A primary school headteacher has defended plans to slaughter pigs raised on its farm to teach pupils about the food chain, after a petition against the project said it would teach children to exploit and kill animals.

Children as young as four at Farsley Farfield primary in Leeds have been helping to feed the Gloucester Old Spot pigs at the mini-farm, which also has vegetable patches and hens.

The school, which was named healthy school of the year in 2017 by the Times Literary Supplement, began keeping the pigs to teach children about the origins of their food and issues around animal welfare.

“The pigs will not be pets and will only be with us for nine months,” Peter Harris, the headteacher, said when the scheme was announced. “The pigs will have a life twice as long as modern commercially reared breeds and will have a truly free-range life.”

However, the project has been criticised by a former student and animal rights campaigner whose mother works at the school.

“[Pigs] are friendly animals that can live for about 12 years or so,” Ix Willow said in her petition. “Yet in the livestock industry they are sent to slaughter as young as six months old. It should be common knowledge that the amount of animal products we eat in the UK is well above sustainable and healthy levels.

“Schools have a duty of care to support children … By teaching them it is OK to exploit and kill animals they are in breach of this, and this could also be traumatising for children getting to know the animals and then knowing they are going to die.”

Willow also called on the school to ban certain processed meats from lunchboxes and encourage students to reduce their consumption of animal products.

Responding to the criticism, Harris said the project had the overwhelming support of parents. “There are educational boards in production that explain that these pigs are better treated than the vast majority of pigs,” he wrote on the school’s website. “These boards also encourage people to greatly reduce their meat intake.”

He added: “Our animals are just one part of a comprehensive, award-winning farming, food and cooking curriculum that means our children are much better informed than most about where their food comes from.”

Pork is the UK’s second favourite meat after chicken, with about 10m pigs slaughtered each year.