Member States shall take all necessary measures to ensure that their competent authorities satisfy themselves:

1. (i)

   by making sampling checks at all stages of the production and marketing of the products referred to by this Directive, that the provisions of this Directive are complied with;

2. (ii)

   in particular, by making sampling checks on farms and slaughterhouses, that medicated feedingstuffs are used in compliance with the conditions of use, and that withdrawal periods have been complied with.