Plant and fungal toxins as contaminants of feed and meat

Abstract

Most plant material used as feed contains natural substances that can be toxic to animals under certain conditions. Such chemicals are referred to as phytotoxins in this chapter, although this term is also used for chemicals that are toxic to plants. Forage plants have evolved under the impact of predation by animals (and insects) and only those containing chemical defenses have survived. Animals (although not necessarily livestock species) have co-evolved with these plants and have developed means to circumvent or neutralize these chemicals, at least to a degree that allows both animal and plant species to survive, and at least under natural foraging situations. Nevertheless, livestock can be poisoned in a range of circumstances that are described in the chapter, with pronounced effects on the costs of meat production and meat quality. In a similar manner, fungi utilize plant material as a food source and have evolved chemical defenses against predators. Those toxic to animals are called mycotoxins; they can be produced by fungal pathogens of plants, by symbiotic endophytes in grasses, or by saprophytes on leaf litter in pasture. Mycotoxins are also produced in seeds (grain, nuts, pulses) before harvest and in any of these materials during storage. Some toxins are produced by both plants and fungi, so the differentiation is not clear-cut. Ruminants are thus exposed to a very wide range of toxins in forage and feed. The direct impact of toxins on the costs of meat production is far higher than is generally recognized and can greatly affect the viability of livestock enterprises. The chapter discusses the effects of a range of phytotoxins and mycotoxins on livestock in both grazing and fed situations, the potential for meat residues, detection methods, and processes to minimize exposure.