Risk assessment of mycotoxins in animal feed materials

The adverse biological effects exerted by mycotoxins have been subjected to various risk assessment strategies, most of them specifically addressing potential risk for humans. EF-SA has generated a series of evaluations of mycotoxins, including aflatoxins, ochratoxins, fumonisins, ergot alkaloids and zearalenone, that specifically address adverse animal health effects (EFSA 2004a,b,c, 2005a,b,c). These evaluations were intended to provide the scien tific rationale for setting guidance levels for these mycotoxins in animal feed materials that are produced in, or enter the European market. These evaluations confirm that the exposure of human consumers to mycotoxin residues in edible products of farm animals is very low. At the same time, they also clearly indicate that current knowledge of exposure and of dose-effect relationships in farm animals is limited. Data on the occurrence of mycotoxins in feed materials reported officially to the EU are scarce, and in many cases it was not clear whether the commodities evaluated were intended for human consumption or for animal feed(s). Data from the feed industry (voluntary quality control programs) generally remain unpublished. A recent survey demonstrated the worldwide occurrence of mycotoxins in animal feeds (Binder et al., 2007), but the number of samples analyzed is too small for detailed exposure assessments for individual animal species.

Exposure assessment for farm animals also is complicated by the large variation in the composition of animal diets. Mixed feeds for poultry and pigs are produced on a large scale by commercial feed businesses. These feeds are composed to meet the nutritional requirements of the target animals (or age category) in terms of major feed constituents, such as proteins and fat (convertible energy), to which minerals and vitamins are added. A standardized diet does not exist, as the production of mixed feeds is a day-to-day business, largely influenced by the price for individual feed materials on the world market. The situation for ruminants is even more complex. For these species, the nutritional requirements are strongly influenced by the production stage, e.g., high-milking cows versus dry cows or steers for fattening, and no standardized model is available that would cover these differences at the level of individual feed materials. Moreover, ruminants generally receive a diet that is composed of forages and concentrates, with the level of the concentrates varying from a few percent up to more than 70% in high yielding dairy cows. The heterogeneous distribution of mycotoxins within any commodity complicates this situation even further.

The large uncertainties in exposure assessment also make it difficult to establish realistic maximum tolerance levels in individual feed components for all animal species. The first feed legislation worldwide addressed the levels of aflatoxins Bi and total aflatoxins in the feed for dairy cows. These levels were established because aflatoxin Mi, an aflatoxin metabolite produced in the liver, can be carried over into milk, and not because of adverse clinical signs in cattle. The current limits on aflatoxins in feed have recently been challenged, due to the high variability in diet composition, particularly the amount of concentrates, which may contain aflatoxins. Differences in the rate of carry-over of aflatoxin Mi into milk, which seems to involve active transport mechanisms, may also be important and dependent upon the physiological and overall health status of individual animals (EFSA, 2004c).

In pig diets, both subclinical and transgenerational effects are of major concern, and these are difficult to analyze in common exposure models. Exposure of a sow to zearale-none may have consequences for the next generation, as intra-uterine exposure of piglets might have an impact in later stages of life, particularly the onset of puberty, the first pregnancy and lactation (Fink-Gremmels, 2007). The intensity of adverse effects of deoxyniva-lenol and other trichothecenes seems to be modulated by infectious agents, and hence varies from farm to farm. This variation explains why the European Union at present has set only guidance levels for mycotoxins in feeds. Evaluation of these levels over a period of several years might result in a more accurate estimate of the adverse health effects.

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