Zearalenone in South African Pig Feeds

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The following article is a special collaboration from AFMA (Animal Feed Manufacturers Association) www.afma.co.za
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.

Field observations
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)

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