Antibiotic growth promoters (AGPs) have been used in animal agriculture for over 50 years, primarily to enhance growth efficiency. However, concerns about antimicrobial resistance have led to regulatory actions in the EU and the US. Denmark was the first country to ban AGPs in 1995, followed by the EU in 1997. The ban resulted in a significant reduction in antimicrobial use, with a 54% decrease in total antimicrobial usage in food animals from 1994 to 2001. Despite this, therapeutic use of certain antimicrobials increased, particularly for diseases like necrotic enteritis. The ban on AGPs did not negatively impact animal productivity in Denmark, with broiler productivity remaining stable. However, swine productivity declined after the ban. The biological basis of AGP effects involves interactions with the intestinal microbiota, which can influence nutrient absorption and microbial balance. AGPs reduce competition for nutrients and microbial metabolites that depress growth. They also affect gut structure and function, improving nutrient digestibility. However, the use of AGPs may lead to the development of antibiotic-resistant bacteria, which can be transmitted to humans. The World Health Organization (WHO) recommends phasing out AGPs in classes also used in human medicine and promoting alternative strategies to reduce antimicrobial use. In the US, AGP use is less regulated, but consumer pressure and industry concerns have led to calls for reduction. Major poultry producers have begun to remove AGPs from feed. The future of AGPs globally is uncertain, with the WHO advocating for the containment of antimicrobial resistance in food animals. Alternatives to AGPs, such as organic acids, are being explored, but they must provide economic benefits and address issues like enteric diseases and airsacculitis. The replacement of AGPs will likely involve a combination of products and management changes to maintain productivity. The gastrointestinal microbiota plays a crucial role in animal health, providing nutrients, protection against pathogens, and influencing immune function. However, it also competes with the host for nutrients and can produce toxic compounds. The balance of the microbiota is essential for optimal growth and health. Manipulating the microbiota through diet and supplements is a key area of research, with antibiotics historically used to modulate gut flora. However, the decline of AGP use has led to increased therapeutic antimicrobial use, highlighting the need for effective alternatives. The future of AGP use will depend on balancing the benefits of growth promotion with the risks of antimicrobial resistance.Antibiotic growth promoters (AGPs) have been used in animal agriculture for over 50 years, primarily to enhance growth efficiency. However, concerns about antimicrobial resistance have led to regulatory actions in the EU and the US. Denmark was the first country to ban AGPs in 1995, followed by the EU in 1997. The ban resulted in a significant reduction in antimicrobial use, with a 54% decrease in total antimicrobial usage in food animals from 1994 to 2001. Despite this, therapeutic use of certain antimicrobials increased, particularly for diseases like necrotic enteritis. The ban on AGPs did not negatively impact animal productivity in Denmark, with broiler productivity remaining stable. However, swine productivity declined after the ban. The biological basis of AGP effects involves interactions with the intestinal microbiota, which can influence nutrient absorption and microbial balance. AGPs reduce competition for nutrients and microbial metabolites that depress growth. They also affect gut structure and function, improving nutrient digestibility. However, the use of AGPs may lead to the development of antibiotic-resistant bacteria, which can be transmitted to humans. The World Health Organization (WHO) recommends phasing out AGPs in classes also used in human medicine and promoting alternative strategies to reduce antimicrobial use. In the US, AGP use is less regulated, but consumer pressure and industry concerns have led to calls for reduction. Major poultry producers have begun to remove AGPs from feed. The future of AGPs globally is uncertain, with the WHO advocating for the containment of antimicrobial resistance in food animals. Alternatives to AGPs, such as organic acids, are being explored, but they must provide economic benefits and address issues like enteric diseases and airsacculitis. The replacement of AGPs will likely involve a combination of products and management changes to maintain productivity. The gastrointestinal microbiota plays a crucial role in animal health, providing nutrients, protection against pathogens, and influencing immune function. However, it also competes with the host for nutrients and can produce toxic compounds. The balance of the microbiota is essential for optimal growth and health. Manipulating the microbiota through diet and supplements is a key area of research, with antibiotics historically used to modulate gut flora. However, the decline of AGP use has led to increased therapeutic antimicrobial use, highlighting the need for effective alternatives. The future of AGP use will depend on balancing the benefits of growth promotion with the risks of antimicrobial resistance.