Nutrigeonomics: Evaluating Mycotoxin Control Strategies

A major source of error in mycotoxin analysis is inadequate sampling of feedstuffs. Proper sampling protocols have been developed and published in an effort to minimize this source of error. Another source of error is the potential presence of different chemical forms of mycotoxins which may escape routine analysis. Attention has been focused on the presence of conjugated forms of mycotoxins that are produced by plants. This may be the result of detoxification of mycotoxins by plant metabolism and it has been suggested that the presence of conjugated mycotoxins might be used in making genetic selection of plant resistance to fungal invasion (Liu et al., 2005). Although conjugated forms of deoxynivalenol (DON, vomitoxin) were identified many years ago (Sewald et al., 1992), little information is available about the relative significance of conjugated and free mycotoxins in poultry diets. Schneweis et al. (2002) identified glucose conjugated zearalenone in samples of wheat. Naturally-contaminated wheat and corn samples from Slovakia have been found to contain glucose-conjugated DON with up to 29% of deoxynivalenol in a glucose conjugated form (Berthiller at al., 2005). More recently, Zhou et al. (2007) reported an increase in DON concentrations of up to 88% when barley samples from North Dakota were treated with trifluoroacetic acid prior to analysis. Such acid treatment would hydrolyze all different conjugates of DON. Similar acid treatment of different barley samples showed up to 21% of total DON found in conjugated forms (Zhou et al., 2008). Most recently, Zachariasova et al. (2008) have found even higher levels of bound DON in barley and beer using a variety of analytical techniques. The frequency of bound fumonisin routinely exceeded free fumonisin in samples of European corn and corn-based foods (Dall’Asta et al., 2008). It is not yet clear if the conjugated forms of mycotoxins are as harmful to poultry as the parent compounds, but it has been shown that some conjugated mycotoxins can be hydrolyzed in the digestive tracts of animals (Gareis et al., 1990).

 

It must be concluded that until we have a better understanding of the frequency, toxicity and nature of conjugated mycotoxins, current mycotoxin analysis of poultry feeds should often be considered to be an underestimate of correct values. It is necessary at this time, therefore, to consider mycotoxin analysis of feeds as offering only an approximation of the true hazard posed by the feeding of contaminated materials to poultry 

 

A series of studies has been conducted to determine the effects of feeding blends of naturally-contaminated feedstuffs, largely corn and wheat, to different types of poultry. The findings have been reviewed by Girgis and Smith (2010). These experiments were conducted in an effort to mimic conditions seen in commercial poultry production where diets contain multiple vectors of mycotoxin contamination. The mycotoxins in such diets were determined to be mainly DON with lesser amounts of zearalenone and 15-acetyl DON in addition to fusaric acid. Four different modes of action of the mycotoxins fed were identified: (1) reductions in cellular protein synthesis (2) reduced immunity (3) alterations in brain neurochemistry (4) damage to the intestinal epithelium. 

Laying hens were very sensitive to the feeding of combinations of Fusarium mycotoxins. Egg production and feed efficiency were reduced while major increases in blood uric acid concentrations were seen (Chowdhury and Smith, 2004). The elevations in blood uric acid levels were likely due to a reduction in hepatic fractional protein synthesis rates (Chowdhury and Smith, 2005). Immunosuppression was also observed (Chowdhury and et al., 2005a).