CASE NAME: Taylor West v. Costco Wholesale Corporation

CASE NO.: 2:26-cv-02182

JURISDICTION: United States District Court for the Western District of Washington

FILED ON: June 23, 2026

CLASS DEFINITION: The complaint seeks to represent a nationwide class of all persons who purchased Kirkland Signature Nature’s Domain grain-free dog food in the United States during the four years preceding the filing of the complaint, along with California subclasses for purchasers under California law.

SUMMARY:

A proposed class action alleges that Costco Wholesale Corporation deceptively marketed and sold its Kirkland Signature Nature’s Domain grain-free dog food as healthy and safe while failing to disclose an alleged association between the products and an increased risk of canine dilated cardiomyopathy (DCM), a potentially fatal heart disease. According to the complaint, the grain-free recipes contain high levels of legumes such as peas and lentils, ingredients that veterinary researchers have associated with diet-related cardiac problems in dogs. The lawsuit alleges Costco knew or should have known about these risks through scientific literature, veterinary recommendations, and the FDA’s investigation into grain-free pet foods, yet continued to market the products as appropriate for dogs of all life stages without warning consumers. The plaintiff contends purchasers paid a premium for products they believed were safe and would not have purchased them, or would have paid less, had the alleged risks been disclosed.

ALLEGATIONS:

According to the complaint, Costco introduced its Kirkland Signature Nature’s Domain grain-free dog food as part of the growing market for grain-free pet diets, promoting the products as providing nutrition, health, and vitality for dogs of all life stages. The lawsuit alleges there is little scientific justification for feeding grain-free diets to most dogs because true grain allergies are uncommon, while grain-free formulations frequently rely on legumes as substitute ingredients.

The complaint alleges that veterinary researchers began identifying cases of diet-associated dilated cardiomyopathy in dogs consuming grain-free, high-legume diets as early as 2012. It further claims that a growing body of scientific studies has reported an association between these diets and indicators of cardiac injury, including enlarged heart chambers, abnormal cardiac biomarkers, arrhythmias, and reduced heart function. The lawsuit also cites research that allegedly found improvement in affected dogs after switching from grain-free diets to traditional grain-inclusive diets.

According to the complaint, Costco either knew or should have known of these findings through published veterinary research, veterinary textbooks, professional recommendations, and the U.S. Food and Drug Administration’s investigation into reports of non-hereditary DCM associated with certain grain-free pet foods. The lawsuit notes that the FDA publicly announced its investigation in 2018 and later identified Nature’s Domain among the pet food brands most frequently reported in DCM cases submitted to the agency.

The plaintiff alleges Costco nevertheless continued to advertise Nature’s Domain as a healthy, nutritious, and safe product for all breeds and life stages. The complaint points to statements on product packaging describing the food as providing “great nutrition for overall health and vitality,” meeting nutritional requirements for all life stages, and supporting healthy lifestyles. It also challenges statements on Costco’s website suggesting the grain-free formulas are suitable for pets with food sensitivities and appropriate from puppyhood through adulthood.

The lawsuit further alleges Costco failed to conduct adequate feeding studies or publish research demonstrating the long-term cardiac safety of the grain-free formulas before marketing them to consumers. According to the complaint, Costco also failed to disclose the alleged association between grain-free, high-legume diets and heart disease anywhere on its packaging or website.

The named plaintiff, Taylor West, alleges he purchased Nature’s Domain grain-free dog food because he believed Costco’s marketing represented the products as healthy and safe. He claims he relied on those representations when making his purchase and would not have purchased the products had he known of the alleged cardiac risks. The complaint seeks to recover economic damages on behalf of consumers who allegedly paid a premium for products that were worth less than represented because of the undisclosed health risks.

The lawsuit asserts claims under the Washington Consumer Protection Act on behalf of a nationwide class, along with claims under California’s Unfair Competition Law, Consumers Legal Remedies Act, False Advertising Law, and various common-law fraud and misrepresentation theories for California purchasers. The plaintiff seeks damages, restitution, injunctive relief, attorneys’ fees, and other relief the court deems appropriate.

TAGS