Research Journal of Agricultural and Environmental Management Vol. 1(1), pp. xxx-xxx, October, 2012
Available online at http://www.apexjournal.org/RJAEM
©2012 Apex Journal
Full Length Research Paper
Influence of phenology on chemical composition and
in-vivo dry matter degradability of Sporobolus
T. Marandure* and E. Masama
Department of Agricultural Management, Faculty of Science and Technology, Zimbabwe Open University, Harare Main
Post Office, 3rd Floor, Cnr Julius Nyerere Way/Nelson Mandela, Harare, Zimbabwe.
Accepted 15 October, 2012
The main objective of this study was to investigate changes in chemical compositions as well as in-vivo
dry matter degradability of Sporobolus pyramidalis with maturity. Samples of Sporobolus pyramidalis
were randomly collected in the main grazing areas of the University of Zimbabwe farm at three different
growth stages (early - 4 weeks, medium - 8 weeks and late maturity stage - 16 weeks). The samples
were air dried and milled through a 2 mm screen using a Hippo mill. The chemical composition of the
samples was then determined by the Proximate Analysis system. 2 g of each sample in triplicate were
packed in nylon bags of 8 x15cm and pore size 40 to 45µm. The samples were then incubated in two
mature Holstein-Friesland steers with a mean weight of 450 kg ± 5 kg and surgically fitted with a rumen
cannula of 8,5cm in diameter. The steers were fed on a basal diet of Katambora Rhodes grass (Chloris
gayana). Incubation was at time intervals of 0 (control), 6, 12, 24, 48, 72, 96 and 120 h. After incubation,
bags were washed under running tap water. The control bags were treated the same way as other
incubated bags to determine the zero time loss of DM. The bags were dried in an oven for 48 h at 60° C.
DM was significantly higher (P < 0.05) at early growth stages, but there was no significant difference in
DM between the medium and late growth stages. EE, Ash, NDF and ADF generally increased
significantly (P < 0.05), while CP decreased significantly (P < 0.05) with maturity. Degradability
characteristics of the early growth stages was significantly higher (P < 0.05) than the medium and late
stages of growth but there was no difference (P > 0.05) in degradability characteristics of the medium
and late stages of maturity. Up to 8 weeks of age Sporobolus pyramidalis contains CP that can meet the
maintenance requirements of cattle and for small ruminants up to 16 weeks. Its maximum in-vivo
degradability is estimated to be at 12 weeks.
Key words: Sporobolus pyramidalis, chemical composition, degradability, in-vivo, phenology.
Sporobolus pyramidalis is described as a densely tufted
perennial grass with tough stems and leaves. It can grow
to an average height of 60 to 90 cm with individual seed
heads of up to 40cm long. Holness (1994) described it as
an aggressive common weed of low palatability that
invades pastures where it out competes other desirable
*Corresponding author. E-mail: firstname.lastname@example.org.
Tel: +263 772 832 640.
pasture grasses thereby reducing rangeland condition
and pastoral productivity. It also dominates areas that
have been heavily trampled by animals, like water points,
as well as disturbed or overgrazed pastures. Sporobolus
species establish themselves quite rapidly by setting
large numbers of seeds throughout the frost-free period
of the year. Seeds are then spread by movement of
animals as well as vehicles and other farm machinery
(Clatworthy, 1991). Although Sporobolus is native to
Africa it has invaded Newzealand and other European
countries through importation of pasture grass species,
particularly Katambora Rhodes grass (Chloris gayana).
Other Sporobolus species include; S. pasmmophilus, S.
indicus, S. eyllsi, S.imiglumis, S. rhodisiensis, S.
stuppens, S. festivus and S. molleri (Holness, 1994).
Besides being a problematic weed, Sporobolus also
has some advantages over other grasses. Sporobolus
species have deeper tufted roots than most grasses and
are able to conserve moisture significantly longer than
other pasture grasses. These species are therefore, said
to have superior persistence, they remain green longer
than other grasses in the dry period where irrigation is not
practiced. Sporobolus species swards are thus, seen as
green islands among dry herbage in the dry season,
thereby, playing a significantly useful role in soil
Control and containment options are available, but the
cost of weed control is high relative to the extra return
from livestock, thus, limiting private investment. Efforts to
completely eradicate Sporobolus species in pastures
have not been successful as it kept reinvading. Among
the methods that were developed for complete
eradication of the grass are; slashing and burning before
the beginning of the rains, using herbicides, ploughing
and replanting star grass
Unfortunately, none of these methods successful
eradicated Sporobolus completely as it kept reinvading.
To maintain the optimum productivity and sustainable
use of the rangeland resources for the future, it is
indispensable to develop ways of optimizing the
knowledge and use of the current rangeland feed
resources. It is therefore, imperative to develop more
knowledge and ways of positively utilizing prominent
rangeland species that are otherwise regarded as
problematic weeds. The objective of this study was,
therefore, to evaluate the chemical composition of
Sporobolus pyramidalis at different stages of growth as
well as to identify the appropriate phenological stage
where it is most highly degradable.
MATERIALS AND METHODS
Sporobolus pyramidalis was obtained from the University
of Zimbabwe farm, which is situated 15km North of
Harare along the Harare - Bindura road. The farm lies in
Natural Region IIb. The area receives mean annual
rainfall of 850 mm. The average annual minimum and
maximum temperatures at the farm are 12.5 ± 2° C and
25 ± 2° C, respectively. Soils found at the farm have
textures ranging from coarse sand to heavy clay. The
natural vegetation at the farm is the Miombo type
woodlands consisting of species including Brachystegia
spiciformis and Julbernadia globiflora.
0.4 ha of the main grazing area of the University of
Zimbabwe farm dominated by Sporobolus pyramidalis
was cultivated in November just before the main rains.
The age of the grass was estimated from the day of
and hand weeding.
about 70% above ground emergency. Harvesting was
randomly done at three different fresh growth stages (4, 8
and 16 weeks). The samples were air dried before being
milled through a 2 mm screen using a Hippo mill. After
milling the samples were placed in clean, sealed plastic
Two mature Holstein-Friesland steers with a mean
weight of 450 ± 5 kg and surgically fitted with a rumen
cannula of 8.5 cm in diameter were used to determine the
in vivo degradability profiles of the forage using the nylon
bag technique. The steers were housed in the Animal
Science bioassay laboratory in the Faculty of Agriculture
at the University of Zimbabwe. They were fed on a basal
diet of Katambora Rhodes grass (Chloris gayana). 2 g of
each sample were weighed in triplicate and placed in
nylon bags of 8 × 15 cm and pore size 40 to 45 µm. The
bags were incubated at different intervals of 0 (control), 6,
12, 24, 48, 72, 96 and 120 h in the rumen of both steers
through the cannula. After incubation, the bags were
washed under running tap water. The control bags were
treated the same way as other incubated bags to
determine the zero time loss of DM. The bags were dried
in an oven for 48 h at 60° C. Disappearance of each
nutrient was calculated using the following formula;
D = Disappearance;
SWa = weight of the original sample and nylon bag;
BW = weight of empty nylon bag;
DMa = dry matter of feed sample;
SWb = weight of the sample and nylon bag after
DMb = dry matter of residue sample.
After rumen incubation the sample residues were
analyzed for DM, CP, EE, Ash, NDF and ADF using the
procedures recommended by the Association of Official
Analytical Chemists (A.O.A.C, 1990). Dry matter
disappearance from nylon bags was analyzed using the
P = a + b (1 - e-ct)
P = the disappearance with time (t) of the potentially
a = a constant that represent the fraction which
disappears rapidly before the earliest removal of the bag
from the rumen
b = a constant representing the slowly degradable
Table 1. Chemical composition (LS±SE) of Sporobolus pyramidalis at different stages of growth.
Stage of maturity DM
Early stage 58.0a±0.78 11.25a±0.43
Medium stage 44.5b±0.78
Late stage 46.0b±0.78
abcWithin column means with the different superscripts significantly differ (P < 0.05).
CP EE ASH NDF ADF
Figure 1. Dry matter disappearance (%) of S. pyramidalis samples collected at different stages of
c = Rate of degradation at time (t)
e = the exponential constant.
To compute parameters (a, b, c) the analysis of variance
using the PROC MIXED procedure of the statistical
analysis system (SAS) (1996) was used. Comparison of
pairs of means was done using the Predicted Different
statistic of SAS (1996). The following model was used for
analysis of the data:
Yijk= µ + Si + Tj + (Si x Tj) + eijk
Yijk = Response variable;
µ = Overall mean common to all observations;
Si = Effect of the ith stage of maturity (i = 1, 2, 3);
Tj = Effect of the jth dry matter degradation during
incubation time (j= 1, 2, 3, 4, 5, 6, 7, 8);
(Si x Tj) = interaction between stage of maturity and dry
matter degradation in-vivo;
eij = Residual error distributed as N (O, I σ2 E).
Dry matter content was significantly higher (P < 0.05) in
the early growth stage but there was no significant
difference (P > 0.05) in dry matter content between the
medium and late stage of growth (Table 1). There was
generally a significant decrease (P < 0.05) in CP content
with maturity, while ether extract, ash, neutral detergent
fibre and acid detergent fibre increased significantly (P <
0.05) with maturity (Table 1).
Stage of growth at harvest of S. pyramidalis and
incubation time (hours) in-vivo affected (P < 0.05) dry
matter disappearance but there was no interaction
between stage of growth and time of incubation in-vivo on
dry matter disappearance (Figure 1). There was a
general increase in dry matter disappearance throughout
the incubation time in-vivo, especially in the first 20 h
Figure 2. Regression mean dry matter disappearance in-vivo of S. pyramidalis at different stages of growth.
were dry matter disappearance was rapid across all
treatments. From 40 h until the end of incubation time,
dry matter disappearance slowed down gradually. There
was no significant difference (P < 0.05) in dry matter
disappearance between samples harvested at the early
stage and medium stage of growth in the first 20 h of
incubation, but both stages had significantly higher (P <
0.05) rates of dry matter disappearance than the samples
harvested at the late growth stage. From 30 h until the
end of incubation time, samples harvested at the early
growth stage had significantly higher (P < 0.05) rates of
dry matter disappearance than the other treatments.
Samples harvested at the medium stage of growth had
significantly higher (P < 0.05) rates of dry matter
disappearance than samples harvested at the late stage
There was a significant (P < 0.05) quadratic
relationship between stage of growth and dry matter
disappearance in-vivo (Figure 2). The regression
equation for stage of growth regressed on mean dry
matter disappearance was
disappearance /wk = -0.391x2 + 9.466x + 10.98, where x
is the dry matter disappearance in-vivo. The R2 value of
the model was 0.98. Maximum degradability of S.
pyramidalis is estimated to be at 12 weeks of age.
mean dry matter
The difference in dry matter content between early
harvested samples and other treatments was probably
due to the fact that during the juvenile stage of growth
there is rapid accumulation of dry matter as most energy
is partitioned towards the vigorous growth that occurs at
this stage. The general decrease in CP with maturity is
supported by Alemayehu (2006) who indicated that range
forage species vary in quality and quantity from time to
time and from place to place. It is during the growth
stages that plants are most nutritious (Alemayehu, 2006).
Similarly the increases in EE, ash, ADF and NDF with
maturity also follows the trends that were recorded by
Theander and Aman (1984) who indicated that as plants
mature, CP, P and the more readily digested
carbohydrates decrease, in contrast, fiber, lignin and
cellulose increase. Once mature (Alemayehu, 2006)
plants are subjected to leaching and dilution of nutrients.
The reduction in the nutritional values, declines in nutrient
composition and leaching are especially serious in the
case of herbaceous plants (Alemayehu, 2006). However,
Van Soest (1994) stipulated that the minimum CP content
that is enough to provide a well balanced supply of amino
acids for rumen microbes as well as the ruminant on
maintenance levels is between 7 to 8%.
The difference in dry matter degradability between the
early and the late stage of maturity could be due to the
fact that in mature Sporobolus there is greater deposition
of lignin and other indigestible secondary cell wall
constituents. According to Mathur (1991) most grasses
and trees leaves in arid environments are low in
nutritional values because of high contents of lignin and
relatively indigestible cellulose and hemicelluloses. These
secondary cell wall components are laid in response to
environmental stress factors such as water shortage or
high temperature. Plants require such substances to
protect themselves from these environmental stressors
(Mathur, 1991). Lignin is also laid as a forage plant’s
response to avoid herbivory.
Increased fibre degradation results in increased volatile
fatty acids (VFA) production leading to greater milk
synthesis from the low quality roughages in dairy cattle
for example (Thomas and Aman, 1984). Increased NDF
disappearance rates are vital in that it leads to faster
rumen fractional outflow rates in livestock and
consequently increased feed intake (Sutton, 1979). This
increased feed intake results in greater availability of
nutrients for maintenance and production requirements
(Thomas and Chamberlain, 1984).
However, there was no literature on degradability of S.
pyramidalis for comparison as to the appropriate
phonological stage of maximum degradability in-vivo.
S. pyramidalis contains CP that can meet the
maintenance requirements of cattle up to 8 weeks of age
and for small ruminants up to 16 weeks. Its maximum in-
vivo degradability is estimated to be at 12 weeks.
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