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The short answer: Castor & Pollux Organix wins by 31 points (A/90 vs C/59). This is the most useful contrast in our organic category: both formulas lead with USDA-certified organic ingredients, but Castor & Pollux Organix carries organic chicken and organic chicken meal in the top two positions, while Gather Endless Valley is fully plant-based with organic peas and lentils. The 31-point gap is almost entirely about whether named animal protein is on the panel — not about ingredient quality, sourcing integrity, or formulation discipline.

The scores

Gather Endless Valley Vegan: C (59/100) — Organic Peas, Organic Barley, Organic Oats, Lentils, Organic Sunflower Oil.

Castor & Pollux Organix Organix Organic Chicken & Brown Rice: A (90/100) — Organic Chicken, Organic Chicken Meal, Organic Oatmeal, Organic Barley, Organic Brown Rice.

How the ingredients compare

The top-five ingredients reveal the formulation split between these two brands:

Gather: Organic Peas, Organic Barley, Organic Oats, Lentils, Organic Sunflower Oil

Castor & Pollux: Organic Chicken, Organic Chicken Meal, Organic Oatmeal, Organic Barley, Organic Brown Rice

The 31-point gap (Castor & Pollux wins by 31 points) shows where the v15 rubric weights ingredient breadth, protein density, and supplement depth differently.

Where Gather pulls ahead

100% plant-based formulation: Gather is the only adult dog kibble in our catalog with no animal-derived ingredients on the panel. For owners with ethical commitments to plant-based feeding, this is the entire reason to consider the product. Shop on Amazon →

Comprehensive synthetic amino-acid backstop: Gather adds taurine, DL-methionine, L-lysine, and L-carnitine — the four amino acids most likely to be limiting in a plant-based diet. The formulation discipline here is unusual for the vegan dog kibble segment.

Quinoa for complete plant amino acids: Quinoa at #7 supplies one of the few plant ingredients with a complete amino acid profile, filling several methionine-and-cysteine gaps that legumes alone do not cover.

Where Castor & Pollux holds its own

Named animal protein lead with USDA Organic certification: Castor & Pollux Organix carries organic chicken at #1 and organic chicken meal at #2 — the structural protein-first lead that the v15 rubric weights heavily. For dogs (facultative carnivores by metabolism), this is the more rubric-aligned formulation. Shop on Amazon →

Marine omega-3 access: Castor & Pollux includes organic chicken liver and chicken fat that contribute trace marine-adjacent omega-3 (limited but present). Gather's only omega-3 source is plant ALA from flaxseed, which converts to EPA/DHA at low efficiency.

Vitamin D3 vs D2: Castor & Pollux uses vitamin D3 (cholecalciferol, the animal-derived form dogs metabolize most efficiently). Gather uses vitamin D2 (ergocalciferol, plant-derived, less efficient conversion in dogs).

The bottom line

Castor & Pollux Organix wins by 31 points (A/90 vs C/59) under the KibbleIQ v15 rubric. The gap is structural: the rubric is calibrated for animal-protein-led formulations, which Gather is intentionally not. For owners with a hard ethical commitment to plant-based feeding for dogs, Gather is the best-formulated option in the segment and we recommend pairing it with regular veterinary nutrition consultation (taurine monitoring, periodic cardiac screening). For owners who want the USDA Organic supply-chain integrity Gather offers without the plant-only formulation, Castor & Pollux Organix is the cleaner pick — same organic certification, named animal protein lead, 31 points higher on the rubric.