The following article is a special collaboration from AFMA (Animal Feed Manufacturers
We thank their kind support.
Zearalenone is a resorcyclic acid lactone compound with estrogenic properties
and it is capable of binding to oestrogen receptors. Pigs are particularly susceptible
to Zearalenone toxicity which elicit the following hyperestogenism toxicity
signs (Etienne and Dourmand 1994):
Pre pubertal gilts: Reddening
and swelling of the vulva, increased size of the uterus, mammary enlargement,
and rectal and vaginal prolapse.
Boars: Testis atrophy, nipple
enlargement, and rectal prolapse.
Mature sows: Prolonged oestrus,
ovarian atrophy, pseudopregnancy, abortion, increased embryonic mortality, stillbirths,
and birth of weak piglets often suffering from straddle leg.
Toxic levels: Pigs are very sensitive to Zearalenone and within the species,
prepubertal gilts seem most sensitive (Dickman and Green, 1992).
- Friend et al. (1990) reported reddening and swelling of the vulva and increased
uterus weight after feeding contaminated feed for 9 weeks. These authors concluded
that 0.5 ppm of Zearalenone was estrogenic.
- Levels of 3.6 to 20 ppm consistently increased the intersrous interval in
gilts (Dickman and Green, 1992).
- Levels of less than 30 ppm appears to have minimal effects on litter size
while levels of 60 to 90 ppm results in the complete loss of foetuses (Patience,
Thacker and de Lange 1995).
- Levels of 60 ppm have no effect on semen quality or libido in mature boars
(Patience et al 1995) while Dickman and Green (1992) summarised that levels
of 40 to 600 ppm reduced testis weight and libido in boars.
- The effect of Zearalenone on growth is less clear. Some experiments have
demonstrated that as little as 10 ppm of Zearalenone depresses pig growth
while other experiments suggest that growth is actually enhanced by Zearalenone.
Part of this variable response may be due to the contamination of test ingredients
with other toxins. Coffey et al. (1990) summarised that Zearalenone improved
growth performance in pig fed aflatoxin.
Zearalenone toxins are often present in feed as indicated by the commonly swollen
and reddened vulvas in prepubertal gilts, which is sometimes even seen in new-born
litters. The widespread presence of Zearalenone contamination is also confirmed
in tests conducted by the Maize Trust Out of 57 samples tested during the 2001-harvesting
season, 55 contained traces of Zearalenone (<0.1 ppm) while only 2 samples
contained more than 0.1 -ppm Zearalenone.
The cost of Zearalenone toxicity to the pig industry is difficult to access.
The only tangible cost is the direct expenditure on Mycotoxin binders. Production
losses caused by Zearalenon are impossible to determine - these losses are probably
confined to units using mouldy ingredients or having poor grain or feed storage
facilities. The reasons why reproduction losses from Zearalenone are believed
to be small are as follows:
- Toxic effects are reversible and disappear 1 -2 weeks after withdrawal of
contaminated feed (Etienne and Dourmand 1994).
- When cases of suspected Zearalenone toxicosis occurs, toxic levels of Zearalenone
have never been detected.
- The reproduction efficiency on top units is consistently good and is not
improved by mycotoxin binders. This may point towards ineffective binding
but nevertheless puts Zearalenone toxicosis into perspective.
* (With acknowledgement to Spesfeed News, Summer Edition, February 2002)