Mycotoxins are toxic secondary metabolites formed naturally by moulds on crops and forages in the field and during storage after harvest. In food and feed they pose a potential threat to human and animal health. Fusarium, Penicillum and Aspergillus moulds are the main sources producing a variety of different types of mycotoxins.
The most commonly known mycotoxins found in animal feed and feed materials are:
Aflatoxin How big is the threat of aflatoxins in poultry diets?
Deoxynivalenol (DON) How does DON affect feed intake in pigs?
Co-occurrence of mycotoxins
However, there are around 500 known mycotoxins. Recent surveys, using liquid chromatography-tandem mass spectrometry to analyse animal feed and feed raw materials, revealed that all of the samples contained a multitude of mycotoxin metabolites. In most cases 26 to 30 different metabolites were detected.
Other studies and surveys analyzing for the more commonly known mycotoxins have shown that 30-100% of feed samples contained more than one type of mycotoxin. The reality is that nutritionists, and producers are often dealing with raw materials and feed with multiple mycotoxin contamination.
A survey conducted on 330 samples of feed ingredients found that Corn was by far the most affected by co-contamination.
Research on toxicological interactions of mycotoxins found that most of the studies reported synergistic or additive interactions regarding adverse effects on animal performance.
This explains, why more severe responses are seen in animals despite low contamination of individual mycotoxins found in the feed, when more than one mycotoxin is present.
Deoxynivalenol (DON) belongs to the trichothecene group of mycotoxins and is the most prevalent mycotoxin found in feed materials around the world. Neogen reports DON in the wheat and barley 2016 harvest of several states in the USA (Figure 1 below) and certain states such as Michigan, Illinois, Indiana and Iowa have also reported DON in corn.
Pigs are particularly sensitive to DON in the diet and generally the first symptoms to be seen in pigs is a reduction in feed intake. This is particularly detrimental to performance in young pigs, but can also impact older pigs. A meta-analysis (Andretta et al 2012) on 85 published papers on the impact of mycotoxins on pig performance showed that feed intake was 26% lower in animals that consumed diets containing DON in comparison with control groups.
Other stress reactions to DON at the cellular level
While the biggest negative impact on pig performance from DON is due to a reduction in feed intake, there are stress reactions at the cellular level and in the gut that can increase the susceptibility to disease and reduce efficiency of performance in pigs.
Increase in inflammatory responses
Shifts in the gut microflora towards more pathogenic bacteria
Reduced gut integrity
Figure 1 attribution to www.wattagnet.com
A well known response to the mycotoxin deoxynivalenol (DON) is a reduction in feed intake. This is particularly the case in pigs. According to a meta-analysis (Andretta et al 2012) DON reduces feed intake by 26% in pigs.
DON is globally the most prevalent mycotoxin in pig diets and there are signs that this year’s harvest of certain crops is contaminated with significant levels of this mycotoxin. Feed intakes at risk with DON in 2016/17 harvest
What controls appetite?
One constant physiological factor of appetite control are certain gut peptides, of which cholecystokinin (CCK) is one of them. CCK is released in response to feed intake and sends signals to the brain contributing to the sensation of satiety, when it binds to certain receptors, such as CCK1R.
Scientific studies show that CCK1R antagonists increase meal size and food intake in experimental animals, and they increase hunger, meal size, and caloric intake in humans.
Physiological effects of CCK include stimulation of gastric acid, gallbladder and pancreatic secretion, decreased gastric motility and suppression of energy intake.
Researchers studied the control of eating by CCK in pigs extensively. As in humans, carbohydrates, proteins and lipids all stimulate CCK secretion in pigs. Active immunization against CCK increased food intake and body weight in pigs (Pekas and Trout 1990) confirming the importance of CCK in feed intake.
How does DON affect appetite?
More recent studies carried out in mice show that the decreased feed intake in mice in response to DON in the diet corresponds with a significant increase in CCK in mice compared to a control diet. Studies with a relevant antagonist known to bind to the same receptors as CCK report that the negative impact of DON on feed intake in mice can be reduced through the antagonist.
The conclusion was that CCK plays a major role in feed intake reduction in response to DON. DON exposure also elicited higher proinflammatory cytokine responses in mice, which could be another cause of DON-induced anorexia.