Zearalenone and zearalenol are produced almost exclusively by Fusarium species that contribute to the ear and stalk rot that occurs in the ears of corn and on the heads of cereal grains (scab) standing in the field or in stored ear corn in the Corn Belt. However, in 1986, these mycotoxins were detected in delayed harvest soybeans at up to 5 ppm. When consumed by swine at more than 0. 1 to 5 parts per million (ppm) (mg toxin per kg body weight), these compounds cause the estrogenic syndrome, which is characterized in females by a swollen and edematous vulva with enlarged mammary glands and in young males by a shrinking of the testes. Young gilts may show uterine prolapse. The financial loss to farmers comes about primarily through poor reproductive performance.
Estrogenism in swine and dairy cows is usually more prevalent in the winter and early spring because, once the fungus is established in the grain, it generally requires a period of relatively low temperatures to produce biologically significant amounts of zearalenone. When some strains of Fusarium graminearum grow in corn they produce a mixture of toxins along with zearalenone. One or more of these can cause severe stunting and other deleterious effects in swine.
Decreased fertility, prolonged estrus, and swelling of the vulva are signs that dairy cows have fed on rations containing zearalenone as well as other natural toxicants produced through natural infection of feed ingredients (corn, hay, barley). Animals vary as to their response, but some will show standing estrus at mid-cycle.
Broiler chicks and laying hens, unlike swine and dairy cows, are affected very little by dietary zearalenone even when fed massive doses. Pure zearalenone fed to broiler chicks and finishing broilers at rates from 10 to 800 ppm produced no effect on weight gain, feed consumption, and feed-to-gain ratio. The weights of the liver, heart, spleen, testicles, oviduct, comb, and bursa were similar to those in the controls that received no zearalenone. In laying hens, zearalenone had no effect on egg production, egg size, feed consumption, body weight, fertility, hatchability of fertile eggs, or reproductive performance. When turkeys ate feed containing 300 ppm of zearalenone (a massive dose), they developed greatly enlarged vents within 4 days, but there were no other gross effects.
The effects of zearalenol are similar to zearalenone, but zearalenol is generally considered to produce estrogenic effects five to ten times greater than those of zearalenone. Fusarium graminearum requires a minimum of 22 to 25 percent moisture to grow in cereal grains. Generally, shelled corn stored at these moistures is likely to be colonized by a mixture of other fungi, yeasts, and bacteria with which F. graminearum competes poorly. F. graminearum ear rot is primarily a problem in stored corn in cribs exposed to low temperatures.