I can feed 3, 5, or 10 cabbages to a pig. But for all other it is 10, 20 or 30. I think the option of 3,5, 10 is better because 3 is the most useful for obtaining the seeds.
gia, it depends on the amount of the food item you are trying to feed to the pig. If you have 20 or less of a particular item in all your inventory, then it will give you All, 1, 3, 5, or 10.
Edit: I do agree that it would be very useful to always have the option of feeding 3 items, no matter how many you have in total.