The scores
Kirkland Signature: B grade, 78/100
Diamond Naturals: B grade, 78/100
A perfect tie. Both foods deliver B-grade nutrition at prices that undercut most C-grade competitors. This isn't a coincidence — Diamond Pet Foods manufactures Kirkland Signature dog food for Costco, which is why the formulas are so similar.
How the ingredients compare
Here are the top five ingredients side by side:
Kirkland Signature: Chicken, Chicken Meal, Whole Grain Brown Rice, Cracked Pearled Barley, Chicken Fat
Diamond Naturals: Chicken, Chicken Meal, Whole Grain Brown Rice, Cracked Pearled Barley, White Rice
The first four ingredients are identical. Chicken and chicken meal provide a strong protein foundation — named animal protein in the first two positions is something many premium brands don't even achieve. Whole grain brown rice and cracked pearled barley are nutritious, fiber-rich carbohydrate sources. The only difference at position five is chicken fat (Kirkland) vs white rice (Diamond Naturals).
Where Kirkland Signature holds its own
Chicken fat in the fifth position is a quality fat source, preserved with mixed tocopherols (vitamin E). It provides essential fatty acids and is one of the more palatable and digestible fat sources for dogs. Having a named animal fat this high in the formula means Kirkland front-loads both its protein and fat from chicken — a clean, single-source protein approach.
Kirkland is also typically the cheaper option per pound, assuming you already have a Costco membership. The 40-pound bags at Costco are some of the best per-pound pricing available for a B-grade food. If you're already a Costco member, the math strongly favors Kirkland. Shop on Amazon →
Where Diamond Naturals holds its own
The biggest advantage Diamond Naturals has is availability. You can buy it at pet specialty stores, farm supply stores like Tractor Supply, and online through Amazon, Chewy, and other retailers. No membership required, no special trip needed.
Diamond Naturals also includes proprietary probiotics (species-specific K9 Strain) that are added after the cooking process to ensure viability. These live beneficial bacteria support digestive health and immune function — a functional extra that not every brand at this price includes. The formula also contains superfoods like chia seed and quinoa further down the ingredient list, along with glucosamine and chondroitin for joint support. Shop on Amazon →
The bottom line
Kirkland Signature (B/78) and Diamond Naturals (B/78) are essentially two versions of the same excellent value proposition — B-grade dog food at budget prices. The fact that Diamond manufactures both explains the near-identical formulas.
If you have a Costco membership, Kirkland is likely cheaper. If you don't, Diamond Naturals delivers the same quality without the membership fee. Either way, you're getting one of the best deals in dog food — a B-grade formula that outscores premium brands like Hill's Science Diet (C/61) and Royal Canin (C/58) at a fraction of the price.