Mycotoxin contamination of pig feeds

Higher humidity due to increased rainfall. The increase in humidity before harvest, due to excess in rainfall and floods, promotes mould growth and increases the risk of mycotoxin contamination.

Droughts. Extremely dry conditions also can increase the chances of mycotoxin contamination. Smaller, cracked grains may allow mould spores to cross mechanic fibrous barriers and grow inside the layers of the endosperm.

Mycotoxins can be produced in:

• Drought (warm and dry conditions) (e.g. aflatoxins, fumonisins)
• In humid and cold conditions (e.g. Deoxynivalenol (DON), zearalenone, fusaric acid)

Advances in analytical methods – LC/MS/MS method

The growing utilisation of the LC/MS/MS method to measure mycotoxins in animal feed constitutes a great advancement in the fight against mycotoxin contamination.

Figure 1. LC/MS/MS analyser

• The technique uses liquid chromatography coupled with two mass spectrometers connected in tandem (Fig. 1).
• LC / MS / MS is a method of high sensitivity, able to quantify simultaneously multiple mycotoxins and metabolites. This constitutes a unique feature.
• LC/MS/MS services are already commercially available.

Emerging mycotoxins

Analysis of historical data of LC/MS/MS tests have pointed out the frequency of feed contamination with several mycotoxins at one time. This method has also shown the presence of mycotoxins rarely measured before, mostly due to the unavailability of ELISA kits to test for them. These mycotoxins are known as “emerging mycotoxins” (Table 1) (Gruber-Dorninger et al., 2016). Little is known about their toxicity to pigs and other species.

A good example of the utilisation of LC/MS/MS is the work by Blandino et al. (2017). Those researchers analysed maize samples cultivated in natural conditions in Italy, throughout several years. They detected 37 different mycotoxins and metabolites. All samples contained fumonisins, fusaric acid, fusaproliferin, DON, DON-3-glucose, culmorin and zearalenone.

The administration of diets contaminated with only one mycotoxin showed a 14% drop in feed intake, and a 17% drop in average weight gain.This concept was backed up by the studies performed by Andretta et al. (2016). They did a metanalysis on data obtained  from 85 published papers on the effect of feeding diets contaminated with mycotoxins to growing pigs.

• Pigs eating diets contaminated with multiple mycotoxins showed a drop in feed consumption of 42%, whilst the daily gain was 45% lower.

These values, once again, emphasise the importance of additive and synergistic effects when diets are contaminated with multiple mycotoxins.

Conjugated (masked) mycotoxins

It seems that some plants have the ability of chemically modifying the mycotoxins produced by invading fungi. This can be a natural defence mechanism if one considers that some mycotoxins are also phytotoxic.

• Some of the first conjugated mycotoxins ever reported, included DON-3-glucose (Berthiller et al., 2005) and Zearalenone-4-glucose (Schneweis et al., 2002)

• These compounds are not detectable with traditional analytical techniques, such as ELISA and HPLC and, therefore, sometimes they are known as “masked” mycotoxins.

• More recently, researchers reported the occurrence of conjugated forms of fumonisin, toxin T-2, rivalenol and fusarenona-X.

However, the relative toxicity of these compounds for pigs have not yet been clarified. The difficulty of the task is given by the fact that bacterial enzymes of the gastrointestinal tract may hydrolyse the mycotoxins conjugates, generating free mycotoxins that can enter the bloodstream to reach the target tissues. Researchers believe that such undetectable conjugates contribute to an unexpectedly high toxicity in pigs, if estimations were based on resuots of conventional analytical techniques.

Feeding pregnant and lactating sows with diets naturally contaminated with mycotoxins produced by Fusarium spp.

First set of studies

A series of trials were performed, in which first-time pregnant sows were given diets consisting of a mix of maize and wheat, naturally contaminated with mycotoxins. Feeding took place during 21 days before farrowing (Diaz-Llano and Smith, 2006) and during the first 21 days of lactation (Diaz-Llano and Smith, 2007).

• The diets contained multiple co-contaminants, including DON, zearalenone, and fusaric acid.
• Since the diets were naturally contaminated, one could suppose that conjugated forms of mycotoxins were also present.

Evaluated parameters

During the trials, the following variables were measured:

• Changes in body weight
• Feed intake
• Blood chemistry
• Reproductive parameters
• Milk composition
• Time return to oestrus.

Treatments

• control (minimal contamination)
• contaminated with 5,5 ppm de DON
• contaminated + 0,2% de mycotoxin binder based on yeast cell wall

Results in the gestational phase

• There was not significant effect on the daily feed intake in the gestational phase.
• However, body weight gain and feed conversion efficiency were depressed in the group receiving contaminated feed.
• Although sows receiving diets containing mycotoxins gained less body weight than sows eating the control diet, there were no effects on the body weight of the piglets born alive.

It was concluded that the lower body weight gain by the end of pregnancy, observed in sows eating contaminated feed, was due to a lower intestinal absorption caused by DON-mediated damage of intestinal mucosa.

The reduction of arterial blood pressure caused by fusaric acid should have affected the transference of nutrients to the foetuses. However, the lack of effect of the contaminated diet on the piglets may have been the result of the sow mobilizing its own energy and protein reserves to compensate for the deleterious effect of mycotoxins.

Results in lactation

• During the lactation phase, sows eating contaminated feed significantly reduced feed intake, and experienced a significant weight loss compared with the control animals.
• Although the sows ingesting contaminated feed may have had negative energy and protein balances, the diets did not have any effect on the nutrient content of the milk or on the body weight gain of piglets.

It was again concluded that the sows compensated the toxic effects of the contaminated diets, by mobilising their own body reserves.

Results in reproductive phase

Contaminated diets affected the reproductive function.

Stillborn piglets

• The frequency of stillbirths was 6.3% for control sows, and 15.5% for sows fed a contaminated ration.
• Groups in which a mycotoxin binder was added to the feed, showed a 4.6% of stillbirths.

Return to oestrus

• The period from weaning to the onset of the new oestrus was of 6.3 days for control sows, and 15 days for the sows eating contaminated feed.

This supports the theory that a prolonged return to oestrus in sows eating contaminated feed was due to a longer time needed to replenish body reserves.

Second set of studies

In a later stage, researchers posed the question of whether body weight loss was due to a direct effect of the mycotoxin, or due to a reduction in feed consumption. A second study was performed (Diaz-Llano et al., 2010) to find an answer to that question. It also aimed to determine the mechanisms whereby the toxin binder reduces the number of stillborn piglets.

The experimental design of the first study was repeated, but with the addition of a fourth treatment. In it, the sows were fed a restricted amount of control diet to emulate the effect of reduced feed intake during lactation, but in absence of mycotoxins. Muscular biopsies were taken to analyse DNA, RNA and proteins.

Results

The results suggested that stillbirths in sows eating contaminated diets was due to an increase in the blood concentration of ammonium. The mycotoxin binders probably adsorbed the ammonia in the digestive tract, preventing the developing foetus from being intoxicated.

Based on the results of muscular biopsies, the severe weight loss during lactation, verified in sows eating contaminated feed, was due to the reduction in feed intake and not because of a direct toxic effect of the mycotoxins.

Conclusions

Gestating and lactating sows are negatively affected when consuming diets naturally contaminated with mycotoxins of Fusarium spp. The greatest economic losses are probably related to the prolonged time needed to restore body condition before entering the new oestrus.

This article was originally published in nutriNews Spain with the title Contaminación por micotoxinas de los alimentos para cerdos