The value of feed enzymes in promoting growth and efficiency of nutrient utilization is well recognized in monogastric animal production. However, the effects of feed enzymes on gastrointestinal (GIT) microbiome are largely unrecognized. That is particularly important since the intestinal microbiota plays a critical role not only for the overall well-being of the animal, but also for its nutrition, performance and quality of the products produced. It is well established that many factors influence the diversity and activity of the GIT microbiota, including the age of the animal and the environment it inhabits, dietary factors (e.g. antibiotics, ingredients), disease load, season, stress and genetics. Feed enzymes appear to impact the GIT microbial ecology by reducing the undigested substrates, particularly in the upper gut, and producing oligosaccharides in situ from cell wall non-starch polysaccharides with potential prebiotic effects. Recent investigations employing high throughput molecular microbiology techniques have demonstrated feed enzymes-mediated responses on energy utilization in broiler chickens that are associated to certain clusters of GIT bacteria. Furthermore, investigations using specific enteric disease challenge models in poultry and swine have demonstrated efficacy of feed enzymes in modulating gut health in antibiotic-free feeding programs. Nonetheless, the response of the microflora to enzyme addition appears to depend on the initial microbial status, which in turn depends on other factors that impact GIT microbiota. Since feed enzymes are likely to change substrate characteristics along the GIT, the subsequent responses will vary according to the populations present at the time of administration and their reaction to suchchanges. It is not surprising that given the huge range of microbial conditions likely to exist between studies, the responses to enzyme use, rather than being absolute, are a continuum or a population of responses. However, recognition that feed enzymescan impact gut microbiota and thus gut health will stimulates development of feed enzymes capable of modulating gut microbiota to the benefit of host health under specific production conditions. The present review brings to light opportunities and challenges for the role of feed enzymes on gut health of poultry and swine species with a specific focus on the impact on GIT microbiota.
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