[daftscotslass]

I wouldn't use T-Gel (or other coal tar) shampoo on a piggy, nor head and shoulders. Both of these are too harsh for a piggy's skin and neither contain a particularly effective anti-fungal active ingredient.

Nizoral, however, is fine to use. A bath in it won't harm the piggy in any way. If you find the piggy has areas of localised fungal like on the ears you can use an athlete's foot cream like Daktarin (miconazole nitrate).