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Mycotoxins produced by Fusarium spp. are of two general types: 1) the nonestrogenic trichothecenes, including DON, nivalenol, T-2 toxin, and diacetoxyscripenol, and 2) the mycoestrogens, including Zearalenone (ZEN) and zearalenol . Zearalenone and zearalenol are both estrogenic resorcylic acid lactone compounds produced by the fungi Fusarium spp. (Diekman and Green, 1992)

Despite their structural dissimilarity to the steriodal estrogens, ZEN and several of its derivatives possess estrogenic activity. ZEN undergoes a folding such that hydroxyl or potential hydroxyl groups become appropriately orientated to facilitate binding to tissue receptors that normally bind estrogens. Similar binding affinities for ZEN have been determined for the estrogen receptor in sheep and calf uterus.(Diekman and Green, 1992)

Poultry show little reaction to ZEN ingestion. However, swine are strongly affected with symptoms in prepubertal gilts including enlarged mammae, swelling of uterus and vulva, and atrophy of the ovaries. In severe cases, prolapse of the vulva and rectum may occur. Boars exhibit enlarge mammae and atrophied testes.(Flannigan, 1991)

Although cattle are not as sensitive to ZEN as swine, a few experiments have been done to determine whether ZEN affects performance of cattle. Infertility, reduced milk production, and hyperestrogenism in cows have been reported in association with ZEN. Hay containing 14 ppm of ZEN caused infertility in cattle. Holstein cows that consumed 25 to 200 ppm of ZEN for 42 consecutive days exhibited swollen and hyperemic external genitalia but had estrous cycles of normal lengths and normal ovulations. Enlarged mammary glands that exhibited secretory activity were reported in prepubertal heifers that consumed moldy corn with ZEN. Dairy cattle fed a ration that contained 385 to 1925 ppb of ZEN for 7 weeks had normal milk productin. No ZEN residues were found in milk, urine, serum or tissues. Corn that contained 500 ppb of ZEN had no effect on milk or butterfat production. (Diekman and Green, 1992)

Virgin dairy heifers fed 250mg of purified ZEN for three estrous cycles had an average conception rate of 62%, compared with 87% in control heifers. Nonlactating, nonpregnant dairy cows given 500 mg of ZEN daily for two estrous cycles had normal serum concentration of progesterone, normal mating behavior, and normal genital tracts. (Diekman and Green, 1992)

In vivo studies have revealed that ZEN is rapidly metabolized in animals and humans and eliminated mainly as water-soluble glucuronsides. Free and conjugated froms of ZEN have been found in the milk of lactating cows under experimental conditions. That high oral doses of the toxin are required to elicit such a response indicates that consumption of contaminated feed by dairy cows would not result in a health hazard to humans.(Wood, 1992)

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