Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol82.Issue1-2.Nov1999:
Animal Feed Science and Technology
82 (1999) 121±130
Influence of nitrogen fertilization and stage of maturity
of mottgrass (Pennisetum purpureum) on its
composition, dry matter intake, ruminal
characteristics and digestion kinetics in
cannulated buffalo bulls
Muhammad Sarwara,*, Mahr-un-Nisa Khanb,
Muhammad Nawaz Saeedb
a
Departmet of Animal Nutrition, Faculty of Animal Husbandry,
University of Agriculture, Faisalabad, Pakistan
b
Department of Livestock and Dairy Development,
Government of Punjab, Lahore, Pakistan
Received 23 April 1998; received in revised form 7 August 1998; accepted 23 June 1999
Abstract
Four ruminally cannulated buffalo bulls (300 kg) were fed mottgrass diets using a 4 4 Latinsquare design. Treatments consisted of mottgrass fertilized with 0 or 110.4 kg N/ha and harvested at
40 (ECM) and 60 (LCM) days. Fertilization increased the concentrations of crude protein (CP) and
fibre contents. The CP contents of the mottgrass decreased and fibre contents increased with
advancing maturity. Intake of dry matter (DM), organic matter (OM), CP, neutral detergent fibre
(NDF) and acid detergent fibre (ADF) were higher in buffalo bulls fed ECM than those fed LCM.
The concentrations of total ruminal volatile fatty acids (VFA) and acetate were higher in animals
fed ECM than those fed LCM. In situ DM and NDF digestibilities of ECM were higher than those
of LCM. However, DM and NDF digestibilities of ECM remained unaltered by N fertilization. The
rates of DM and NDF disappearance of ECM were faster than those of LCM. However, N
fertilization did not affect the DM and NDF rates of disappearance. In situ lag time of DM and NDF
digestion were shorter for ECM than those for LCM but no effect was noted due to N fertilization.
The digestion extent of DM and NDF at 96 h was affected by maturity. However, N fertilization did
not have any effect. The digestibilities of DM, OM, CP, NDF and ADF were higher in buffalo bulls
fed ECM than those fed LCM. However, the N fertilizer did not affect digestibilities of these
*
Corresponding author.
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 8 7 - 5
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
nutrients. In conclusion, the N fertilization increased the CP concentration of the mottgrass but
could not reverse the ill effect of maturity on the quality of mottgrass. # 1999 Elsevier Science
B.V. All rights reserved.
Keywords: Mottgrass; Digestion; Maturity; Buffalo; Fertilizer
1. Introduction
Poor nutrition as a consequence of nutritionally inadequate forages limits the
productivity of livestock. The rapidly expanding human population may not permit
further allocation of land for growing fodder crops due to the emphasis on production of
grains for human consumption. The challenge lies in developing innovative practices for
enhancing forage quality.
Utilization of forage by ruminants is limited by its neutral detergent fibre content and
nondegradability. Forage neutral detergent fibre can be divided into potentially digestible
and indigestible neutral detergent fibre fractions. Digestion of neutral detergent fibre has
been characterized as a two-stage process, involving a lag time followed by microbial
degradation (Buxton, 1989). Both, lag time and the digestion rate of potentially digestible
neutral detergent fibre determine the rumen residence time needed for digestion of
potentially digestible neutral detergent fibre. The digestion lag is probably related to
hydration rate of neutral detergent fibre and/or time needed for microbial attachment to
the neutral detergent fibre (Buxton, 1989). Digestion rate of potentially digestible neutral
detergent fibre has been related to the intrinsic chemical characteristics of the neutral
detergent fibre as well as the conditions in the rumen (Buxton, 1989).
The stage of maturity and nitrogen fertilization are important agronomic practices that
affect yield and quality of forage (Sarwar et al., 1994). There is no reported information
of the impact of N fertilization of mottgrass on its crude protein (CP) concentration and
digestion kinetics. The objectives of this study were to determine the influence of
nitrogen fertilization and stage of maturity on mottgrass composition, feed consumption,
ruminal characteristics, in situ digestion kinetics and in vivo digestion.
2. Materials and methods
2.1. Animals and diets
Four ruminally cannulated buffalo bulls were used in a 4 4 Latin-square design
within a 2 2 factorial arrangement of treatments. The two factors were early-cut
mottgrass (ECM) and late-cut mottgrass (LCM) hays and two levels (0 or 110.4 kg N
fertilizer/ha) for each stage of forage maturity.
Mottgrass was planted on March 5, 1997, at the Research Station of Livestock
Management Department, University of Agriculture, Faisalabad, Pakistan. The early- and
late-cut mottgrass plots were harvested manually with sickle after 40 and 60 days of the
planting date, respectively. The hays from four plots were sun-cured and the size of each
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
123
plot was 0.25 ha. The mean maximum daily temperature ranges between 105 and 1148F
in May and June. Pakistan extends over a considerable expanse of latitudes (24±378N)
and longitudes 60±758E).
2.2. Feeding and sampling schedule
Animals were housed on a concrete floor in separate pens. Each experimental period
was 15 days in length. The first 10 days were for adaptation to the new feed followed
by five days of sample collection. Feed offered and orts were weighed and recorded twice
daily. Faecal grab samples were taken twice daily such that a sample was obtained
for every 3 h of the 24-h period (8 samples). Acid insoluble ash was used as the
digestibility marker (Van Keulen and Young, 1977). On Day 11, ruminal contents were
sampled (500 ml) at 3, 6, 9 and 12 h after the morning feeding. After mixing of these
samples, 50 ml was retained from each and the remaining 450 ml was returned to the
rumen.
Ruminal pH was measured immediately in the retained sample and it was then
squeezed through four layers of cheese cloth. Thereafter 3 ml of 6 N HCl was added to
terminate fermentation and the samples were frozen. After thawing, these samples were
used to determine ammonia (Chaney and Marbach, 1962) and volatile fatty acids (VFA)
concentrations by gas chromatoghraphy (Firkins et al., 1990). Feed, orts and faecal
samples were dried at 558C and ground through a Wily mill (2 mm screen). These
samples were analyzed for dry matter (DM), N, and organic matter (OM) using method
described by AOAC, (1990), neutral detergent fibre (NDF), acid detergent fibre (ADF),
acid detergent lignin (ADL) by the methods of Van Soest et al. (1991). The ADL was
determined by the H2SO4 method.
2.3. Nylon bag experiment
Nylon bags, measuring 10 23 cm with an average pore size of 50 mm, were used for
determination of rate and extent of NDF and DM disappearance in situ. Incubations were
duplicated with a blank. The two sample bags were used for determination of NDF and
DM digestion and the third as a blank for DM and NDF disappearance.
On Day 12 of each period, the bags containing the same forage treatment were placed
in the rumen of animals being fed that particular treatment after being soaked in warm
(398C) water for 15 min (Anderson et al., 1988) and were exposed to ruminal
fermentation for 1, 2, 4, 6, 10, 16, 24, 36, 48 and 96 h. After removal from the rumen, the
bags were washed in running tap water until the rinse water was clear. These bags were
dried in a forced air oven at 558C for 48 h. After equilibration with air for 48 h, the bags
were weighed and the residues transferred to containers for later analysis.
In situ digestion kinetics parameters, i.e. extent of digestion, rate of digestion and lag
time, were determined for each incubation individually. Degradation rates were
determined by subtracting the indigestible residue, i.e. the 96 h residue, from the amount
in the bag at each time point and then regressing the natural logarithm of that value
against time (Waldo et al., 1972) after correcting for lag (Mertens, 1977). Lag was
calculated according to Mertens and Loften (1980).
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
2.4. Statistical analysis
Data were analyzed as a 4 4 Latin-square design within a 2 2 factorial
arrangement of treatments using the GLM procedure of SAS (1988). The two factors
were maturity and fertilizer. The sum of squares of the model were separated into animal,
period, treatment and the treatment interaction. In case of an interaction, means were
separated by Duncan's multiple range test (Steel and Torrie, 1980).
3. Results and discussion
3.1. Forage composition
Fertilization appeared to result in higher concentrations of CP as well as all fibre
components of the mottgrass. In contrast, advancing maturity appeared to result in lower
concentration of CP and higher concentration of fibre components (Table 1).
3.2. Feed intake
Intakes of DM, OM, CP, NDF and ADF were lower by buffalo bulls when fed the LCM
vs. the ECM (Table 2) and is consistent with the results of Christen et al. (1990), who
reported decreased intake with advancing forage maturity. The increase in fiber level of
mottgrass with advancing maturity may have exerted a physical limitation on the
gastrointestinal tract that reduced voluntary intake (Baile and Forbes, 1974), which is
consistent with the observations of Balch and Campling (1962), who demonstrated that
voluntary intake was inversely related to the fibre content of the forage. Increased forage
maturity has been positively correlated with rumen fill and negatively with DM intake
(Shaver et al., 1988). Intestinal transit time and gastrointestinal mean retention time
Table 1
Chemical composition of fertilized and unfertilized mottgrass at varying maturities (DM basis)a
ECMb
d
OM
CPe
NDFf
ADFg
ADLh
a
LCMc
ÿN
N
ÿN
z
95.1
08.6
70.6
40.8
07.4
94.7
12.7
73.6
43.0
08.3
93.2
07.1
78.3
49.4
10.9
90.1
10.8
79.1
49.9
12.9
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Organic matter.
e
Crude protein.
f
Neutral detergent fibre.
g
Acid detergent fibre.
h
Acid detergent lignin.
b
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 2
Nutrient intake by buffalo bulls fed fertilized and unfertilized mottgrass at varying maturitiesa
ECMb
LCMc
SE
ÿN
N
ÿN
N
7.5
7.1
0.6
5.3
3.1
0.6
8.9
8.4
1.1
6.6
3.8
0.7
6.5
6.1
0.5
5.1
3.2
0.7
7.8
7.0
0.8
6.2
3.9
1.0
p-valued
M
F
MF
0.05
0.05
0.02
0.21
0.29
0.05
0.03
0.04
0.03
0.07
0.10
0.05
0.56
0.49
0.21
0.51
0.58
0.07
e
Intake, kg/day
DM
OM
CP
NDF
ADF
ADL
0.5
0.4
0.1
0.3
0.3
0.1
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
Late-cut mottgrass.
d
Effects were: maturity (M), fertilizer (F) and their interaction (MF).
e
DM, dry matter; OM, organic matter; CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent
fibre; and ADL, acid detergent lignin.
b
c
increased with advancing plant maturity (Park et al., 1994). Forage quality, as estimated
by physiological maturity, affects digesta passage rate from the rumen and subsequent
forage intake (Minson, 1973; Worrell et al., 1986 and Emanuele and Staples, 1988).
Nitrogen fertilization also increased consumption of these nutrients, which is
consistent with Puoli et al. (1991) and Minson (1973), who reported that application of
N fertilizer increased DM intake of pangola digitgrass (Digitaria decumbens) by sheep.
The LCM at zero-level N had low CP concentration (7.1%), suggesting that a CP
concentration of 5 mg/dl
which is considered essential for optimum microbial growth (Satter and Slyter, 1974).
The concentrations of total ruminal VFA and acetate were higher when animals were fed
ECM than those fed LCM. The results of the present study are consistent with those of
other researchers (McCollum and Galyean, 1985; Adams et al., 1987; Krysl et al., 1987)
who reported decreases in total ruminal VFA concentrations with advancing forage
maturity.
3.4. In situ digestion kinetics
Early-cut mottgrass had higher in situ digestibility of DM and NDF than that of LCM
(Table 4). This is consistent with Park et al. (1994) who reported reduced OM
digestibility as forage matured. The ECM might have provided less structural resistance
to bacterial attachment from lignification, resulting in increased bacterial colonization
and digestion of less mature vs. more mature forage (Hastert et al., 1983).
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 3
Ruminal pH, ammonia and volatile fatty acids (VFA) in buffalo bulls fed fertilized and unfertilized mottgrass at
varying maturitiesa
ECMb
3h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
SE
F
MF
0.3
1
09
0.21
0.05
0.05
0.07
0.04
0.21
0.29
0.05
0.31
60.0
22.8
2.7
5
2
0.1
0.05
0.22
0.34
0.16
0.35
0.45
0.23
0.41
0.56
7.22
16.0
125
0.2
1
8
0.31
0.05
0.04
0.30
0.05
0.23
0.25
0.11
0.31
N
ÿN
N
6.15
17.0
133
7.22
24.0
132
6.10
12.0
124
7.11
18.8
126
66.9
24.1
2.9
59.2
21.3
2.8
7.35
20.5
130
6.9
12.0
120
6.20
14.5
131
Individual VFA (mol/100 mol)
Acetate
63.9
Propionate
22.3
Butyrate
2.5
p-valuesd
M
ÿN
Individual VFA (mol/100 mol)
Acetate
65.5
Propionate
23.5
Butyrate
3.0
6h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
LCMc
65.9
24.8
2.1
58.2
20.3.
2.0
59.1
21.3
1.9
5
2
0.2
0.05
0.41
0.10
0.24
0.34
0.17
0.42
0.40
0.28
6.78
11.3
132
7.0
13.3
132
6.94
10.0
121
6.95
11.3
127
0.3
0.8
8
0.22
0.11
0.04
0.13
0.13
0.28
0.35
0.41
0.35
Individual VFA (mol/100 mol)
Acetate
64.8
Propionate
23.0
Butyrate
3.0
66.0
24.2
2.8
59.0
20.8
1.8
60.9
22.5
2.2
5
2
0.3
0.05
0.10
0.19
0.22
0.41
0.25
0.30
0.39
0.34
6.87
9.8
130
7.17
8.9
123
7.08
9.5
127
0.3
0.4
8
0.19
0.21
0.04
0.17
0.19
0.12
0.31
0.41
0.31
64.8
24.9
3.1
57.0
20.7.
2.2
58.6
21.6
2.3
4
1
0.2
0.05
0.22
0.35
0.21
0.34
0.29
0.38
0.41
0.48
9h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
12 h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
6.85
9.6
135
Individual VFA (mol/100 mol)
Acetate
63.5
Propionate
22.5
Butyrate
2.9
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Effects were: maturity (M),fertilizer (F) and their interaction (MF).
b
The increased ruminal degradation of DM and NDF of fertilized LCM in our study is
consistent with Reid et al. (1992) who reported that N fertilization increased NDF
digestibility of switchgrass. This might have resulted from an improvement in the ruminal
environment by supplying deficient nutrients or a readily fermentable cell-wall substrate
for cellulolytic bacteria. Nitrogen fertilization might have used the plant carbohydrates
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 4
Effect of maturity and levels of nitrogen fertilizer on in situ dry matter and neutral detergent fibre digestion
kinetics of mottgrassa in buffalo bulls
ECMb
ÿN
Dry matter
Lag (h)
Rate (%/h)
Extent.(%)
At 48 h
At 96 h
Neutral detergent fibre
Lag (h)
Rate (%/h)
Extent (%)
At 48 h
At 96 h
1.0
5.85
67.7
71.8
1.5
5.11
65.8
64.1
LCMc
N
1.1
5.90
68.1
70.6
1.3
5.20
64.7
64.8
ÿN
3.0
3.84
58.7
60.8
3.3
3.71
52.7
56.1
SE
N
p-valuesd
M
F
MF
2.8
4.0
0.01
0.1
0.04
0.02
0.61
0.25
0.41
0.31
64.1
66.0
7
08
0.05
0.04
0.05
0.81
0.15
0.21
0.02
0.5
0.02
0.05
0.61
0.25
0.11
0.31
8
8
0.05
0.03
0.05
0.05
0.05
0.41
3.3
3.79
59.4
61.7
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Effects were: maturity (M), fertilizer (F) and their interaction (MF).
b
for the formation of new cells, resulting in reduction of thickening of the cell walls. This
type of cells are more exposed to the bacterial degradation in the rumen and, hence, result
in increased digestibility of the plant.
In situ lag time (h) of DM and NDF digestion were shorter for ECM than for LCM
(Table 4), but there was no effect due to N fertilization. Greater reduction in lag time for
the ECM may have resulted from a more readily degraded structural polysaccharide
content in the less mature forage (Bowman et al., 1991).
The rates of DM and NDF disappearance of ECM were faster than those of LCM.
However, N fertilization did not affect the DM and NDF disappearance rates. Similar
results were reported by Bowman et al. (1991) who observed greater rates of NDF
digestion in early-cut orchard grass hay than in late-cut grass hay.
The extents of digestion of DM and NDF at 96 h were greater for the ECM. However,
N fertilization did not have any effect on ECM but the extent was higher in LCM
fertilized with N. The effect of forage maturity on rate and extent of fibre digestion is
probably a reflection of differences in fibre concentration between ECM and LCM. Latecut mottgrass, when fertilized, might have extended the period of plant maturity and,
thus, behaved like early-cut mottgrass during the ruminal digestive processes, indicating
that N fertilization reduced the ill effects of maturity on the forage quality.
3.5. In vivo digestion
Digestibilities of DM, OM, NDF and ADF were higher when the buffalo bulls were fed
ECM, than when they were fed LCM (Table 5). However, N fertilization was without
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 5
In vivo digestibility of feed components by buffalo bulls fed fertilized and unfertilized mottgrass at varying
maturitiesa
ECMb
e
DM
OMf
NDFg
ADFh
LCMc
SE
ÿN
N
ÿN
N
54.2
56.6
59.8
48.9
61.5
64.7
58.4
51.8
50.7
53.8
52.9
43.9
48.9
51.2
51.1
42.8
1
1
2
1
p-valuesd
M
F
MF
0.02
0.03
0.03
0.05
0.11
0.13
0.17
0.16
0.27
0.31
0.42
0.39
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
Late-cut mottgrass.
d
Effects were: maturity (M),fertilizer (F) and their interaction (MF).
e
Dry matter.
f
Organic matter.
g
Neutral detergent fibre.
h
Acid detergent fibre.
b
c
effect. The former effect suggests an effect of grass maturity on the amount of digesta
exiting the rumen. Mature forage, containing high fibre levels that have a larger
proportion of slowly degradable fibre, mechanoreceptor- stimulated capacity has been
shown to increase digesta DM flow to the omasum (Weston and Kennedy, 1984), a
phenomenon that would not occur when forage samples are evaluated in situ (Table 4).
Higher nutrient digestibility by bulls when fed ECM may be due to greater amounts of
nonstructural carbohydrate in the ECM compared to LCM. The ECM has not only
supplied greater amounts of rapidly degradable carbohydrates but also provided higher
ruminal ammonia, resulting in better ruminal fermentation. Other workers (Park et al.,
1994; Barton et al., 1992; Nelson et al., 1989; White, 1983; Adams et al., 1987) also
reported reduced DM and fibre digestibilities as the forage advanced in maturity. Cherney
et al. (1993) reported both, reduction in digestion and reduced rate of digestion with
increasing maturity with the sharpest decline in rate being associated with the highest
concentrations of NDF and lignin of forage. The reduced digestibility of LCM in our
study may be due to the protective role of structural components, especially lignin against
microbial degradation in the rumen. Lignification resulting from plant maturation
depresses digestion of cell walls of hays (Jung, 1989). Some of the phenolic compounds
of the lignin have been demonstrated to inhibit fibre degradation by ruminal microflora in
vitro (Theodorou et al., 1987).
4. Conclusions
Nitrogen fertilization enhanced the concentrations of CP at both maturities, but the CP
content of the mottgrass decreased with advancing maturity which might have reduced
the DM intake by buffalo bulls when fed LCM. The ECM exhibited greater in situ DM
and NDF digestibilities and remained unaltered by N fertilization but were higher in
fertilized LCM vs. unfertilized LCM. The increased ruminal degradation of DM and NDF
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
129
of fertilized LCM might have resulted from an improvement in the ruminal environment
by supplying deficient nutrients or a readily fermentable cell-wall substrate for
cellulolytic bacteria. The rates of DM and NDF disappearance of ECM were faster
and lag time shorter, but no effect was noted due to N fertilization. Greater reduction in
lag time for ECM may have resulted from a more readily degraded structural
polysaccharide content in the less mature forage. The effect of forage maturity on rate
and extent of fibre digestion probably is a reflection of differences in fibre concentration
between ECM and LCM. The N fertilized might have extended the period of maturity.
Thus, the adverse effects of maturity on the forage quality can be minimized to some
extent by N fertilization.
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82 (1999) 121±130
Influence of nitrogen fertilization and stage of maturity
of mottgrass (Pennisetum purpureum) on its
composition, dry matter intake, ruminal
characteristics and digestion kinetics in
cannulated buffalo bulls
Muhammad Sarwara,*, Mahr-un-Nisa Khanb,
Muhammad Nawaz Saeedb
a
Departmet of Animal Nutrition, Faculty of Animal Husbandry,
University of Agriculture, Faisalabad, Pakistan
b
Department of Livestock and Dairy Development,
Government of Punjab, Lahore, Pakistan
Received 23 April 1998; received in revised form 7 August 1998; accepted 23 June 1999
Abstract
Four ruminally cannulated buffalo bulls (300 kg) were fed mottgrass diets using a 4 4 Latinsquare design. Treatments consisted of mottgrass fertilized with 0 or 110.4 kg N/ha and harvested at
40 (ECM) and 60 (LCM) days. Fertilization increased the concentrations of crude protein (CP) and
fibre contents. The CP contents of the mottgrass decreased and fibre contents increased with
advancing maturity. Intake of dry matter (DM), organic matter (OM), CP, neutral detergent fibre
(NDF) and acid detergent fibre (ADF) were higher in buffalo bulls fed ECM than those fed LCM.
The concentrations of total ruminal volatile fatty acids (VFA) and acetate were higher in animals
fed ECM than those fed LCM. In situ DM and NDF digestibilities of ECM were higher than those
of LCM. However, DM and NDF digestibilities of ECM remained unaltered by N fertilization. The
rates of DM and NDF disappearance of ECM were faster than those of LCM. However, N
fertilization did not affect the DM and NDF rates of disappearance. In situ lag time of DM and NDF
digestion were shorter for ECM than those for LCM but no effect was noted due to N fertilization.
The digestion extent of DM and NDF at 96 h was affected by maturity. However, N fertilization did
not have any effect. The digestibilities of DM, OM, CP, NDF and ADF were higher in buffalo bulls
fed ECM than those fed LCM. However, the N fertilizer did not affect digestibilities of these
*
Corresponding author.
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 8 7 - 5
122
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
nutrients. In conclusion, the N fertilization increased the CP concentration of the mottgrass but
could not reverse the ill effect of maturity on the quality of mottgrass. # 1999 Elsevier Science
B.V. All rights reserved.
Keywords: Mottgrass; Digestion; Maturity; Buffalo; Fertilizer
1. Introduction
Poor nutrition as a consequence of nutritionally inadequate forages limits the
productivity of livestock. The rapidly expanding human population may not permit
further allocation of land for growing fodder crops due to the emphasis on production of
grains for human consumption. The challenge lies in developing innovative practices for
enhancing forage quality.
Utilization of forage by ruminants is limited by its neutral detergent fibre content and
nondegradability. Forage neutral detergent fibre can be divided into potentially digestible
and indigestible neutral detergent fibre fractions. Digestion of neutral detergent fibre has
been characterized as a two-stage process, involving a lag time followed by microbial
degradation (Buxton, 1989). Both, lag time and the digestion rate of potentially digestible
neutral detergent fibre determine the rumen residence time needed for digestion of
potentially digestible neutral detergent fibre. The digestion lag is probably related to
hydration rate of neutral detergent fibre and/or time needed for microbial attachment to
the neutral detergent fibre (Buxton, 1989). Digestion rate of potentially digestible neutral
detergent fibre has been related to the intrinsic chemical characteristics of the neutral
detergent fibre as well as the conditions in the rumen (Buxton, 1989).
The stage of maturity and nitrogen fertilization are important agronomic practices that
affect yield and quality of forage (Sarwar et al., 1994). There is no reported information
of the impact of N fertilization of mottgrass on its crude protein (CP) concentration and
digestion kinetics. The objectives of this study were to determine the influence of
nitrogen fertilization and stage of maturity on mottgrass composition, feed consumption,
ruminal characteristics, in situ digestion kinetics and in vivo digestion.
2. Materials and methods
2.1. Animals and diets
Four ruminally cannulated buffalo bulls were used in a 4 4 Latin-square design
within a 2 2 factorial arrangement of treatments. The two factors were early-cut
mottgrass (ECM) and late-cut mottgrass (LCM) hays and two levels (0 or 110.4 kg N
fertilizer/ha) for each stage of forage maturity.
Mottgrass was planted on March 5, 1997, at the Research Station of Livestock
Management Department, University of Agriculture, Faisalabad, Pakistan. The early- and
late-cut mottgrass plots were harvested manually with sickle after 40 and 60 days of the
planting date, respectively. The hays from four plots were sun-cured and the size of each
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
123
plot was 0.25 ha. The mean maximum daily temperature ranges between 105 and 1148F
in May and June. Pakistan extends over a considerable expanse of latitudes (24±378N)
and longitudes 60±758E).
2.2. Feeding and sampling schedule
Animals were housed on a concrete floor in separate pens. Each experimental period
was 15 days in length. The first 10 days were for adaptation to the new feed followed
by five days of sample collection. Feed offered and orts were weighed and recorded twice
daily. Faecal grab samples were taken twice daily such that a sample was obtained
for every 3 h of the 24-h period (8 samples). Acid insoluble ash was used as the
digestibility marker (Van Keulen and Young, 1977). On Day 11, ruminal contents were
sampled (500 ml) at 3, 6, 9 and 12 h after the morning feeding. After mixing of these
samples, 50 ml was retained from each and the remaining 450 ml was returned to the
rumen.
Ruminal pH was measured immediately in the retained sample and it was then
squeezed through four layers of cheese cloth. Thereafter 3 ml of 6 N HCl was added to
terminate fermentation and the samples were frozen. After thawing, these samples were
used to determine ammonia (Chaney and Marbach, 1962) and volatile fatty acids (VFA)
concentrations by gas chromatoghraphy (Firkins et al., 1990). Feed, orts and faecal
samples were dried at 558C and ground through a Wily mill (2 mm screen). These
samples were analyzed for dry matter (DM), N, and organic matter (OM) using method
described by AOAC, (1990), neutral detergent fibre (NDF), acid detergent fibre (ADF),
acid detergent lignin (ADL) by the methods of Van Soest et al. (1991). The ADL was
determined by the H2SO4 method.
2.3. Nylon bag experiment
Nylon bags, measuring 10 23 cm with an average pore size of 50 mm, were used for
determination of rate and extent of NDF and DM disappearance in situ. Incubations were
duplicated with a blank. The two sample bags were used for determination of NDF and
DM digestion and the third as a blank for DM and NDF disappearance.
On Day 12 of each period, the bags containing the same forage treatment were placed
in the rumen of animals being fed that particular treatment after being soaked in warm
(398C) water for 15 min (Anderson et al., 1988) and were exposed to ruminal
fermentation for 1, 2, 4, 6, 10, 16, 24, 36, 48 and 96 h. After removal from the rumen, the
bags were washed in running tap water until the rinse water was clear. These bags were
dried in a forced air oven at 558C for 48 h. After equilibration with air for 48 h, the bags
were weighed and the residues transferred to containers for later analysis.
In situ digestion kinetics parameters, i.e. extent of digestion, rate of digestion and lag
time, were determined for each incubation individually. Degradation rates were
determined by subtracting the indigestible residue, i.e. the 96 h residue, from the amount
in the bag at each time point and then regressing the natural logarithm of that value
against time (Waldo et al., 1972) after correcting for lag (Mertens, 1977). Lag was
calculated according to Mertens and Loften (1980).
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
2.4. Statistical analysis
Data were analyzed as a 4 4 Latin-square design within a 2 2 factorial
arrangement of treatments using the GLM procedure of SAS (1988). The two factors
were maturity and fertilizer. The sum of squares of the model were separated into animal,
period, treatment and the treatment interaction. In case of an interaction, means were
separated by Duncan's multiple range test (Steel and Torrie, 1980).
3. Results and discussion
3.1. Forage composition
Fertilization appeared to result in higher concentrations of CP as well as all fibre
components of the mottgrass. In contrast, advancing maturity appeared to result in lower
concentration of CP and higher concentration of fibre components (Table 1).
3.2. Feed intake
Intakes of DM, OM, CP, NDF and ADF were lower by buffalo bulls when fed the LCM
vs. the ECM (Table 2) and is consistent with the results of Christen et al. (1990), who
reported decreased intake with advancing forage maturity. The increase in fiber level of
mottgrass with advancing maturity may have exerted a physical limitation on the
gastrointestinal tract that reduced voluntary intake (Baile and Forbes, 1974), which is
consistent with the observations of Balch and Campling (1962), who demonstrated that
voluntary intake was inversely related to the fibre content of the forage. Increased forage
maturity has been positively correlated with rumen fill and negatively with DM intake
(Shaver et al., 1988). Intestinal transit time and gastrointestinal mean retention time
Table 1
Chemical composition of fertilized and unfertilized mottgrass at varying maturities (DM basis)a
ECMb
d
OM
CPe
NDFf
ADFg
ADLh
a
LCMc
ÿN
N
ÿN
z
95.1
08.6
70.6
40.8
07.4
94.7
12.7
73.6
43.0
08.3
93.2
07.1
78.3
49.4
10.9
90.1
10.8
79.1
49.9
12.9
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Organic matter.
e
Crude protein.
f
Neutral detergent fibre.
g
Acid detergent fibre.
h
Acid detergent lignin.
b
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 2
Nutrient intake by buffalo bulls fed fertilized and unfertilized mottgrass at varying maturitiesa
ECMb
LCMc
SE
ÿN
N
ÿN
N
7.5
7.1
0.6
5.3
3.1
0.6
8.9
8.4
1.1
6.6
3.8
0.7
6.5
6.1
0.5
5.1
3.2
0.7
7.8
7.0
0.8
6.2
3.9
1.0
p-valued
M
F
MF
0.05
0.05
0.02
0.21
0.29
0.05
0.03
0.04
0.03
0.07
0.10
0.05
0.56
0.49
0.21
0.51
0.58
0.07
e
Intake, kg/day
DM
OM
CP
NDF
ADF
ADL
0.5
0.4
0.1
0.3
0.3
0.1
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
Late-cut mottgrass.
d
Effects were: maturity (M), fertilizer (F) and their interaction (MF).
e
DM, dry matter; OM, organic matter; CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent
fibre; and ADL, acid detergent lignin.
b
c
increased with advancing plant maturity (Park et al., 1994). Forage quality, as estimated
by physiological maturity, affects digesta passage rate from the rumen and subsequent
forage intake (Minson, 1973; Worrell et al., 1986 and Emanuele and Staples, 1988).
Nitrogen fertilization also increased consumption of these nutrients, which is
consistent with Puoli et al. (1991) and Minson (1973), who reported that application of
N fertilizer increased DM intake of pangola digitgrass (Digitaria decumbens) by sheep.
The LCM at zero-level N had low CP concentration (7.1%), suggesting that a CP
concentration of 5 mg/dl
which is considered essential for optimum microbial growth (Satter and Slyter, 1974).
The concentrations of total ruminal VFA and acetate were higher when animals were fed
ECM than those fed LCM. The results of the present study are consistent with those of
other researchers (McCollum and Galyean, 1985; Adams et al., 1987; Krysl et al., 1987)
who reported decreases in total ruminal VFA concentrations with advancing forage
maturity.
3.4. In situ digestion kinetics
Early-cut mottgrass had higher in situ digestibility of DM and NDF than that of LCM
(Table 4). This is consistent with Park et al. (1994) who reported reduced OM
digestibility as forage matured. The ECM might have provided less structural resistance
to bacterial attachment from lignification, resulting in increased bacterial colonization
and digestion of less mature vs. more mature forage (Hastert et al., 1983).
126
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 3
Ruminal pH, ammonia and volatile fatty acids (VFA) in buffalo bulls fed fertilized and unfertilized mottgrass at
varying maturitiesa
ECMb
3h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
SE
F
MF
0.3
1
09
0.21
0.05
0.05
0.07
0.04
0.21
0.29
0.05
0.31
60.0
22.8
2.7
5
2
0.1
0.05
0.22
0.34
0.16
0.35
0.45
0.23
0.41
0.56
7.22
16.0
125
0.2
1
8
0.31
0.05
0.04
0.30
0.05
0.23
0.25
0.11
0.31
N
ÿN
N
6.15
17.0
133
7.22
24.0
132
6.10
12.0
124
7.11
18.8
126
66.9
24.1
2.9
59.2
21.3
2.8
7.35
20.5
130
6.9
12.0
120
6.20
14.5
131
Individual VFA (mol/100 mol)
Acetate
63.9
Propionate
22.3
Butyrate
2.5
p-valuesd
M
ÿN
Individual VFA (mol/100 mol)
Acetate
65.5
Propionate
23.5
Butyrate
3.0
6h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
LCMc
65.9
24.8
2.1
58.2
20.3.
2.0
59.1
21.3
1.9
5
2
0.2
0.05
0.41
0.10
0.24
0.34
0.17
0.42
0.40
0.28
6.78
11.3
132
7.0
13.3
132
6.94
10.0
121
6.95
11.3
127
0.3
0.8
8
0.22
0.11
0.04
0.13
0.13
0.28
0.35
0.41
0.35
Individual VFA (mol/100 mol)
Acetate
64.8
Propionate
23.0
Butyrate
3.0
66.0
24.2
2.8
59.0
20.8
1.8
60.9
22.5
2.2
5
2
0.3
0.05
0.10
0.19
0.22
0.41
0.25
0.30
0.39
0.34
6.87
9.8
130
7.17
8.9
123
7.08
9.5
127
0.3
0.4
8
0.19
0.21
0.04
0.17
0.19
0.12
0.31
0.41
0.31
64.8
24.9
3.1
57.0
20.7.
2.2
58.6
21.6
2.3
4
1
0.2
0.05
0.22
0.35
0.21
0.34
0.29
0.38
0.41
0.48
9h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
12 h
Ruminal pH
NH3-N (mg/dl)
Total VFA (mM)
6.85
9.6
135
Individual VFA (mol/100 mol)
Acetate
63.5
Propionate
22.5
Butyrate
2.9
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Effects were: maturity (M),fertilizer (F) and their interaction (MF).
b
The increased ruminal degradation of DM and NDF of fertilized LCM in our study is
consistent with Reid et al. (1992) who reported that N fertilization increased NDF
digestibility of switchgrass. This might have resulted from an improvement in the ruminal
environment by supplying deficient nutrients or a readily fermentable cell-wall substrate
for cellulolytic bacteria. Nitrogen fertilization might have used the plant carbohydrates
127
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 4
Effect of maturity and levels of nitrogen fertilizer on in situ dry matter and neutral detergent fibre digestion
kinetics of mottgrassa in buffalo bulls
ECMb
ÿN
Dry matter
Lag (h)
Rate (%/h)
Extent.(%)
At 48 h
At 96 h
Neutral detergent fibre
Lag (h)
Rate (%/h)
Extent (%)
At 48 h
At 96 h
1.0
5.85
67.7
71.8
1.5
5.11
65.8
64.1
LCMc
N
1.1
5.90
68.1
70.6
1.3
5.20
64.7
64.8
ÿN
3.0
3.84
58.7
60.8
3.3
3.71
52.7
56.1
SE
N
p-valuesd
M
F
MF
2.8
4.0
0.01
0.1
0.04
0.02
0.61
0.25
0.41
0.31
64.1
66.0
7
08
0.05
0.04
0.05
0.81
0.15
0.21
0.02
0.5
0.02
0.05
0.61
0.25
0.11
0.31
8
8
0.05
0.03
0.05
0.05
0.05
0.41
3.3
3.79
59.4
61.7
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
c
Late-cut mottgrass.
d
Effects were: maturity (M), fertilizer (F) and their interaction (MF).
b
for the formation of new cells, resulting in reduction of thickening of the cell walls. This
type of cells are more exposed to the bacterial degradation in the rumen and, hence, result
in increased digestibility of the plant.
In situ lag time (h) of DM and NDF digestion were shorter for ECM than for LCM
(Table 4), but there was no effect due to N fertilization. Greater reduction in lag time for
the ECM may have resulted from a more readily degraded structural polysaccharide
content in the less mature forage (Bowman et al., 1991).
The rates of DM and NDF disappearance of ECM were faster than those of LCM.
However, N fertilization did not affect the DM and NDF disappearance rates. Similar
results were reported by Bowman et al. (1991) who observed greater rates of NDF
digestion in early-cut orchard grass hay than in late-cut grass hay.
The extents of digestion of DM and NDF at 96 h were greater for the ECM. However,
N fertilization did not have any effect on ECM but the extent was higher in LCM
fertilized with N. The effect of forage maturity on rate and extent of fibre digestion is
probably a reflection of differences in fibre concentration between ECM and LCM. Latecut mottgrass, when fertilized, might have extended the period of plant maturity and,
thus, behaved like early-cut mottgrass during the ruminal digestive processes, indicating
that N fertilization reduced the ill effects of maturity on the forage quality.
3.5. In vivo digestion
Digestibilities of DM, OM, NDF and ADF were higher when the buffalo bulls were fed
ECM, than when they were fed LCM (Table 5). However, N fertilization was without
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M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
Table 5
In vivo digestibility of feed components by buffalo bulls fed fertilized and unfertilized mottgrass at varying
maturitiesa
ECMb
e
DM
OMf
NDFg
ADFh
LCMc
SE
ÿN
N
ÿN
N
54.2
56.6
59.8
48.9
61.5
64.7
58.4
51.8
50.7
53.8
52.9
43.9
48.9
51.2
51.1
42.8
1
1
2
1
p-valuesd
M
F
MF
0.02
0.03
0.03
0.05
0.11
0.13
0.17
0.16
0.27
0.31
0.42
0.39
a
Harvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N).
Early-cut mottgrass.
Late-cut mottgrass.
d
Effects were: maturity (M),fertilizer (F) and their interaction (MF).
e
Dry matter.
f
Organic matter.
g
Neutral detergent fibre.
h
Acid detergent fibre.
b
c
effect. The former effect suggests an effect of grass maturity on the amount of digesta
exiting the rumen. Mature forage, containing high fibre levels that have a larger
proportion of slowly degradable fibre, mechanoreceptor- stimulated capacity has been
shown to increase digesta DM flow to the omasum (Weston and Kennedy, 1984), a
phenomenon that would not occur when forage samples are evaluated in situ (Table 4).
Higher nutrient digestibility by bulls when fed ECM may be due to greater amounts of
nonstructural carbohydrate in the ECM compared to LCM. The ECM has not only
supplied greater amounts of rapidly degradable carbohydrates but also provided higher
ruminal ammonia, resulting in better ruminal fermentation. Other workers (Park et al.,
1994; Barton et al., 1992; Nelson et al., 1989; White, 1983; Adams et al., 1987) also
reported reduced DM and fibre digestibilities as the forage advanced in maturity. Cherney
et al. (1993) reported both, reduction in digestion and reduced rate of digestion with
increasing maturity with the sharpest decline in rate being associated with the highest
concentrations of NDF and lignin of forage. The reduced digestibility of LCM in our
study may be due to the protective role of structural components, especially lignin against
microbial degradation in the rumen. Lignification resulting from plant maturation
depresses digestion of cell walls of hays (Jung, 1989). Some of the phenolic compounds
of the lignin have been demonstrated to inhibit fibre degradation by ruminal microflora in
vitro (Theodorou et al., 1987).
4. Conclusions
Nitrogen fertilization enhanced the concentrations of CP at both maturities, but the CP
content of the mottgrass decreased with advancing maturity which might have reduced
the DM intake by buffalo bulls when fed LCM. The ECM exhibited greater in situ DM
and NDF digestibilities and remained unaltered by N fertilization but were higher in
fertilized LCM vs. unfertilized LCM. The increased ruminal degradation of DM and NDF
M. Sarwar et al. / Animal Feed Science and Technology 82 (1999) 121±130
129
of fertilized LCM might have resulted from an improvement in the ruminal environment
by supplying deficient nutrients or a readily fermentable cell-wall substrate for
cellulolytic bacteria. The rates of DM and NDF disappearance of ECM were faster
and lag time shorter, but no effect was noted due to N fertilization. Greater reduction in
lag time for ECM may have resulted from a more readily degraded structural
polysaccharide content in the less mature forage. The effect of forage maturity on rate
and extent of fibre digestion probably is a reflection of differences in fibre concentration
between ECM and LCM. The N fertilized might have extended the period of maturity.
Thus, the adverse effects of maturity on the forage quality can be minimized to some
extent by N fertilization.
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