Police have been called in over the death of a dog who competed at Crufts, after a claim that it was poisoned.

Three-year-old Thendara Satisfaction, known as Jagger, died on Friday after returning home to Belgium following the show at the NEC in Birmingham. The Kennel Club, which organises Crufts, has said it will work with police to establish what happened.

Dee Milligan-Bott, a dog breeder for 30 years, told the Guardian that she and Jagger’s co-owner, Alexandra Lauwers, were devastated by his death.

“They [the Lauwers] got home on Friday night and the dog was ill,” she said. “By the time the vet got there he was dead.

“The vet did an immediate autopsy because the death was very suspicious. It was found the dog had beef cubes in his stomach that had been poisoned. The only day the dog had been left alone all week was while being left on the bench at Crufts while the judging of our other dogs was taking place.”

Milligan-Bot said the vet had also suggested the poisoning happened at the time Jagger was at Crufts. Lauwers called the Belgian police but, according to Milligan-Bott they said that the crime had not taken place on Belgian soil. The breeder, from Leicestershire, said she had not contacted British police but was expecting that their Belgian counterparts would do so.

“I am devasted,” said Milligan-Bott. “We had probably one of the best days in our showing career and our breeding career. We should be celebrating as Noodle, Jagger’s half-brother, won best in breed.” She said Lauwers is similarly distraught. “He [Jagger] lived with them,” she said. “They are first and foremost pets, he was hers and she’s devastated.”

After a report in the Times on Friday suggested breeders and owners are increasingly worried that the intensity of competition has led to people engaging in underhand practices such as people snipping dogs’ fur or lacing food with laxatives, the Kennel Club warned that anyone attempting to deliberately sabotage another competitor’s performance would face severe disciplinary procedures.

Milligan-Bott had earlier told Dog World that breeding had turned into a “nasty sport” and suggested someone might have been jealous at her success. But she told the Guardian that she could not believe that another dog owner or breeder could have been responsible for Jagger’s death.

“I can only imagine it’s some awful random person who did this. I don’t want to believe that another dog owner did this. The only thing we all have in common is we love dogs – we are not going to kill someone else’s dogs.”

Kennel Club secretary, Caroline Kisko said: “We are deeply shocked and saddened to hear of Jagger’s death and our heartfelt sympathies go out to his owners. Whilst we are unclear of exactly what happened, we understand that a toxicology report is due next week and that this matter has been reported to the police – we will work with them and help however we can. We are in contact with the owners and will do all we can to support them at this sad time.”