Zearalenone in pig feed – a challenge to solve

Zearalenone is a secondary metabolite of fungi of the Fusarium genera, in particular F. culmorum, F. graminearum and F. crookwellense. These fungi colonise cereals mostly during the harvest and are typically found in regions with a temperate climate. Zearalenone is very often co-occurring with another important mycotoxin, deoxynivalenol (DON). Co-occurrence can potentiate negative effects.

Zearalenone is a so-called myco-oestrogen. This means that it binds to the same receptors as 17ß-oestradiol and the most important effects are on the reproductive system. Thus, the economic losses through feed contaminated with ZEA are clearly evident in farrowing units: gilts with delayed reproductive performance, heat repetition in gilts and sows, increase in the number of stillborn piglets/sow/cycle and therefore a decrease in weaned piglets/sow/year.

Metabolism of zearalenone

When the mycotoxin is ingested by an animal, most of it is immediately transformed by the intestinal mucosa cells into two different molecules: α- and β-zearalenol, being the first and most abundant metabolite. This transformation is the first part of the xenobiotic metabolism process and is an attempt of the organism to create compounds that can be easily excreted.

Remaining ZEA and its metabolites pass the intestinal barrier and enter the bloodstream. The rate of absorption is estimated to be around 80% in swine. Once in the blood, the toxins are bound to lipoproteins and transported to the liver. There, further transformation of ZEA into α- and β-zearalenol takes place.

The second part of the metabolism of the toxin is the conjugation: a polar molecule (mainly glucuronic acid) is paired with the toxin, resulting in a water-soluble complex that can be excreted with the urine.

The glucuronidation is managed by the enzyme glucuronil-transferase. Its quantity in the organism of every animal species is variable and so also the capacity of the animal to process toxins. Amongst all livestock animals, swine have a low glucuronidation capacity and are therefore the most sensitive to zearalenone as well as to other toxins.

ZEA and its metabolites are not toxic in the ordinary sense; their negative effect lies in their similarity to normal sex hormones (17β-oestradiol). In animals, the receptors of these hormones ‘recognise’ the mycotoxins as hormones causing respective symptoms. This phenomenon is known as hyper-oestrogenism, an excessive oestrogenic activity in the organism.

Figure 1 – Chemical structure of zearalenone compared to 17 β-Oestradiol.

Hyper-oestrogenism

Signs of hyper-oestrogenism in gilts like oedema and reddening of vulva can be seen with levels of zearalenone as low as 180 ppb of the toxin in the feed, and they become more pronounced at higher levels. Guidance levels from the European Feed Safety Authority (EFSA) are 250 ppb in complete feed for sows and finishing pigs, 100 ppb for piglets and gilts.

Figure 2 shows a survey of different studies and the presence and absence of hyper-oestrogenism in newborn female piglets, gilts and sows, showing that symptoms can already appear at around 200 ppb of the toxin. The clinical symptoms depend on age, nutrition, health status of the animals and their environment.

Figure 2 – Zearalenone levels in feed and signs of hyper-oestrogenism (HO) in gilts.

It is a well-known fact that zearalenone affects fertility and reproduction. The symptoms in sows are clear and at medium or high contamination consist of oestrus cycle irregularities, abnormal vaginal bleeding, and enlargement of the volume of the uterus. The milk of weaning sows can contain the toxin if they are fed with diets contaminated with more than 200 ppb. The toxin also crosses the placental barrier and newborn female piglets have swollen and reddened vulva.

At high levels (3,000 ppm and higher), ZEA additionally is associated with anoestrus, abortion, increased embryonic death, foetal death and increased incidence of stillborn and splay legged piglets. A summary of effects can be found in Table 1.

Moreover, ZEA can also interfere with the immunity of the animals e.g. lead to a decrease of pro-inflammatory mediators like TNF-α, IL-8, IL-6, IL-1b and IFN-γ.

Toxin risk management

Even with thorough preventive measures it is quite improbable that feedstuffs are entirely free of mycotoxins. Most of the contamination occurs on the field, where external factors such as weather conditions cannot be controlled by man. However, there has been a lot of research in the field of mycotoxin counteraction over the past few years and today several solutions are available to reduce the negative effects of mycotoxins in animals.

In order to evaluate the effectiveness of an anti-mycotoxin product (Mastersorb Gold, EW Nutrition) against ZEA, a trial was conducted. Three groups of gilts were formed, one negative control, one challenged with 1,500 ppb of ZEA in the feed, and one group fed with contaminated feed and 3 kg/tonne of the anti-mycotoxin product.

Figure 3 – Average vulva volume of female piglets challenged with ZEA with and without an anti-mycotoxin product*.

As an indicator of hyper-oestrogenism, which is expected at the levels at which the mycotoxin was fed, the vulvar volume (Figure 3) and the relative weight of the reproductive tract were measured. Figure 3 shows the positive effects of the product, which significantly reduced the vulva volume of the gilts after 21 days of challenge (p<0,01, Tukey Test, from day 9 on). Furthermore, a positive effect in reducing the weight of the reproductive tract of the animals could be demonstrated.

The best approach to manage a mycotoxin risk is to implement an integrated strategy that includes good practices for growing and storing grain, as well as regular sampling and analysis. The results of a mycotoxin analysis can then be used to make decisions regarding the inclusion levels of raw materials and also the choice of products with anti-mycotoxin action that prevent the passage of mycotoxins into the bloodstream, and that at the same time support the liver function.