Introduction
Aflatoxins are primarily produced by fungi of the genus Aspergillus (Aspergillus flavus, Aspergillus parasiticus, and Aspergillus nomius) These are found in animal feeds as well as in 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 quite toxic to animals.
NDDB Survey of Cattle Feed Ingredients
Extensive surveys conducted in India suggest that Aflatoxins are often encountered in substantial levels in feeds and feed ingredients, but are rarely found in forages. To study the incidence of Aflatoxin B1 in different raw materials, a survey was conducted by the University of Agricultural Sciences, Bengaluru, in collaboration with NDDB (Devegowda, et al 2019). The survey results showed that out of 246 samples analyzed, 206 were found to be positive for the presence of Aflatoxins.
The cereal and cereal byproducts analyzed were maize, de-oiled rice bran, rice polish, and wheat bran. The samples were positive for Aflatoxins to the tune of 88%. The oilseed meals analyzed were soybean meal, full-fat soy, sunflower meal, groundnut cake/extract/expeller, rapeseed meal, and til (sesame) cake. It has been generally observed that oilseed meals contain a higher incidence of Aflatoxin (up to 96%) contamination compared to cereals and cereal byproducts. Aflatoxin B1 content was analyzed in 254 samples of cattle feed (NDDB, 2018) suspected to be contaminated with Aflatoxins. The results found that the average level of Aflatoxin B1 was 68 ppb in these samples.
The common types of raw materials which are used in cattle feed that are susceptible to Aflatoxins, could be listed under three categories:
a. Feeds that contain high levels of Aflatoxins: Groundnut cake, cottonseed cake, copra cake, dried distillers’ grains with solubles (DDGS), and maize gluten meal.
b. Feeds that contain moderate levels of Aflatoxins: Maize, rice polish, de-oiled rice bran, and wheat bran.
c. Feeds that contain low levels of Aflatoxins: Rapeseed meal, soybean meal, straw, and hay.
Measures to Reduce Aflatoxin Production
Pre-harvest level
The most practical approach is good agricultural practice, which includes plant breeding measures to develop mold resistance crops. Alternatively, the second approach is fungal bio-competition. This application involves the use of non-toxigenic strains of Aspergillus flavus and Aspergillus parasiticus in soil in maize plots, which could lead to a reduction in the colonization of toxigenic fungi in subsequent years. The non-toxigenic bio-competitive Aspergillus strains out-compete the toxigenic isolates, resulting in reducing preharvest contamination with Aflatoxin in groundnut and cotton.
Harvest & Storage-level
- Raw material should be dried immediately after harvesting, in order to reduce the moisture content to less than 13%.
- One should avoid damaged and broken grains as these are more susceptible to fungal growth.
- One should void insect-damaged grains as these are more susceptible to fungal growth.
- Grains should be pre-cleaned and dried before storage in silos or in bags.
- Mold inhibitors use is desirable to prevent fungal growth, especially if the moisture content in raw materials is more than 13%.
- Raw materials should be stored on wooden pallets or crates and should be kept away from the walls, to prevent moisture migration from the floor and walls.
Cattle feed plant
- Maize should be pre-cleaned to remove all waste material and dust that may contain high levels of Aflatoxins.
- Mold inhibitors should be used in finished feed, especially during hot and humid conditions.
Finished feeds should be stored on wooden pallets or crates in order to prevent moisture migration from the floor. - A systematic inspection and clean-up program should be adopted to keep bins, delivery trucks, and other equipment free of adhering or caked feed ingredients.
Standard sampling procedure for Aflatoxin analysis
It is a very tricky affair to take a representative sample of feed material for aflatoxin estimation. Major problems associated with sampling for testing of mycotoxins are:
Mycotoxins are not evenly distributed
- Mycotoxins are present in very small amounts (ppb)
- To sample the feed, one should take at least 8-12 representative samples at each of 3-5 locations from the feed bin/truck/gunny bags, etc.
The sub-samples should be mixed again and then about 500-gram composite sample should be taken. Subsequently, the composite sample should be divided into two parts of 250 grams each. One of the samples should be placed in a cool, dry place, and the other sample should be used for testing in the laboratory. The stored 250-gram sample may be used for possible confirmatory testing later.
Source: Compiled and con-sized from NDDB Report
