Well a staffie is a strong dog but as it's getting on in time maybe cutting right back may be called for. Ask the Vet next time your there & see what they have to say.
I'm only pointing this out cause our Yorkiepoo (yes yorkiepoo) cross between yorkie & poodle, get hold of some chocolate the grandson left on a table, about 60grams of it, phoned the vet & we had to take he straight down as an emergency to have an injection that makes them violently sick to remove the chocolate. Bill £100, only to return home to find the littlen monkey had hid it & not eaten it, poor little chap having to go through that when he had not eaten it at all. They work it on an amount to size ratio.