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In general, the use of low doses of antibiotics decreases the number of the most susceptible bacterial communities and enhances the growth of the resistant bacteria. Nutritional composition of feed and thus local availability of raw materials as well as seasonal changes will impact the intestinal flora.
By Gino Lorenzoni, technical manager Biomin, Austria
Through the years the assessment of microbial populations has relied on in vitro culture techniques using selective or non-selective media. One of the main disadvantages of this method is that it can only assess culturable microorganisms. Recently, other culture-independent methods that rely on molecular techniques have been developed to study bacterial populations. Through these modern approaches we have learnt that there are many species of bacteria that we are not able to grow in vitro, including many unknown genera of bacteria.
Actually, it has been estimated that less than 25% of the intestinal bacteria have been cultured. Consequently, when analysing intestinal bacterial populations we must consider that we are observing a modest portion of the real ecosystem and conclusions drawn from diverse studies must be taken carefully. It has been reported that the microbial communities present in the intestinal tract of poultry are modified by a number of factors including stocking density, diet, feeding practices, housing conditions, age of birds and pathogens. Even though bacterial ecosystems among flocks tend to be similar, quantitative and qualitative differences exist among individuals even if raised in the same pen with a common source of feed and water. It is also very well established that bacterial communities change radically between the different anatomical segments of the digestive tract.
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