An already over-the-top and acrimonious US Senate race in Pennsylvania has escalated after John Fetterman – the Democratic candidate – accused his Republican opponent, the celebrity physician Dr Oz, of having killed more than 300 dogs.

Calling his rival “sick” and a “puppy killer”, Fetterman cited reporting published on Monday alleging that Mehmet Oz oversaw numerous animal deaths while conducting medical research at Columbia University.

“[A] review of 75 studies published by Mehmet Oz between 1989 and 2010 reveals the Republican Senate candidate’s research killed over 300 dogs and inflicted significant suffering on them and the other animals used in experiments,” Jezebel, the publication that broke the story, wrote.

The research also harmed pigs, rabbits and small rodents, according to Jezebel.

Oz’s political staff have denied the allegation. When asked about it by Newsweek, a spokesperson for the Oz campaign said: “Only the idiots at Newsweek believe what they read at Jezebel.”

A veterinarian who worked with Columbia, Catherine Dell’Orto, previously accused Oz’s research team of violating the Animal Welfare Act. Among other allegations, she said that the team was euthanizing dogs without sedation using expired drugs and, in other cases, failing to euthanize dogs who were suffering.

Dell’Orto said that Oz did not personally euthanize the dogs but that his research methods contributed to their mistreatment and benefited from their exploitation.

Oz and Fetterman have been locked in a highly negative and unusually personal political race marked by frequent Twitter sparring and meme warfare. Fetterman, the lieutenant governor, has painted Oz as a rich and out-of-touch non-Pennsylvanian, while Oz has accused Fetterman – who had a stroke earlier this year and reportedly has trouble talking – of hiding from public appearances.

Earlier in his campaign, Fetterman had a strong edge over Oz, but polls have shown that advantage shrinking, according to the Philadelphia Inquirer. The race is now tight, and Fetterman’s campaign has wasted no time in making hay with the latest Oz controversy.

“BREAKING: Dr Oz is a puppy killer,” Fetterman tweeted on Monday. Later he posted a picture with his two dogs and wrote: “Hugging them extra tight tonight.”