.2
VS.
62.7%,
SE
=
.8; 65.5
VS.
63.8%,
SE
=
.8; 62.8
VS.
62.3%,
SE
1.3,
respectively) in the two treatments. However,
NDF digestibility for the early treatment
(45.7%,
SE
1.4)
was higher than that for the
late treatment
(41.3%.
SE
=
.8).
Milk yield for the early treatment cows was
higher
(P
<
.001)
than that of the late treatment
cows by
2.5, 3.7,
and
3.2
kg/d in primiparous
cows, multiparous cows, and all cows, respec-
tively (Table
4).
Milk fat percentage was
higher
(P
<
.001)
in the late treatment, but milk
fat yield
was
similar between treatments. Milk
protein percentage
was
similar between treat-
ments, but
milk
protein yield was higher
(P
<
.001)
in
early treatment cows by
.07,
.lo,
and
.09
kg/d in primiparous cows, multiparous
cows, and all cows, respectively. Lactose yield
also was higher
(P
<
.001)
in the early treat-
ment cows by
.13, .16,
and
.14
kg/d in
primiparous cows, multiparous cows, and all
cows, respectively.
Body scores at wk
0,
4,
and
8
in early
treatment cows were
2.19,
SE
.06;
2.48,
SE
.04;
and
2.61,
SE
.07
(n
=
80).
respectively,
and were similar
(P
>
.05)
to the corresponding
values for late treatment cows:
2.34,
SE
.06;
2.54,
SE
.04;
and
2.60,
SE
.04
(n
=
81).
Journal
of
Dairy
Science
Vol.
77.
No.
1,
1994
WHEAT
SILAGE
MATURITY
AND
MILK
YIELD
24
1
**
** **
**
+it
+*
*it
**
*+
**
** **
I+
*+
+it
**
**
**
However, the increases in body condition
scores during the 8-wk period differed between
treatments. Body condition scores in
primiparous cows increased by
SO
(n
=
25)
for
early treatment and by
.27
(SE
.06,
n
=
22)
in
late treatment cows. In multiparous cows, the
increase in body score condition was
.38
(SE
.07,
n
=
55)
for
early and
.25
(SE
.05,
n
=
59)
for late treatment cows. Averaged over the
total number
of
cows, body condition score
gain was
.42
(SE
.04,
n
=
80)
for early and
.26
(SE
.04,
n
=
81)
in late treatment cows.
Concentration of total VFA, pH, and NH3
N
in the rumen were similar between treat-
ments (Table
5).
However, the acetate concen-
tration and acetate:propionate ratio were
25
and
39%
lower, respectively, in the early treat-
ment than in
the
late treatment cows. In addi-
tion, valerate and caproate concentrations were
85
and
40%
lower, respectively, in
the
cows
receiving the early cut silage.
DISCUSSION
The main objective of this study was
to
explore the performance of high yielding dairy
cows fed wheat silage at two different stages
of maturity. Wheat is an unusual forage in that
NDF content in
the
total plant remains
virtu-
ally constant
as
the
reproductive phase ad-
vances
(27).
This
phenomenon, caused by the
matching of starch accumulation with lignocel-
lulose formation, does not
occur
in other com-
mon forages, such as grass silage
(3)
or mixed
grass-legume silage
(3,
in which NDF content
increases with advancing maturity. However,
these plants
do
not have the starch component
that exists in
the
whole wheat plant.
In
the early treatment cows, in vivo NDF
degradability
(46%)
was
5
percentage points
higher
than
that of the late treatment cows.
Likewise, in situ rumen NDF degradability
(29%)
was
6
percentage points higher for the
early cut silage. In situ silage NDF degradabil-
ities
were
64
and
57%
of dietary in vivo NDF
digestion in the early cut and late cut silages,
respectively. Because wheat silage contributed
about
50%
of
the
dietary NDF in each treat-
ment,
the
difference between in vivo and in
situ NDF digestion might be explained by
assuming that NDF is only digested in the
rumen and that NDF digestibility
of
the dietary
components other than silage was about
65%.
Journal
of
Dairy
Science
Vol.
77,
No.
1,
1994
WHEAT SILAGE MATURITY AND MILK YIELD
241
However, the increases in body condition
scores during the 8-wk period differed between
treabnents. Body condition scores in
primiparous cows increased by .50
(n
=25) for
early treabnent and by .27 (SE .06, n=22) in
late treabnent cows. In multiparous cows, the
increase in body score condition was .38 (SE
.07, n=55) for early and .25 (SE .05, n=
59)
for late treabnent cows. Averaged over the
total number
of
cows, body condition score
gain was .42 (SE .04, n=
80)
for early and .26
(SE .04, n=
81)
in late treabnent cows.
Concentration
of
total VFA, pH, and
NH3
Nin the rumen were similar between treat-
ments (Table 5). However, the acetate concen-
tration and acetate:propionate ratio were 25
and 39% lower, respectively, in the early treat-
ment than in the late treatment cows. In addi-
tion, valerate and caproate concentrations were
85 and 40% lower, respectively, in the cows
receiving the early cut silage.
DISCUSSION
The main objective
of
this study was to
explore the performance
of
high yielding dairy
cows fed wheat silage at two different stages
of
maturity. Wheat is an unusual forage in that
NDF content in the total plant remains virtu-
ally constant as the reproductive phase ad-
vances (27). This phenomenon, caused by the
matching
of
starch accumulation with lignocel-
lulose formation, does not occur in other com-
mon forages, such as grass silage
(3)
or mixed
grass-legume silage (5), in which NDF content
increases with advancing maturity. However,
these plants do not have the starch component
that exists in the whole wheat plant.
In
the early treatment cows, in vivo NDF
degradability (46%) was 5percentage points
higher than that
of
the late treabnent cows.
Likewise, in situ rumen NDF degradability
(29%) was 6percentage points higher for the
early cut silage. In situ silage NDF degradabil-
ities were
64
and 57%
of
dietary in vivo NDF
digestion in the early cut and late cut silages,
respectively. Because wheat silage contributed
about 50%
of
the dietary NDF in each treat-
ment, the difference between in vivo and in
situ NDF digestion might be explained by
assuming that NDF is only digested in the
rumen and that NDF digestibility
of
the dietary
components other than silage was about 65%.
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Journal
of
Dairy Science
Vol.
77,
No.
I, 1994
242
ARIEL1
AND
ADIN
TABLE
5.
Effect
of
wheat
silage
maturity
on WA. pH, and
NH3
in
cumen
fluid.
&lY
Late
SE
Acetate
(A),
mmoUmol 472b
5888
26
Propionate
(P),
mmoUrnol
306'
223b
18
Butyrate,
mmoYmol
150
143
11
Valerate,
mmOYmo1
41.
21b
5
Caproate.
mmoVmol
11'
7b 2
Total VFA,
mmoVL
64.0 67.8
6.8
A:P
1.54b 2.648 .21
PH
6.22 6.34
.ll
NH3.
mg
of
N/dl
10.9 8.9
1.5
B.bMeans
with
no
common
superscripts differ
(p
<
.05).
Furthermore, in concentrate diets such
as
those
used
in
the current study, hindgut degradation
of fiber may account for up
to
25%
of
that
occurring in the whole digestive tract (l),
which may partially explain the difference
be-
tween total in vivo and in situ
NDF
digestibili-
ties.
A
decrease
in
NDF
degradability with
maturity has been shown (18) for a few
types
of
forage.
This
process apparently is related
to
cell-wall lignification, leading to a reduction in
substrate susceptibility to microbial degrada-
tion (21).
The fermentation of wheat in the rumen can
be described by two time-dependent
peaks
(2);
the higher propionate production in early
treat-
ment cows suggests that maturation affects the
fermentation pattern at its first
peak,
which
corresponds to digestion of the nonstructural
carbohydrate fraction. Although
the
lower
acetate:propionate ratio in the rumen of early
treatment cows could
be
related to difference
in concentrate composition, it agrees with
the
effect of maturity on the supply of less easily
fermentable substrates and, therefore, on the
type of fermentation (16).
In
addition, wheat
plant maturity could influence rumen fermen-
tation via its effect on mastication and saliva-
tion
(30).
The lower milk fat percentage
of
early treatment cows (Table
5)
is compatible
with lower acetate
in
the rumen.
The higher milk yield and concomitant
in-
creme in body condition score
may
indicate
higher NEL content in the early treatment diet.
The difference in
milk
constituent yields
im-
plies a difference of .85 McaYd of
NEL
be-
tween treatments, which is equivalent to .12
McaVkg of silage
DM.
This
difference might
account for
5
points of the
TDN
gap between
Ioumal
of
Dairy
Science Vol.
77.
No.
1,
1994
the two silages (15). The variance of
1.5
per-
centage points in the digestibility of dietary
DM
measured in vivo
also
corresponds to
a
5-point difference in TDNkg of
DM
between
the two silages, although the difference seems
to have
been
too small to detect
in
our
experi-
ment.
Our
study agrees with earlier studies (14,
25)
using diets containing similar
NDF
percen-
tages,
in
which
an
increase in fermentable
NDF
was associated with similar feed intake
but higher
milk
energy output.
A
reduction in
milk yield with forage maturity, corresponding.
to that of dietary
NDF,
has
been
shown re-
cently (10). However, our study differs in an
important respect; in the former studies, con-
trol over fiber degradability was achieved by
formulation of diets to include different fiber
sources,
but we studied the effect of fiber
degradability while keeping nearly constant the
content of whole dietary
NDF
and the
NDF
contributed by forage.
Based
on regression analyses of different
forage types,
NDF
content may indicate energy
content in forage, thereby providing a possible
method of formulating dairy diets
(8,
13).
Numerous attempts have been made to relate
feedstuff digestibility
to
fiber characteristics,
but the precision of these methods
is
limited
(24).
Our
results, which suggest that
NDF
con-
tent alone is an inaccurate predictor of energy
content in wheat silage, agree with the finding
of Harlan et al.
(8)
that grasses had low corre-
lation coefficients for
NDF
or
ADF
versus
"EL.
Whether a measure of
NDF
degradability
could improve predictions of quality for wheat
forage
as
well
as
that of other grasses is still
unknown
.
The increase in forage quality was
as-
sociated with a gain in net income. Although
WHEAT SILAGE
MATURITY
AND
MILK YIELD
243
DM
production per hectare from the early cut
silage
was
30%
less than that of the late cut
silage, leading to a more expensive diet by
about
$.20
(US),
the value of the additional
milk yield
as
a
consequence of the early cut
silage
was
twice that of the initial loss. There-
fore, a prediction
of
the
NDF
degradability of
forage is economically important. Currently,
preharvesting
NDF
content in crops can
be
evaluated by the near infrared absorbance
method
(11).
Optimal harvesting date could
be
determined more accurately
if
the measure-
ment were to
be
calibrated according to
fiber
degradability characteristics. Such information
is even more valuable for high yielding cows
(20).
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Journal of
Dairy
Science Vol. 77, No. 1, 1994