The scores
Kirkland Signature Nature’s Domain Puppy Chicken & Pea: B (79/100) — Very Good. Chicken + chicken meal as the first two ingredients, grain-free legume stack, and Costco’s quality-control contract keeps the ingredient deck tight.
Diamond Naturals Small & Medium Breed Puppy Chicken & Rice: B (78/100) — Very Good. Chicken + chicken meal lead, followed by white rice + chicken fat + cracked pearled barley. A grain-inclusive approach built for small/medium-breed puppy metabolism.
How the ingredients compare
The top five ingredients:
Kirkland Signature Puppy: Chicken, Chicken Meal, Pea, Garbanzo Bean, Lentil
Diamond Naturals Puppy: Chicken, Chicken Meal, White Rice, Chicken Fat (preserved with Mixed Tocopherols), Cracked Pearled Barley
Both formulas lead with the same two ingredients — fresh chicken and chicken meal — the gold-standard opening move for a mid-tier puppy kibble. They diverge on carbohydrate architecture. Kirkland uses a grain-free legume stack (pea, garbanzo bean, lentil) across positions three through five. Diamond Naturals uses a grain-inclusive rice + barley stack with chicken fat wedged in at position four.
The grain-free vs grain-inclusive split is the same structural conversation FDA’s 2018–2022 DCM investigation opened. The evidence didn’t establish causation but did show a nutritional association between grain-free legume-heavy formulas and DCM in non-predisposed breeds. For at-risk breeds (Golden Retrievers, Dobermans, Great Danes, Cocker Spaniels, Newfoundlands), grain-inclusive formulas are the cardiologist-recommended default during the growth window. For breeds with no DCM predisposition, either approach is acceptable as long as taurine is supplemented or dense in the protein source.
Further down, Kirkland adds chicken fat, egg product, flaxseed, salmon oil, and the Nature’s Domain premix (probiotics, chelated minerals, DHA). Diamond Naturals adds dried plain beet pulp, egg product, fish meal, flaxseed, salmon oil, and the Diamond Naturals premix (chelated minerals, DHA, probiotics). Both hit the puppy-nutrition fundamentals — DHA for brain development, appropriate calcium:phosphorus ratios, probiotics for sensitive puppy digestion.
Where Kirkland Puppy pulls ahead
Value per pound: Kirkland Signature is sold exclusively at Costco (and Costco.com for members) and is priced materially below Diamond Naturals on a $/lb basis — often 30–40% cheaper for a functionally comparable formula. Costco’s volume contract with Diamond Pet Foods delivers manufacturer cost pricing straight to the member.
Salmon oil instead of fish meal: Kirkland lists salmon oil explicitly as the omega-3 source, while Diamond Naturals lists fish meal + salmon oil. Salmon oil is a cleaner, higher-EPA/DHA-concentration source than pooled fish meal.
Grain-free option at budget price: For owners who specifically want a grain-free puppy formula without paying premium-brand prices (Acana, Orijen, Canidae PURE), Kirkland Nature’s Domain Puppy is the cheapest functional grain-free option on the market. Shop on Amazon →
Where Diamond Naturals Puppy holds its own
Grain-inclusive safety profile: For at-risk puppy breeds, Diamond Naturals’ grain-inclusive rice-and-barley base is the cardiologist-recommended default. The DCM association with grain-free legume-heavy formulas doesn’t implicate Diamond Naturals.
Size-specific formulation: Diamond Naturals Small & Medium Breed Puppy is specifically engineered for the faster metabolic rate and smaller kibble size needs of small and medium puppies. Kirkland Puppy is a single formula across sizes.
Available without Costco membership: Diamond Naturals is stocked at independent pet stores, Tractor Supply, Amazon, Chewy, and Petco. No membership fee, wider availability, easier to find if you’re traveling or moving. Shop on Amazon →
The bottom line
If you’re a Costco member feeding a non-DCM-predisposed puppy breed and the bag size works for your storage, Kirkland Signature Nature’s Domain Puppy is the best raw-dollar value on the puppy kibble market. For at-risk breeds or households that prefer grain-inclusive puppy nutrition, Diamond Naturals Small & Medium Breed Puppy delivers a very similar score at slightly higher cost and broader retail availability. Both are manufactured in the same Diamond Pet Foods facilities to the same quality-control standards. See our best affordable dog food guide for more options.