My vet suggested using fly tags.

However I've been using a rub with the "flyps" hanging down and strung across the lane to the waterer. I dose the rub with a diesel/insecticide mix every couple weeks and it seems to give good face and body protection. I can't see how an ear tag could protect the whole body as well as the rub and I don't like putting tags in and out.

Maybe there are some advantages to tags where you can't put up a rub that they will pass thru frequently.

Jim at Dawn