Saccharomyces Boulardii

Saccharomyces Boulardii is a single-ingredient probiotic yeast for dogs — paired with organic inulin from Jerusalem artichoke as its prebiotic fuel. Unlike bacterial probiotics, S. boulardii is a yeast, which means it is not affected by antibiotics or most gut-stressing medications. This makes it the Four Leaf Rover probiotic to reach for when a dog is actively on antibiotics, recovering from a course of medication, or dealing with the kind of digestive upset that bacteria-based probiotics can't fully resolve.

Unusually for the category, Four Leaf Rover's formula contains no maltodextrin — the high-glycemic carrier most probiotic supplements are bulked out with. No fillers, no synthetics, no artificial ingredients. Just probiotic yeast and whole-food prebiotic. Available in 49.5g.

Most probiotics — Lactobacillus, Bifidobacterium, and their variants — are bacteria. That has a significant consequence: antibiotics destroy them. If your dog is on a course of antibiotics, a bacterial probiotic given at the same time is largely wasted, because the same medication that's killing the infection is also killing the probiotic. Saccharomyces boulardii is different. It's a yeast, not a bacteria, so antibiotics leave it untouched. This makes it the rare probiotic that can be given during active antibiotic treatment — not just after — and that's when gut support matters most.

S. boulardii is a transient probiotic — it doesn't colonise the gut permanently the way bacterial probiotics try to. Instead, it passes through, working while it's present. Research shows it supports a healthy intestinal tract, helps maintain gut lining integrity, influences parts of the immune system that regulate gut permeability, and defends against problematic yeast and opportunistic bacteria. It's particularly well-studied for its role in managing antibiotic-associated diarrhoea and helping the gut recover faster after a course of medication.

This is the probiotic for specific situations rather than everyday use. Dogs on antibiotics. Dogs recovering from a recent course of medication. Dogs with chronic loose stools that haven't responded to other probiotics. Dogs with yeast-related gut disruption. Dogs with recurring digestive upset where bacterial probiotics have been tried and come up short. For everyday probiotic maintenance, Protect is the better choice. For acute digestive flare-ups in dogs not on medication, BiFido for Fido delivers broader multi-strain coverage. S. Boulardii is the specialist tool.

Most probiotic supplements use maltodextrin as a bulking carrier — a highly processed, high-glycemic filler with no nutritional value. Four Leaf Rover's formula uses organic inulin from Jerusalem artichoke instead: a whole-food prebiotic that supports microbial diversity, encourages beneficial gut bacteria to flourish, and keeps the probiotic yeast viable during storage. Inulin is a soluble fibre that ferments slowly in the colon, providing steady prebiotic support without the glycemic spike.

Maltodextrin carries the highest glycemic index of any common food ingredient — higher than sugar. It's used in most probiotic supplements because it's cheap and bulks out the powder, but it contributes nothing of nutritional value and can work against the gut environment probiotics are trying to support. Four Leaf Rover makes a point of excluding it from every product in their range. Saccharomyces Boulardii contains no maltodextrin, no dextrins of any kind, no fillers, no flavours, and no preservatives.

Every batch of Saccharomyces Boulardii is third-party tested for pesticides, heavy metals, and microbial contaminants, with a Certificate of Analysis available on request. Four Leaf Rover holds the NASC Quality Seal — the benchmark for quality control in the pet supplement industry — and is certified Plastic Negative by rePurpose Global, removing twice the plastic from the environment that it creates. Manufacturing is GMP-compliant. Ingredients are sourced from trusted suppliers across New Zealand, North America, and Europe, with organic chosen wherever possible.

Active ingredients. Source: Four Leaf Rover.

Saccharomyces boulardii (probiotic yeast). Organic Inulin from Jerusalem Artichoke.

Free from: maltodextrin, dextrins of any kind, preservatives, fillers, binders, synthetics, artificial flavourings, artificial colourings, GMO ingredients, gluten, and dairy.

Give once or twice daily, mixed into food. Measure according to your dog's body weight using the guide below. For dogs on antibiotics, twice-daily dosing alongside the medication is recommended throughout the course.

A 49.5g jar typically lasts anywhere from around two weeks to several months depending on your dog's size and whether S. Boulardii is used during an antibiotic course, for acute support, or as an ongoing supplement.

Refrigerate after opening to preserve the probiotic yeast — S. boulardii is living and degrades faster at warmer temperatures. If refrigeration isn't possible, store in a cool, dark place and use within 30 days of opening. Keep the lid tightly sealed.