An historical overview of field disease outbreaks known or suspected to be caused by consumption of feeds contaminated with Fusarium toxins

The interest in mycotoxins began when aflatoxins were found to be carcinogens and to be widespread in foodstuffs and feedstuffs. Today, mycotoxins and mouldy feedstuffs are known causes of animal disease. Symptoms are often subtle and there can be many equally non-definitive contributing factors; for example, environmental stress, exposure to multiple mycotoxins and infectious agents, and nutrient/vitamin deficiencies. Thus, it is often difficult to establish cause-effect relationships with contaminated feedstuffs. The Fusarium toxins of greatest concern are deoxynivalenol (DON), fumonisins, and zearalenone. For each, mould-contaminated feed was implicated as the cause of animal disease long before the toxins were identified. In the field, changes in performance or behaviour and increased susceptibility to infectious disease are possible subtle signs of exposure to mycotoxins in feed. Because most cases of toxicity present non-specific clinical signs, cases of suspected mycotoxicosis often remain unreported. Nonetheless, for DON, fumonisin and zearalenone there are signs that are highly suggestive of exposure. For DON a commonly observed effect is feed refusal which has been reported in cattle, pigs and chickens; however, pigs appear to be the most sensitive. Although DON is not considered to be acutely toxic to farm animals, it is considered to be a major cause of economic loss due to reduced performance. In pigs, the reduction in feed intake occurs relatively soon after consuming feeds containing greater than 1 mg deoxynivalenol/kg and emesis at > 10 mg/kg. Field outbreaks of mouldy maize-induced equine leukoencephalomalacia (ELEM) have been reported since 1891 and in 1988 pure fumonisin was shown to produce ELEM in a horse. ELEM syndrome is a fatal disease that apparently occurs only in equids. The length of exposure, level of contamination, individual animal differences, previous exposure, or pre-existing liver impairment may all contribute to the appearance of the clinical disease. Analysis of feeds from confirmed cases of ELEM indicates fumonisin 131 concentration greater than 10 mg/kg in the diet is associated with increased risk of ELEM. Another disease caused by fumonism is porcine pulmonary edema syndrome. Zearalenone has been implicated in field outbreaks of reproductive problems, vulvovaginitis and anestrus in pigs. The primary effect of zearalenone is estrogenic and prepubertal female pigs are the most affected animal. The history of discovery of mycotoxin involvement in animal diseases serves as a warning that yet to be discovered mycotoxins could also be involved in current or future inexplicable animal production problems. Published by Elsevier B.V.