Copper-associated hepatitis (CAH) has a complex inheritance pattern in Labrador retrievers. After silently progressing for years, the clinical phase often results in liver failure and death within months. Dietary copper and zinc may play roles in pathogenesis. To investigate association between hepatic copper and zinc levels, histology, and dietary copper and zinc, 55 client-owned Labrador retrievers fed a single brand and type of commercial dry food for ≥1 year were evaluated. Eighty percent were first-degree relatives to dogs with CAH. Liver biopsies were used to determine copper and zinc content. Diets were analyzed at a commercial laboratory.

Hepatic copper concentrations were high (>400 mg/kg dry weight liver) in 75% of dogs. Hepatic copper concentrations were significantly higher in dogs with hepatitis lesions than those without; hepatic zinc concentrations were not significantly different. There was a significantly positive association between dietary and hepatic copper and a negative association between dietary zinc and hepatic copper. Results no longer reached significance when data from 8 dogs fed a diet with a higher zinc:copper ratio and significantly lower hepatic copper concentrations were removed from analysis.

Copper levels in many commercial diets may be too high for dogs genetically predisposed to CAH. These results cannot yet be applied to the general Labrador retriever population without greater understanding of CAH genetics.

Commentary
This study supported the need for breed-specific diets. It would be helpful to have diets formulated to address each breed’s specific healthcare need—in this case, inherited CAH in Labrador retrievers, which may be more common than previously thought. Finding over-the-counter diets with lower copper levels is almost impossible, as label reporting is not required or may not represent entire copper content.—Sandra Sawchuk, DVM, MS

Source
Association of dietary copper and zinc levels with hepatic copper and zinc concentration in Labrador Retrievers. Fieten H, Hooijer-Nouwens BD, Biourge VC, et al. JVIM 26:1274-1280, 2012.