Changes in Oxalate and Some Mineral Concentrations of Setaria sphacelata Under Cutting and Uncutting Conditions
W.E. Wan Khadijah
Oxalate concentration in forage plants is important, because it results mineral deficiency in ruminants. Data on oxalate concentration in forage plants in conjunction with cutting and uncutting conditions throughout the growing period are limited. This study was aimed to investigate the changes in oxalate and some mineral concentrations of setaria (Setaria sphacelata). The plants were harvested at different stages (vegetative, boot, pre-flowering, flowering and seed) of maturity and at about 50 cm in length of regrowth (second to sixth cuttings) for evaluation of soluble oxalate, insoluble oxalate and some mineral concentrations. Soluble oxalate and total oxalate concentrations, as well as mineral concentrations, decreased with advancing maturity. Both oxalate concentrations (soluble or insoluble) were higher in leaf compared to stem. Soluble oxalate and total oxalate concentrations of regrowth were the highest at third cutting and lowest at sixth cutting. Insoluble oxalate concentration of regrowth was almost similar in all cuttings, except for the sixth cutting. The highest concentrations of potassium, sodium and magnesium of regrowth were observed at third cutting, while the highest concentration of calcium was observed at sixth cutting. A relationship between oxalate and mineral concentrations was partially observed. Results suggest that cutting materials of setaria from June to October could achieve oxalate levels that are toxic to ruminants.
Received: March 28, 2013;
Accepted: May 06, 2013;
Published: November 26, 2013
Oxalate is an anti-nutritional nutrient in forage plants that affects mineral
utilization in ruminants (De Carvalho et al., 2011).
It can bind with some minerals and form insoluble oxalate, which are not readily
available for ruminants. Evensen and Standal (1984) reported
that tropical plants accumulate more oxalate than temperate plants. Among the
tropical forage plants, setaria (Setaria sphacelata) contains moderate
to high levels of oxalate (Rahman et al., 2013).
Oxalate concentration in forage plants is affected by many internal and external
factors (Rahman and Kawamura, 2011). For example, the
oxalate concentration was much higher in leaves than in stems and this concentration
declined rapidly in both leaf and stem parts with increasing age (Middleton
and Barry, 1978; Rahman et al., 2006). Oxalate
concentrations were also observed higher in autumn and winter seasons compared
to other seasons when plant growth rates were low (Middleton
and Barry, 1978). In contrast, plants grown in early summer showed higher
oxalate concentration when compared to plants grown later in the season (Rahman
et al., 2006). Rahman et al. (2008)
reported that oxalate concentration has relationship with some mineral concentrations
in Napier grass (Pennisetum purpureum), and it varies not only between
forage plants, but also varies according to the soil, water and climatic conditions
where the forage is grown (Rahman and Kawamura, 2011).
Since oxalate concentration varies with advancing season, it is necessary to
investigate the oxalate concentration of setaria throughout the growing period.
The aim of this study was to investigate the changes in oxalate and some mineral
concentrations of setaria (cultivar: Splenda) under cutting and uncutting conditions
in Kyushu, Japan.
MATERIALS AND METHODS
Experimental site and planting management: Plot was established from
the overwintered setaria (cultivar: Splenda) in an Experimental Field of Faculty
of Agriculture, University of Miyazaki, Japan. Climatic conditions during the
plant growth period (May to Nov., 2010) were recorded at the Miyazaki Meteorological
Station (Latitude 31°56.3'N Longitude 131°24.8'E) about 10 km north
from the experimental site. Average temperature and monthly precipitation during
the plant growth period were 19.9°C and 253.8 mm, respectively, with maximum
precipitation (778.5 mm) in June. The mean maximum and minimum temperatures
were 32.1 and 9.1°C, recorded in August and November, respectively. The
soil type of the plot was a sandy soil. At the early stage of plant growth (after
overwinter), the plot received nitrogen (N), phosphorus (P2O5)
and potassium (K2O) (60 kg h-1 of each element) as NPK
compound fertilizer in May 2010.
Treatments and experimental design: To follow the maturity, the plot
was split into subplot for five stages of cutting with five replicates (1) Vegetative
(50 cm in plant length), (2) Boot, (3) Pre-flowering (5-10% flowering), (4)
Flowering and (5) Seed. To follow the botanical fractions, plant at pre-flowering
stage was harvested with five replicates and separated into leaf (leaf blade)
and stem (stem with leaf sheath). To follow the regrowth, plants regrown from
first cutting subplot at vegetative stage were sampled with five replicates
on five occasions (when the plant length was about 50 cm): 28 June, 16 July,
10 Aug., 13 Sept. and 4 Nov. Summary of sampling date and plant length are presented
in Table 1.
Chemical analysis: Approximately 400 g samples for each replication
were dried at 70°C for 48 h. The dried samples were ground in a Wiley mill
through a 1 mm screen.
|| Summary of sampling date and plant length
These samples were analyzed for soluble and total oxalates concentration by
the method of Rahman et al. (2007). Insoluble
oxalate was estimated by subtracting soluble oxalate from total oxalate. Concentrations
of Ca, magnesium (Mg), potassium (K) and sodium (Na) in samples were determined
by flame atomic spectroscopy after wet digestion with nitric acid and hydrogen
peroxide (Laboratory of Agricultural Chemistry the University
of Tokyo, 1978).
Statistical analysis: Data of changes in oxalate and some mineral concentrations
were analyzed using the General Linear Model (GLM) procedure of SPSS (version
12.0, SPSS Inc., Chicago, IL, USA). When the F-test was significant (p<0.05),
Least Significant Difference (LSD) test for comparisons was used to compare
RESULTS AND DISCUSSION
Uncutting condition: The effect of uncutting condition on oxalate and
mineral concentrations in setaria is presented in Table 2.
Soluble oxalate concentration decreased gradually with advancing maturity. It
was the highest (36.2 g kg-1) at vegetative stage and the lowest
(13.1 g kg-1) at the seed stage. Insoluble oxalate concentration
was also affected by maturity, but no trend was observed among the different
stages. Similar to soluble oxalate concentration, insoluble oxalate concentration
was the highest (9.6 g kg-1) at the vegetative stage and the lowest
(1.5 g kg-1) at the seed stage. In most of the cases, the concentrations
of K, Na, Ca and Mg decreased gradually with advancing maturity. Maturity is
usually considered to be the primary factor affecting the chemical composition
and nutritive value of forage. The present findings are in line with the findings
of Middleton and Barry (1978) who observed that the
oxalate concentration of Setaria splendida declined rapidly with increasing
age. Rahman et al. (2009) also observed that
the oxalate concentration declined as the harvest interval increased.
|| Effect of uncutting on oxalate and mineral concentrations
|SEM: Standard error of the mean; ***p<0.001; *p<0.05,
Means in the same row with different superscripts differ significantly at
Much of this decline could be due to a dilution effect caused by higher yield
as the harvest interval increased. In addition, this decline with age would
also be enhanced by an increasing proportion of stem as the proportion of leaf,
as stems contain less oxalate than leaves (Rahman et
Even though oxalate declined with advancing maturity, setaria still maintained
toxic levels of oxalate (more than 30 g kg-1 soluble oxalate) until
the pre-flowering stage. Setaria exhibited a rapid decrease in oxalate and mineral
concentrations during the flowering and seed stages compare to other growth
stages (vegetative, boot or pre-flowering). Setaria also contained low amount
of Ca (1.1-3.7 g kg-1), it is suggested that bioavailability of Ca
from this plant is low due to interactions between nutrients and antinutrients
(especially oxalate) in the feed. Due to the low solubility of Ca oxalate, extremely
little soluble Ca can exist in forages in the presence of oxalic acid. Because
of its low solubility, the Ca in Ca-oxalate is poorly available to the grazing
herbivore, passes through the digestive tract and is excreted in the faeces
(Ward et al., 1979).
Botanical fractions: The effect of botanical fractions on oxalate content
in setaria at pre-flowering stage is shown in Table 3. Leaf
contained higher soluble oxalate (43.1 vs. 17.8 g kg-1), insoluble
oxalate (9.9 vs 0.5 g kg-1) and total oxalate (53.0 vs. 18.3 g kg-1)
compared to stem. This result is in agreement with the findings of Rahman
et al. (2006) who reported that leaf of napiergrass exhibited higher
oxalate concentration than stem. Similar result was also found in kikuyugrass
(Pennisetum clandestinum) (Marais et al.,
Cutting condition: The soluble and total oxalate concentrations of regrowth
were the highest (45.9 and 56.7 g kg-1) at third cutting and the
lowest (30.5 and 37.2 g kg-1) at sixth cutting, respectively (Table
4). The insoluble oxalate concentration of regrowth was almost similar in
all cuttings, except for the sixth cutting. The effect of regrowth on mineral
concentration in setaria is presented in Table 4. The concentrations
of K, Na, Ca and Mg in regrowth plant were affected by cutting. The highest
concentrations of K (43.7 g kg-1), Na (22.6 g kg-1) and
Mg (3.8 g kg-1) of regrowth were observed at third cutting and the
highest concentration of Ca (4.5 g kg-1) of regrowth was observed
at sixth cutting. There are limited data regarding the influence of regrowth
on oxalate concentration, particularly when no significant changes in the leaf:
stem ratio occur. Since leaf contains higher oxalate than stem, oxalate concentration
declines with age due to increasing proportion of stem compared to leaf. Results
of this study showed that oxalate and mineral concentrations of regrowth were
not similar among all the cuttings (cut when the plant was 50 cm in length),
though proportion of leaf and stem was not measured. This change may be associated
with advancing season, because many environmental effects associated with seasonal
change which may alter oxalate levels (e.g., temperature, precipitation, day
length, hours of sunlight, floral induction etc.,) (Rahman
and Kawamura, 2011). Rahman et al. (2006)
reported that oxalate concentration affected by the season with the highest
value being associated with early summer samples and the lowest value with late
Setaria is widely grown for grazing by dairy and beef cattle. In most of the
cases, pastures usually graze when the grass is about 30-50 cm high. In the
present study, all regrowth plants contained more than 30 g kg-1
soluble oxalate when the grass was about 50-60 cm in length and these oxalate
levels can cause toxic to ruminants. Radostits et al.
(2000) reported that acute oxalate poisoning and death have been observed
in cattle eating Setaria sphacelata.
Relationship between oxalate and mineral concentration in plants: Table
5 represents the correlation coefficient between the oxalate and mineral
concentrations in plants. For maturity (first growth), the soluble and total
oxalate concentrations were positively correlated with each type of cation (K,
Na, Ca and Mg) content, while the insoluble oxalate concentrations was positively
correlated with the Na and Ca concentrations.
||Effect of botanical fractions on oxalate concentrations (g
kg-1) at pre-flowering stage
|SEM: Standard error of the mean, ***p<0.001
|| Effect of cutting on oxalate and mineral concentrations (g
|SEM: Standard error of the mean, *p<0.05; **p<0.01;
***p<0.001; Means in the same row with different superscripts differ
|| Correlation coefficients between oxalate and mineral concentrations
under uncutting and cutting conditions
|ns: Not significant (p>0.05), *p<0.05, **p<0.01;
For regrowth (second to sixth cuttings), the soluble and total oxalate concentrations
were positively correlated with the K and Na concentrations, while the insoluble
oxalate concentration was negatively correlated with the Ca concentration. This
result agreed partially with Rahman et al. (2008)
who observed that the soluble oxalate concentration in Napier grass was positively
correlated with K concentration, while the insoluble oxalate concentration was
positively correlated with Ca and Mg concentrations. The results of the present
study suggest that the relationship between oxalate and mineral concentrations
may differ with growth stages of development of plant.
It is concluded that oxalate and mineral concentrations declined gradually
with advancing maturity. With regard to the botanical fractions, oxalate concentration
was higher in leaf compared to stem. Oxalate and mineral concentrations were
also affected by the regrowth plant. A relationship between oxalate and mineral
concentrations was partially observed. All stages of growth (except for flowering
and seed stages) or regrowth of setaria showed more than 30 g kg-1
soluble oxalate, which may be considered harmful for ruminant.
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