Effects on poultry and livestock of feed contamination with bacteria and fungi

Animal feed may serve as a carrier for a wide variety of microorganisms. The primary mode of inoculation of feed materials is the transference of soil by wind, rain, mechanical agitation, or insects to standing crops. Some of the microorganisms are adapted to the desiccated and relatively nutrient-poor conditions in soil and survive in similar niches on growing crops. Gastrointestinal pathogens can also introduced into the food chain by animals defecating in the farm environment or by fertilization of crops with manures. Other microorganisms are introduced during storage. In general, the amount of available water in the feed matrix determines whether a microorganism will grow or survive. Some microorganisms, primarily moulds, are adapted to the low amount of available moisture and grow actively within stored seeds and grains. Others will produce spores or enter survival state until the moisture is high enough for bacterial action. There are numerous ways contaminating microorganisms can affect feed quality negatively including reducing dry matter and nutrients, causing musty or sour odours, causing caking of the feed and producing toxins. Finally, feed can act as a carrier for animal and human pathogens. The type of feed, processing treatments and storage conditions can all be factors that influence the population levels and types of microorganisms present. The incidence and variation in the microflora found in animal feed and feed materials are reviewed. A select number of important human and animal pathogens are discussed. Finally there is a brief overview over the detection, surveillance and management strategies of microbial contamination in feed and feed materials.