Significantly higher hepatic copper concentrations in dogs compared to coyotes implicate excessive copper in most commercial dog foods.

Abstract

OBJECTIVE: Compare liver copper (Cu) concentration, as a metric of dietary Cu exposure, in senior dogs euthanized for geriatric health concerns against free-foraging coyotes. METHODS: Liver samples (April 7, 2023, to April 22, 2024) from 104 dogs and 88 coyotes were histologically evaluated, assigned rhodanine Cu scores, and had liver Cu quantified (µg/g of dry weight liver [dwl]). Medical records, signalment, and dietary history were acquired for dogs. Water Cu from relevant geolocations was analyzed. Dietary Cu (manufacturer typical analyses or inductively coupled plasma atomic emission spectroscopy [USDA micronutrient laboratory]) was normalized as mg of Cu/100 kcal (metabolizable energy was calculated with modified Atwater factorials). Dietary Cu intake was categorized as Cu-restricted (0.15 to 0.24 mg of Cu/100 kcal) or Cu-replete (0.31 to 0.39 and ≥ 0.40 mg of Cu/100 kcal). Nonparametric statistics defined significant differences and associations. RESULTS: There were 35 of 104 rhodanine-positive samples (34%) from dogs versus 0 of 88 from coyotes. Median (range; 95% CI) liver Cu concentration (µg/g of dwl) in dogs (248 [70 to 1,795; 267 to 369]) significantly exceeded that in coyotes (25 [5 to 114; 27 to 36]). Liver Cu concentrations of 69 rhodanine-negative dog samples, including 13 dogs fed Cu-restricted diets, also were significantly higher than those of coyotes. Liver Cu was 201 (70 to 370; 182 to 218) µg/g of dwl in all rhodanine-negative dogs and was 190 (79 to 355; 132 to 250) µg/g of dwl in dogs fed Cu-restricted diets. CONCLUSIONS: Significantly greater liver Cu concentration in geriatric dogs compared to free-foraging coyotes corroborates concern regarding higher dietary Cu intake in dogs fed commercial dog foods. Findings did not imply, without further investigation, whether lower coyote liver Cu is optimized for canid health and metabolism or merely reflects food-derived Cu intake and interspecies differences. CLINICAL RELEVANCE: Findings added case-based evidence supporting concern for excessive Cu in commercial dog foods.