Mycotoxins and adsorbents
Trevor Smith, Ph.D.

 

Mycotoxins are pervasive and dangerous fungal metabolites in feedstuffs formed in the field pre-harvest and under sub-optimal storage conditions post-harvest. Consumed by livestock and poultry, they can reduce performance and alter metabolism, possibly causing pathological states-mycotoxicoses-in both animals and humans. Mycotoxin contamination can result from a range of mycotoxin-producing fungi depending upon the feedstuff source, crop conditions, storage temperature, available moisture, etc. On a global basis, Fusarium mycotoxins are likely the most common mycotoxins (Wood, 1992)

Both the global frequency of mycotoxin contamination of feedstuffs and severity of mycotoxicoses in livestock and poultry appear to be increasing in recent years (see appendix of the article). However, increased international trading of feedstuffs contributes to the severoty of mycotoxicoses as this increases the chance that a given compound feed will contain components of widely varying geographical origins. Such blends of ingredients increase the chance of the feed containing mixtures of different mycotoxins. This can result in toxicological synergies that increase the severity of mycotoxicoses (Speijers and Speijers, 2004).

 

Synergy of multiple mycotoxins

One clue that toxicological synergy involving mycotoxins occurs is that symptoms typical of mycotoxicoses are seen despite analysis of the feed that indicates only very low concentrations of mycotoxins (Trenholm et al., 1983). In this situation, it is not clear if a mycotoxin problem really exists, or if poor performance is due to management or nutritional factors. It is now known that unexpected toxicity may be due to toxicological interactions between different mycotoxins that exaggerate the toxicity. The likelihood of this occuring is greatest for the Fusarium mycotoxins.

Other research shows that feeding naturally-contaminated feedstuffs produces grater toxicity than feeding of an equivalent amount of purified mycotoxin (Trenholm et al., 1994). Fusaric acid, the most common of the Fusarium mycotoxins (Bacon et al., 1996), can increase the toxicity of the trichothecenedeoxynivalenol (DON or vomitoxin) (Smith et al., 1997). Fusaric acid, however, is seldom analysed in feeds due to its low toxicity when consumed in the absence of other toxins (Smith and MacDonald, 1991; Smith and Sousadias, 1993).

 

Adsorbents against mycotoxicoses

A variety of approaches have been used to prevent and treat mycotoxicoses in livestock and poultry, but the use of speciality feed additives referred to mycotoxin adsorbents is the most common (Huwig et al., 2001); Romos et al., 1996). For example, alfalfa fibre can have protective effects against zearalenone (James and Smith, 1982; Stangroom and Smith, 1984) and T-2 toxin (Carson and Smith, 1983b) but alfalfa is also often a source of Fusarium contamination in diets.

Hydrated sodium calcium aluminosilicate (HSCAS) has been shown to have potential to reduce aflatoxicosis, but has been shown not to be effective against Fusarium toxicoses (Patterson and Young, 1993). Bentonite has been shown to be effective against T-2 toxin (Carson and Smith, 1983a), but only at levels that are not practical in animal feeds. Other types of clays also have some potential benefits against T-2 toxin, but again only at very high levels of dietary inclusion (Smith, 1984). The problem of high levels of dietary inclusion of adsorbents has been overcome with the development of polymeric glucomannan mycotoxin adsorbents (GMA), which are extracted from the cell wall of yeast.

Another approach for the prevention of mycotoxicoses is the use of feed additives containing enzymes selected to ‘detoxify’ mycotoxin molecules in the lumen of the digestive tract. The challenge to this approach is to identify enzymes non-specific enough to detoxify combinations of mycotoxins that might produce toxicological synergies, but also specific enough to not cause structural damage to the digestive tract or to interfere with digestive function. Van der Eijk (2003) described such an enzyme product that will compromise the effectiveness of ELISA mycotoxin assay kits when assaying feeds. This would imply a high degree of non-specificity which could impair digestive function. Thermal stability of enzymes in pelleted or extruded feeds is also a concern.

 

In-vitro and in-vivo testing of additives

Van der Eijk (2003) also addresses the comparison of in-vitro and in-vivo methods for determining the efficacy of mycotoxin detoxification technologies. Simple in-vitro systems (constant pH and duration of incubation) do not correlate well with in-vivo feeding trials. This was demonstrated by Rotter et al., (1989) in the testing of activated charcoal to overcome ochratoxin A toxicity in poultry. Similar conclusions were drawn by Diaz et al., (2002, 2004) in determining the efficacy of different adsorbents to reduce aflatoxin M1 in milk. Nonetheless, even the most sophisticated in-vitro models (Zeijdner and Havenaar, 2003) cannot account for environmental factors that can indirectly influence the severity of mycotoxicoses under field conditions.

To approximate field conditions it is necessary to conduct in-vivo demonstrations of the efficacy of mycotoxin adsorbents. While the body of research on pigs continues to grow, some of the most recent work focuses on poultry.

 

Broilers

A total of 360 broiler chicks of a commercial strain were fed 4 diets for 56 days (Swamy et al., 2002a). The diets included: (1) control; (2) low level of contaminated grains (4.7 ppm deoxynivalenol + 20.6 ppm fusarc acid + 0.2 ppm zearalenone); (3) high level of contaminated grains (8.2 ppm deoxynivalenol + 21.6 ppm fusaric acid + 0.56 ppm zearalenone); and (4) high level of contaminated grains + 0.2% GMA (9.7 ppm deoxynivalenol + 21.6 ppm fusaric acid + 0.8 ppm zearalenone). Weight gain and feed intake were determined weekly. Blood and biliary samples were collected after 3 and 8 weeks and were analysed for hematology and serum chemistry.

The feeding of increasing levels of contaminated grains to broilers resulted in a linear decrease in growth rates and feed intake (P<0.05, Table 1).

 

Table 1.

Broilers: Effect of feeding blends of grains naturally-contamined with Fusarium mycotoxins on weight gain and feed consumption

 

 

Feed consumption (g/bird)1

 

Weight gain (g/bird)1

Diet

0-21 d

21-42 d

42-56 d

 

0-21 d

21-42 d

42-56 d

Control

908

2797

2544

 

435

1678

1303

Low mycotoxins

841

2565

2437

 

376

1522

1274

High mycotxins

923

2392

2456

 

386

1479

1319

High mycotoxins + 0.2% GMA3

968

2472

2532

 

392

1538

1348

SEM

 37

   60

   27

 

   6

   16

   13

Linear effect

NS4

0.05

NS

 

NS

0.04

NS

1Values are least square means; n = 3.

2Values are least square means; n = 90.

3Glucomannan mycotoxin adsorbent (MTB-100 glucomannan polymer from Alltech in all trials described in this article).

4Not significant (P>0.05). Source: Adapted from Swamy et al., 2004a.

 

This was not seen, however, until birds were in the grower phase. Elevations in red blood cell count and in serum hemoglobin and uric acid concentrations were noted at the end of the study (Table 2).

 

Table 2.

Broilers: Effect of feeding blends of grains naturally-contamined with Fusarium mycotoxins on hematology, serum chemistry and breast meat colouration

 

Diet

RBC1

Hb2

Uric acid3

Redness4

Biliary IgA5

Control

2.66

95.0

259

0.45

7.54

Low mycotoxins

2.84

101.1

286

0.67

7.28

High mycotoxins

2.83

99.2

357

0.80

4.99

High mycotoxins + 0.2% GMA6

2.54

91.2

281

0.21

6.54

SEM

0.04

1.37

10.9

0.07

0.29

Linear effect

0.01

0.01

0.009

 

0.01

1Red blood corpuscle counts (1012/L); n = 12.

2Hemoglobin concentration (ppm); n = 12.

3Uric acid concentration (μmoles/L); n = 12.

4Unitless scale, 0 = green, 1 = red; n = 15.

5Immuno-globulin A (mm precipitate); n = 15.

6Glucomannan mycotoxin adsorbent.

Source: Adapted from Swamy et al., 2002a.

 

Most of these effects were prevented by the feeding of GMA.

 

In this work, the feeding of contaminated grains to broilers resulted in reduced growth only in the grower and finisher phases, which supports the concept that broilers do not exhibit feed refusal in manner similar to swine fed Fusarium mycotoxin contaminated diets (Smith et al., 1997). The absence of this protective behaviour in broilers results in numerous adverse metabolic changes that progress with the consumption of contaminated materials. The reason for this species difference has been shown to be differences in the effects on brain neurochemistry (Swamy et al., 2004b). The feeding of contaminated grains to pigs elevated brain serotonin concentrations. In broilers, such treatments elevated both serotonin and catecholamines, thereby canceling the effect of serotonin on appetite suppresion.

It is likely that mycotoxin-induced growth suppression in the broilers in these trials was due to gradual alternations in metabolism that occured with extended feeding of contaminated grains. The alterations in red blood cell counts and hemoglobin contrentrations were similar to blood changes seen in ascites. In the current study, this may have been partially due to the hypotensive effect of fusaric acid. Reduced blood flow to the lungs may have constituted a stress which resulted in an adaptation and increased oxygen trapping capacity of the blood. The elevations in serum uric acid concentrations may be a reflection of the reduction in hepatic protein synthesis caused by the trichothecene mycotoxins deoxynivalenol and 15-acetyldeoxynivalenol. Elevated free amino acid concentrations would result in increased amino acid oxidation and increased nitrogen excretion in the form of uric acid.

 

Layers

For 12 weeks, a total of 145 laying hens (45 weeks old) were fed diets including: (1) control; (2) contamined grains + 0.2% GMA (Chowdhury and Smith, 2004). The diets including contaminated grains were found to contain 12 ppm deoxynivalenol, 0.5 ppm 15-acetyldeoxynivalenol and 0.6 ppm zearalenone. Parameters measured after 4, 8 and 12 weeks included feed consumption, rate of lay, egg and egshell quality and plasma chemistry.

The feeding of contaminated grains to laying hens decreased feed intake relative to controls in the first month, but increased feed intake relative to controls in the first month, but increased feed intake thereafter (Table 3).

 

Table 3.

Layers: Effect of feeding blends of grains naturally-contamined with Fusarium mycotoxins on feed consumption and feed efficiency

 

 

Feed consumption1

Feed efficiency2

Diet

Wk 0-4

Wk 4-8

Wk 8-12

Wk 0-4

Wk 4-8

Wk 8-12

Control

119

120

117

1.88

1.92

1.90

Mycotoxins

106

127

132

1.94

2.29

2.23

Mycotoxins + 0.2% GMA3

114

124

121

1.90

2.10

1.94

Pooled SD

9

9

7

0.18

0.27

0.17

Control vs. mycotoxins

0.008

0.04

0.0001

NS4

0.001

0.001

Mycotoxins vs. GMA

NS

NS

0.0006

NS

NS

0.003

1g/hen/day; n = 12.

2Feed consumed/egg mass; n = 12.

3Glucomannan mycotoxin adsorbent.

4Not significant (P>0.05).

 

This resulted in a large deterioration of feed efficiency in the latter months of the experiment. Egg production  also declined in months 1 and 2 (Table 4).

 

Table 4.

Layers: Effect of feeding blends of grains naturally-contaminated with Fusarium mycotoxins on organ weights and plasma uric acid concentrations

 

 

Organ weights (g)

Uric acid (μmol/L)

Diet

Liver

Spleen

Kidney

Wk 4

Wk 8

Wk 12

Control

44,51

2.2

5.9

  376

  392

  390

Mycotoxins

44.2

2.4

7.6

1009

1154

1030

Mycotoxins + 0.2% GMA2

46.2

2.2

6.6

  500

  539

  487

Pooled SD

7.58

0.66

0.98

188

156

159

Control vs. mycotoxins

NS3

NS

0.002

0.001

0.001

0.001

Mycotoxins vs. GMA

NS

NS

0.02

0.001

0.001

0.001

1n = 12.

2Glucomannan mycotoxin adsorbent.

3Not significant (P>0.05).

 

Serum uric acid concentrations were highly elevated throughout the study when contaminated grains were fed (P<0.001). This effect was prevented by the feeding of GMA.

The trial demonstrates that laying hens are less sensitive to the anorectic effects of contaminated grains than broilers. This is perhaps why metabolic changes, such as elevated serum uric acid concentrations in layers, are exaggerated compared to those seen in broilers.

 

Turkeys

A total of 225 day-old male turkey poults were fed corn, wheat and soybean meal-based diets for a total of 12 weeks, including starter (0-3 weeks), grower (4-6 weeks), developer (7-9 weeks) and finisher (10-12 weeks). Diets included: (1) controls; (2) contaminated grains; (3) contaminated grains + 0.2% GMA. Parameters measured included weight gain, feed consumption and serum chemistry (Tables 5 and 6).

 

Table 5.

Turkeys: Effect of feeding blends of grains naturally-contaminated with Fusarium mycotoxins on growth (g/bird)

 

Diet

Starter

Grower

Developer

Finisher

Overall

Control

632

1845

2446

2747

7670

Mycotoxins

573

1676

2220

2484

6953

Mycotoxins + 0.2% GMA1

624

1745

2468

2791

7628

Control vs. mycotoxins

0.01

0.01

0.01

0.01

0.01

Mycotoxins vs. GMA

0.02

NS

0.01

0.01

0.01

1Glucomannan mycotoxin adsorbent

 

Table 6.

Turkeys: Effect of feeding blends of grains naturally-contaminated with Fusarium mycotoxins on organ weights and plasma uric acid concentrations

 

 

Organ weights (g)

Uric acid (µmol/L)

Diet

Bursa

Spleen

Kidney

Wk 4

Wk 8

Wk 12

Control

  5.31

5.6

16.1

437

339

276

Mycotoxins

5.5

6.1

17.7

299

210

305

Mycotoxins + 0.2% GMA2

6.5

5.1

15.8

321

197

235

SEM

0.30

0.33

0.71

27

15

43

Control vs. mycotoxins

NS3

NS

NS

0.001

0.001

NS

Mycotoxins vs. GMA

0.03

0.05

0.05

NS

NS

NS

1n = 12.

2Glucomannan mycotoxin adsorbent.

3Not significant (P>0.05).

 

Thus, broilers, layers and turkeys are all sensitive to Fusarium mycotoxicoses. The adverse effects of the diets fed in the current studies are greater than literature reports based on the DON content. This is likely because of the relatively short duration of previously reported trials. The blending of different naturally-contaminated grains, moreover, also results in a more complex mixture of mycotoxins, thereby increasing the chances of toxicological synergy between mycotoxins.

Data from the research described above and other sources indicate that the adverse effects of Fusarium mycotoxins in a wide range of animal species can be overcome by the feeding of a suitable mycotoxin adsorbent such as GMA. This has important economic consequences when widespread contamination of the feed supply forces the feeding of contaminated grains or when favourable pricing prompts the intentional feeding of contaminated materials.

 

Appendix

 

Mycotoxin contamination: More cases, more severe effects

Based on recent data, both the global frequency of mycotoxin-contamination of the feedstuffs and the severity of mycotoxicoses in livestock and poultry appear to be increasing.

A recent survey of maize-based foods and feeds in Indonesia indicated the presence of zearalenone, an estrogenic Fusarium mycotoxin, in 36% of samples (Nuryono et al., 2004). Contamination was recorded in the range of the 5.5-526 µg/kg with poultry feeds being most commonly contaminated (>85.7%). Maize samples collected in Karnataka, India, were analysed for mycotoxins and were found to have contamination rates of 15.2% for ergosterol, 17.7% for aflatoxin, 4.5% for T-2 toxin, 1.5% for ochratoxin, 9.6% for zearalenone and 1.0% for deoxynivalenol (DON) (Janardhana et al., 1999). Fusarium mycotoxins were analysed in Nepalese maize and wheat by Desjardins et al. (2000). Fumonisins were found in 22% of maize samples while DON and nivalenol were found in 16% of maize samples. Wheat was less contaminated. Surveys of mycotoxin contamination of Brazilian corn used for animal feed have been reviewed by Salay and Mercadante (2002). Very high levels of fumonisin were reported with some significant contamination with DON and zearalenone in addition to pockets of aflatoxin.

The European market is continuously surveyed for mycotoxins including aflatoxin, ochratoxin and Fusarium mycotoxins (Creppy, 2002). Maize harvested in nothern Italy during the period 1995-1999 was most often contaminated with fumonisins, although aflatoxin, DON and zearalenone were also detected (Pietri at al., 2004). DON content of winter wheat harvested in Germany from 1995-1998 was monitored by Birzele et al. (2002). The highest level of DON contamination was in 1998 (310 µg/kg). Other, less commonly reported Fusarium mycotoxins such as beauvericin and enniatins have also been reported in European wheat (Logrieco et al., 2002).

This higher frequency of mycotoxin contamination may be due, in part, to increased monitoring of suspect materials and an increased awareness of the symptoms of mycotoxicoses by veterinarians and producers. Global climate change has also contribute to an increased grequency of mycotoxin contamination of feed grains. Drought, excessive rainfall and flooding can all promote mould growth.

 

Dr. Smith is a professor in the Department of Animal and Poultry Science at the University of Guelph, Ontario, Canada, who may be contacted by tsmith@uoguelph .

A complete list of references is available directly from the author.

 

Feed International,Vol.26,# 4,april 2005,Watt Publication,U.S.A.

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