The scores
Kirkland Signature Nature’s Domain: B (78/100) — Above average. Dual chicken proteins, quality whole grains, and a supplement stack that includes probiotics and joint support at a budget price point.
Wag Chicken & Lentils: C (73/100) — Average. Whole chicken first is a good start, but a heavy legume base, pea protein filler, and grain-free formulation hold it back.
How the ingredients compare
The top five ingredients tell the story:
Kirkland Signature: Chicken, Chicken Meal, Brown Rice, Barley, Oatmeal
Wag: Chicken, Lentils, Peas, Chicken Fat, Chickpeas
Both formulas start with chicken, but they diverge immediately after that. Kirkland follows with chicken meal — a concentrated protein source — then three quality whole grains. Wag follows with three different legumes (lentils, peas, chickpeas) and chicken fat. That’s the fundamental difference: Kirkland builds on a grain-inclusive, dual-protein foundation while Wag leans on a legume-heavy, grain-free one.
The grain question matters. The FDA has been investigating a potential link between grain-free diets high in legumes and dilated cardiomyopathy (DCM) in dogs. Kirkland avoids this concern entirely with brown rice, barley, and oatmeal — well-studied, digestible grains with their own nutritional benefits. Wag sits squarely in the DCM-flagged category.
Where Kirkland pulls ahead
Supplement stack: This is Kirkland’s biggest advantage. Glucosamine and chondroitin for joint support, plus dried Lactobacillus and Enterococcus probiotics for digestive health. These are premium additions you normally see in foods costing two to three times as much. Wag has dried chicory root for prebiotic fiber but nothing for joint health and no live probiotics.
Quality grains over legume loading: Brown rice, barley, and oatmeal are nutrient-dense, easily digestible carbohydrate sources with proven safety records in dog nutrition. They provide sustained energy, B vitamins, and soluble fiber. Wag’s lentils, peas, and chickpeas are functional, but stacking three legumes in the top five raises the kind of ingredient profile the FDA flagged in its DCM investigation.
No protein padding: Kirkland’s protein comes from chicken and chicken meal — both named animal sources. Wag uses pea protein at position six to boost protein numbers with a cheap plant isolate. When a formula needs a plant protein concentrate to hit its guaranteed analysis, it usually means the animal protein base is thinner than it looks. Shop on Amazon →
Where Wag holds its own
Wag starts with whole chicken, same as Kirkland, and includes sweet potatoes — a nutrient-dense complex carb with beta-carotene and fiber that Kirkland’s formula doesn’t feature. Sweet potatoes are one of the better carbohydrate sources available in dog food.
Convenience is Wag’s practical advantage. It’s available on Amazon with Prime shipping, Subscribe & Save discounts, and the frictionless ordering that comes with the Amazon ecosystem. Kirkland requires a Costco membership and either a store trip or Instacart delivery. For busy households already in the Amazon ecosystem, Wag’s accessibility is a genuine factor in feeding consistency.
Wag’s formula is also simpler overall, which can appeal to owners who want a shorter, more transparent ingredient list without the supplement complexity. Shop on Amazon →
The bottom line
Kirkland Signature is the better food by a clear margin. A 5-point gap that crosses from C to B grade reflects real differences: grain-inclusive versus grain-free, joint supplements versus none, probiotics versus none, and dual animal protein versus pea protein padding. Both are house brands built for value, but Costco’s version delivers noticeably more nutritional depth and avoids the DCM-linked grain-free profile.
If you have access to both retailers, Kirkland is the stronger choice for your dog’s long-term health. Read our full reviews of Kirkland Signature and Wag for the complete ingredient breakdowns.