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PAT June, 2014; 10 (1): 38-52
ISSN: 0794-5213
Online copy available at
www.patnsukjournal.net/currentissue
Implication of Aflatoxin In Fish Feeds and Management Strategies For
Sustainable Aquaculture
Sotolu, A.O*1, Sule, S.O2, Oshinowo, J.A.3 and Ogara I. M4
1
Department of Forestry, Wildlife and Fisheries, Nasarawa State University, keffi, Shabu-Lafia campus,
P.M.B. 135, Lafia, Nigeria.
2
Department of Aquaculture and Fisheries Management, University of Ibadan, Ibadan, Nigeria.
3
Department of Vocational Studies, Emmanuel Alayande college of Education, Oyo.
4
Department of Agronomy, Nasarawa State University, keffi, Shabu-Lafia campus, P.M.B. 135, Lafia,
Nigeria.
*
Corresponding Author: [email protected]
Abstract
Successful fish production has continued to be bedeviled with myriads of problems. Despite
high costs incurred on fish feed production, aflatoxins caused by Aspergillus flavus and A.
parasiticus are great threat to the eventual use of the expensive feed. They are capable of
impacting high mortalities of fish and consequently heavy loss to farmers. Prevailing storage
condition, use of plant protein sources in aquafeed production and relatively high tropical
weather situation work in favour of high occurrence of aflatoxicosis recorded in Nigeria.
Factors that increase the production of aflatoxins in feeds include environmental temperatures
above 27°C, humidity levels greater than 62%, and moisture levels in the feed above 14%
especially during storage. The extent of contamination varies with geographic location,
processing and feed storage practices. Improper storage is one of the most important factors
favouring the growth of aflatoxin-producing molds, and it is a major element that the fish
producer need to control. International trade has been reported affected by cases of aflatoxins
contamination and several aquafeed ingredients and finished feeds are known to be
susceptible to aflatoxins. It is of great importance therefore that all stakeholders in the
aquaculture industry be on the alert to arrest cases of aflatoxicosis immediately once it is
inevitable thereby averting crisis on the farm and save-guard human health. Management of
aflatoxins can be achieved by focusing on moisture content regulation in feed ingredients
during processing and finished feeds at storage. Good hygiene of ingredients processing,
machines and the environment is highly recommended as well as use of mold inhibitors and
copper sulphate among others.
Keywords: Aflatoxins, Aquaculture, Moisture contents, Molds, Storage condition
Introduction
Aflatoxin is a toxic compound produced by Aspergillus flavus and A. parasiticus. The
molds can grow in improperly stored feeds and feeds with inferior quality of
ingredients. Aflatoxins represent a serious source of contamination in foods and feed in
many parts of the world (Murjani, 2003). Aflatoxicosis is a disease that can affect many
species of fish and shellfish and results when feed contaminated with aflatoxins is eaten
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by the fish (Ashley, 1970; Hernández et al., 2005; Bautista et al., 1994). The first
documented incidences of aflatoxicosis affecting fish health occurred in the 1960s in
trout hatcheries. Domesticated rainbow trout (Oncorhynchus mykiss) that were fed a
pelleted feed prepared with cottonseed meal contaminated with aflatoxins developed
liver tumors (Ashley, 1970) and as much as 85% of stock of fish died in another
hatchery as reported by Taniwaki (2001) in a similar instance. In tropical and
subtropical conditions, this potential is further increased due to storage under humid and
hot conditions. International trade has been reported affected by such commodities
affected by exposure to aflatoxins given worldwide concerns as the economic impacts
are enormous (Golan and Paster, 2008). Four major aflatoxins (AFB1, AFB2, AFG1 and
AFG2) are direct contaminants of grains and finished feeds including fish pellets.
Aflatoxin B1 is known to be the most significant form that causes serious risk to animals
and human health. The carcinogenic effect of aflatoxin B1 has been studied in fishes
such as salmonid, rainbow trout, channel catfish, tilapia, guppy and Indian major carps
(Jantrarotai and Lovell, 1990; Lovell, 2001; Tacon, 1992; Wu, 1998; Chavez et al.,
1994; Murjani, 2003) and Penaeus monodon (Bautista et al., 1994). Factors that
increase the production of aflatoxins in feeds include environmental temperatures above
27°C (80°F), humidity levels greater than 62% and moisture levels in the feed above
14%. The extent of contamination will vary with geographic location, feed storage
practices and processing methods. Improper storage is one of the most important factors
favoring the growth of aflatoxin-producing molds and it is a major element that can be
controlled by the fish producer (Payne et al., 1988). Rainbow trout and nile tilapia are
extremely sensitive to AFB1, while channel catfish are much less responsive (Jantrarotai
and Lovell, 1990; Tuan, 2001). The Rainbow trout was widespread in the Province of
West Azarbajan. This condition was observed in several farms which administered
moldy feeds to their fish. Interview with farmers indicated that moldy feed was caused
by high moisture content and improper storage of their feeds. Fish feed occupy about
75% of the total cost of fish production (Lovell, 1992). Despite this obvious fact some
of the already prepared fish feeds and/or ingredients become wasted as a result of
Aflatoxin contamination since they are unhealthy for fish consumption. The resultant
effect of Aflatoxin on fish feed will lead not only to high cost of production but also,
decrease in total farm production. Improper feed storage is detrimental to fish
production as it can result in economic loss when the feed is no longer fit for fish
consumption and increase in the cost of production due to medication of affected fish
and such economic wastage should be allowed to persist. The review aimed at
recreating the conscience and awareness of stakeholders in the aquaculture industry
regarding socio-economic problems associated with incidence of aflatoxins on farms
and suggesting practical ways of its successful management.
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Aflatoxins and Aflatoxicosis
Aflatoxicosis is a disease that can affect many species of fish, and results when feed
contaminated with aflatoxins is eaten by the fish (Ashley, 1970). Aflatoxins are
chemicals produced by some species of naturally occurring fungi (Aspergillus flavus
and Aspergillus parasiticus) commonly known as molds. Aflatoxins are common
contaminants of oilseed crops such as cottonseed, peanut meal, and corn. Wheat,
sunflower, soybean, fish meal, and nutritionally complete feeds can also be
contaminated with aflatoxins. Four major aflatoxins (AFB1, AFB2, AFG1 and AFG2)
are direct contaminants of grains and finished feeds. Factors that increase the
production of aflatoxins in feeds include environmental temperatures above 27°C,
humidity levels greater than 62%, and moisture levels in the feed above 14%. The
extent of contamination will vary with geographic location, feed storage practices and
processing methods. Improper storage is one of the most important factors favouring the
growth of aflatoxin-producing molds, and it is a major element that the fish producer
needed to control.
Importance of Aflatoxins In Aquaculture
Aflatoxins can cause disease indirectly through their effects on essential nutrients in
diet. For example fat soluble antioxidants such as vitamin C (necessary for immune
function) and thiamin (necessary for metabolism nervous function) in feed can be
destroyed by those toxins. Hence, it is not surprising that aflatoxins depress the immune
system, making fish more susceptible to bacterial, vital or parasitic diseases (Herrera,
1996). Those subtle effects often go unnoticed and profits are lost due to decreased
efficiency in production, slow growth rate, reduced weights of the fished product,
wastage of fish feed and increased medical cost (Ferguson, 1989; Tacon, 1992; Wu,
1998; Royes and Yanong, 2002). However when fish eat feed contaminated with
aflatoxins, different kinds of adverse conditions can be observed in fish such as;
i.
Liver tumor (Ashley, 1970)
ii.
Reduced growth and appetite (Royes and Yanong, 2002)
iii.
Tissue abnormality or lesion in the livers (Wu, 1998)
Aflatoxins can cause about 60% of the total fish mortality in any production system
(Tuan, 2001). AFBI contaminated feed result to reduced weight gain and reduced red
blood cell counts when fed to fish (Nile Tilapia) (Chavez et al., 1994). The extent of
disease, caused by consumption of Aflatoxins depends upon the age and species of the
fish. Fry are more susceptible to Aflatoxicosis than adults and some species of fish are
sensitive to Aflatoxins than others (Jantrarotai and Lovell, 1990). Other livestock that
can also be affected by aflatoxicosis include: swine, horses, dairy cattle etc. Table 1
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presents among summary of signs of feed contaminated with aflatoxins while Table 2
shows signs of aflatoxicosis in fish respectively.
Table 1: Signs of Feed Contaminated With Aflatoxins
Signs
i) Feed stored for a longer time and probably contaminated with
molds appear stale.
Reference
Ashley (1970)
ii) Contaminated feed are discoloured
iii) Contaminated feed lump together and smell musty.
Ashley (1970)
Lovell (1992)
iv) The presence of blue/grey mold on feed, stale feed are often saturated
with moisture and appear to ‘sweat’.
Smith (2005)
Table 2: Signs of Aflatoxicosis in Fish
Signs
i) Pale gills
ii)Impaired blood clotting
iii) Anemia
iv) Prolong feeding of concentration of AFBI causes liver
tumours which appear as pale yellow lessons and can spread to
kidney.
v) Poor growth rate and lack of weight gain.
Reference
Wu (1998)
Chavez et al. (1994)
Ferguson (1989)
Ashley (1970)
Royes and Yanong
(2002)
vi) Increase in fish mortality (higher Number of dead fish) Tuan (2001)
maybe observed
vii) Fin and tail rot
Chavez et al. (1994)
viii) Aflatoxin contaminated feeds results in eye opacity Chavez et al. (1994)
leading to cataract and Blindness.
Implications of Aflatoxins in Fish Feeds
Aflatoxin B1 has been the most extensively studied. Twenty to 200 ppb will cause a
decrease in feed intake and growth performance, which can be partially offset by
increasing specific dietary nutrients such as lysine or methionine.
In severe cases (1,000 to 5,000 ppb) of aflatoxicosis, one can expect acute effects
including death. Aflatoxin B1 (AFB1) is one of the most potent, naturally occurring,
cancer-causing agents in animals. Conditions increasing the likelihood of acute
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aflatoxicosis in humans include limited availability of food, environmental conditions
that favor fungal development in crops and commodities, and lack of regulatory systems
for aflatoxin monitoring and control. It has been known that aflatoxins, especially
aflatoxin B1, are potent carcinogens in fish, some animals and man (Fig. 1). The
expression of aflatoxin-related diseases in humans may be influenced by factors such as
age, sex, nutritional status, and/or concurrent exposure to other causative agents such as
viral hepatitis (HBV) or parasite infestation. In tropical and subtropical conditions, this
potential is further increased due to storage under humid and hot conditions.
International trade in affected commodities and exposure to aflatoxins are worldwide
concerns and the economic impact due to animal losses can be enormous. Aflatoxicosis
and resulting epizootic hepatoma have been reported among a wide range of fish where
Aspergillus species-contaminated foodstuffs are incorporated into the diet. Aflatoxin B1
(AFB1) is among the most potent known hepatotoxins and carcinogens. Therefore, it is
an important potential toxicant to the most of the popularly cultured fish species.
Figure 1: Pathways and consequences for aflatoxin in animal metabolism
Source: Eaton et al. (1993)
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Increased Danger of Aflatoxicosis
Aflatoxin production is the consequence of a combination of species, substrate and
environment. The factors affecting aflatoxin can be divided into three categories:
environment, nutritional and biological factors. Physical factors include temperature,
pH, moisture, light, aeration and level of atmospheric gases. Aflatoxins are produced
only between temperatures of 12 and 14°C and the optimal temperatures is 25 to 35°C
(Asis et al., 2002). However, interest in the toxic effects on cultured warm-water fishes,
such as tilapia (Oreochromis spp.) and catfish (Clarias gariepinus), has increased as
diets for these species are now being formulated to contain more plant and less animal
ingredients towards least-cost feed production as well as the existing tropical weather
conditions suitable for its occurrence in Nigeria. This increases the potential for
development of aflatoxicosis in these species because, plant ingredients have a higher
potential than animal ingredients for contamination with aflatoxins.
Human Exposure to Aflatoxin.
Two main populations of exposure exist in the world. In countries with commercial
food systems the rate of exposure is generally low because the food system allows the
levels of exposure to be regulated to <10 ppb, and managed, and the economic
conditions in these countries allow for the additional costs and capital requirements to
achieve these levels to be absorbed, and production methods that minimize the risk to
be adopted. In the countries where these economic conditions do not exist there is little
protection of people from the toxin even where regulations do exist. However, the level
of exposure is such that only occasionally does acute illness and death from
aflatoxicosis occur, and the majority of exposure seems to be at the chronic level.
i. Acute Exposure to Aflatoxin.
The incidents of poisoning and death from AF that are reported serve to indicate that
AF is a risk in most developing countries. Some example reports of death and serious
illness from AF are consolidated in table 3.
Table 3: Cases of Outbreaks of Acute Aflatoxicosis.
Country
References
Malaysia
Cheng (1992)
Taiwan
Shank (1977)
India
Van Rensburg (1977); Shank (1981)
Kenya
Cheng (1992)
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ii. Chronic Exposure to Aflatoxin.
Two main approaches have been used to measure the extent of exposure to AF in
people in developing countries. The first approach has been the use of food samples
collected either from prepared meals, ingredients, or the market. The most reliable
sample source for a measure of 58 exposures is analysis of prepared meals, since people
may sort grain and remove those that are considered unfit to eat. Data from this
approach shows that exposure in many countries of the developing world is potentially
high. Variations exist between countries largely as a function of diet. Data collected by
Hall and Wild (1993) reports the levels of exposure (ng/kg/day) to AF based on food
samples in the following countries as being: Kenya (3.5-14.8), Swaziland (5.1- 43.1),
Mozambique (38.6 - 183.7), Transkei (16.5), The Gambia (4-115), southern Guangxi
(11.7 - 2027), Thailand (6.5 -53), compared with the USA (2.7). Independently, Awuah
(2000) estimated the exposure in Ghana to be 9.9 - 99.2 ng/kg/day, based only on
peanut consumption. Other commonly consumed corn-based foods (Kenkey) are also
known to be contaminated (Kpodo, 1995; Hell et al., 2000), so the exposure is likely to
be higher. The currently favored method of measuring human exposure is by the
analysis of body fluids for the presence of AF derivatives (Pier et al., 1985; Wild and
Pisani, 1998).
Prevention and Management of Mycotoxins In Farms
Prevention in Silages
Prevention of mycotoxins in silages includes following accepted ensiling practices
aimed at inhibiting deterioration primarily through elimination of oxygen. Some silage
additives (such as ammonia, propionic acid, microbial cultures, or enzymatic silage)
may be beneficial in preventing mycotoxins because they are effective at reducing mold
growth (Asis et al., 2002). Silo size should be matched to herd size to ensure daily
removal of silage at a rate faster than deterioration. Feed bunks should be cleaned
regularly. Care should be taken to ensure that high moisture grains are stored at proper
moisture content and in a well-maintained structure (Asis et al., 2002).
Prevention of Feed Contamination
Controlling mold growth and mycotoxin production is very important to the feed
manufacturer and livestock producer. Control of mold growth in feeds can be
accomplished by keeping moisture low, keeping feed fresh, keeping equipment clean,
and using mold inhibitors (Pier et al., 1985). Grains and other dry feed such as hay
should be stored at a moisture level 14 percent or less to discourage mold growth.
Aeration of grain bins is important to reduce moisture migration and to keep the
feedstuffs dry (Pier et al., 1985).
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Moisture in Feed Ingredients
Moisture is the single most important factor in determining if and how rapidly molds
will grow in feeds. Moisture in feeds comes from three sources namely; feed
ingredients, feed manufacturing processes and the environment in which the feed is held
or stored. In order to control the moisture content of feeds successfully, moisture from
all three sources must be controlled. Since corn and other grains are a primary source of
the moisture and molds found in feed, the first important step in controlling moisture in
feed is to control it in the grains from which the feed is prepared (Pier et al., 1985.
Since all feed ingredients contain moisture, they should be monitored and their moisture
content controlled. It is commonly believed that the amount of moisture in grain is too
small to permit mold growth except in rare and unusual circumstances. However,
moisture is not evenly distributed in grain kernels. A batch of grain containing an
average of 15.5 percent moisture may, for example, contain some kernels with 10
percent moisture and others with 20 percent moisture (Jarvis, 2008). The moisture
content of individual grain kernels is directly related to the amount of mold growth that
occurs: that is, kernels with higher moisture contents were more susceptible to mold
growth. In addition to moisture, the amount of mold growth is about five times greater
for broken kernels than for intact kernels. Thus the fraction of commercial grain, known
as broken kernels and foreign matter, can be expected to have a higher mold and
mycotoxin content than the portion composed of whole kernels.
Moisture in Feed Manufacturing Processes
Grains are commonly ground with a hammer mill to aid in mixing and handling, to
improve digestibility, and to improve the pelleting process. This grinding process
creates friction, which causes heat to build up. If unchecked, temperature increases
greater than 10 degrees Fahrenheit will cause significant migration of grain moisture
encouraging mold growth (Jarvis, 2008). This is particularly true in cold weather when
temperature differences cause moisture to condense on the inside walls of bins. Airassisted hammer-mill systems reduce heat buildup in the product and, in turn, reduce
moisture problems. The pelleting process involves mixing steam with the feed, pressing
the mixture through a die, and then cooling the pellets to remove heat and moisture.
Generally, heat and 3 to 5 percent moisture are added to the feed during the pelleting
process in the form of steam. If the pelleting process is done correctly, this excess
moisture is removed from the feed before shipment. If, however, this excess moisture is
not removed when the pellets are cooled, mold growth will be encouraged. Since feeds
containing moisture are warmer than normal, storing hot or warm pellets in a cool bin
will cause moisture to condense on the inside of the bin. Although pelleting of feed has
been shown to reduce mold counts by a factor of 100 to 10,000, many mold spores
remain in the feed after it has been pelleted. After pelleting, the remaining spores can
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grow if conditions are right. Thus the pelleting process delays, but does not prevent the
onset of mold growth and plays only a minor role in efforts to control molds (Jarvis,
2008). In addition, pelleted feeds may be more easily attacked by molds than nonpelleted feeds.
Moisture and Feed Storage Environment
The moisture content of the substrate and temperature are the main factors regulating
fungal growth and mycotoxin formation (Jarvis, 2008). In order t-o control mold
growth, obvious sources of moisture in the feed processing and storage equipment must
be eliminated. These sources may include leaks in feed storage tanks, augers, roofs
(either at the barn or at the feed mill), and compartments in feed trucks. A fact about
feed moisture often overlooked is that it changes in relation to the feed's environment.
Since animals kept in confinement housing add moisture to their environment by
respiration and defecation, the air in these houses can be very humid. Feed that was
initially very low in moisture content will gain moisture when placed in a humid
environment. The humidity in confinement housing should therefore be controlled by
providing adequate ventilation. Koehler (1938) established that a moisture content of
18.3% on a wet weight basis was the lower limit for the growth of A. flavus in shelled
corn and this was corroborated by the reports of Sanders et al., (1968) and Taniwaki
(2001).
Keeping Feeds Fresh
Time is required for both mold and mycotoxin production to occur (Sanders et al.,
1968). It is therefore important to have feeds delivered often so that they will be fresh
when used. Feeds should generally be consumed within 10 days of delivery. It is
equally important to manage the feed delivery system to ensure that feeds are uniform
in freshness. Feed store should be managed in a first-in-first-out principle. The feed
next to the wall is last to exit the store and therefore stays in the store the longest. The
feed in contact with the wall is also the only portion of the feed that changes
appreciably due to temperature. These factors make feed in contact with the wall
susceptible to moisture migration and mold growth. It is best to maintain two feed
stores so that one store can be completely emptied and cleaned before it is refilled with
new feed Koehler (1938).
Equipment Cleanliness
When feed is manufactured and delivered to farms, it may come in contact with old feed
that has lodged or caked in various areas of the feed storage and delivery systems. This
old feed is often very moldy and may "seed" the fresher feed it contacts, increasing the
chances of mold growth and mycotoxin formation. To prevent this problem, caked,
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moldy feed should be removed from all feed manufacturing and handling equipment
such as grinder, hammer mill, pelleting machine etc. it was revealed that, the farms
which had executed the hygienic principals of stocking, showed lower levels of toxin in
the diet and vice versa (Motalebi et al., 2008).
Use of Mold Inhibitors
The use of chemical mold inhibitors is a well-established practice in the feed industry.
However, mold inhibitors are only one of several tools useful in the complex process of
controlling the growth of molds, and they should not be relied upon exclusively. The
main types of mold inhibitors are (1) individual or combinations of organic acids (for
example, propionic, sorbic, benzoic, and acetic acids), (2) salts of organic acids (for
example, calcium propionate and potassium sorbate), and (3) copper sulfate. Solid or
liquid forms work equally well the inhibitor is evenly dispersed through the feed (Eaton
et al. 1993). Generally, the acid form of a mold inhibitor is more active than its
corresponding salt.
Dispersion
Many factors influence the effectiveness of mold inhibitors, and proper attention to
these factors can enhance the benefits they provide. Mold inhibitors cannot be effective
unless they are completely and thoroughly distributed throughout the feed. Ideally, this
means that the entire surface of each feed particle should come in contact with the
inhibitor and that the inhibitor should also penetrate feed particles so that interior molds
will be inhibited. The particle size of the carriers for mold-inhibiting chemicals should
be small so that as many particles of feed as possible are contacted generally, the
smaller the inhibitor particles the greater the effectiveness (El-Sayed and Khalil, 2009).
Some propionic acid inhibitors rely on the liberation of the chemical in the form of a
gas or vapor from fairly large particle carriers. Presumably, the inhibitor then penetrates
the air spaces between particles of feed to achieve even dispersion.
Effect of Feed Ingredients
Certain feed ingredients may also affect mold inhibitor performance. Protein or mineral
supplements (for example, soybean meal, fish meal, poultry by-product meal, and
limestone) tend to reduce the effectiveness of propionic acid. According to Eaton et al.
(1993), these materials can neutralize free acids and convert them to their corresponding
salts, which are less active as inhibitors. Dietary fat tends to enhance the activity of
organic acids, probably by increasing their penetration into feed particles. Certain
unknown factors in corn also alter the effectiveness of organic acid inhibitors.
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Time Dependence
When mold inhibitors are used at the concentrations typically recommended, they in
essence produce a period of freedom from mold activity. If a longer mold-free period is
desired, a higher concentration of inhibitor should be used. The concentration of the
inhibitor begins to decrease almost immediately after it is applied as a result of chemical
binding, mold activity, or both (Sanders et al., 1968). When the concentration of the
inhibitor is reduced until it is incapable of inhibiting mold growth, the mold begins to
use the inhibitor as a food source and grows. In addition, feeds that are heavily
contaminated with molds will require additional amounts of inhibitor to achieve the
desired level of protection.
Influence of Pelleting
The widespread use of pelleted feeds in the feed industry is beneficial to the use of mold
inhibitors. The heat that the feed undergoes during pelleting enhances the effectiveness
of organic acids. Generally, the higher the pelleting temperature, the more effective the
inhibitor. Once mold activity commences in pellets, however, it proceeds at a faster rate
than in non-pelleted feed because the pelleting process that makes feed more readily
digestible by animals also makes it more easily digested by molds.
Copper Sulfate
The practice of recommending copper sulfate as a treatment for fungal diseases in
animals goes back many decades. The effectiveness of copper as a mold inhibitor is
difficult to document. Although copper sulfate in the diet has been shown to improve
body weight and feed conversion efficiency in broilers, excessive levels of copper may
be toxic to young animals and will accumulate in the environment (Eaton et al. 1993).
In addition, recent research has indicated that feeding copper sulfate to poultry causes
the formation of mouth lesions similar to those formed by some mycotoxins. Similar
mouth lesions might be formed in other animal species.
The use of inorganic binders/clays
Mineral clays to Chemi-bind mycotoxins, and prevent them from being absorbed by the
animal's GIT, has received a lot of research attention recently. These clay products
(which include zeolites, bentonites, and bleaching clays and hydrated sodium calcium
aluminosilicates [HSCAS]) have been shown to change the responses of rats to
Zearalenone and T-2 toxin (Eaton et al., 1993). However, it should be clearly
understood that binding of some mycotoxins may be weak or nonexistent and that clay
products differ in their ability to bind mycotoxins. While HSCAS products has been
shown to bind aflatoxin protecting animals against aflatoxicosis, they have not shown to
possess binding affinity to Fusarium Toxins.
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Mycotoxin Sampling, Testing, and Test Kits
Since mycotoxins are not evenly distributed in grain or in mixed feeds, taking a feed or
grain sample which will give a meaningful result in mycotoxin analyses is difficult.
Grab samples generally give very low estimates of mycotoxin content. In fact, nearly 90
percent of the error associated with mycotoxin assays can be attributed to how the
original sample was collected. This is due to only 1 to 3 percent of the kernels in a
contaminated lot containing mycotoxin, and these contaminated kernels are usually not
evenly distributed within the lot of grains. For whole kernel grains, a properly taken
composite sample of at least ten pounds is required for a reasonably accurate,
mycotoxin analysis (Eaton et al., 1993). Trucks can usually be sampled with a grain
probe, but bins must often be sampled as grain is being withdrawn. Analytical
techniques for the detection of mycotoxins continue to improve. Several commercial
laboratories now test for a variety of mycotoxins. Although analytical costs can be a
constraint, these costs may be insignificant compared with the economic consequences
of production and health losses associated with mycotoxin contamination. Commercial
antibody test kits for screening or quantitation are currently available for aflatoxins,
zearalenone, deoxynivalenol (DON), T-2 toxin, ochratoxin A, and fumonisins. These
antibody methods, while they are still being improved, are good if used properly.
Conclusion and Recommendations
To prevent aflatoxicosis, follow manufacturer`s recommendations regarding shelf-life
and try to determine the feed manufacture date and storing feeds ingredients and
finished feeds under optimum condition of moisture content not greater than 14%
should be observed. Regular testing for aflatoxins is a good idea. Simple on-farm
inspection can be done visually (look for the presence of blue/grey mold on feed) or
with a black light which may cause a bright greenish/yellow fluorescence if A. flavus is
present. Avoid using feeds that appear discolored, lump together and smell musty.
Clean feed storage bins and automatic feeders regularly. Aflatoxins lower production
efficiency of cultured fish by reducing growth rates, impairing immunity and in some
cases, causing colossal mortality. Storing feed properly (in a cool, dry area on pallets
and at least one foot away from any walls) can prevent unnecessary economic losses
and avoid health hazards in man. Effective control of aflatoxicosis in farm animals can
be achieved by the addition of small amounts of certain clays to feeds, protecting the
animals from contamination that would otherwise result in economic losses. This is a
really cheap technology and could rapidly change human exposure to the toxin.
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References
Ashley, L.M (1970). Pathology of fish feed Aflatoxins and other anti-metabolites. In: A
symposium on diseases of Fishes and shell fishes. American Fisheries Society
Special Publication 5, 366-379.
Asis, R.D., Paola, D.R. and Aldao, A.M. (2002). Determination of aflatoxin B1 in
highly contaminated peanut samples using HPLC and ELISA. J. Food Agric.
Immunol., 14: 201-208.
Awuah E. (2000). Assessment of risk associated with consumption of aflatoxin contaminated groundnut in Ghana. In: Awuah RT, Ellis WO, eds. Proceedings
of the National Workshop on Groundnut and Groundnut Aflatoxins, pp 27-33.
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