Dog Anal Gland Supplements: What the One Trial Found

Supplemental fibre is a real recommendation — Merck says it increases faecal bulk, which helps the anal sacs compress and empty during defecation — but the published evidence behind the supplements sold for it is one small manufacturer-authored trial of 35 dogs, and none of it applies until a veterinarian has established that impaction is what the scooting is.

What the evidence actually is

Two things are true at once, and most pages selling these products only print the first.

Merck recommends supplemental fibre for anal sac disease, and gives the mechanism: adding supplemental fibre to the diet increases faecal bulk, facilitating anal sac compression and emptying during defecation. The sacs are emptied by the pressure of a firm stool passing them, so making the stool bulkier is a rational intervention aimed at the cause.

But the clinical evidence behind the supplements sold for it is thin, and the authors of the largest study of this disease said so in their own title. A VetCompass analysis of 104,212 dogs across 110 UK primary-care practices — which found a one-year period prevalence of non-neoplastic anal sac disorders of 4.40% (95% CI 4.22–4.57) — concluded that the high prevalence, strong breed predispositions and the antimicrobial and analgesic prescribing seen marked anal sac disease as a research-neglected syndrome.

That gap is the honest headline of this page. A recommendation with a good mechanism and almost no trial data is not the same thing as a proven product.

The one trial, in full

There is a published randomised trial, and it is worth reading properly rather than citing as a win.

Salichs and colleagues, in Veterinary Dermatology in 2025, ran a prospective randomised field trial of an oral chew containing fibre sources and the probiotic Bacillus velezensis C-3102, in 35 client-owned dogs with anal sac impaction — 22 given the chew for 90 consecutive days and 13 given nothing. Any dog that needed its sacs manually expressed counted as a failure and left the study.

The results: cumulative failures in the untreated group rose from 15% at day 30 to 61.5% at day 120. In the treated group the cumulative failure rate rose more slowly and stabilised at 19% from day 90 to day 120, a statistically significant difference at p = 0.025. The authors concluded the chew was a safe and effective management option for recurrent anal sac impaction.

Three limitations belong next to that result, and none of them are hidden — they are in the paper.

It is small. Thirty-five dogs, thirteen of them controls. A 13-dog control arm makes the untreated failure percentages coarse.

The control group received nothing, not a placebo. The design is described as negative-controlled, which means the comparison is treatment versus no treatment. That cannot separate the chew's effect from the effect of owners and clinicians knowing which dogs were being managed.

The authors work for the manufacturer. The paper's own conflict-of-interest statement records that two of the three authors are full employees of the company behind the product and the third is a consultant to the same group. That does not make the result wrong. It does mean the result has not yet been reproduced by anyone without a commercial interest in it.

And one structural point: it tested a combination of fibre and a probiotic. Whichever component did the work, the trial cannot tell you, so it is not evidence for fibre specifically.

Why the pumpkin advice is empty

The most repeated home remedy for anal glands is a spoonful of pumpkin. The arithmetic is published and it does not survive contact.

Tufts calculated that to give a dog the fibre found in one common high-fibre therapeutic diet you would have to feed nearly 12 cups of pumpkin per day to a medium-sized dog — and more than 2½ cups a day to a cat. The doses people actually give run from a quarter of a teaspoon to two tablespoons.

The per-tablespoon comparison makes the same point without the extrapolation. Tufts' table of common fibre supplements gives canned pumpkin 0.4 grams of total dietary fibre per tablespoon against psyllium seed husk at 3.5 grams — nearly nine times as much, with most of psyllium's being soluble.

Two extra traps in the same aisle. Canned pumpkin pie mix runs up to 281 calories per cup against 83 for plain canned pumpkin, and some salted canned pumpkins carry nearly 600 mg of sodium per cup.

What "supplement" means legally, and why that matters here

Supplements are not regulated like drugs, and Tufts spells out the asymmetry: dietary supplements do not require the FDA to review effectiveness, safety or quality before marketing, and where a drug manufacturer must prove a drug is safe, the FDA must prove that a supplement is unsafe.

Quality control is the practical consequence. Tufts: numerous studies have shown many supplements have poor quality control, so a product labelled 500 mg per tablet may contain 500 mg, may contain 1,000 mg, or may contain nothing at all — and some are contaminated with mercury, lead or other substances.

That is not an argument that no supplement works. It is an argument that "it contains fibre" on a label is a claim rather than a measurement, and that a purified fibre source with a known composition is easier to dose correctly than a proprietary chew with a proprietary blend.

The causes actually worth fixing

Merck's list of what leads to retention of the sac contents is short, and three of the four items are things an owner can change.

Soft stool. The sacs are compressed by a firm stool. This is the mechanism fibre is aimed at, and it is also why a dog with chronic loose stool has an anal gland problem downstream of a gut problem. See colitis in dogs.

Obesity. Merck names poor muscle tone in obese dogs directly among the factors leading to retention. It is the single most modifiable risk factor on the list and it costs nothing.

Skin disease. Merck: generalised seborrhoea produces glandular hypersecretion, which contributes to retention. A dog whose glands fill every few weeks and whose allergic or seborrhoeic skin disease is untreated is being managed at the wrong end of the animal.

Breed and conformation, which cannot be changed but sets expectations. The VetCompass study found brachycephalic types carried 2.6 times the odds of anal sac disease compared with dolichocephalic types.

A supplement that ignores all four is treating the last step in a chain.

When it is not the glands at all

Scooting is a sign, not a diagnosis. Merck's route to the answer is a digital rectal examination, at which point the sacs can usually be expressed — the exam that diagnoses this is also the treatment for most cases, which is why it is a poor thing to skip.

Two presentations must not be self-treated. An infected or abscessed sac is hot, swollen and painful, and Merck notes fistulous tracts can form and rupture through the skin. And in an older dog, Merck says a tumour should be suspected in anal sacs that are firm, enlarged and non-expressible even with irrigation — apocrine gland anal sac adenocarcinoma typically occurs in older dogs and may present with signs of high blood calcium such as increased drinking and urinating.

Our full anal gland problems in dogs page carries the urgency ladder and the diagnostic path.

What this costs when the supplement is the whole plan

Managed early, this is one of the cheaper problems in veterinary medicine. Merck's reassuring key point is that most cases are handled with manual expression and local medication, and the VetCompass data agrees: anal sacculectomy was performed in under 1% of cases.

Managed late, it stops being cheap. An impaction that abscesses becomes sedation, lancing, antibiotics and pain relief. Years of recurrence eventually make removal look attractive, and Merck is blunt about the price of that: faecal incontinence is a common complication of anal sacculectomy, from damage to the caudal rectal branch of the pudendal nerve, and can be complete if the damage is bilateral.

All three of those figures are below, from our own US price data. The cheapest line on the list is the exam.

Should I have my dog's glands expressed routinely?

Not in a dog that has never had a problem. Nothing in Merck or in the VetCompass paper supports routine expression as prevention, and repeated manual expression of healthy sacs can itself cause inflammation. Expression belongs to dogs that actually need it, on veterinary advice.

If I do use fibre, which one and how much?

That is a question for the veterinarian who examined the dog, because the type of fibre matters as much as the amount and the right answer differs between a dog with soft stool and a dog with firm stool.

For scale rather than as a dose: the one published dosing figure in dogs comes from a study of chronic large-bowel diarrhoea in which the median initial dose of a psyllium supplement was 2 tablespoons per day, with a range across cases from 0.25 to 6 tablespoons. Tufts notes there is otherwise limited guidance on standardised fibre dosing, that fibre should always be introduced gradually over days to weeks, and that human products should be checked for xylitol, which is toxic to dogs. Our high-fibre diet guide sets out the soluble-versus-insoluble question that decides which product is even the right shape.

The chew worked for my dog. Does that settle it?

For your dog, it may well. For the question of whether these products work, no — that is what the trial above is for, and one small unblinded study by the manufacturer is where the published evidence currently stops. A dog whose sacs stop filling after a diet change may also have lost weight, or had its skin disease treated, at the same time.

What skipping this costs

This is not only a quality-of-life question. Where it ends in a veterinary bill, we publish the price of that bill from our own dataset rather than leaving the stakes abstract. These are the outcomes it leads to, and what they cost.

Buying a fibre chew for scooting instead of having the sacs examined

The consultation and rectal exam that diagnoses an impaction and empties it in the same visit. We price it at routine vet checkup (wellness exam), $56 to $130 — $66 typical.

Waiting out an impaction that has become hot, swollen and painful

Sedation, lancing or flushing, antibiotics and pain relief for an abscessed anal sac. We price it at dog anal gland abscess treatment, $100 to $1,000 — $550 typical.

Managing recurrence with supplements alone for years without addressing weight, stool or skin disease

Surgical removal of the sacs, which Merck warns commonly complicates with faecal incontinence. We price it at dog anal gland removal (anal sacculectomy), $650 to $5,600 — $1,500 typical.

Related guides

• dog fiber diet — The fibre number on a dog food label leaves out soluble fibre entirely.
• dog diet for sensitive stomach — Sensitive stomach is a symptom, not a diagnosis.

Every guide we have written is on the preventive care index.

Sources

1. Anal Sac Disease in Dogs and Cats — Merck Veterinary Manual, 2025.
2. Efficacy of an oral chew containing fibre and Bacillus velezensis C-3102 in the management of anal sac impaction in dogs — Salichs M, Beasley S, Homedes J; Veterinary Dermatology 36(1):74-82, 2025.
3. Non-neoplastic anal sac disorders in UK dogs: Epidemiology and management aspects of a research-neglected syndrome — O'Neill DG, Hendricks A, Phillips JA, Brodbelt DC, Church DB, Loeffler A; Veterinary Record 189(2):e203, 2021.
4. The Problem with Pumpkin — Lisa M. Freeman, DVM, PhD, DACVIM (Nutrition), Tufts Petfoodology, Cummings School of Veterinary Medicine, 2017.
5. Fiber Frustrations — Cailin R. Heinze, VMD, MS, DACVIM (Nutrition), Tufts Petfoodology, Cummings School of Veterinary Medicine, 2019.
6. Dietary Supplements for Pets: Harmful or Helpful? — Lisa M. Freeman, DVM, PhD, DACVIM (Nutrition), Tufts Petfoodology, Cummings School of Veterinary Medicine, 2017.
7. Treatment of chronic idiopathic large-bowel diarrhea in dogs with a highly digestible diet and soluble fiber: a retrospective review of 37 cases — Leib MS; Journal of Veterinary Internal Medicine 14(1):27-32, 2000.