One of the most amazing scientific discoveries of the last decade has been the important roles that the trillions of micro-organisms in our guts (called the "microbiota") play in promoting good physical health and emotional well-being. Unfortunately, many aspects of the modern world conspire to alter the composition and function of the gut microbiota in ways that damage health, especially in the elderly where strong correlations have been seen between microbiota composition and frailty. Work from our research group and others suggests that one very important factor that damages the microbiota in the modern world is our separation from many micro-organisms with which the investigators co-evolved and which have the ability to lower the types of chronic inflammation that are ubiquitous in the modern world and that contribute to the development of most of our most pressing health issues, from diabetes and heart disease to depression and dementia (Huang et al., 2013; Mayer et al, 2014; Naseribafrouei, 2013). While much has been written about the positive psycho-social impacts that animal-human relationships have on human psychological health (Allen et al, 1991; Allen et al.; 2002; Collins et al, 2006; Kwong & Bartholomew, 2011; Kurdek, 2008; Wells, 2007), less is known about the direct physical effects that animals have on human health. What is known, however, is largely related to animals' effects on stress reduction (Allen et al, 1991; Allen et al., 2002) anxiety (Foster & McVey Neufeld, 2013), mood (Collins et al, 2006) and cardiovascular disease (Allen et al., 2002) What has been largely unexplored, however, is the mechanism by which these interactions and positive impacts on human health are taking place. Thus, working with colleagues who are world leaders in studying links between the microbiota and health, the investigators propose to conduct a study designed to explore the potential of dogs to serve as "probiotic delivery systems" to enhance the physical health and cognitive and emotional functioning of at-risk elderly persons.