Hill's Science Plan honest review: why B and not A
Hill's Science Plan is the most vet-recommended dry dog food in North America and Western Europe. Its very name suggests science, rigour, clinical proof. And yet, on PetFoodRate, it scores B (72/100) - not A. How does a brand with that much research behind it miss the top tier?
The answer is in the ingredient list. And that answer is worth explaining honestly, without jargon, so you can make an informed decision about what goes in your dog's bowl.
The French version of this review is available at /fr/blog/fr-hills-avis-honnete/. For a head-to-head comparison of the two vet-recommended giants, see our full Hill's vs Royal Canin breakdown.
You can also check the full dog food rankings and our scoring methodology to understand how every score is calculated.
The product reviewed: Hill's Science Plan Adult Medium Chicken
We are reviewing the best-selling and most-prescribed product in the range: Hill's Science Plan Adult Medium with Chicken, formulated for adult dogs 10-25 kg. This is the product most commonly found in vet clinics across the UK and US.
Declared ingredients: Chicken (20%), corn, wheat, chicken meal, chicken fat, hydrolyzed animal proteins, cellulose, soybean meal, minerals, vitamins, beta-carotene, taurine, L-carnitine.
Overall score: B (72/100)
Sub-scores:
| Dimension | Score | Grade |
|---|---|---|
| Protein quality | 68/100 | C |
| Nutrition profile | 78/100 | B |
| Undesirables | 70/100 | B |
| Transparency | 74/100 | C |
| Clinical research | 96/100 | A |
| Adaptability | 82/100 | B |
The clinical research dimension is the highest in our entire standard kibble database. Hill's is the only mainstream brand to publish full AAFCO feeding trials with biometric measurements across multiple generations. But five other dimensions pull the overall score down - and we will go through each one.
What is good: why Hill's earns its B
Chicken is listed first - with a declared percentage
"Chicken (20%)": first position, species named, percentage declared. Not every brand does this. Royal Canin declares "meat and animal by-products" without specifying species or percentage in several of its standard formulas. Hill's names the meat and gives the number. That is a genuine transparency positive.
20 pourcent fresh chicken in position 1 guarantees that meat meaningfully contributes to total protein - not just symbolically. By contrast, a product listing "chicken" first but without a percentage can legally contain as little as 5 pourcent chicken: position alone offers no protection without the figure.
Chicken meal is a concentrated protein source
Chicken meal (position 4) is dehydrated chicken meat. Contrary to what many believe, quality chicken meal is an excellent protein source - more concentrated than fresh meat because it contains no moisture. A kibble with "20% fresh chicken" plus "chicken meal" can have a higher total animal protein content than a product with "30% chicken" alone. Hill's combines both, which is nutritionally efficient.
Feeding trials: the advantage challengers do not yet have
Hill's Pet Nutrition is one of the very few companies in the world to conduct full AAFCO feeding trials - meaning they feed real animals the finished product for a minimum of 6 months and measure health outcomes. The vast majority of A-grade and B-grade brands rely only on lab analysis (formulated to meet AAFCO guidelines) without ever testing the product on living animals.
This does not mean products without feeding trials are unsafe - most are nutritionally sound. But the difference is real: a feeding trial detects bioavailability problems that a lab analysis cannot see. Hill's has published studies on kidney health, joint mobility, and cognitive health in aging dogs - with control groups, peer-reviewed protocols, in journals like the Journal of Veterinary Internal Medicine.
Taurine and L-carnitine are explicitly supplemented
Hill's systematically supplements taurine and L-carnitine. Taurine is critical for cardiac health in dogs, especially since the 2018 studies linking dilated cardiomyopathy to certain diets. L-carnitine supports lipid metabolism and muscle mass preservation. Explicit supplementation of these two nutrients is a real nutritional plus.
What is missing for an A grade
Corn and wheat occupy positions 2 and 3
This is the core problem. After fresh chicken (20%) in position 1, the next ingredients are: corn at position 2, wheat at position 3. These two cereals are sources of carbohydrates and vegetable protein, not meat. For a product designed to feed an opportunistic carnivore with high animal protein needs, this sequence indicates that the product contains more cereals than meat by weight.
Corn is not toxic for dogs - contrary to what some radical blogs claim. FEDIAF nutritional guidelines confirm that dogs digest cooked corn perfectly well. But corn has lower protein digestibility than animal sources (65-72 pourcent vs 82-90 pourcent for fresh meat), and its presence in large quantities dilutes the supply of essential amino acids from animal sources.
Wheat at position 3 adds gluten - a vegetable protein with adequate digestibility in dogs (roughly 70-75 pourcent) but below animal protein, and which can cause problems in dogs with digestive or skin sensitivities.
For comparison, Taste of the Wild Pacific Stream (A grade, 88/100) lists salmon, salmon meal, peas, sweet potato. Carnilove Adult Lamb & Wild Boar (A grade, 86/100) lists lamb (35%), wild boar (15%), peas. Neither places a cereal in the top 3.
Hydrolyzed animal proteins: the vague ingredient
"Hydrolyzed animal proteins" at position 6 is an imprecise ingredient. Hydrolyzed means the proteins have been chemically or enzymatically broken into shorter amino acid chains. It is used to improve palatability (taste) and sometimes digestibility. But "animal" without a named species reveals nothing about origin: chicken, pork, beef, unidentified by-products - anything is possible.
Our transparency dimension penalises this vagueness. An A-grade brand names its protein sources precisely.
Soybean meal: vegetable protein filler
Soybean meal contains vegetable proteins that inflate the crude protein figure on the label without contributing the same amino acid profile as animal proteins. Digestibility of soy protein in dogs is 74-78 pourcent according to NRC data. Functional but suboptimal.
Detailed comparison: Hill's vs A-grade alternatives
| Product | Score | 1st ingredient | Positions 2-3 | Feeding trial | Cost/day (55 lb dog) |
|---|---|---|---|---|---|
| Hill's Science Plan Adult Medium | B (72/100) | Chicken 20% | Corn, wheat | Yes | ~$2.10 |
| Taste of the Wild Pacific Stream | A (88/100) | Salmon | Salmon meal, peas | No | ~$2.20 |
| Carnilove Adult Lamb & Wild Boar | A (86/100) | Lamb 35% | Wild boar 15%, peas | No | ~$2.45 |
| Acana Heritage Adult | A (90/100) | Fresh chicken 15% | Fresh turkey, mackerel | No | ~$2.70 |
| Royal Canin Medium Adult | C (58/100) | Corn | Dehydrated chicken, wheat | Yes | ~$2.00 |
This table reveals something important: Hill's costs only about $0.10 more per day than Royal Canin yet scores 14 points higher. And Taste of the Wild, an A-grade, costs only $0.10 more per day than Hill's for a 55 lb dog. The annual budget difference is roughly $36 - for a well-fed dog vs a very well-fed dog.
The 14-point gap with Royal Canin: explained
The C score (58/100) of Royal Canin Medium Adult vs the B (72/100) of Hill's comes down to three major differences:
1. Position of the first ingredient. Royal Canin Medium Adult places corn first. Hill's places chicken (20%) first. This single difference indicates a fundamentally different meat-to-cereal ratio from the outset.
2. Source transparency. Royal Canin declares "meat and animal by-products" without species or percentage in several formulas. Hill's declares "chicken (20%)" and "chicken meal" separately. Hill's transparency is measurably better.
3. Published research. Royal Canin publishes fewer independent clinical studies on its standard formulas than Hill's. Both have serious scientific teams, but Hill's has a larger publicly accessible literature base.
This does not mean Royal Canin is dangerous - its C grade indicates a functional product with significant limitations. But Hill's is objectively better on almost every dimension in our methodology, at a nearly identical price point.
The "vet-recommended" argument: what you need to know
A VIN (Veterinary Information Network) survey of 2,000 American vets in 2023 found that 80 pourcent of vets who recommend specific kibble brands cite Hill's or Royal Canin. The same survey found that 62 pourcent acknowledged receiving fewer than 4 hours of nutrition coursework in their base veterinary training.
This is not a criticism of vets - it is a reality of medical education. Animal nutrition is a speciality in its own right. Vets recommend Hill's for valid reasons: it is a reliable brand, consistent in quality, backed by serious scientific research, and available in clinics. For a healthy animal, it is a solid, very far from bad choice.
But "vet-recommended" is a trust criterion, not a composition-optimisation criterion. Hill's earns this B. A grades exist and are accessible.
Hill's Senior and the specialised ranges
Hill's has developed Prescription Diet ranges and senior formulas with real clinical functionality:
- Hill's Science Plan Senior 7+ integrates antioxidants and PUFAs (polyunsaturated fatty acids) for cognitive health - a clinically tested formulation
- Hill's Prescription Diet k/d (kidney health) is one of the very few formulas for which randomised controlled studies show a measurable impact on survival time
- Hill's z/d (food allergies) uses very low molecular weight hydrolyzed proteins, genuinely reducing immune response in sensitised animals
These specialist and veterinary ranges occupy a different category from what we are reviewing here. For senior-specific recommendations, see our best senior dog food ranking.
What you can actually do
If you are currently feeding Hill's Science Plan: your dog is well-fed. There is no urgency to switch. Hill's covers all baseline nutritional needs with consistent quality.
If you want to optimise without blowing your budget: Taste of the Wild Pacific Stream or Carnilove Adult cost $0.10-0.30 more per day for a 55 lb dog - roughly $36-110 per year. These products offer a significantly better animal protein profile.
If you want the best available composition: Acana and Orijen ranges offer 65-85 pourcent animal protein profiles, grain-free, with multiple named meat sources. The cost is higher ($2.70-4.00/day for a 55 lb dog) but the nutritional difference is objective and measurable.
To compare products directly, use our comparison tool or browse the full dog food rankings.
The GMO ingredient question
Hill's does not declare whether its corn and soy are GMO or non-GMO. EU regulations require GMO labelling above 0.9 pourcent for human food products, but this obligation applies differently to pet food. Hill's uses ingredients from conventional American agriculture, a significant proportion of which is statistically from GM crops.
This is not a documented health problem for dogs - no peer-reviewed study has demonstrated harmful effects of GM crops on domestic carnivores to date. But if this is an important criterion for you, European A-grade brands like Carnilove or Orijen Canada certify the absence of GMOs in their formulations.
Transitioning away from Hill's: what to know
If you want to move from Hill's Science Plan to an A-grade kibble, the transition must be gradual to avoid digestive upset. Your dog's gut flora adapts to the specific composition of the food it regularly consumes.
Recommended transition protocol over 14 days:
| Days | Old food (Hill's) | New food (A-grade) |
|---|---|---|
| 1 to 3 | 75 pourcent | 25 pourcent |
| 4 to 7 | 50 pourcent | 50 pourcent |
| 8 to 11 | 25 pourcent | 75 pourcent |
| 12 to 14 | 0 pourcent | 100 pourcent |
If your dog has a history of digestive sensitivities (loose stools, frequent gas), extend the transition to 21 days with a slower pace in the early stages. For dogs that have eaten cereal-based kibble their entire lives, moving to a grain-free formula may temporarily increase stool volume during the first few weeks as the gut microbiome adjusts. See our grain-free dog food guide for a full breakdown of the transition process.
Hill's variants: Science Plan is not the only range
It is important to distinguish the Science Plan range (the standard range) from the Prescription Diet range (veterinary, prescription-only in some countries). Our review covers Science Plan exclusively. Prescription Diet k/d, c/d, u/d, w/d were developed with specific clinical protocols for defined medical conditions and are not comparable to standard kibble.
Science Plan variants available in the UK and US:
- Puppy Medium - growth formula, adjusted calcium/phosphorus ratio
- Adult Medium - the formula reviewed in this article
- Senior 7+ Medium - added glucosamine and antioxidants, slightly reduced protein
- Sensitive Stomach - hydrolyzed proteins for improved digestive tolerance
- Light - caloric reduction (~15 pourcent), increased L-carnitine
- Perfect Weight - active weight management
The Light and Perfect Weight variants have reduced fat levels but maintain the same cereal structure (corn, wheat in positions 2-3). The B grade applies to standard variants. Sensitive Stomach and Light variants may have slightly different scores depending on exact formulation - see the individual product pages for detailed scores.
What dog owners actually report: real-world observations
One thing the ingredient label cannot capture is how individual dogs respond. We reviewed independent owner reports across veterinary forums, Reddit communities, and product review platforms to find recurring patterns. These are observations, not clinical data - but they are consistent enough to be worth noting.
Positive patterns reported for Hill's Science Plan:
- Very consistent stool quality across extended use (a direct effect of stable formulation - Hill's rarely reformulates)
- Good palatability: even fussy eaters tend to accept Hill's without transitional issues
- Stable body weight over months of use - the moderate fat content and cereal base provide predictable energy
- Widely available in veterinary clinics, useful for owners who want one product they can get everywhere
Negative patterns reported:
- Dull, dry coat in some dogs after 6+ months - often attributed to insufficient omega-3 fatty acids (no fish oil in the standard formula)
- Increased itching and scratching in dogs with suspected cereal sensitivities - the wheat and corn in positions 2-3 are a plausible factor
- Owners who switched to A-grade formulas often report shinier coats within 4-8 weeks, attributed to the direct EPA/DHA from fish oil sources
These owner observations align with what the ingredient analysis predicts: Hill's is a nutritionally complete, stable baseline product. But it does not optimise for coat quality, skin health, or anti-inflammatory benefit the way fish-oil-supplemented A-grades do.
If your dog is thriving on Hill's with a great coat and no skin issues, the formula is working well for that individual. If you notice coat or skin issues, the move to an A-grade with direct fish oil is a well-motivated next step to try before assuming a medical cause.
How Hill's scores compare across dog sizes
Hill's Science Plan is available in Small/Toy, Medium, and Large breed formulations. The scoring differences between these are modest but worth noting:
Small & Miniature Adult - B (74/100): slightly higher first-meat percentage than Medium, same cereal positions 2-3.
Medium Adult - B (72/100): the formula reviewed here.
Large Breed Adult - B (70/100): reduced fat, added chondroitin for large breed joint support, but same cereal base.
XL Adult - B (69/100): similar to Large, with caloric adjustments for giant breeds.
If you have a large breed dog, the Large formulation's added chondroitin is a genuine plus, though still not enough to reach A-grade territory. Compare to Acana Large Breed Adult (A, 86/100) for a direct alternative.
Summary: what Hill's B score actually means
Hill's Science Plan is not a bad kibble. Its B (72/100) score means: reliable product, nutritionally adequate, with serious clinical research that no competitor at this price point can match. The vet recommendation has a real scientific basis.
But positions 2 and 3 (corn, wheat) and the vague "hydrolyzed animal proteins" ingredient prevent Hill's from reaching an A. Those missing 28 points represent a real composition difference: fewer named and traceable animal proteins, more cereals by proportion.
If the goal is to feed your dog as well as possible on a reasonable budget, A-grades like Taste of the Wild or Carnilove do better for $0.10-0.30 more per day. That is not an easy call when your vet recommends Hill's - but it is a documented one.
Sources
- FEDIAF Nutritional Guidelines for Complete and Complementary Pet Food - 2023 edition
- AAFCO Dog and Cat Food Nutrient Profiles - 2024 edition
- National Research Council - Nutrient Requirements of Dogs and Cats - National Academies Press
- VIN Survey on Veterinary Nutrition Education - Veterinary Information Network, 2023
- Hill's Pet Nutrition Scientific Research Publications - Hill's Pet Nutrition Inc.
- FDA Pet Food Labeling Regulations - U.S. Food & Drug Administration
- Theo Blanchard, Brand Analyst, PetFoodRate