There is also another supplement similer which most vets have called pro fibre.
This helps by adding more "good bacteria" as well as extra fibre to bulk up faeces and hopefully enable natural gut motility.
You will have to be careful tho, swapping and changing food is not good, I hope the vet advised you to re introduce his normal food gradually following his hills diet.
Colitis can be caused by numerous things and dont forget with the recent hot, humid spell that pets esp if they rummage in the garden park etc can pk up minor ailment which if they already have a sensitive gut could cause a flair up.
http://www.vetscriptions.co.uk/mm5/m...Category_Code=