St Bernards and puppies were among those found at the farm
Polish police are questioning a woman suspected of fattening up dogs and slaughtering them to sell the lard as a health supplement, reports say.
The police said 28 well-fed dogs, including St Bernards and puppies, were found in cages on a farm, along with bottles of lard, AFP news agency said.
An animal welfare group tipped off the police after buying some lard at the farm near Czestochowa, southern Poland.
It said some dogs "were overfed to the point of no longer being able to walk".
The For Animals group's undercover inspector, Renata Mizera, said the farmer had stressed the health benefits of the lard and told her that she herself added a spoonful to her daughter's evening meal, Agence France-Presse reported.
"Half a litre of fat was being sold for 37 euros ($53, £31)," said Ms Mizera.
The police are checking whether the lard - which was found in bottles in a refrigerator at the woman's farm - comes from dogs.
The 37-year-old farmer could face up to two years in jail for animal cruelty and distributing an unsafe substance, Poland's TVN24 reported.
The dogs are being cared for by the For Animals group, which is looking for new homes for them.