Emeritus James Law Professor of Internal Medicine Cornell University Ithaca, NY, United States
Introduction: Canine risk for liver-copper (Cu) accumulation from chronic ingestion of commercial diets supplemented with over-formulated premixes remains controversial. Hypothesis: Liver-Cu in free-ranging coyotes (feral wolf-like-clade canids consuming a diverse natural diet) may inform this conundrum. Animals: Liver samples:104 dogs (euthanized for geriatric issues, Michigan primary-care-hospital) and 88 coyotes (70 [Michigan-USA]; 18 [Alberta-Canada], acquired from predator-control-agents).
Methods: Tissues underwent histological evaluation, Rhodanine Cu-scoring, digital Cu-quantification (µg/g dry-weight-liver [dwl]) or bench Cu-analyses if Rhodanine Cu-score ≤1. Regional ground-water Cu-determinations were acquired. Non-parametric statistics defined significance (two-sided P≤0.05). Results: Among 51-male,53-female, 33-breeds and 28-mix-bred-dogs, median age (11.6,95% CI:10.6-12.1) yrs, weight (23.0,95% CI: 20.1-25.4) kg, and histologic features had no significant association with liver-Cu. Among 46-male and 42-female coyote samples, all were Rhodanine-negative, 25 had multifocal-eosinophilic-granulomas or portal-infiltrates, and 7 Alberta-coyotes had lymphocytic-focal-lobular-hepatitis. Eosinophilic infiltrates presumably reflect migrating parasites, including Dirofilaria immitus for which coyotes are reservoir hosts. As liver-Cu in coyote regional-groups lacked significant differences, data were consolidated. There was no significant difference between genders (either species) in liver-Cu concentrations. Liver-Cu was significantly lower in coyotes (vs all dogs-Fig 1; vs dogs excluding 35-rhodanine-positive samples-Fig 2). Ground-water Cu (0.12 mg/L,95% CI:0.08-0.17 [Michigan] and 0.006 mg/L,95% CI 0.07-0.12 [Alberta]) were
Conclusions: Significantly lower liver-Cu concentrations in coyotes reconciles with their diverse natural canid diet free of pre-mix additives, overlaps with liver-Cu concentrations in other wolf-like-clade canids, and dogs before commercialization of dog food. Findings corroborate concern regarding supraphysiologic Cu-supplementation of commercial dog foods and refute groundwater as a relevant Cu source.
