The northern Spanish city of Gijon has cancelled its century-old bullfighting festival, accusing it of “crossing various lines” after two of the bulls slain this week were named “Feminist” and “Nigerian”.

“The bullfighting festival is over,” the city’s Socialist mayor, Ana Gonzalez, told reporters. “They have crossed various lines … A city that believes in equality between men and women, that believes in integration, that believes in open doors for everyone cannot allow these sorts of things to happen.”

The Socialist party had decided at its most recent congress to do away with the 133-year-old Begona bullfighting festival, citing growing opposition among the city’s residents. These plans were accelerated after it appeared that bullfighting was being “used to display an ideology contrary to human rights”, said Gonzalez on Wednesday.

The current contract with festival organisers would not be extended nor would the city’s bullring be leased for the event, meaning a loss of EUR50,000 (GBP43,000) in annual income for the city, she added.

Proponents of bullfighting hit back, arguing the controversy stemmed from a misunderstanding of how bulls are named.

The Union de Criadores de Toros de Lidia, which represents the interests of 345 breeders of fighting bulls, linked the names to regulations set out by Spain’s ministry of agriculture. Aimed at ensuring the traceability of the bulls, the protocol sees bulls given the names of their mothers, it said in a statement.

The bulls from this past weekend were “descended from the cows ‘Feminist’ and ‘Nigerian’, both acquired by the rancher in 1986, with a lineage of more than 35 years and more than four generations, far from any social and political context,” it added.

Spain’s ministry of agriculture did not reply to a request for comment.

Others cited the names of previous bulls, from Spaniard to Parishioner, to argue there was little deeper meaning to be read into them. Even so, names changes in bullfighting are not without precedent; at a festival held shortly after Spain’s civil war came to an end in 1939 one of the bull’s names was changed from “Communist” to “Mirador” amid concerns over offending sensibilities, noted newspaper El Pais.

The conservative People’s party in Gijon said it was looking into whether the mayor’s decision could be legally challenged. “From the People’s party we’re going to be absolutely against anyone who wants to take away freedoms,” said the party’s Pablo Gonzalez. He pointed to elections slated to be held in two years and vowed to hold the city’s “best bullfighting festival for decades”, if elected.

The mayor’s decision was welcomed by many animal rights campaigners as well as opposition parties on the left. Some, such as the journalist Anita Botwin, couldn’t help but note the irony of how the polarising festival met its demise. “That a feminist bull put an end to the bullfighting festival in Gijon is poetic justice,” she tweeted.