THIS IS A LITERATURE REVIEW
1.1
SNAIL PRODUCTION
IN NIGERIA
Archachatina marginata
swaison (African Giant Siam) is one of the important minor forest products
which is endemic in tropical West African (Swaninson, 1991). It is restricted to
areas like Benin republic in West Africa (Bequeert, 1950 and Moad, 1950). Omole
(2000) asserted that archachatina margniata is the largest snail in Africa.
Literature
review on the body weight of snails has remained inconsistent (Ebenebe
et al., 2011). Omole, (2002)
reported a body weight gain of 0.41g.day. Hamzet et al (2005) reported a mean daily weight gain of 1.16g while Ejidike
(2000) reported 0.50g in a six months study period.
The
inconsistency agrees with Stievenart (1992) that prove that variation in body weight
on snails are related to the hydration stage, stoutness and shall the heaviness
live thickness of calcium deposit during the process of shell calcification.
Archachatina
marginata is economically important because the species is in high demand as a
protein source in many West Africa countries including Nigeria (Ajayi et al., 1978), where the meat is a
luxury food.
Despite
the importance of the species, archachatina marginata is not cultivated on a
commercial level and as a result of human-related problems like deforestation
and its collection for food and its long pre-reproduction life and low fecundity
(Ajaysi et al., 1978 and Egonmwan,
2004), the natural population in the wild is dwindling.
However, in recent years, the commercial
potential of the species being
investigated by many amateur snail farmers and more attention
is being paid to farming of the giant snail as
opposed to exploitation of the wild
population. In Nigeria, snails have been raised in small pens in many
areas either as backyard activity to supplement house hold income and protein
supply or as large scale commercial activity.
2.2 NUTRIENT REQUIREMENT OF SNAILS
Snails like
other animals need the basic nutrients (energy, protein, fats, amino-acid,
vitamins and mineral for optimum functioning of metabolic chemical reactions
involved in growth maintenance, shell formation, production and reproduction
(Imevbore and Ademosun, 1988). The choice of feeding materials are based on
available information that snails are vegetarians (FAO, 1986 and Philips, 1992)
to the extent to which each of the feeding materials can influence the growth
rate of snails. Snails’ requirements for calcium, phosphorus, potassium and
magnesium are relatively high compared to other animals. These minerals
determine the rate of shell secretion by the mantle and for the rapid development
of shell (Imevbore and Ademosun, 1988). Vitamins can not be synthesized by
snails so must be provided in the diets (Imevbore and Ademosun, 1988)
2.2.1
Crude Protein
Snails require
crude protein like other speices of animals for growth and production.
According to Ejidike (2001) snails, require crude protein leaves of 20-25% for
optimal growth.
2.2.2
Energy Requirement
Metabolisable
energy requirement for maintenance of animals is affected by ambient
temperature (Balnave and Farrel, 1978), snail should therefore eat more high
energy ration.
2.3
POTENTIALS OF SNAILS AS AN ANIMAL
PROTEIN
The potential of
snails as an animal protein source has been emphasized by many authors
(Nigbert, 1974; Jennifer, 1975; Datin, 1992; Hamzat et al., 2005; Adetono, 2000; Awah, 2000; Ejidike 2001; Omole, 2002).
Snails have been
reported to be rich in protein, 12-18% on wet basis (Awah, 2000) and 52- 53% on
dry matter basis (Barcelo, 1981). Snail meat is also low in fat and it is
reported to have some medical properties (Aweh, 2000).
Many feasibility
tests have been down on snails as a source of nutrition (protein) in developing
countries like Nigeria. Researchers baked snails’ pies and give them to young
mothers and children living in Nigeria, to their surprise, most of the children
as well as their mothers preferred the tests and texture of the snail pie over
that of beef pie. This is good news since snails are readily available source
of nutrition that can be easily collected and prepared as food. No farmland is
required to raise them and large pool of labour is not needed to collect them
and turn them into meals.
Considering this
question. Is eating snail nutritious? Snails are surprisingly nutritious. High
in protein and very low in saturated fat. One ounce of snail has five grams of
protein and is an excellent source of essential fatty acids. They are also a
good source of vitamin E, Vitamin D, Vitamin B12, Vitamin K, magnesium, iron,
and selenium.
Ajayi (1978) indicated
that snail meat is particularly rich in protein and iron. Bender (1992)
reported that the amino acids in the protein of snail would complement the
cereal source of protein by making good of their relative deficiency of lysine.
The low fat content and low cholesterol level make snail meat a good antidote
for vascular disease such as heart attack cardiac arrest, hypertension and
stroke.
2.4 ENVIRONMENTAL
FACTORS FAVORING SURVIVAL AND
RAISING OF
SNAIL.
Environment is
the combination of external physical conditions that affect and influence the
growth, development and survival of organisms. Snail farming can be indoor or
outdoor provided environmental conditions necessary for survival following
environmental factors are ideal.
2.4.1 Temperature: Temperature
influences the activities of snails such that the temperature above 200C will cause the snails
to stivate or hibernate in order to regulate the body fluid. Sails thrive well under ambient temperature of
200C with considerable growth rate all year round with zero chance
of aestivation. Temperature and humidity of 80 hand in hand are very critical
in the survival of snails.
2.4.2 Humidity: Humidity is a
very critical factor to snails as they have to maintain a constant equilibrium
between fluids. A humid environment is
required for snails to remain active and bred all year round. It is therefore,
necessary to moisten the environment during dry periods. Humidity and water availability
are very important in snail rearing and influence feeding. During dark hours, air humidity of 80% will promote good snail activity and growth through snails need water but their
environment must not be water logged.
2.4.3 Light
Snails naturally require light
for optimal growth. Lighting can be achieved by natural and artificial means. At the level
of our technological advancement, natural lightening is mostly employed. Light essentially
is necessary for some biological process such as photosynthesis which is very
vital in energy cycle in food chain. Intensive snail production involves
artificial lighting system to prompt the snails into their natural reproductive
cycle. Three environmental factors (daylight, temperature and humidity) influences
the reproductive cycle of snails (Yusuf,
2002). Research has
shown the exposure of
snails to continuous light
increased their activity and rate
of food consumption and thus promote
their rapid growth (Akinusi, 2002).
2.4.4 Soil: Soil is a m
medium for reproduction of snails. Good
management practice involves selection
and mixture of soil. It should be recalled that soil harbours a lot
of pests and predators,
and so should be properly
analyzed before using it
in snail activities. A mixture of sand and
clay in a good proportion retains
water and therefore not suitable
because during raining season it
becomes water logged and cakes up
during dry season which makes it too
hard for snails to burrow through. Loamy
soil is recommended as it contains enough organic matter with good retentive
capacity. Acidic soils should be avoided. If
an acid soil cannot be avoided,
lining is encouraged. Periodic application of calcium is also encouraged where
and when it is absent. The soil should not contain harmful sails or be so
alkaline so as not to burn the snails (Akinnusi, 2002).
2.5 HOUSING A SNAIL
Snails are known to escape from
enclosures that are not properly protected or covered. It therefore becomes
imperative that snail houses should be protected to prevent the snails from escaping
and be predator free.
The
housing for raising snails varies with purpose. However, it could be made of wooden
materials, wire mesh or even local materials whether outdoor or indoor.
Depending on the size of the farm, cages or hitch boxes, trench pens, used
types local baskets, movable pens and mini paddock are used to prevent snails
from escaping. The cage should not be exposed to direct sunlight as this can
raise the temperature of the enclosed container to injurious levels. However,
they should be exposed to normal day/might cycle (Akinnusi, 2002) where cage
boxes are used the cover should be meshed to acid spraying of water without
having to open the box. No matter the type of housing, the habitat of snails
must be taken into shade as snails like hiding places. When snails are raised
indoors under controlled environmental factors favouring production must be
provided. The housing must be provided
with devices for measuring humidity
(hygrometer), temperature (thermometer),
soil moisture and light (in-foot candles) weighing balance, soil testing kit, magnifying glass and
watering cans.
2.5.1 Housing System
There are three
main housing system for rearing snails namely extensive, semi -intensive and
intensive system.
Extensive system: This type of system is essentially
practical in the open parks/gardens. The snails are reared in their natural
habitat except that choice plants are
planted and park or fenced gardens are provided to avoid the escaping of the
snails.
Semi intensive system: This system
combines both indoor and outdoor practices. The reproductive and nursery stages
raised indoors while the growing period are outdoors. This system
enable the farmer to grow and produce snails all year round making them
available to numerous consumers.
Intensive system: As the name implies, the system
requires a high capital investment with modification of the environment to
stimulate what happens naturally during the park period to ensure optimum
reproduction and growth. This system ensures all year production of snail and
regular supply on demands.
2.5.2 Pest and Diseases
The natural enemies/ predators of
snails are members of many vertebrate groups such as beetles, cricket,
centipedes, snakes, toads, turtles and birds. Human also impose very serious
threat to snails through pollution and destruction of natural habitats of
snails which have led to extinction of a number of species. Cannibalism among
hatching (first snails that hatch) is also common. These young snails gather up
the shells of their eggs which give them the much needed calcium for building
their own shells, after which they may begin to eat the unhatched eggs.
Parasites
nematodes, trematodes, fungi and
anthropods may equally attack snails. Such problem occur as a result of over
crowding, pseudomonas acruginosa causes intestinal infections that can spread
rapidly in over crowded pens farm. Where it attacks egg clutches preventing
them from hatching.
Control is not
difficult in semi intensive and intensive systems. Once there is infection of
fungi, the egg can not be redeemed, all that could be done is to burn and
dispose the soil where the eggs are laid (Akinnusi, 2002).
2.6 POTENTIAL OF MULBERRY FOR ANIMAL PRODUCTION
The urgent need for a high
quality feed for animals in the tropics and the excellent characteristics of
mulberry are the justification for the great enthusiasm for its intensive
cultivation and use or feed supplement for animals and mini livestock like
snails.
The
nutritional quality of locally produced mulberry leaves is equivalent to that
of grain based concentrates thus, they are an ideal supplement in most forage
diets.
The
nutritive value of mulberry leaves becomes greater in inverse proportion to
animal size, since metabolic rate and hence nutrient requirements decrease in size. Mulberry leaves should be
the preferred feed for guinea pigs, rabbits, and perhaps snails, (Oviedo et al., 1994) many more excellent
results are to be expected when mulberry is offered to other herbivores small
species in particular. There is a report of ad
libitum dry matter intake of 4.18% of liveweight (average of three
lactating goats) which is much higer than in other tree fodders, the dry matter
intake of mulberry leaves of 3.44% of the body weight in sheep under
experimental conditions.
In
costa rica, liveweight gains of bulls belonging to the Romosinuano breed (a
criollo type) fed elephant grass, increased to over 900g/day when mulberry was
offered as a supplement at 1.7% of their body weight on dry matter basis.
Growing
Zebu and Brown Swiss steers being fed increasing levels of mulberry as supplement
to a sorghum silage diet, the animals showed good growing rate.
Although the
growing rates with the highest mulberry level are not impressive (195g/day)
most likely due to poor quality of the silage a combination of mulberry and
trichantera gigantea leaves as the protein source and blocks made of molasses,
cassava root meal and rice brains as the energy source gives better
reproduction and growth performance than a diet of commercial concentrates and
grass supplement. In conclusion, mulberry leaves provides enough nutrients for
maintenance.
2.7
COMPOSITION AND NUTRITIVE VALUE OF MULBERRY PLANT
Mulberry plant is a perennial plant,
usually cultivated as mono crop for its leaf to rear silk worms majorly (Gunase
khar et al., 1998). The chemical composition of mulberry Leaves
has been studied by many authors. The crude protein content in leaves varies
from as low as 15% to 28% depending on the variety, age of the leaves and
growing conditions. In general, crude protein values can be considered similar
to most legume forages. Machii (1989) reported that the protein quality of
mulberry leaf is comparable to that of soya bean meal.
Fibre
fractions are low in mulberry leaves compared to other foliages. Shayo (1997)
reported lignin (acid detergent lignin) contents of 8. 1% and 7. 1% for leaves
and barks respectively. A striking feature of mulberry leaves is the mineral
content, with ash values up to 25%. Typical calcium contents are around
1.8-2.4% and phosphorous 0.14-0.24%. Espinoza et al. (1999) found potassium values of 1.90- 2.8% in leaves and
1.33-1.53% in young stems. The essential amino acids are over 46% of the total
amino acid in mulberry. The average nitrogen (N) is 16.6% of the total
molecular weight of the mulberry amino acids (Plus ammonia). Mulberry leaves
contain 1130 kcal -2240kcal of metabolisable energy and absence of anti-
nutritional factors (Omar et al., 2006)
2.8
NUTRITIVE VALUE OF SIAM WEED
Chromoleana odorata belongs to
the family Asteraleae .Its common names are Awolowo, independence weed or siam
weed (Okon and Amalu, 2003). It is used as a livestock feed because of its high
protein content and less anti-nutritional factor (Iwu, 1993 and Phan et al., 2001) Chromoleana odorata after
4-12 weeks of re-growth showed that the leaf fraction had a crude protein
content about 194/kg dry matter (DM) and average leaf of stem ratio of 2: 1: 1.
Chemical analysis of the leaf fraction of an 8- week-old regrowth indicated a
high crude protein content of 258 g/kg
DM and a high degradable nitrogen content but low in neutral detergent fibre
(33l g/kgDM) acid detergent lignin (53 kg/DM), total extractable phenolic (37.1kg/DM)
extractable tannin 0.72, absorbance at 550 mm) and extractable condense tannin
(1.4 g/kgDM) in sacco degradability analysis of the 8- weeks old regrowth, leaf
sample showed a higher 48% organic
matter (935g kg -1DM) and crude protein (953 g/kgDM) degradability the leaf
sample has an organic matter degradability of 670 g/kg DM as estimated by
cumulative gas production in vitro after 24hrs incubation. There was a little
or no phenolic- related anti nutritive factors in chromoleana odorata.
Additionally, leaf samples had no effect on rumen protozoa activity. Chromoleana
odorata leaves are of high nutritive value and might have the potential to be
used as a protein supplement of leaf meal of chromoleana odorata in feeding animals
is the presence of anti- nutritional factor (Checke and Myer, 1975) and this
probably could be avoided by adopting proper harvesting and sun- drying
procedures (Fasuyi et al., 2005)
2.8.1 OTHER USES OF CHROMOLEANA ODORATA
Chromoleana Odarata has medicinal values
and are usually used in treating inflammation and serves as an anti-fungi,
anti-hypertensive and anti-fungal agent (Akimoladun et al., 2007).
2.9
CHROMOLEANA ODORATA IN LIVESTOCK FEEDING
Information on
the use of chromoleana odorata in livestock nutrition is very scanty. This
might be as a result of the widespread speculation about of its toxicity to
animals and offending nature of its odour. Reports of Madrid (1974) of the
consequent death that occurred in cattle following ingestion of Chromoleana
odorata leaves attested to the toxic nature of the plant in livestock nutrition
are as reviewed below
Nwokolo
(1987) delved edaborately on the mineral and amino acid composition of Chromoleana
odorata. He reported on the amino acid composition and availability of these
leaf meals (Table 2). He concluded that the values obtained for both mineral
and amino –acid availability could be attributed to the presence of anti
nutrient factors, especially of tannins since they occur in high concentration
in plant materials and are associated with toxicity and poor growth rate and
depressed dietary nutrient utilization in livestock animals.
Table
1
Mineral composition (Mg/kg) of C.O leaf meal (dry matter basis)
Mineral hromoleana
odorata leaf meal
Phosphorus 4.532
Calcium 11,551
Magnessium 3202
Potassium 13 800
Copper 37
Zinc 52
Manganese 71
Iron 79
Source: Nwokolo (1987),
Table2: Animo Acide
composition of C.O. leaf meal Amino acid
Amino acid Chromoleana odorata leaf meal
Asparte acid 8.2
Threonin 3.5
Serine 3.5
Elutamic acid 8.0
Proline 4.5
Elycine 4.2
Alanine 4.4
Cysteine 0.8
Valine 4.1
Methionine 1.3
Isoleucine 3.2
Leucin 6.4
Tyrosine 2.0
Phenylalanine 3.7
Histidine 3.2
Lysine 4.7
Arginine 4.
Amino acid availability (%) 65.40
Source: Nwokolo (1987).
Table
3
Dry matter gross energy and proximate composition of Chromoleana odorata leaf
meal.
Nutrient Chromoleana odarata leaf
meal nutrient
Dry matter (%) 87.40
Crude protein (%) 18.67
Crude fibre (%) 11.67
Ether extract(%) 1.01
Ash (%) 3.63
Nitrogen free extractive (%) 3.332
Source:
Aro (1990)
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