Aflatoxin: Prevalence and control in Dairy Feeds and Milk

Prof Dr. G. Devegowda, Dr. V. Sridharand Dr. PL Sherasia

Part – I Prevalence

1.0    Executive summary

Aflatoxins are the most widespread and the most studied group of all the  mycotoxins,  and they  are  prevalent  in  warm  and humid climatic conditions;  as exists in  India and in  many Asian countries.  Aflatoxins  are  primarily  produced  by fungi  of the genus Aspergillus  (Aspergillus flavus, Aspergillus parasiticus, and Aspergillus  nomius),  and  are found  in  dairy feeds  and human food products.  Major forms of Aflatoxins found in feeds include Aflatoxins B1, B2, G1  and G2; with Aflatoxin B1  being the most common and toxic. Aflatoxin M1  is found in  milk and milk products.

Strict control of Aflatoxin  B1  level  in feeds for lactating  dairy cattle and buffaloes is required in order to minimize the level of Aflatoxin M1 in milk and milk products. The United States Food and Drug Administration (USFDA,  2018) and Food Safety and Standards Authority of India (FSSAI,  FSS Regulation 2011) set a maximum permissible level for Aflatoxin  M1  in milk at 0.5 µg/ kg (ppb; parts per billion) of milk, which means that one ton of milk should not contain more than 500 micrograms of Aflatoxin M1.

Aflatoxin B1 is readily transmitted from feed to milk; approximately 1.0 to 6.0% of Aflatoxin B1  present in feed is transferred to milk as Aflatoxin  M1,  depending on factors  such as the genetics of animals,  seasonal  variation,  the  milking  process  and the environmental conditions. The occurrence of Aflatoxins in commercially available milk, and milk products is of concern, as milk is a key source of nutrients for humans

2.0    Introduction

There are more than 10,000 known species offungi. Fortunately, most of them are beneficial to man in the production of bread, cheese, antibiotics etc. There are about 50 fungi species harmful to livestock, poultry, and man known to produce toxins, which are collectively called mycotoxins. Mycotoxins are metabolites produced by fungi  during  metabolism of nutrients  present in feeds and feed ingredients.

Fungi produce mycotoxins in  the field (“field toxins”: fusarium toxins) or in  storage (“storage toxins”: Aflatoxins,  ochratoxins), or both.  Mycotoxins are mainly produced by the fungi genera of Aspergillus, Fusarium, Penicillia, and Claviceps. Their formation may occur when the fungi grow on crops in the field, at harvest, in storage or during the processing of feed when conditions are favorable.

No region of the world  escapes these silent killers,  and their negative   impact  on  animal   productivity   and  human  health is   enormous.   According  to  the  United  Nation’s   Food  and Agriculture  Organization (FAO),  approximately 25% of World’s grain supply is  contaminated with  mycotoxins.  Recently,  a 38 member scientific  task-force from the Council  for Agricultural Science  and Technology (CAST,  2003) in  the USA released a

200 page report entitled  “Mycotoxins:  Risks in Plant, Animal, and Human systems”. According to the report,  in  the United States alone the  economic  costs  resulting from  mycotoxins exceed $ 1.5 billion annually.

3.0    Mycotoxins: An overview

The threat of mycotoxins has been described as early as the Second World War when the soldiers from the Russian army suffered severe dermal  necrosis,  hemorrhages and destruction of bone marrow after eating mouldy grains (Fusarium contaminated,  Figure 1).  However,  it was not until  1960,  when the entire turkey population of Britain was decimated in a fatal liver disease called ‘Turkey X Disease’, that the scientific community  recognized the  negative  effects  associated  with mycotoxins.  British  agriculture  officials  later traced the source of the outbreak to Aflatoxin in a shipment of peanut (groundnut) meal that originated from Brazil.

Figure 1: Maize cobs contaminated with Fusarium fungus

The occurrence of mycotoxins in nature is considered a global problem. However, in certain geographical areas of the world, some mycotoxins are produced more readily than others.  In colder,  more temperate regions such as Canada,  the Northern US and most of the European countries, Aflatoxins are not considered to be a major problem except in imported feedstuffs grown in warmer southern climates. Economically, in these regions  the  most  important  mycotoxins  are  deoxynivalenol (DON,  Vomitoxin),  Zearalenone  (ZEA),  T-2 toxin  produced by Fusarium fungi (Figure 1).

In  Europe,  the  differences in  climatic  conditions among the northern, middle and southern parts favor the development of different fungal species.  In the maize growing areas of southern and middle Europe (Sweden, Austria and Hungary) mainly fusariotoxins  (DON,  ZEA,  T-2 toxin)  cause illness  and poor performance of dairy animals.

3. 1. 1  Deoxynivalenol (DON,  Vomitoxin) Deoxynivalenol  is  produced by several  Fusarium species  of mould primarily Fusarium graminearum and may co-occur with other mycotoxins in contaminated commodities. DON in cattle and buffaloes has been associated with  reduced feed intake and lower milk production when fed with feed containing more than 5 parts per million (ppm).

3.1.2 Zearalenone Zearalenone is produced primarily by Fusarium graminearum and Fusarium roseum. Zearalenone is responsible for reproductive disorders because of its estrogenic effect. In dairy animals, the clinical manifestations such as udder enlargement, decreased milk yield, vaginal discharge, continuous estrus, infertility and abortions are observed when the level of zearalenone in  the feed is more than 0.5 ppm.

3. 1.3 Fumonisins

Fumonisins are primarily  produced by  Fusarium moniliforme and Fusarium proliferatum, the most toxic being fumonisin B1. Fumonisin mycotoxins are found in a wide range of commodities from millets to grains to banana fruits. They are a major concern to food and feed producers since they affect human and animal health.  The toxin  causes  liver  damage and decreased  milk production in dairy cattle at levels greater than 50 ppm in the ration. Usually, level of fumonisins exist between 5-20 ppm in feed.

4.0   Global scenario of Aflatoxins

Aflatoxins;  the  most widespread  of  all  the  mycotoxins,  are common in warm and humid climatic conditions like those existing in India, Latin American, Asian and African countries, southern regions of US, and certain parts of Australia. Extensive surveys conducted in  India, Pakistan, Egypt and South Africa suggested that Aflatoxins are often encountered in substantial levels in feeds and feed ingredients (Figure 2).

In Latin American countries including Brazil, Peru, Mexico, Columbia, Venezuela and Argentina, reports exist on the presence of Aflatoxins.  Due to the increase  in  global  trading of feedstuffs, mycotoxins are no longer solely found in certain geographical  regions but are now more widely distributed than before (Devegowda et al., 1998).

Aflatoxins B1, B2, G1, and G2 refer to toxins which fluoresce blue (B1, B2) or green (G1, G2) under ultraviolet light. Among all Aflatoxins, B1  is the more prevalent and toxic.

Figure 2:  Maize naturally contaminated with Aspergillus  fungus

5. Limits of Aflatoxins  in  feed  and  milin  other countries

Strictly speaking, there is no safe level. With reference to mycotoxins, the risk directly depends on the level of the major mycotoxins and also on the presence and levels of other mycotoxins in feeds. A mycotoxin level considered safe in one farm may not be safe in another farm because of differences in management and disease prevalence. Additionally, factors such as interaction of mycotoxins with pathogens, genetic variability, environmental conditions, and nutritional status etcinfluence the severity of the manifestation of mycotoxicosis.

In order to reduce the toxic and economic impact of mycotoxins, severa countrie regulate  the  level of  some  mycotoxins in foods and feeds. Worldwide, food and feed legislation safeguards the health of consumers and the economic interests of animal  producers and tradersVirtuallyall countries with fully developemarket economies  have regulations with the exception of some African countries.

Table 1: Limits for Aflatoxin B1 in dairy feed

CountryAflatoxin B1 (µg/kg or ppb)
United States (FDA)20
European Union (for milking animals)5
European Union (for calves)10
India (BIS)20

Table 2: Limits for other mycotoxins in dairy feed

Mycotoxins (EU Guidelines)Limits (mg/kg or ppm)
Deoxynivalenol: Adult animals : Calves5 2
Zearalenone: Adults and calves0.5
Fumonisins B1 and B2: Adult animals : Calves50 20

Table 3: Limits for Aflatoxin M1 in milk

Country(µg/kg or ppb)
United States (USFDA)0.5
European Union0.05
European Union, for baby foods/ infants0.025
Australia (FSANZ)0.05
Australia, for infants0.02
India (FSSAI)0.5

6.0      Overview of Aflatoxins in feed and feed raw materials in India

Aflatoxins are primarily produced by fungi of the genus Aspergillus (Aspergillus flavus, Aspergillus parasiticus, and Aspergillus nomius; Figure 3) and are found in dairy feed and human food products. Major forms of Aflatoxins found in feeds include Aflatoxins B1, B2, G1 and G2; with Aflatoxin B1 being the most common and toxic.

Figure 3: Growth of Aspergillus flavus on rice

Extensive surveys conducted in India suggest that Aflatoxins are often encountered in substantial levels in feeds and feed ingredients. Aflatoxins are rarely found in forages. To study the incidence of Aflatoxin B1 in different raw materials, a survey was conducted by the Division of Animal Sciences, University

of Agricultural Sciences, Bengaluru. The results of the survey showed that out of 246 samples analyzed by Thin Layer Chromatography (TLC), 206 samples were found to be positive for the presence of either Aflatoxin.

The cereal and cereal byproducts analyzed were maize, de- oiled rice bran, rice polish and wheat bran. The samples were found 88% positive for Aflatoxins. The oilseed meals analyzed were soybean meal, full-fat soy, sunflower meal, groundnut cake/ extract/ expeller, rapeseed meal and til cake. The oilseed meals contain higher incidence of Aflatoxin (96%) contamination as compared to cereals and cereal byproducts.

Aflatoxin B1 content was analysed in some samples of cattle feed (n=254) suspected to be contaminated with Aflatoxins at NDDB, Anand (NDDB, 2018). The results found that the average level of Aflatoxin B1 was 68 ppb in these samples.

7.0      Metabolism    of    Aflatoxin     in    ruminants    and conversion of Aflatoxin B1 to Aflatoxin M1

In milk, Aflatoxin appears as Aflatoxin M1, one of its metabolites. Aflatoxin B1 is metabolized by enzymes found primarily in the liver (Cytochrome P450) to Aflatoxin M1. Strict control of Aflatoxin B1 level in feeds for dairy animals is required in order to minimize the level of Aflatoxin M1 in milk and milk products.

In the US (FDA) and in India (FSSAI), it is required by the law that Aflatoxin M1 in milk should be less than 0.5 ppb; which means that one ton of milk should not contain more than 500 micrograms of Aflatoxin M1. In European Union, the regulations are much more stringent, and maximum levels are set

at 0.05 ppb (EC, 2002). Aflatoxin is readily transmitted from feed to milk; approximately 1.0 to 6.0% of Aflatoxin B1 present in feed is transferred to milk as Aflatoxin M1 (Figure 4). After Aflatoxin M1 is formed, it is excreted in milk and urine of the dairy animals.

Aflatoxin B1                                                              Aflatoxin M1

Figure 4: Conversion of Aflatoxin B1 to M1

Diaz et al. (2004) have indicated that Aflatoxins appear in milk within 12 hours following oral administration of Aflatoxin B1. The peak concentration in milk occurs after 24 hrs. Clearance is also very rapid, since Aflatoxin disappears from the milk four days after cessation of oral administration (Diaz et al., 2004). These results confirm the rapid absorption and metabolism of Aflatoxins in ruminants.

The USFDA and BIS (India) stipulate a maximum level of 20 ppb of Aflatoxin in dairy feed, which means that one ton of feed should not contain more than 20 milligrams of Aflatoxin B1. The European Union regulations are much more stringent and the maximum level set at 5.0 ppb. Like Aflatoxin B1, Aflatoxin M1 is toxic, although toxicity of Aflatoxin M1 is somewhat lower than that of Aflatoxin B1.

8.0      Impact of feeding Aflatoxin-contaminated feed in dairy animals

Milk producers may not be able to see visual symptoms of aflatoxicosis in the animals at low level Aflatoxin in the feed. However, high concentrations of Aflatoxins and/ or prolonged duration may cause visual symptoms in dairy animals. Feed refusal, reduced growth rate and decreased feed conversion efficiency are the predominant signs of chronic Aflatoxin poisoning. In addition, listlessness, weight loss, rough hair coat and mild diarrhea may occur. The disease may also impair reproductive efficiency, including abnormal estrous cycles (too short and too long) and abortions. Other symptoms include impaired immune system response, and increased susceptibility to diseases.

Leave a Reply

Your email address will not be published. Required fields are marked *