A False Sense of Security

Concerns over the presence of mycotoxins, the secondary toxic metabolites produced by various moulds in poultry feed, are nothing new. Major effects on birds include poor weight gain/egg production, reproduction and immunity.

Historically, mycotoxin research focused on the effects of a single mycotoxin, but in the last decade or so, research has turned towards uncovering the menacing world of toxic interactions that can occur when two or more different mycotoxins are present in feed. “These interactions can lead to toxicity at very low concentrations – concentrations at which no toxicity is expected when we look at each mycotoxin in isolation,” says Dr. Swamy Haladi, global technical manager, mycotoxin management team at Alltech Canada in Guelph, Ontario.

Haladi and his Alltech colleague Dr. Ted Sefton, along with University of Guelph scientists Dr. Herman Boermans and Dr. Niel Karrow, have been trying to understand these interactions based on the published research work. “Toxicity from interactions has already been assessed when two different mycotoxins are present in the same feed (see table), but the issue gets more complicated when three or more mycotoxins are present,” Haladi explains. “With some mycotoxins, their combined toxicity is simply their individual toxicity levels added together. However, with some, there is a synergistic interaction that makes the feed far more toxic than one would predict.”

Mycotoxins in feed

The most significant mycotoxins for the global poultry industry include aflatoxins, ochratoxins, T-2 toxin, deoxynivalenol (DON), fumonisins and zearalenone (ZEA). Fusarium mycotoxins such as DON and ZEA are the most common and widespread throughout Canada, while ergot toxins tend to be a bigger challenge in Western Canada. Haladi says other Fusarium mycotoxins such as 3-acetyl DON, and 15-acetyl DON are also frequently found in Canadian feedstuffs at low levels, but they are seldom tested for. “Although not common, T-2 toxin and its related compounds may also be present,” he notes.

Haladi also says that research from Dr. Trevor Smith’s lab at University of Guelph shows that turkeys are the most sensitive poultry species to Fusarium mycotoxins, and among chickens, laying hens have higher risk than broiler chickens due to their long-term exposure.

Since one mould can produce several mycotoxins, and several moulds can be present in one feedstuff, it is expected that there are likely more mycotoxins present in a given feed sample than are being tested for. “If a sample contains T-2 toxin, for example, chances are there are several others, likely HT-2 toxin and neosolaniol, present as well,” Haladi explains. “We know now that these toxins contribute to the toxicity of T-2 toxin, but because we neither test for their presence nor had a way of analyzing their interactions, we have a false sense of security about that sample of feed. This is why it’s so important to be able to test for and analyze as many toxins as possible in an affordable and timely manner.”

To be able to assess the toxicity of a feed containing multiple mycotoxins, Haladi and his colleagues propose a ‘Toxicity Index’ (TI) for each mycotoxin present in the feed based on published ‘LD50 values’ (these values are the concentration at which half the one-day-old chicks that ingest it, perish).

“The TIs are calculated using the ratio of LD50 value of the least toxic mycotoxin by the LD50 value for each of the other mycotoxins identified,” Haladi explains. “Each TI is then multiplied by the corresponding mycotoxin concentration in the feed. The products of such multiplication are then added to obtain a total mycotoxin concentration, which can then be used to predict the potential toxicity of the feed.”

Next steps

Being able to calculate a TI value for every feed sample depends on two main factors – the first being to identify and quantify all mycotoxins in feed. Haladi says quick ELISA mycotoxin tests are important for use on grain at Canadian feed mills, but that test only screens for DON. “This is where Alltech’s 37+ Program will be able to help,” Haladi says. “It will be commercialized this year, and will allow 38 mycotoxins to be analyzed in a single run using sophisticated analytical equipments such as Ultra Pressure Liquid Chromatography with double mass spectrometry.” According to Haladi, this methodology is very accurate and sensitive. “Our recent analysis of 37+ Program has shown that more than 90 per cent of North American feed ingredients contained one or more mycotoxin,” says Haladi. “About 45 per cent of samples contained five or more mycotoxins.”

The other factor is that not all LD50 values have been determined. “More research to find LD50 values for the less-studied mycotoxins is needed,” Haladi notes.

“There is no single magic bullet for mycotoxin control,” he concludes. “Mycotoxins are formed in the field as well as in storage. Minimizing mycotoxin production is a matter of using various management programs on-farm and at feed mills.

However, knowing the toxicity that results from interactions between toxins is another tool to help the poultry industry reach better bird health and productivity.”

Some mycotoxin interactions in poultry

Dr. Swamy Haladi says that with some mycotoxins, their combined toxicity is simply their individual toxicity levels added together. However, with some, there is a synergistic interaction that makes the feed far more toxic than one would predict.

Mycotoxins  –  Type of interaction
Aflatoxin  B1 X Ochratoxin A – Synergistic
Aflatoxin B1 X Diacetoxyscirpenol – Synergistic
Aflatoxin B1 X T-2 toxin – Synergistic
Aflatoxin B1 X Cyclopiazonic acid –   Additive
Aflatoxin B1 X Deoxynivalenol –   Additive
Ochratoxin A X T-2 toxin   –  Additive
Ochratoxin A X Cyclopiazonic acid  –  Additive
T-2 toxin X Deoxynivalenol  –  Synergistic
T-2 toxin X Fumonisin B1 –   Additive
Fumonisin B1 X Moniliformin  –  Additive
Fumonisin B1 X Fusaric acid   – Synergistic
(source: Devegowda and Krishnamurthy, 2005)