Concern over mycotoxin contamination of feed ingredients emerged before harvest of the 2009 corn crop which was delayed by prolonged rainy weather over the corn belt. Delivery of consignments of corn to elevators with moisture content in excess of 20% and low bushel weight following drying were obvious indications of poor quality.
Surveys conducted at elevators and especially by ethanol producers confirmed unacceptable levels of deoxynivalenol [DON] with some samples contaminated with fumonisins, T-2 trichothecenes and occasionally aflatoxins.
The detection and assay of samples for the presence of mycotoxins was reviewed in detail in the March/April edition of Feed Management following a survey of available commercial tests kits suitable for elevators, feed mills and laboratories operated by producers of milk, eggs and meat.
Significance of mycotoxin problem
The extent and severity of the level of DON contamination of corn is the outstanding problem resulting from the 2009 harvest. In addition, producers are obliged to use DDGS as this product represents approximately a third of the corn diverted to ethanol production.
In the process of fermentation, aflatoxins are concentrated in the solid residue resulting in a level of three to four times the content in the corn feedstock. A number of DDGS suppliers, especially a company producing a branded product, have instituted monitoring programs and have attempted to blend consignments of DDGS containing high and low levels where possible. It is noted that corn for a specific plant is usually derived from the surrounding area and in the event of adverse weather conditions, there is virtually no uncontaminated product to blend in an attempt to reduce final levels of mycotoxins, especially DON.
One large, publicly-quoted producer of ethanol issued a blanket warning to users that all DDGS produced by their company was potentially contaminated. This was a veiled attempt to place the onus for testing and the disposition of the ingredient onto manufacturers of feed and integrators. Given the increasing demand for DDGS in the international market, it is cynical to consider that ethanol producers may in fact benefit from domestic rejection of their product since more will be available for export.
At this stage there is no sanction or apparent action by regulatory authorities concerning levels of mycotoxins in DDGS. This is based on the fact that FDA is overwhelmed by issues which is it obliged to regulate and DDGS is not a human food. Mycotoxins which find their way into livestock are, with the exception of aflatoxin in milk, not a problem with respect to biologically active residues in eggs and meat.
Given the high degree of protection afforded the ethanol industry it is doubtful that any regulatory agency will address the issue of mycotoxin contamination in DDGS and until regulations are issued and enforced the situation of potential contamination of DDGS is relegated to caveat emptor or “buyer beware.”
The situation relating to DON contamination is principally confined to swine production. Given the levels of contamination recorded by state laboratory and surveys conducted by producers of test kits, conventional corn/DDGS/soybean diets for poultry have not exceeded 5ppm of DON.
Producers of swine feeds and pork integrators have applied greater diligence to formulation and quality control to ensure that DON levels have not exceeded a total of 3ppm in diets. Chickens can tolerate at least 5ppm to 10ppm total DON in diets without deleterious effects.
Fortunately aflatoxins have not been encountered frequently in the 2009 harvest and if so with relatively low levels. This is considered fortunate since widescale rejection of corn at elevators would have occurred at levels exceeding 50ppb and suppression of growth rate and feed conversion efficiency in addition to elevated mortality from immunosuppression may well have been encountered in immature poultry and swine with dietary levels in excess of 100ppb.
Neither fumonisins nor T-2 toxins have caused problems in 2010 other than in specific areas where contamination has been encountered.
Responding to mycotoxin contamination
Consignments of corn with high levels of moisture should be dried either before or subsequent to delivery to elevators or feed mills. It is possible that many consignments were incompletely dried due to shortage of propane or the need to rapidly harvest and deliver grain between rain storms during last quarter of 2009. It is a matter of record that there was more corn in the fields at the turn of the year than ever previously recorded.
Blending of ingredients with high and low levels of mycotoxins is generally not possible under commercial conditions given the availability of silos, logistic restraints and in the case of the 2009 harvest, the extent of contamination. Obviously feed ingredients for critical species such as swine which are extremely sensitive to DON should be subject to assay and attempts at blending or diversion of contaminated consignments from mills dedicated to hog feed.
Propionic acid and mixtures of this organic acid with formic and butyric acids inhibit fungal growth. These additives do not address the problem of pre-formed toxins synthesized by fungi during the late stages of growth and immediately following harvest.
A number of companies manufacture mycotoxin binders to be added to diets to either sequester mycotoxin or to inactivate the toxic principle by enzymatic destruction. The FDA has not established standards for either safety or efficacy for mycotoxin binders. Accordingly suppliers use euphemistic and coded descriptions for these products including “anti-caking agents.” Some products available in the EU, Latin America and Asia are therefore not marketed in the U.S.
Zeolites are porous structures incorporating sodium and calcium attached to an aluminosilicate matrix. Natural zeolites are derived from volcanic rocks interacting with alkaline ground water. Due to their porous structure zeolites are capable of absorbing some mycotoxins, principally aflatoxin.
The zeolites clays and natural zeolites are frequently contaminated with heavy metals and may also contain dioxins formed during volcanic activity. Their ability to absorb mycotoxins in the intestinal tract is frequently inferior to the data suggested by laboratory studies which show acceptable efficiency. Generally “natural” products such as clays are unsuitable due to variable efficacy and potential contamination. Synthetic zeolites have limited ability to bind other than aflatoxins.
The inner cell wall of the yeast Saccharomyces cerevisiae contains beta glucan components with the capability to bind aflatoxin and other commonly encountered mycotoxins preventing absorption. The commercially available product which is formulated for inclusion in diets is marketed in the U.S. as Integral and is essentially the same as Mycosorb approved in Europe, Latin America and Asia as a specific mycotoxin binder. A similar product MTB-100 is used widely in areas outside North America for livestock feeds and pet food.
Biomin of Austria supplies Mycofix which is not available in North America. This product functions by biotransformation of mycotoxins by specific enzymes which alter the structures of trichothecenes, zearalenone and ochratoxin. In addition the compound contains absorbents which sequester aflatoxins.
The problems of the 2009 harvest clearly indicate the need for wider use of available rapid-test systems. In addition, the FDA must recognize the problem of mycotoxicosis and its economic impact and establish standards for registration based on efficacy and safety.
Competitors of U.S. producers operating in Latin America and the Asia-Pacific regions have the benefit of effective mycotoxin binders which are able to ameliorate the impact of toxicity. In an imperfect world mycotoxicosis will persist and detract from efficient food production. Suppression of the effects of mycotoxicosis depends on coordinated responses extending from crop production through to feed manufacture.