Understanding labels and ingredients
Probiotics vs prebiotics for dogs: what’s the difference?
A probiotic is a live micro-organism; a prebiotic is a substance, such as inulin or FOS, that micro-organisms already living in the gut selectively use. A product containing both is sometimes called a synbiotic — though that word, too, has a precise scientific meaning.
7 min read · Written by the PAWVIVE team. Sources are listed at the end of every guide.
The short answer
The two words sound alike, but they describe very different things. A probiotic is alive: the international consensus definition is “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”. A prebiotic is not alive: it is “a substrate that is selectively utilized by host microorganisms conferring a health benefit” — in plain terms, something the microbes already in the gut can use as food.[1],[2]
Both definitions come from consensus statements published by the International Scientific Association for Probiotics and Prebiotics (ISAPP) in Nature Reviews Gastroenterology & Hepatology. They are worth knowing because each one contains a test — a substance doesn’t become a probiotic or a prebiotic just because a label says so.[1],[2]
What is a probiotic?
The ISAPP panel, convened in 2013, kept the long-standing FAO/WHO definition with a minor grammatical correction. Three parts of it matter: the micro-organisms must be live, they must be given in adequate amounts, and a benefit to the host must have been shown. The panel also noted that probiotics can be aimed at different target host species, including animals as well as people.[1]
- Dead microbes, microbial products and microbial components do not come under the probiotic classification.
- Live cultures traditionally associated with fermented foods, where there is no evidence of a health benefit, sit outside the probiotic framework.
- The panel listed minimum criteria that products labelled “probiotic” too often fail to meet: defined contents, an appropriate viable count at the end of shelf life, and suitable evidence for a health benefit.
- Some effects may be shared across many strains of well-studied species; others are more likely to be strain-specific.
Source [1]
Because “probiotic” is a defined term, some labels describe their bacteria more literally. The DIGEST+ label, for example, calls its bacteria “active bacteria” and a “live culture blend”, and lists each strain by name.
What is a prebiotic?
In 2016 an ISAPP panel updated the definition of a prebiotic to “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. The word that does the work is selectively: a prebiotic must be used by particular members of the gut’s microbial community, not simply digested or fermented by everything. The panel retained the requirement for selective, microbiota-mediated mechanisms, and said beneficial effects must be documented for a substance to count as a prebiotic.[2]
The updated definition can include non-carbohydrate substances and body sites beyond the gut, and the panel stated that it applies to prebiotics for animals as well as for people. Prebiotics have been studied and used in companion animals, livestock, poultry and aquaculture.[2]
Inulin and FOS: the classic prebiotic fibres
Inulin and fructooligosaccharides (FOS) are fructans — chains built from fructose units. When the prebiotic idea was first defined, fructans (FOS and inulin) and galactans (galactooligosaccharides, or GOS) were the substances that fitted it, and the ISAPP panel describes FOS and GOS as the most researched prebiotics today. Chicory root is a well-known source of inulin; the ISAPP statement discusses inulin extracted from chicory specifically.[2]
On a dog supplement label, you may see inulin listed with its source and a note that it contains fructooligosaccharides — the DIGEST+ label lists “inulin from chicory root (fructooligosaccharides)” under composition. There is more on this ingredient at inulin and FOS.
What is a synbiotic?
In 2019 ISAPP convened a further panel on synbiotics and defined a synbiotic as “a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host”. The panel described two kinds:[3]
- A complementary synbiotic is a probiotic plus a prebiotic, each meeting its own criteria, that haven’t been designed to work together.
- A synergistic synbiotic is one where the substrate is designed to be selectively used by the micro-organisms given alongside it; its parts need not each qualify as a probiotic or prebiotic on their own.
Source [3]
The same statement says a synbiotic’s beneficial effect must be confirmed in the target host — which might be people, companion animals or farmed species. It also notes that, in studies to date, the substrate part is usually GOS, inulin or FOS. So a product that simply contains live bacteria and a prebiotic fibre has the ingredients of a synbiotic, but the term itself implies evidence in the animal it is intended for.[3]
Probiotics, prebiotics and synbiotics compared
| Probiotic | Prebiotic | Synbiotic | |
|---|---|---|---|
| What it is | Live micro-organisms | A substrate selectively used by the host’s own micro-organisms | A mixture of live micro-organisms and substrate(s) |
| Alive? | Yes | No | Partly — the micro-organisms are |
| ISAPP consensus statement | 2014 (panel met 2013) | 2017 (panel met 2016) | 2020 (panel met 2019) |
| Familiar examples on labels | Named Lactobacillus and Bifidobacterium species | Inulin, FOS, GOS | A named live culture plus inulin or FOS |
| How the amount is usually shown | Colony-forming units (CFU) per tablet, gram or serving | Milligrams, or a percentage of the product | Both of the above |
| Key test in the definition | Live, adequate amount, shown benefit | Selective use by microbes, documented benefit | Benefit confirmed in the target host |
For what a CFU figure does and doesn’t tell you, see what CFU means.
How micro-organisms are regulated in dog feed in GB
Dog supplements sold as complementary feed, such as DIGEST+, come under animal feed law in Great Britain, and micro-organisms added to feed are regulated as feed additives. The Food Standards Agency describes feed additives as substances, micro-organisms or preparations (other than feed materials and premixtures) intentionally added to feed or water to perform specific functions. They are regulated products: they may be placed on the market only if they have been authorised, and used only for the purpose stated in the authorisation.[4]
The legal basis is assimilated Regulation (EC) No 1831/2003. It sorts additives into categories; the zootechnical category includes “gut flora stabilisers: micro-organisms or other chemically defined substances, which, when fed to animals, have a positive effect on the gut flora”. The FSA keeps a register of the feed additives permitted for use in Great Britain, with references to their terms of authorisation.[5],[4]
How they appear on a label
- Live micro-organisms are normally named by genus and species — for example Lactobacillus acidophilus or Bifidobacterium lactis — sometimes with a strain code, and their quantity is given in CFU.
- For pet feed, additives in the zootechnical category must be listed with their specific names and/or identification numbers, the added amount, and the name of their functional group or category.
- Feed materials — the ingredients that make up the product — are listed under the heading “composition”, in descending order by weight.
- Some labels emphasise a prebiotic fibre on the front of the pack; where a feed material is emphasised in words or pictures, its percentage by weight must be shown.
You may also notice that bacterial names are changing. In 2020 a taxonomic study proposed splitting the genus Lactobacillus into 25 genera, creating new names such as Lactiplantibacillus and Lacticaseibacillus, while species such as Lactobacillus acidophilus stayed in Lactobacillus. Many labels, including ours, still use the long-established names; the strain pages explain the newer ones.[8]
What’s on the DIGEST+ label
DIGEST+ is a complementary feed for dogs that lists both kinds of ingredient, plus enzymes. Its live culture blend contains five strains — Lactobacillus acidophilus, Lactobacillus brevis, Bifidobacterium lactis, Lactobacillus rhamnosus and Lactobacillus plantarum — providing 2 billion CFU per tablet. Its composition lists inulin from chicory root (fructooligosaccharides), and it also contains a 150 mg digestive enzyme complex.
Because the ISAPP definition of a synbiotic asks for a benefit confirmed in the target host, we simply describe DIGEST+ by what its label lists: active bacteria, a prebiotic fibre and enzymes, for daily digestive support. The number of tablets depends on your dog’s weight — see the dose calculator.
Questions people ask
What is the difference between a probiotic and a prebiotic?
A probiotic is made of live micro-organisms given in adequate amounts with a shown benefit to the host. A prebiotic is not alive: it is a substance, such as inulin or FOS, that the micro-organisms already living in the gut selectively use.
Is inulin a prebiotic?
Inulin and fructooligosaccharides (FOS) were among the first substances to fit the prebiotic definition, and FOS and GOS are described by the ISAPP consensus panel as the most researched prebiotics. Chicory root is a common source of inulin.
What is a synbiotic?
Under the 2020 ISAPP definition, a synbiotic is a mixture of live micro-organisms and substrates selectively used by host micro-organisms that confers a health benefit on the host. The benefit is expected to be confirmed in the target host, such as a dog.
Are probiotics for dogs regulated in the UK?
In Great Britain, micro-organisms added to animal feed are feed additives under assimilated Regulation (EC) No 1831/2003. Feed additives must be authorised before they are placed on the market and used only for their authorised purpose, and the Food Standards Agency keeps a register of those permitted.
Work out your exact supply
The calculator on the product page takes your dog’s weight band and how many dogs you have, then shows the daily dose, how long a bottle lasts and a sensible refill rhythm.
Sources
- Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic (Hill et al., 2014) — Nature Reviews Gastroenterology & Hepatology. Checked 2026-10-15.
- Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics (Gibson et al., 2017) — Nature Reviews Gastroenterology & Hepatology. Checked 2026-10-15.
- The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics (Swanson et al., 2020) — Nature Reviews Gastroenterology & Hepatology (via PubMed Central). Checked 2026-10-15.
- Animal feed additives — Food Standards Agency (GOV.UK). Checked 2026-10-15.
- Regulation (EC) No 1831/2003 on additives for use in animal nutrition — Annex I: Additive groups — legislation.gov.uk. Checked 2026-10-15.
- Regulation (EC) No 767/2009 on the placing on the market and use of feed — Annex VII: Labelling particulars for feed for non-food producing animals — legislation.gov.uk. Checked 2026-10-15.
- Regulation (EC) No 767/2009 — Article 17: Specific mandatory labelling requirements for compound feed — legislation.gov.uk. Checked 2026-10-15.
- A taxonomic note on the genus Lactobacillus: description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae (Zheng et al., 2020) — International Journal of Systematic and Evolutionary Microbiology (via PubMed). Checked 2026-10-15.
Updated