Novel Protein vs Hydrolysed Diet: Which Elimination Trial Approach

By Gary Innes

Affiliate disclaimer: This article contains affiliate links to products I've researched and, in some cases, fed my own Cockapoo. If you click through and buy, I may earn a small commission at no extra cost to you. It does not change which products my vet, or any vet, would recommend.

Last Updated: 2 May 2026

An elimination diet trial is the gold-standard test for canine adverse food reactions, and it usually runs along one of two tracks: a novel-protein limited-ingredient diet (a meat the dog has never eaten) or a hydrolysed prescription diet (proteins broken into peptides too small for the immune system to recognise). Both can work. Which your vet recommends depends on your dog's feeding history, household discipline, the severity of signs, and your budget.

Quick Summary

• Novel protein diets work because the immune system has never met the protein, so it cannot react to it.
• Hydrolysed prescription diets work because the source protein has been chopped into fragments typically under 10 kDa (Cave 2006), below the threshold most IgE antibodies recognise.
• Novel protein is cheaper, retail-available in the UK, and often more palatable, but truly novel meats are getting harder to find as modern dogs have eaten widely.
• Hydrolysed diets are more controlled and slightly more forgiving of accidental crumbs, but require a UK vet prescription and cost more per month.

Quick Answer: If your dog's feeding history is clear and you can name every protein they have ever eaten, your vet may suggest a novel protein limited-ingredient diet first. If the history is murky, multiple proteins are suspected, or the household struggles with strict compliance, a hydrolysed prescription diet is often the more pragmatic starting point. Neither is universally "better" — the right one is the one your household can actually run for eight to twelve weeks without cheating.

Table of Contents

1. How each approach works
2. Comparison table
3. Pros and cons of novel protein
4. Pros and cons of hydrolysed
5. Decision factors
6. UK availability
7. Common products in each category
8. What vets often try first
9. What happens if approach #1 fails
10. Cost comparison (UK)
11. Honest Take
12. Sources
13. Related Articles
14. FAQ

How Each Approach Works

Novel protein, limited ingredient

The premise is straightforward. An adverse food reaction is, in most well-characterised cases, an immune response to a protein the dog has been exposed to repeatedly (Mueller 2016). If you feed a protein the dog has never seen — kangaroo, venison, alligator, certain fish — the immune system has no memory of it and, in theory, no antibodies pre-formed against it. Reactions stop, signs resolve, and you have your diagnosis when a deliberate re-challenge with the old food brings them back.

The catch: "novel" is a moving target. A dog raised on a rotating supermarket diet may have eaten chicken, beef, lamb, salmon, turkey and pork before age two. Even some "novel" commercial diets have been shown to contain trace amounts of mainstream proteins from shared production lines (Olivry 2015 review of dietary trials). The diet only works as a diagnostic tool if you can be reasonably confident the dog has never encountered the listed protein.

Hydrolysed prescription diet

Hydrolysis is a chemical process that uses enzymes (and sometimes acid) to break a parent protein — usually soy or chicken feather — into much smaller peptide fragments. According to Cave's 2006 review in Veterinary Clinics of North America, the goal is fragments under approximately 10 kDa, the size below which most IgE antibodies struggle to bind and trigger a reaction. Royal Canin's Anallergenic line takes this further, with most peptides reportedly under 1 kDa.

The practical effect: the dog can eat protein derived from chicken or soy without their immune system "seeing" it as chicken or soy. This makes hydrolysed diets useful precisely when feeding history is unclear, because it does not matter what the dog has eaten before — the protein is, immunologically speaking, invisible.

Comparison Table

| Factor | Novel Protein | Hydrolysed Prescription | |---|---|---| | Mechanism | New protein the immune system hasn't encountered | Protein fragmented to <10 kDa peptides (Cave 2006) | | Cost (UK) | £40–80/mo medium dog | £60–100/mo medium dog | | Prescription | Not required | Required (UK vet) | | Compliance forgiveness | Very low | Slightly higher | | Best when | Clear feeding history | Murky history or multi-trigger suspected |

Pros and Cons of Novel Protein

Pros

• Cheaper. UK retail prices for limited-ingredient diets sit roughly £40–80 per month for a medium dog, depending on brand and protein.
• No prescription. Available on Amazon UK, Pets at Home and most independent pet stores.
• Generally more palatable. Real meat protein, intact, often goes down better than hydrolysed.
• Long-term flexibility. If the trial succeeds, the diet can usually continue indefinitely as a maintenance food.

Cons

• Truly novel proteins are scarce. Modern UK dogs have often eaten lamb, salmon, duck and venison at some point. Kangaroo, alligator and certain insect proteins remain genuinely novel for most.
• Strict compliance failures are diagnostic. A single chicken-flavoured worming tablet, a flavoured toothpaste, a dropped piece of toast — any can derail an eight-week trial. Veterinary literature reports compliance is the single most common reason elimination trials fail (Olivry 2015).
• Cross-contamination risk. Some retail "limited ingredient" diets are produced on shared lines, and case-series suggest trace contamination can sustain low-level reactions in highly sensitive dogs.

Pros and Cons of Hydrolysed

Pros

• More controlled formulation. Veterinary therapeutic diets are made under stricter ingredient and contamination controls.
• Slightly more forgiving of accidental exposure. Because the immunogenic threshold is lower, an occasional crumb of a treat is less likely (though not guaranteed) to derail the trial.
• Useful when history is unknown. Rescue dogs, dogs from multiple homes, or any dog whose past diet you cannot reconstruct are good candidates.
• Often the recommended choice in moderate-to-severe cases, where rapid, reliable improvement matters clinically.

Cons

• Requires a UK vet prescription. That means a consultation, often £40–60, before you can buy.
• More expensive. Roughly £60–100 per month for a medium dog.
• Palatability issues. Some dogs refuse Royal Canin Anallergenic outright; the smell and texture differ from regular kibble.
• Not a long-term ideal for every dog. Some vets prefer to use hydrolysed diets diagnostically and then transition to an identified novel protein for maintenance.

Decision Factors

Feeding history

If you can list every protein your dog has ever eaten — including treats, table scraps, flavoured medications and dental chews — and a genuinely novel option exists, novel protein is reasonable. If you cannot, hydrolysed avoids the guesswork.

Household compliance

A household with small children, multiple feeders, or a dog that scavenges on walks is a household where strict novel-protein compliance is hard. Hydrolysed buys a small margin of error.

Severity of signs

A dog with mild seasonal-looking itch may be a candidate for a slower, cheaper novel protein attempt. A dog with raw, infected skin, chronic ear disease and gut signs often benefits from the more controlled hydrolysed route to get a clear answer faster (Mueller 2016).

Cost

Over an eight-to-twelve week trial, the difference between £40/month novel protein and £100/month hydrolysed is real — roughly £120–180 across the trial. That is not negligible, and an honest conversation with your vet about budget is appropriate.

Availability

Both routes are available in the UK. Novel protein limited-ingredient diets are stocked at retail; hydrolysed diets come through veterinary channels including Pets at Home Vets, independent practices, and online veterinary pharmacies once a prescription is in hand.

UK-Specific Availability

Novel protein: Acana Singles, Natural Balance LID and Wellness Simple are widely available through Amazon UK and specialist online retailers. Zignature kangaroo and similar exotic-protein options ship to the UK but availability fluctuates. Stock issues are not unusual, and switching mid-trial is itself a confounder.

Hydrolysed: Royal Canin Hypoallergenic (HP), Hill's Prescription Diet z/d and Royal Canin Anallergenic are stocked by most UK veterinary practices. Pets at Home's vet clinics carry the Royal Canin range. With a written prescription, online pharmacies such as VetUK or Animed Direct are usually cheaper than buying directly from a clinic.

Common Products in Each Category

These are examples — your vet may recommend any of these or others depending on what they have seen work in their patients.

Novel protein options often discussed:

• Acana Singles — limited-ingredient single-protein options including pork, lamb and duck.
• Natural Balance LID — long-running US LID line with options such as venison and salmon.
• Wellness Simple — limited-ingredient turkey, lamb, salmon and duck recipes.
• Zignature Kangaroo — genuinely novel for most UK dogs.

Hydrolysed prescription options often discussed:

• Royal Canin Hypoallergenic (HP) — soy hydrolysate, the most commonly prescribed hydrolysed diet in UK practice.
• Hill's Prescription Diet z/d — hydrolysed chicken liver.
• Royal Canin Anallergenic — feather hydrolysate at peptide sizes typically under 1 kDa, used when standard hydrolysed has failed.

What Vets Often Try First

In UK general practice, anecdotal patterns are visible but not universal. Vets often reach for:

• Novel protein first when the owner can give a clear, complete feeding history; the dog is otherwise stable; signs are mild to moderate; and a genuinely novel option exists.
• Hydrolysed first when the dog is a rescue with unknown history; multiple proteins are suspected; signs are severe and a fast, reliable answer matters; or the household has compliance challenges.

This is the pattern documented in the ACVD (American College of Veterinary Dermatology) consensus and reflected in Merck Veterinary Manual guidance, although individual practitioners differ. Your vet's recommendation is informed by your specific dog and household.

What Happens if Approach #1 Fails

A failed elimination trial is not the end of the road. The usual escalation:

• Failed novel protein: Move to hydrolysed. The novel protein attempt may have failed because of cross-contamination, an unsuspected past exposure, or genuine non-food disease. Hydrolysed addresses the first two.
• Failed standard hydrolysed: Move to ultra-hydrolysed (Royal Canin Anallergenic) or revisit the diagnosis. Some case reports describe dogs reacting to standard hydrolysed but tolerating Anallergenic.
• Failed Anallergenic: Reconsider whether food is the right target. Atopic dermatitis, parasitic disease, secondary infections and other dermatological conditions can mimic adverse food reaction signs.

A failed trial is informative as long as it was run properly. A trial that was undermined by cheating tells you nothing.

Cost Comparison (UK)

For a 15 kg medium dog on an eight-week trial, expect roughly:

• Novel protein retail: £40–80 per month, so £80–160 total.
• Hydrolysed prescription: £60–100 per month, plus a £40–60 vet consultation, so £160–260 total.

These are 2026 indicative figures. Online veterinary pharmacies with a prescription often save 20–30% on the vet-bought price for hydrolysed diets.

Honest Take

When my Cockapoo started chewing his paws and developing gunky ears, our vet's first move was a novel-protein fish-based limited-ingredient diet. Feeding history was clear, signs were moderate, and the diet was easy to source. He improved — partially. About six weeks in, with persistent low-level itch, the vet suggested a hydrolysed approach to confirm whether a residual food trigger was still in play, or whether we were looking at concurrent atopic dermatitis. The hydrolysed phase was harder. Palatability dropped, my dog clearly preferred the fish, and we had to be much more disciplined about treats. But it gave us a cleaner answer.

If I had to do it again, I would still start with novel protein because his history made it sensible. If I had been adopting an unknown-history rescue, I would probably start with hydrolysed straight away on the vet's advice. There is no universally best route. The route that works is the one you can run honestly for eight weeks.

A note on YMYL realities: nothing in this article is veterinary advice. Bring this question to your own vet, who has examined your dog. Brand recommendations vary by region, by clinic and by clinical experience, and the right diet for your dog is the one your vet endorses for your dog's specific picture.

Sources

• Mueller RS, Olivry T, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Veterinary Research, 2016.
• Olivry T, Mueller RS, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Veterinary Research, 2015.
• American College of Veterinary Dermatology (ACVD), consensus statements on elimination diet trials.
• Merck Veterinary Manual, Adverse Food Reactions (Food Hypersensitivity) in Small Animals.
• Cave NJ. Hydrolyzed protein diets for dogs and cats. Veterinary Clinics of North America: Small Animal Practice, 2006; 36(6):1251–1268.

Related Articles

• Best Hypoallergenic Dog Foods Guide
• Dog Food Allergies: The Complete Guide
• Hydrolysed Protein Dog Food Explained
• Novel Protein Dog Foods: A UK Buyer's Guide
• How to Run an Elimination Diet Trial at Home
• Dog Food Allergy Symptoms vs Atopic Dermatitis

FAQ

1. Is hydrolysed always better than novel protein?

Not necessarily. Veterinary literature reports both can deliver a definitive elimination diet diagnosis when run correctly. Hydrolysed has the edge when feeding history is unclear or compliance is shaky; novel protein has the edge on cost, palatability and long-term flexibility when a genuinely novel option exists. Your vet weighs your dog's specific picture.

2. Can I do an elimination diet without a vet?

You can buy a novel protein limited-ingredient diet over the counter, but doing the trial without veterinary oversight is generally not recommended. A vet rules out parasitic, infectious and atopic causes first, monitors progress, and interprets the re-challenge phase. Skipping that step risks treating the wrong disease.

3. How long does each diet need to run before I know if it's working?

Current consensus, summarised in Olivry's 2015 review, is at least eight weeks for the elimination phase, with many dermatologists preferring twelve weeks for cutaneous signs. Gastrointestinal-only signs may resolve faster, sometimes within two to four weeks, but a full trial is still standard practice.

4. My dog refuses the hydrolysed diet — what now?

Speak to your vet. Options can include trying a different hydrolysed brand (Hill's z/d versus Royal Canin HP have different palatability profiles), warming the food, or switching the trial route to a novel protein if feeding history allows. Forcing a refused diet is not a viable trial.

5. Are home-cooked novel protein diets a valid alternative?

They can be, but only when formulated by a board-certified veterinary nutritionist. Case-series suggest unbalanced home-cooked diets risk nutritional deficiency over a multi-week trial, particularly in growing dogs. If home-cooked is on the table, ask your vet for a referral.

6. Once I know my dog has a food allergy, do I have to stay on the diet forever?

Generally yes, although some dogs successfully transition from a hydrolysed diagnostic diet to an identified novel-protein maintenance diet once the trigger protein is known. Your vet will advise based on the re-challenge results. A protein a dog reacted to once typically remains a lifelong trigger.