Originally Posted by Yosemite
I would personally give them canned pumpkin (not the pie filling, the pure pureed pumpkin). Yoghurt has been recommended by some but others think that if your cat has any lactose intolerance (which is fairly common in cats), that it may not do the trick.
I think with the pumpkin that a spoon full mixed in with their regular food is fine.
The bacteria in live yoghurt actually digest the lactose - so it shouldn't cause a problem at all. I wouldn't mind betting that anyone who has experienced problems hasn't been using yoghurt with live bacteria, make sure it is labelled 'live' rather than 'plain', and follow the storage instructions as incorrect temperatures will kill off the bacteria.
I give about 1/2 to 1 teaspoon a day as needed - usually after oral antibiotics to help restore digestive bacterial levels, healthy cats shouldn't need it.