Vanzant v. Hill's Pet Nutrition, Inc., 1:17-cv-02535

Plaintiffs, led by Holly Blaine Vanzant, sued Hill’s Pet Nutrition (Hill’s) and PetSmart, alleging marketing and sale of “Prescription Diet” (PD) pet food was unfair and deceptive under Illinois law.
The core of the suit was that Hill’s labeled pet food as “Prescription Diet” and required a prescription, allegedly implying the products contained medicine or drugs, when they did not.
The Court previously certified a class for the deceptive and unfair practices claims against Hill’s, but not for PetSmart due to issues with class representation and damages model inadequacy.
On summary judgment, only Plaintiffs’ deceptive-practices claim against Hill’s survived; unfair-practices claims were dismissed, and claims against PetSmart failed.
After summary judgment, Hill’s moved to decertify the class arguing that the damages model did not match the surviving claims.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the damages model remains suitable after summary judgment	The model is still appropriate; it accounts for deceptive practices, and results would be the same even if focused only on deception	The model is no longer appropriate; model captures both unfair and deceptive conduct, but only deception remains	Decertification granted: model does not fit only the deceptive-practices claim
Scope of the deceptive-practices claim	Deceptive-practices claim includes therapeutic marketing as deceptive	Deceptive-practices claim is limited to prescription requirements and labeling	Court agrees with Hill’s; claim is limited to labeling/prescription practices
Permissibility of supplementing expert report	Netz (expert) should be allowed to modify her report to fit the narrowed claim	Supplementation would require an entirely new damages theory	Supplementing report not allowed; too fundamental a change
Predominance of common questions without common proof of damages	Common questions still predominate even if damages must be decided individually	Without common proof of damages, individual issues would swamp common ones	Individual issues predominate; class treatment inappropriate

Comcast Corp. v. Behrend, 569 U.S. 27 (2013) (damages models in class actions must measure only those damages attributable to the certified theory of liability)
Krieger v. United States, 842 F.3d 490 (7th Cir. 2016) (earlier rulings control later phases unless a compelling reason to depart)
In re IKO Roofing Shingle Prods. Liab. Litig., 757 F.3d 599 (7th Cir. 2014) (commonality of damages is not required for class certification; practicalities matter)