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 Sarwar
a,*, Mahr-un-Nisa Khan
b,
Muhammad Nawaz Saeed
baDepartmet of Animal Nutrition, Faculty of Animal Husbandry,
University of Agriculture, Faisalabad, Pakistan
bDepartment 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 44 Latin-square 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
82 (1999) 121±130
*Corresponding author.
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 44 Latin-square design within a 22 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
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 H2SO4method.
2.3. Nylon bag experiment
Nylon bags, measuring 1023 cm with an average pore size of 50mm, 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.
2.4. Statistical analysis
Data were analyzed as a 44 Latin-square design within a 22 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 LCMc
ÿN N ÿN z
OMd 95.1 94.7 93.2 90.1
CPe 08.6 12.7 07.1 10.8
NDFf 70.6 73.6 78.3 79.1
ADFg 40.8 43.0 49.4 49.9
ADLh 07.4 08.3 10.9 12.9
aHarvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N). bEarly-cut mottgrass.
cLate-cut mottgrass. dOrganic matter. eCrude protein. fNeutral detergent fibre. gAcid detergent fibre. hAcid detergent lignin.
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 <8% limited DM intake.
3.3. Ruminal characteristics
Results of this study support those of other workers (Adams et al., 1987; Funk et al., 1987; Krysl et al., 1987) who reported decreases in ruminal ammonia with advancing plant maturity (Table 3). However, ruminal ammonia concentrations were >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).
Table 2
Nutrient intake by buffalo bulls fed fertilized and unfertilized mottgrass at varying maturitiesa
ECMb LCMc SE p-valued
ÿN N ÿN N M F MF
Intake, kg/daye
DM 7.5 8.9 6.5 7.8 0.5 0.05 0.03 0.56
OM 7.1 8.4 6.1 7.0 0.4 0.05 0.04 0.49
CP 0.6 1.1 0.5 0.8 0.1 0.02 0.03 0.21
NDF 5.3 6.6 5.1 6.2 0.3 0.21 0.07 0.51
ADF 3.1 3.8 3.2 3.9 0.3 0.29 0.10 0.58
ADL 0.6 0.7 0.7 1.0 0.1 0.05 0.05 0.07
aHarvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N). bEarly-cut mottgrass.
cLate-cut mottgrass.
dEffects were: maturity (M), fertilizer (F) and their interaction (MF).
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 Table 3
Ruminal pH, ammonia and volatile fatty acids (VFA) in buffalo bulls fed fertilized and unfertilized mottgrass at varying maturitiesa
ECMb LCMc SE p-valuesd
ÿN N ÿN N M F MF
3 h
Ruminal pH 6.15 7.22 6.10 7.11 0.3 0.21 0.07 0.29
NH3-N (mg/dl) 17.0 24.0 12.0 18.8 1 0.05 0.04 0.05
Total VFA (mM) 133 132 124 126 0 9 0.05 0.21 0.31
Individual VFA(mol/100 mol)
Acetate 65.5 66.9 59.2 60.0 5 0.05 0.16 0.23
Propionate 23.5 24.1 21.3 22.8 2 0.22 0.35 0.41
Butyrate 3.0 2.9 2.8 2.7 0.1 0.34 0.45 0.56
6 h
Ruminal pH 6.20 7.35 6.9 7.22 0.2 0.31 0.30 0.25
NH3-N (mg/dl) 14.5 20.5 12.0 16.0 1 0.05 0.05 0.11
Total VFA (mM) 131 130 120 125 8 0.04 0.23 0.31
Individual VFA(mol/100 mol)
Acetate 63.9 65.9 58.2 59.1 5 0.05 0.24 0.42
Propionate 22.3 24.8 20.3. 21.3 2 0.41 0.34 0.40
Butyrate 2.5 2.1 2.0 1.9 0.2 0.10 0.17 0.28
9 h
Ruminal pH 6.78 7.0 6.94 6.95 0.3 0.22 0.13 0.35
NH3-N (mg/dl) 11.3 13.3 10.0 11.3 0.8 0.11 0.13 0.41
Total VFA (mM) 132 132 121 127 8 0.04 0.28 0.35
Individual VFA(mol/100 mol)
Acetate 64.8 66.0 59.0 60.9 5 0.05 0.22 0.30
Propionate 23.0 24.2 20.8 22.5 2 0.10 0.41 0.39
Butyrate 3.0 2.8 1.8 2.2 0.3 0.19 0.25 0.34
12 h
Ruminal pH 6.85 6.87 7.17 7.08 0.3 0.19 0.17 0.31
NH3-N (mg/dl) 9.6 9.8 8.9 9.5 0.4 0.21 0.19 0.41
Total VFA (mM) 135 130 123 127 8 0.04 0.12 0.31
Individual VFA(mol/100 mol)
Acetate 63.5 64.8 57.0 58.6 4 0.05 0.21 0.38
Propionate 22.5 24.9 20.7. 21.6 1 0.22 0.34 0.41
Butyrate 2.9 3.1 2.2 2.3 0.2 0.35 0.29 0.48
aHarvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N). bEarly-cut mottgrass.
cLate-cut mottgrass.
dEffects were: maturity (M),fertilizer (F) and their interaction (MF).
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. Late-cut 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 Table 4
Effect of maturity and levels of nitrogen fertilizer on in situ dry matter and neutral detergent fibre digestion kinetics of mottgrassain buffalo bulls
ECMb LCMc SE p-valuesd
ÿN N ÿN N M F MF
Dry matter
Lag (h) 1.0 1.1 3.0 2.8 0.01 0.04 0.61 0.41
Rate (%/h) 5.85 5.90 3.84 4.0 0.1 0.02 0.25 0.31
Extent.(%)
At 48 h 67.7 68.1 58.7 64.1 7 0.05 0.05 0.15
At 96 h 71.8 70.6 60.8 66.0 0 8 0.04 0.81 0.21
Neutral detergent fibre
Lag (h) 1.5 1.3 3.3 3.3 0.02 0.02 0.61 0.11
Rate (%/h) 5.11 5.20 3.71 3.79 0.5 0.05 0.25 0.31
Extent(%)
At 48 h 65.8 64.7 52.7 59.4 8 0.05 0.05 0.05
At 96 h 64.1 64.8 56.1 61.7 8 0.03 0.05 0.41
aHarvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N). bEarly-cut mottgrass.
cLate-cut mottgrass.
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 Table 5
In vivo digestibility of feed components by buffalo bulls fed fertilized and unfertilized mottgrass at varying maturitiesa
ECMb LCMc SE p-valuesd
ÿN N ÿN N M F MF
DMe 54.2 61.5 50.7 48.9 1 0.02 0.11 0.27
OMf 56.6 64.7 53.8 51.2 1 0.03 0.13 0.31
NDFg 59.8 58.4 52.9 51.1 2 0.03 0.17 0.42
ADFh 48.9 51.8 43.9 42.8 1 0.05 0.16 0.39
aHarvested at two maturities (40 and 60 days) and fertilized with 0 (ÿN) or 110.4 kg N/ha (N). bEarly-cut mottgrass.
cLate-cut mottgrass.
dEffects were: maturity (M),fertilizer (F) and their interaction (MF). eDry matter.
fOrganic matter. gNeutral detergent fibre. hAcid detergent fibre.
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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