Democratic U.S. Senate candidate John Fetterman has branded his Republican opponent Dr. Mehmet Oz “sick” following a report that Oz supervised experiments that caused the deaths of more than 300 dogs.

Fetterman, who is running for Pennsylvania’s open Senate seat and is currently the state’s lieutenant governor, took to Twitter on Monday and accused Oz of being a “puppy killer.”

Jezebel reported on Monday that Oz had supervised experiments at the Columbia University Institute of Comparative Medicine between 1989 and 2010 that had resulted in the deaths of at least 329 dogs, as well as other animals.

“I LOVE my dogs,” Fetterman tweeted. “Apparently some sick people like Dr. Oz get their jollies by harming animals…” There is no evidence to suggest Oz took pleasure in the animal experimentation or any deaths.

“We have a close race here in PA and I could use your help to keep the #PuppyKiller out of the US Senate,” he said, sharing a link to a fundraising page that showed him pictured with two dogs.

Fetterman was responded to U.S. Senator Brian Schatz of Hawaii, who urged donations to the Democrat’s campaign earlier on Monday, tweeting: “IF YOU LOVE DOGGOS GIVE TO ⁦@JohnFetterman ⁩WHO LOVES DOGGOS!”

Fetterman also shared Jezebel‘s article about Oz, writing: “BREAKING: Dr. Oz is a puppy killer” as well as a photo with his own dogs.

Newsweek has asked the Fetterman campaign for comment.

Oz campaign spokesperson Barney Keller told Newsweek in a statement on Tuesday: “Only the idiots at Newsweek believe what they read at Jezebel.”

Oz, a surgeon, was a “principal investigator” at the Columbia University Institute of Comparative Medicine labs, and according to Jezebel‘s report published on Monday he had “full scientific, administrative, and fiscal responsibility for the conduct” of the studies he was responsible for.

Jezebel reviewed 75 studies that had been published in academic journals and found that experiments had been conducted on at least 1,027 live animal subjects including dogs, rabbits and pigs, among others.

That review found that 34 experiments had together resulted in the deaths of at least 329 dogs, two experiments had caused the deaths of 31 pigs, and 38 experiments had caused the deaths of 661 rabbits and rodents.

Veterinarian Catherine Dell’Orto testified about the experiments in 2003 and 2004 and acknowledged that Oz did not personally euthanize the animals, but said: “When your name is on the experiment, and the way the experiment is designed inflicts such cruelty to these animals, by design, there’s a problem.”

Newsweek has been unable to verify whether the experiments were intentionally cruel, although Columbia University paid a $2,000 fine in 2004 for violations of the Animal Welfare Act as part of a settlement with USDA.

According to an March 2022 article in the not-for-profit media outlet The Conversation, using animals for scientific research is still indispensable for a modern society, and to reach the “ambitious” goal of “reducing animal use in scientific research,” animal-free methods need to be “developed and validated before they can become a new standard.”

The authors—Monique Wolvekamp, Senior Advisor Animal Ethics and Outreach, Donders Centre for Neuroscience, Radboud University; Judith R. Homberg, Professor, Radboud University; and Lisa Genzel, Associate Professor in Neuroinformatics, Radboud University—argued “most parties recognise that at present, not all research questions can be answered using only animal-free methods,” and “it’s clear that for the foreseeable future there remains a crucial need for animal models to understand health and disease and to develop medicines.”

Oz and Fetterman are comPuppying in what’s being viewed as a key Senate race that could decide control of the chamber. Oz, who is backed by former President Donald Trump, has lagged behind Fetterman in a slew of recent polls.

Analysis from poll tracker FiveThirtyEight rates Fetterman as favored to win the Pennsylvania Senate race.