Not sure it will help. I have rabbits and am ever fretful of fly strike - to the point of distraction. I have got myself into a routine which suits me with several measures...

After the usual washing down with ' jayes fluid' ... brilliant stuff. changing fly papers etc.

I find these measures work well for me.

I purchace citronella oil in 100 ml bottles from a company on the internet i make up a powerful wash from this with warm water and place it in a hand pump garden presure spray which i use liberally over surfaces, door ways, windows and walls. - natural and none toxic. i see no reason why a moistened cloth could not be used to wipe the animals down.

I also burn citronella incense modestly in and around the sheds.

I plant pots of mint- spear or pepperment  and lavender.. all over which deter flies and mosquitos.

I have ordered from an on line company solar powered lanters with fly trap in them.. and egerly await their delivery to she how well the work.

Appart from stating the obvious... leave not still water uncovered were possible ( rain water barrels etc)