The following videos, while not equine specific, give an excellent overview of the latest research on human and animal microbes, and why gut microbes are so crucial for good health. Keep in mind that while these videos talk primarily about humans, a vast amount of research was conducted on animals.
Here are some books that you may want to purchase and read, to educate yourself concerning probiotics, bacteria, and genetics.
10% Human gives an excellent look at the latest research that has uncovered how our (and animals) microbiota are affected by diet, drugs, gluten, weather, stress, pregnancy, and birthing methods. The author also presents information that links gut microbes and diseases such as diabetes, obesity, autism and mental illnesses.
Fascinating and easy to understand, this book will change the way you view your (and your animals) world, in addition to providing you with information to make healthier choices on a daily basis.