Veterinary journal retracts pet food company’s paper about copper in dog food

leisergu, CC BY 2.0, via Wikimedia Commons

A veterinary journal has retracted a paper from a major pet food company after criticism prompted the authors to re-examine their data. 

The retraction is the first in the Journal of the American Veterinary Medical Association’s 180 years of publication, Lisa Fortier, the journal’s editor in chief, told Retraction Watch. But veterinary researchers who wrote to the journal with concerns about the article say the retraction doesn’t address all the issues they raised. 

The article, “Sixteen years of canine hepatic copper concentrations within normal reference ranges in dogs fed a broad range of commercial diets,” appeared online March 7. Most of the authors are affiliated with Hill’s Pet Nutrition. 

Within weeks of the article’s publication, the journal got the first of seven letters “crying foul,” Fortier said. 

The topic of copper in dog food has been “very controversial,” she said – the authors of a 2021 editorial in JAVMA called for re-examining guidelines about the copper content of dog food because they had “seen what we believe to be an increased incidence” of dogs with liver damage from copper

The paper from Hill’s scientists, with Leslie Hancock, the company’s chief medical officer, as the last author, concluded “although there is an increase in copper concentrations, it is not clinically significant,” and the recommendations for copper content in dog food “are not resulting in hepatic copper toxicity.”  An article in Petfood Industry about the study’s findings (which has been updated to highlight the retraction) stated the team “didn’t note any clear correlations between copper levels in dogs’ livers and their varied diets.” 

Fortier sent the critical letters to Hancock and her team, who re-examined their work and found an error in their data. The effect of the mistake on the paper was too much for a correction, Fortier said, so she told the authors to draft a retraction. 

The following notice appeared on May 21: 

On behalf of my coauthors, I write to formally request a retraction to accurately respond to concerns expressed in the received Letters to the Editor regarding “Sixteen years of canine hepatic copper concentrations within normal reference ranges in dogs fed a broad range of commercial diets,” published online on March 7, 2024. Unfortunately, with further investigation, new data were discovered that materially change the results of the article as it reads today. The latest information revealed a change in reported liver copper concentration results imported from a portion of the 2006 to 2014–era sample. As a result of these findings, it is necessary to make corrections to uphold the integrity of scientific research and maintain the trust of our readers and the veterinary community. All coauthors agree with the retraction, with the full intention to resubmit and share the full results of this meaningful study in a timely manner. We regret that these new findings were unavailable to the authors earlier and apologize to the readers and editors for any confusion. We look forward to the opportunity to share corrected data in the future.

Hancock told Retraction Watch the study’s first author, a master’s student, obtained additional data files that led to identifying the error in the company’s internal database: 

We discovered a critical field necessary for analysis was lost during an update to our electronic medical records and data system after 2014. This data loss was not due to negligence or inadequate methods; instead, it resulted from a sequence of unforeseen events. The error might have remained undetected for years, which would have been even more disheartening for the author who initially pointed out the inconsistency. 

Hancock said her team is preparing a corrected manuscript with a reanalysis of the internally procured samples. (Her full comments are available here.)

“​​I think the master’s student who found this is amazing to have dug that far, it’s real due diligence,” Fortier said. 

None of the journal’s editorial team had ever dealt with a retraction before, but an associate editor had recently attended a session about retractions at the Council of Science Editors meeting just weeks ago. (A speaker recommended editors reach out to Retraction Watch ahead of the retraction, which they did.) 

Fortier said her focus was on “how can I make this process fair and honest for our authors, and therefore our readers.” Hill’s is a sponsor of the AVMA, which owns the journal, but Fortier said she “didn’t treat them any differently.” She expressed respect for the authors, and the scientists who wrote to her about the article: “I think the process worked.” 

Several of the letter-writers said they disagreed with Fortier’s decision not to publish their letters. In an email seen by Retraction Watch, Keith Richter, a veterinarian in San Diego, Calif., wrote to Fortier: 

The retraction statement does not address many of our concerns, and it is hard to imagine how correction of “a change in reported liver copper concentration results imported from a portion of the 2006 to 2014–era sample” can overcome deficiencies in study design, study subjects, and errors in copper quantification. 

Richter’s formal letter to the editor, signed by two other veterinary researchers, detailed those concerns and said the paper’s authors “make several unsubstantiated conclusions.”

In a longer letter Richter and his colleagues sent to Fortier personally, they wrote: 

The authors state the objective of this study is to “examine the effects of age, sex, breed, liver histopathology, and year of death on liver copper concentrations in dogs fed commercial dog foods”. We believe the real underlying objective was to prove that commercial dog foods are not responsible for increasing hepatic copper concentrations and copper associated hepatopathies.

“The whole thing is concerning, both from an ethics standpoint as well as from the numerous design and method flaws along with misguided conclusions,” Daniel Langlois, an associate professor at Michigan State University’s College of Veterinary Medicine, in East Lansing, told Retraction Watch. In a formal letter to the editor, Langlois and two other colleagues wrote some of the article’s findings “defy logic,” and the liver specimens seemed not to have been processed properly, according to the study’s methods. 

“This was a massively flawed study,” Langlois said, and was not designed to address any link between copper in dog food and copper-associated liver disease in the animals. 

“The authors’ conclusions were also completely overstated, and they immediately disseminated their results and conclusions to a number of veterinary news outlets with the final message being that regulations for dietary copper supplementation are not involved in the etiology of copper-associated hepatopathy in dogs,” Langlois said. “Even if their results were accurate, this would not be a reasonable conclusion based on their study populations and design.”

“One thing is clear,” he added. “This paper was not appropriately reviewed.” 

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