Prebiotics

Prebiotics are fibres the animal cannot digest but its gut bacteria can. They pass through the stomach and small intestine largely untouched, reach the colon, and get fermented by the resident microbial population. The distinction that trips everyone up:

• Prebiotics are food for bacteria — fibres.

• Probiotics are the bacteria themselves — live organisms.

• Synbiotics combine both.

• Postbiotics are the useful compounds bacteria produce.

Prebiotics have one clear practical advantage over probiotics: they are fibres, not living things, so they survive storage, heat and stomach acid without any of the viability problems that make probiotic products unreliable.

How They Work

Fermentation in the colon produces short-chain fatty acids — principally butyrate, propionate and acetate. Butyrate is the main fuel source for the cells lining the colon, which means feeding the bacteria is indirectly feeding the gut wall itself. Fermentation also lowers colonic pH, which disadvantages several pathogenic species, and the increase in beneficial bacteria crowds out less desirable ones by competing for space and nutrients.

The Main Types

Type · Common sources · Notes

• Fructo-oligosaccharides (FOS) — Chicory, added to many foods — The best-studied true prebiotic

• Inulin — Chicory root, Jerusalem artichoke — Strongly fermentable; gas if overdone

• Mannan-oligosaccharides (MOS) — Yeast cell wall — Works mainly by binding pathogens rather than feeding bacteria

• Beet pulp — Sugar beet fibre — Moderately fermentable; good for stool quality

• Psyllium — Plantago husk — Mostly bulking; specific equine use below

• Galacto-oligosaccharides (GOS) — Dairy, legumes — Also present in goat milk

• Lactulose — Synthetic disaccharide — Prescription use in liver disease

Prebiotics in Everyday Foods and on Pet Food Labels

You don’t have to buy a tub to find prebiotic fibre. Today’s Veterinary Nurse notes that only two classes fully meet the strict definition: oligofructose (the short-chain FOS, which ferments quickly) and inulin (longer chains, which ferment more slowly).

• Oligofructose occurs naturally in soybeans, oats, beets and tomatoes.

• Inulin occurs in Jerusalem artichoke, jicama and chicory root.

• Other fermentable fibre — Hill’s lists oats, barley, peas, beans, potatoes and bananas as natural prebiotic sources. Psyllium husk and beet pulp are the fibres most often added to pet foods.

On an ingredient list, look for chicory root, dried chicory, inulin, fructooligosaccharides, beet pulp, dried yeast or yeast cell wall (a MOS source) and galactooligosaccharides. Their presence doesn’t tell you much about the amount. Prof. Kelly Swanson notes via the ISAPP that most commercial pet foods include prebiotics at under 0.5 percent of the formula, deliberately, to limit gas and loose stool.

What the Evidence Supports

The canine evidence is respectable without being dramatic. Studies have shown FOS and inulin shift faecal microbial populations and increase short-chain fatty acid production in dogs, and beet pulp has reasonable evidence for stool quality. What has not been shown is that a healthy dog on a good diet becomes measurably healthier with a prebiotic added. The clearer uses are recovery after antibiotics, animals with loose stool of no serious cause, and supporting management of chronic digestive conditions.

It is worth saying that the most effective prebiotic intervention for most animals is the diet itself. A complete food with appropriate fibre does this job. A supplement makes most sense when something has disturbed the system.

Which Animals Benefit Most

According to the same ISAPP summary of the research by Prof. Swanson of the University of Illinois, prebiotics in dogs and cats have been shown to improve stool consistency, shift gut bacteria and their by-products in a favourable direction, and reduce the incidence or severity of some infections. Some studies also found better glucose metabolism and insulin sensitivity. The animals most likely to benefit are:

• Older animals — see our senior dogs entry.

• Animals on or recovering from antibiotics. Prebiotics are fibre, not live bacteria, so the antibiotic can’t kill them. Ask your vet whether to start during the course or straight after.

• Animals under stress — boarding, travel, a move, kennelling.

• Animals with certain gastrointestinal disorders, with a diagnosis and your vet’s agreement.

Two tolerance points matter for how much you give. Dogs and cats evolved on low-fibre diets, so their short digestive tracts can ferment only so much. Dogs tolerate more than cats, and small dogs tolerate more per kilogram than large dogs, which are more prone to loose stool — so ramp even more slowly in a big dog. More is not better either: at higher levels, FOS and inulin reduce how well protein is digested.

How Much to Give

Animal · Inulin or FOS daily · Psyllium daily

• Cat — 1/4 to 1/2 gram — 1/4 to 1/2 teaspoon

• Dog under 20 lbs — 0.5 to 1 gram — 1/2 teaspoon

• Dog 20 to 50 lbs — 1 to 2 grams — 1 teaspoon

• Dog over 50 lbs — 2 to 4 grams — 1 to 2 teaspoons

• Horse, psyllium for sand — — — See equine section

Start at a quarter of the target and build over two weeks. This is not optional advice. Too much fermentable fibre too quickly produces gas, bloating, borborygmus and loose stool — the exact symptoms you were trying to fix. This is the single most common reason people conclude prebiotics do not suit their animal, when the problem was the ramp rate.

How to Give It

Mix the powder into food, ideally split across meals rather than given in one hit. Psyllium must be given with plenty of water, since it works by absorbing fluid and swelling. Give prebiotics consistently and judge them over three to four weeks.

One timing note: if you are also using slippery elm, that coats the gut lining and should be separated from other supplements and medication by an hour or two.

Dogs, Cats and Horses

Cats are less fibre-tolerant than dogs and need smaller amounts. MOS and FOS are both used, and cats with inflammatory bowel disease sometimes react badly to highly fermentable fibre, so go slowly. See cat safety.

Horses deserve a genuine reframing here, because the horse is the most sophisticated fibre-fermenting animal of the three and most equine prebiotic marketing misses the point. The most important prebiotic for a horse is adequate long-stem forage — hay and grazing. The equine hindgut is a fermentation vat designed to run continuously on fibre, and the main way it gets damaged is starch overload: a large grain meal that overwhelms small intestinal starch digestion, spills into the hindgut, ferments rapidly, drops caecal pH and kills fibre-fermenting bacteria. That is the mechanism behind hindgut acidosis and a contributor to colic and laminitis risk. No supplement fixes that as well as feeding less grain in more meals with more forage.

Where equine supplementation does have a specific, well-established use: psyllium for sand accumulation. Horses grazing sandy paddocks ingest sand that settles in the colon and can cause sand colic. Psyllium is fed in courses — commonly around one pound per 1,000 lbs of body weight daily for five to seven consecutive days each month rather than continuously, on the reasoning that continuous feeding lets gut bacteria adapt and degrade it. Always with ample water. Our equine research covers the hemp side of equine care.

What to Look For When Buying

• The specific fibre named and quantified — "inulin 2 g" rather than "prebiotic blend".

• Single ingredient if you want to control the ramp rate precisely.

• No added sugar or xylitol.

• A synbiotic if you also want live organisms, with strain names and a guaranteed count through to the expiry date rather than at time of manufacture.

• Sealed, dry, dated storage. The same reasoning as our certificates of analysis: a quantity you cannot verify is not a dose.

If You Are Choosing a Synbiotic

The prebiotic half of a synbiotic is the easy half — fibre is stable. The probiotic half is where products fail. Today’s Veterinary Nurse describes a University of Guelph evaluation of 25 commercial probiotic products in which only 2 closely matched what their labels claimed, all tested before expiry. The same article notes that after five to six months of storage, some products contained almost no live organisms.

• Choose a product with published research behind that exact formula, since probiotic effects are strain specific.

• Look for a live count guaranteed to the expiry date, not to the date of manufacture.

• Buy small and fresh, store as the label directs, and don’t use it past its date.

Side Effects and Cautions

• Gas, bloating, rumbling and loose stool, almost always from starting too high or ramping too fast.

• Inflammatory bowel disease — some animals flare on highly fermentable fibre. Introduce very slowly and stop if things worsen.

• Acute diarrhoea is not the moment to add fermentable fibre. Settle the episode first.

• Bacterial overgrowth — in suspected small intestinal bacterial overgrowth, feeding fermentable substrate can make things worse. Veterinary input first.

• Psyllium without adequate water risks impaction rather than relieving it.

• Bloat-prone dogs — there is no direct evidence linking prebiotics to gastric dilatation and volvulus, but in a deep-chested breed with a history, discuss any gas-producing supplement with your vet.

• Onion and garlic are sometimes cited as natural prebiotic sources. They are toxic to dogs and cats. Do not use them.

When to Talk to Your Veterinarian

If diarrhoea lasts more than forty-eight hours, contains blood, comes with vomiting, lethargy or abdominal pain, or occurs in a very young, very old or unvaccinated animal. Chronic digestive disease deserves a diagnosis — inflammatory bowel disease, exocrine pancreatic insufficiency, food responsive enteropathy and parasites are all treatable and all look similar from the outside. Our digestive enzymes entry covers how to recognise pancreatic insufficiency specifically. For horses, any colic sign is a call now.

How It Fits With Hemp

Different mechanisms, no conflict, and one practical consideration. Prebiotics work in the colon; cannabinoids are absorbed higher up in the small intestine along with dietary fat, so a fibre supplement is unlikely to interfere with a hemp serving in the way that a coating agent like slippery elm can.

The reason owners often run both is that gut discomfort and behaviour are linked — a dog with an unsettled stomach is restless, off its food and uncomfortable, and hemp is used for that side of it while prebiotics work on the gut itself. Our serving guide has amounts by weight, onset and duration covers timing, and every batch of our hemp seed oil is third-party tested.

Frequently Asked Questions

What is the difference between prebiotics and probiotics? Prebiotics are fibres that feed gut bacteria. Probiotics are live bacteria. Prebiotics have the practical advantage of not needing to stay alive through storage and stomach acid.

How much prebiotic should I give my dog? Around 1 to 2 grams of inulin or FOS daily for a 20 to 50 lb dog. Start at a quarter of that and build over two weeks to avoid gas.

Why did prebiotics give my dog gas? Almost always because the starting amount was too high or increased too fast. Drop back to a quarter dose and ramp more slowly over two weeks.

Do horses need prebiotic supplements? Forage is the prebiotic that matters, and reducing grain does more for hindgut health than any supplement. The clear exception is psyllium fed in monthly courses for sand accumulation.

Can I give prebiotics during a bout of diarrhoea? Better to wait. Adding fermentable fibre to an acutely inflamed gut often makes things worse. Settle the episode first, then use prebiotics to rebuild.

Are onions or garlic good natural prebiotics for dogs? No. Both are toxic to dogs and cats. Use chicory-derived inulin or FOS instead.

For the underlying definitions and science, the International Scientific Association for Probiotics and Prebiotics publishes consensus statements at isappscience.org. For equine hindgut function and starch overload, the University of Kentucky's equine programme publishes research summaries at equine.ca.uky.edu.

Is pumpkin a good prebiotic for dogs?

Plain cooked or canned pumpkin supplies soluble and insoluble fibre, some of which gut bacteria ferment, so it is a gentle whole-food option. Use plain pumpkin, never pie filling, which carries sugar and spices. Start small, and if loose stool lasts more than a couple of days, see your vet rather than adding more fibre.

Can I give my dog or cat yogurt instead?

It is not a reliable substitute. Today’s Veterinary Nurse notes that no studies have shown yogurt or other fermented foods benefit pets, because the bacteria they carry are limited in amount and type. Hill’s adds that most cats are lactose intolerant. If you want a fermented food, our kefir entry covers how to do it sensibly.

Are prebiotics safe to give every day?

For most healthy dogs, yes, once you have ramped up slowly. No harmful effects have been seen with long-term prebiotic use in animals. The exceptions are the ones listed under side effects: acute diarrhoea, suspected bacterial overgrowth and some cases of inflammatory bowel disease.

Do cats need prebiotics?

Not routinely. Cats are strict carnivores with limited ability to ferment fibre and tolerate less than dogs. Prebiotics make most sense for a cat with loose stool, after antibiotics or with constipation, in small amounts and with your vet’s input.