Worms are very rare in piggies.I do not personally worm my pigs and the majority of them live to 7 years +.If I had a piggy that was losing weight for no obvious reason and was at the same time eating more than usual,then I would give a dose of Panacur just in case.
I think that the routine use of Ivermectin and Panacur could make the parasites immune to the drugs and eventually we will have no affective drug to use.
I know a lot of other piggy owners who do not worm and their pigs also live to old age.
There are a few members of the board who do worm,so the subject is contraversial.
In the end,you must do what you think best for your piggies.
If you do decide to worm,get the drugs from your vet,as those sold on the internet could be the wrong strength for gps,and remember these are very strong chemicals.