Rice husk is the hard protective
covering of grains of rice, its obtained during the processing of paddy rice
into head rice in rice milling industries.
2.4.1 Nutrient Composition of Rice Husk
In
the milling of rice, it has three fractions which are the bran, the hull, and
brown rice. Rice bran has the highest energy and protein content followed by
the brown rice while the rice hull has the lowest (Juliano, 1999b). Rice brown
is the edible fraction. Abrasive
milling to remove the pericarp, seed coat, testa, aleurone layer and embryo to
yield milled rice results in loss of fat, protein, crude fibre and neutral detergent
fibre, riboflavin, ash, thiamine, niacin and
alpha tocopherol (Barber 2008)
2.4.2
Starch Content of Rice Husk
Starch remains the major
constituent of milled rice at about 90 percent of the dry matter – starch is a polymer
of D- glucose linked
α (1-4) and usually consists of a linear
fraction, amylase and a branched fraction amylopectin. Branched points are α
(1-6) linkages.
Through innovative techniques it has
been shown that rice amylose has two to four chains with a number of average
degrees of polymerization (DPN) of 900 to glucose unit and a β-amylolysis limit
of 73 to 87 percent (Hizukuri et al.,
2010). It is a mixture of branched and linear molecules with DPN of 1100 to
1700 and 700 to 900, respectively. The branched fraction constitutes 25 to 50
percent by number and 30 to 60 percent by weight of amylase. The iodine affinity
of rice amylase is 20 to 21 percent by weight.
Rice
amylopectins have β-amylolysis limits of 56 to 59 percent chain length of 19 to
22 glucose units, DPN of 500 to 1500 glucose units and 220 to 700 chains per
molecule (Hizukuri et al., 1989).
The
iodine affinity of rice amylopectin is 0.4 to 0.9 percent in low and
intermediate amylase rice but 2 to 3 percent in high amylase rice. Iso amylase disbranched
amylopectins showed longest chain fractions (DPN >100) (9 to14 percent) in high
amylose sample with higher iodine affinity than in low and intermediate amylose
samples (2 to 5 percent) and waxy amylopectin (0 percent) (Hizukuri et al., 1989).
Juliano (1999), showed that the maximum
true amylose content is 20 percent and also the additional iodine binding is
due to the long linear chains in amylopectin (Takeda et al., 1987).
2.4.3 Protein Content of Rice Husk
Endosperm (milled rice) protein
consists of several fractions comprising of 15 percent albumin and the rest are
alkaline soluble (Juliano, 1985b). Using sequential protein extraction, the
mean ratio for 33 samples was found to be 9 percent prolamin, 7 percent albumin
+ globulin and 84 percent glutelin (Huebner et
al., 1990).
Ogawa
et al., (1987) estimated that
endosperm storage proteins were composed of 60 to 65 percent Pβ-11proteins 20
to 25 percentPβ-1proteins and 10 to 15 percent albumin and globulin in the cytoplasm.
Rice
starch granule amylose binds up to 0.7 percent protein that is mainly the waxy gene
protein or granule- bound starchy synthase with a molecular mass of about 60
kilo daltons (kd) (villereal and
juliano, 1989b)
The
essential amino acid content of rice glutelin and prolamin sub-unit’s showed
lysine as limiting in these polypeptides except in prolamin sub-unit which has
5.5 percent lysine and is limiting in methionine plus cystein.
Thus,
glutelin has a better amino acid score than prolamin except for the 16-kd
prolamin sub-units. The 10-kd prolamin sub-units have high percent cystein content.
2.4.4 Lipid Content
Lipid
content of rice is mainly found in the bran fraction about 20 percent on dry
matter basis, specifically as lipid bodies or spherosome in aleurone layer of
the bran. About 1.5 to 1.7 percent is present in milled rice mainly non-starch lipids
extracted by ether chloroform methanol and cold water saturated butanol
(Juliano and Goddard, 1986). The major fatty acids of this lipid are linoleic
acid, oleic and palmitic acids (Hemayathy and Prabhaker, 1987). The essential
fatty acids in rice oil are about 29 to 42 percent linoleic acid and 0.8 to 1.0
percent linolenic acid (Jaiswal, 1983).
The
content of essential fatty acid may be increased with temperature during grain
development but at the expense of reduction in total oil content (Taira and
Fujii, 1979).
2.5 Multipurpose Trees
Conventional
feed stuff like the concentrates are usually expensive and not readily
available in areas where goats are kept makes it difficult for small – scale farmers
to adopt the suggested practice (Shoo, 1986).
Some multipurpose trees like Gmelina
arborea have been documented as good alternatives feed supplement to
animals (Majgaonka et al., 1987). In
general, it has been seen as a fast – growing hard wood for plantation forestry
and has a dual purpose agro forestry role.
Carew
et al., (1980) reported that sheep
and goats have been traditionally sustained more on browse than on grasses in
the rain forest areas of southern Nigeria, where there are hardly any pasture
lands comparable to those in savannah regions of Northern Nigeria.
Mecha
and Adegbola (1980) studied the chemical composition of many browse plant and grasses
eaten by goats, in Southern Nigeria. They reported that browse tree leaves tend
to have lower crude fibre content than grasses harvested at same time. On the
average, the browse species had more crude protein content even in the rain
season (July-August).
Most
multipurpose plant provides green leaves for longer periods of the year than
grasses. Otsyina and McKell (1985) stated that wide spread traditional use of
browse as an available source of quality feed during the dry season is vitally
important to maintain seasonal and yearly stability in livestock production and
body conditions.
Seria
et al., (1995) described the effect
of supplements on sheep grazing a dry season upland pasture which was part of
an agro forestry system involving Gmelina
arborea.
Gmelina arborea has a high digestibility
(Lowry, 1995) but showed that most of the rumen fermentation occurred very
rapidly in the first 24 hours. Gmelina
arborea is grown at wide spacing in pasture, in the wet – dry tropics. There
would be a substantial dry – season leaf fall with digestibility so high that
it could be regarded as an energy supplement (Wilson, 1990). Gmelina arborea is not nitrogen fixing,
and the canopy is moderately dense, more so in the wet tropics than in
Townville and there is every possibility that its shading would promote shade
tolerant grasses (Lowry, 1995),
Studies
have shown that partial replacement of energy and protein sources from
conventional feeding materials by browse plant leaves neither affect
productivity in terms of growth performance and cost reduction (Amata and
Bratte, 2008, Amata et al., 2009) nor
haematological and serological characteristics (Amata, 2010).
Table:
1 Proximate composition of three browse plant
|
Parameters
|
Dacroydes edulis
|
Gmelina arborea
|
Terminalis captappo
|
|
Moisture content (%DM)
|
69.4
|
74.7
|
74.1
|
|
Ash content (%DM)
|
1.16
|
1.3
|
1.2
|
|
Ether extract(%DM)
|
8.3
|
12.7
|
9.8
|
|
Energy (kcal. kg)
|
1457.0
|
1368
|
1175.0
|
|
Cruds protein (%DM
|
11.9
|
14.6
|
11.7
|
|
Crude fibre (%DM)
|
10.6
|
6.7
|
8.3
|