I do know for a fact that feral cats (true ferals, not wildcats or abandoned housecats) DO cooperate in raising each others' young.

I was watching a TLC special on feral cats. A mother/daughter team had kittens at the same time. They took turns nursing, the only problem was that one of them had a tendency to move the kittens. When it happened once, one mother couldn't find the kittens. Apparently, if a mother loses her litter (sometimes, we all know of exceptions to THAT one), she loses her mothering instinct and goes back into heat.

Moving mama wound up having to raise two litters without help!