Mycotoxins: Their effects on health
By H.V.L.N. Swamy PhD Alltech Canada Guelph Ont.Features Profiles Researchers
Turkeys are susceptible to deoxynivalenol
Did you know that mycotoxins are the second most important issue faced
by the animal industry today next only to feed cost? This sentiment was
expressed by 30 animal industry leaders – representing 15 per cent of
world feed production – who attended Alltech’s President Club recently.
H.V.L.N. Swamy discusses mycotoxins and their effects on turkeys, and how CFIA regulations need to be revisited.
Despite common thought, turkeys are susceptible to deoxynivalenol mycotoxin
Did you know that mycotoxins are the second most important issue faced by the animal industry today next only to feed cost? This sentiment was expressed by 30 animal industry leaders – representing 15 per cent of world feed production – who attended Alltech’s President Club recently. A part of this increased concern on mycotoxins can be attributed to phenomenal increase in the cost of feed ingredients and the subsequent increased dependence on alternative raw materials.
MYCOTOXINS COST MONEY
In Canada it is often difficult to obtain a control feed free of mycotoxins to conduct animal research, thus exemplifying the magnitude of the problem. In support of the economic consequences of mycotoxins, a recent publication in the Journal of Agricultural and Food Chemistry estimates a loss of $147 million to the U.S. swine industry due to fumonisin mycotoxin alone¹. What would be the loss due to more than 300 known mycotoxins and thousands of unknown or masked mycotoxins to the entire livestock and poultry industry?
‘FIELD’ FUNGI AND MYCOTOXINs
Field fungi invade the seeds while the crop is still in the field and require high moisture conditions (20-21 per cent). These include species of Fusarium, Alternaria, Clodosporium, Diplodia, Gibberella and Helminthosporium.
The predominant Fusarium mold that infests grains in Canada is Fusarium graminearum (refer to Figures 1 and 2) but Fusarium proliferatum, Fusarium verticilloides, Fusarium moniliforme and several other Fusarium species cannot be ruled out.
The most frequent mycotoxins occurring in Canada from these molds include deoxynivalenol (DON or vomitoxin), zearalenone (ZEA), T-2 toxin, HT-2 toxin, diacetoxyscirpenol (DAS), fusaric acid etc.
‘STORAGE’ FUNGI AND MYCOTOXINS
Storage fungi are those that invade grains or seeds during storage, need less moisture than field fungi (13-18 per cent) and usually do not present any serious problem before harvest. Storage fungi include species of Aspergillus and Penicillium. Among the two, Penicillium fungi are more common in Canada, especially in the Manitoba region. Ochratoxin A and citrinin have been detected in grains such as wheat, rye, barley and oats, which were overwintered in the field due to weather at harvest time in the autumn.
Aspergillus species are less common in Canada, although they do occur. Aspergillus ochraceus produces ochratoxin A, whereas A. parasiticus and A. flavus produce various aflatoxins. These fungi occur predominantly in areas of high temperature (68+ F) and high humidity. Aflatoxicoses can possibly be a problem for animals and humans who consume products such as peanuts and cottonseed meal imported from warm or humid countries.
CANADIAN POULTRY FEED REGULATIONS
The Canadian Food Inspection Agency has set upper limits for several mycotoxins in poultry feeds (Table 1). Based on these limits and some of the research conducted on mycotoxins using purified DON, it was concluded that poultry may be resistant to DON.
This was the impetus for Prof. Trevor Smith’s laboratory at University of Guelph to initiate research on feeding DON-contaminated grains (corn, wheat and barley) to various classes of poultry and study the impact of mycotoxins on performance, neurochemistry, immunity and gut health.
The term “DON-contaminated grains” is generally used to imply grains contaminated with DON and several other Fusarium mycotoxins. The summary of the research conducted in turkeys using DON-contaminated grains at University of Guelph is presented herewith. In all the four trials turkey poults were fed three diets from 0 to 12 weeks; (1) Control diet with low level of mycotoxins, (2) Contaminated diet containing mycotoxin-contaminated corn and wheat and (3) Contaminated diet with Mycosorb® – a polymeric glucomannan mycotoxin absorbent (Alltech Inc.) derived from the cell wall of yeast.
ARE TURKEYS SUSCEPTIBLE?
Here are the results of these trials:
Trial 1: Turkey poults fed diets naturally contaminated with an average of 9.6 ppm DON, 0.9 ppm 15-acetyl DON and 0.6 ppm ZEA. They observed reductions in weight gain, plasma total protein, albumin, globulin, calcium, bilirubin and uric acid concentrations (data not shown).2
Trial 2: Turkey poults fed the same levels of mycotoxins as in Trial 1. They observed a decrease in cell-mediated immune response to dinitrochlorobenzene (DNCB) measured as per cent increase in web foot thickness.3 This implied that long-term consumption of grains naturally contaminated with Fusarium mycotoxins could render turkeys susceptible to infectious diseases where CD8+ cells play a major role.
Moreover, the results pertaining to biliary IgA indicated a need for investigation of the impact of Fusarium mycotoxins on the resistance of turkeys to intestinal infections such as coccidiosis. The research on this aspect is in progress.
Trial 3: A study was conducted similar to Trials 1 and 2, but at levels of mycotoxins three times lower.4 These levels represent the actual levels encountered in the field. DON levels in these studies were around 3 ppm. Birds fed contaminated grains grew slower (Figure 3) and showed decreased cell-mediated response to DNCB (Figure 4). These observations were same as in Trial 1 and 2 and further confirmed that DON-contaminated grains depress growth and cell-mediated immunity even at low concentrations. The decrease in cell-mediated immunity indicated that turkeys exposed to DON-contaminated grains will be less prepared in an event of disease outbreak.
Trial 4: Study same as in Trial 3 but the focus was on gut health.5 Mycotoxin concentrations in contaminated diets are same as in Trial 3. Feeding of contaminated grains reduced villus height and absorptive villus surface area (AVSA, Figure 5) in duodenum and jejunum but not in ileum. The reduced villus height and AVSA may contribute to reduced nutrient absorption in duodenum and jejunum ultimately affecting production performance as observed in Trial 3.
It is possible that levels even lower than 3 ppm DON from naturally contaminated grains can compromise performance and health of commercial turkeys. One of the reasons for this is that, unlike turkeys in the research facilities, turkeys in the field are subjected to various stressors related to environment, management and nutrition.
These stressors compromise the immune system and enhance the immunosuppressive effects of mycotoxins. Another reason is that a significant amount of DON and ZEA can be present as masked mycotoxins in contaminated grains thus escaping the routine mycotoxin detection procedures.5 For this reason, their toxicity is underestimated, yet they are exerting adverse effects on turkeys.
Feeding Mycosorb® reduced the market days of turkeys exposed to mycotoxins by 3.2 days.
PREVENTING NEGATIVE EFFECTS
In general, pre-harvest control of mold growth is somewhat compromised by the inability of man to control the climate, since both insufficient and excessive rainfall during critical phases of crop development can lead to mold contamination, spoilage of grain, and mycotoxin production.
However, the post-harvest handling of grain presents many more opportunities for controlling mold growth and its consequences. Careful drying of grains and good storage management should minimize post-harvest fungal growth and therefore, mycotoxin production. Removal of affected grains, dilution of contaminated grains with clean grains, and the dietary inclusion of a broad-spectrum mycotoxin binder can be beneficial in reducing the negative effects of mycotoxins on poultry.
Similar to commercial layers, in the studies discussed above, feeding of Mycosorb® prevented most of the negative effects caused by DON-contaminated grains in turkeys (Figures 1, 2, 3).2-5 Turkeys fed Mycosorb® achieved the market weight 3.2 days before the turkeys fed mycotoxin-contaminated diet.
|Figure 1: Effect of low level DON-contaminated grains on
body weight gain
|Figure 2. Effect of low level DON-contaminated grains on DTH
response to DNCB
|Figure 3. Effect of low level DON-contaminated grains on villus height and absorptive surface area in jejunum|
Unlike the popular belief turkeys can be susceptible to DON-contaminated grains. Caution must be exercised when diverting DON-contaminated grains into turkey diets. The findings may also suggest the need to revisit the guidelines set by Health Canada on maximum allowable concentrations of DON in poultry feed.
Producers can minimize economic losses from mycotoxins with the use of a mycotoxin absorbsent.
1. Wu and Munkvold. 2008. J. Agric. Food Chem. 56:3900-3911.
2. Chowdhury and Smith. 2007. Can. J. Anim. Sci. 87:543-551.
3. Chowdhury et al., 2005. Poult. Sci. 84:1698-1706.
4. Girish et al., 2008. Poult. Sci. 87:421-432.
5. Girish and Smith. 2008. Poult. Sci. 87:1075-1082.
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