From the dog, tiger and pig website that is ModernPooch.com we have this amazing story.

In a zoo in California, a mother tiger gave birth to a rare set of
triplet tiger cubs. Unfortunately, due to complications in the pregnancy,
the cubs were born prematurely and due to their tiny size, they died shortly
after birth.
The mother tiger after recovering from the delivery, suddenly started to
decline in health, although physically she was fine. The veterinarians felt
that the loss of her litter had caused the tigress to fall into a
depression. The doctors decided that if the
tigress could surrogate another mother's cubs, perhaps she would improve.

After checking with many other zoos across the country, the depressing news
was that there were no tiger cubs of the right age to introduce to the
mourning mother. The veterinarians decided to try something that had never
been tried in a zoo environment. Sometimes a mother of one species will take
on the care of a different species. The only "orphans" that could be found
quickly, were a litter of weaner pigs.
The zoo keepers and vets wrapped the piglets in tiger skin and placed the
babies around the mother tiger.

Thanks to Jodi for this!