I prefer Engemycin to Terramycin, it seems to work quicker, you can spray it from the can up-side down (for example when handling in-lamb ewes that cannot be turned up, and you have to do it like you would do goats/horses by lifting the foot).
But I have one every other day with scald atm - wet ground and slightly long grass - bad combination. Could also just bee that your girls went onto new (to them) ground - it seems to hit the bought-in ewes more than the homebred ones.