160 The past, present, and future of biotics in companion animal nutrition

Abstract Being members of Carnivora, dogs and cats have a relatively simple gastrointestinal tract designed for diets rich in protein and fat and relatively low in dietary fiber. Despite their simplicity, the canine and feline gastrointestinal tracts harbor complex microbial communities that are important for immune system development, pathogen resistance, energy harvest, and overall host health. Over the past few decades, researchers have not only demonstrated the importance of diet on pet nutritional status but also how it impacts the gastrointestinal microbiota and consequent health outcomes. Even though most pets are healthy, loose stools, constipation, and various gastrointestinal disorders and diseases are common. Therefore, pet food products supporting gastrointestinal health are some of the most popular. For decades, dietary fibers have been used to maintain stool quality, provide laxation, reduce fecal odor, and modulate fermentative end-products. Similar benefits have been demonstrated for prebiotics, a term that was coined by Glenn Gibson in 1995. Its most recent definition is a “substrate that is selectively utilized by host microorganisms conferring a health benefit.” Probiotics are another popular strategy to promote the gastrointestinal and immune health of pets and are commonly present in supplement form, although they may be present in treats, toppers, and complete and balanced diets. Probiotics are “live microorganisms that when administered in adequate amounts confer a health benefit”. Synbiotics, “mixtures comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confer a health benefit”, may reap the benefits of both components whether they are operating independently (complementary synbiotic) or in unison (synergistic synbiotic). In recent years, yeast- and bacteria-based postbiotic products have been shown to provide benefits and become quite popular in companion animals. Postbiotics are “preparations of inanimate microorganisms and/or their components that confer a health benefit.” Even though the benefits of biotics have been demonstrated and they are widely used by the pet food and supplement industries, responsiveness and efficacy are known to be highly variable. As microbiome science advances and more powerful laboratory assays, robotics, and equipment become available, more targeted and effective strategies for health promotion are expected. Top-down (health-associated microbes, substances, and preparations) and bottom-up (target-based discovery) strategies may be used to identify novel biotics from host organisms, fermented foods, chemically or physically modified substances, or the environment. In the future, next-generation biotics that are based on host genetics, diet, health status, and commensal microbiome composition are expected to provide greater precision and personalization. As global human and animal populations, animal-human interactions, and antimicrobial resistance continue to rise, the use of biotics will become increasingly important. Biotics may not only be useful on a micro level, but may reduce the density of pathogens and antimicrobial residues that impact water and waste management systems.