40 minutes is a long time for any staffy to chace any thing, i bet your very proud.
i had been out in the woods and feilds near me for about 3 hours with my staffie bitch throing sticks letting her swim and what not, any way on the way home we were both pretty tired allready when all of a sudden we came across something, she took off strait after it and chased it for about 10 minutes but it got down a hole we were both pretty knackered after that one, she was only a pup (6 month) at the time, i was very proud of her.
atb josh.