Antibiotic feed supplements have been used in commercial poultry farming to promote growth and prevent disease. However, the spread of antibiotic resistance has been linked to the widespread use of these antibiotics, in particular resistance to fluoroquinolones. In 2006, the European Union (EU) banned antibiotics in chicken feed and in 2015, the United States Federal Drug Agency issued a Veterinary Feed Directive restricting the use of antibiotics only for assuring animal health under veterinary supervision. As a result, there is great interest in alternative growth-promoting and prophylactic feed supplements, such as probiotics, live microorganisms that confer a health benefit on the host. Many probiotic products are already available for commercially farmed poultry, and a number of these contain bacterial spores of the genus Bacillus. Bacterial spores are well suited for use as probiotics as they are metabolically dormant and resistance to environmental stresses resulting in long shelf life during distribution and storage. Furthermore, they are able to able to survive the bacteriocidal environment of the stomach and germinate in the chicken GI tract where they become metabolically active, secreting either antimicrobial compounds and/or competing for essential nutrients with the normal microbiome.
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