Prof. Rich Moccia, an associate vice-president at the school, said relinquishing control of the "enviropigs" posed unacceptable risks.
"Although we have had many generous and well intentioned offers from individuals and groups who would like to adopt the enviropigs, there is absolutely no opportunity for this to occur for many reasons," Moccia said.
"The possibility of escapement or inadvertent release, however remote, could occur, with the possibility that they could intermix with either feral or domesticated pigs, or even end up in the human food chain by accident."
The pigs, genetically modified to generate less-polluting waste, were set to become among the first produced for human consumption until the project's main financial backers, Ontario Pork, pulled the plug.
Moccia said the school was still hoping to find new partners or others interested in continuing the research and commercializing the swine technology.
If no one else is interested, the pigs might have to be put down, a prospect that has upset Farm Sanctuary, an animal-rights group based in Watkins Glen, N.Y.
In a letter to Moccia Tuesday, the group called on the school to ensure the pigs would be spared.
"Rather than killing these poor animals, won't you work with us to give them a happy retirement?" the letter states.
"The University of Guelph brought these animals into the world, and you have a moral obligation to them; please don't betray that responsibility by killing them."
The letter calls pigs "interesting individuals" that are similar in emotion and behavioural needs to dogs and cats.
"For the same reason you wouldn't kill 16 healthy dogs at the end of a research project, please don't kill these poor pigs, who deserve a chance to live out their final years basking in sunshine, taking mud baths, and simply being pigs."
Moccia, however, said the university was bound by protocols requiring the school to maintain strict care and control over the pigs.
In fact, he added, the university was legally bound to keep the animals in closed containment.
Any transfer to another institution would require it have approved care and containment facilities, as well as adequate protocols for the use of research animals, he said.
Farm Sanctuary's Bruce Friedrich, a former activist with People for the Ethical Treatment of Animals, called it "bizarre" to talk about care protocols when 16 healthy pigs could be killed.
"We don't believe that there is a law that prevents them from working with us to save these animals," Friedrich said.
"If there is a law, they should work with us to get an exemption."