Dairy calves are born with sterile gastrointestinal tracts (Uyeno et al., 2015). Microflora ingested during the birth process are the first colonizers of the calf gastrointestinal tract (GIT). Thereafter, bacteria from the calf’s environment are ingested. Ingested bacteria can be one of 2 types: pathogenic or commensal. In dairy calves, pathogenic bacteria cause illness and diminish efficiency of digestion and overall growth. Commensal bacteria, on the other hand, pose no such problem and often have favorable outcomes on calf growth. Probiotics are living organisms that, when consumed, maintain or restore beneficial bacteria to the digestive tract. Strains from the Lactobacillus, Enterococcus, and Bifidobacterium genera have been used efficaciously as probiotics in dairy calves (Uyeno et al., 2015). Times where probiotics may be especially beneficial to dairy calves include after a course of antibiotics during heat stress (Ruppert et al., 1998) and during the weeks surrounding weaning. Calves that consume probiotics tend to consume higher amounts of milk, grain, and forage earlier than non-treated calves, resulting in higher average daily gains (Quigley et al., 2014). Probiotics can be purchased over the counter at feed stores and anywhere that sells veterinary medicine. They are available in many forms to make administration easier. When used as a preventative, probiotics are an affordable first line of defense for dairy calves.