Common probiotic strains for pets include Lactobacillus acidophilus, Enterococcus faecium, and Bacillus coagulans. They work by colonizing the intestinal tract, producing antimicrobial substances, and competing with harmful bacteria for resources and attachment sites on the gut lining. Probiotics are particularly helpful during and after antibiotic treatment, during dietary transitions, in stressful situations (boarding, travel), and for pets with chronic soft stools. They come as powders, chews, capsules, or are incorporated directly into pet food. Refrigerated products often maintain higher viable bacteria counts. Not all human probiotics are suitable for pets, so choose products specifically formulated for your pet's species.