I was in a shed during the week where lice had become a problem. The cattle were treated at housing but had become re-infected.
On some farms a second treatment will be necessary. Make sure the product you use is effective against both biting and sucking lice.
Animals will lose weight if badly infected, so make sure the shed is free from lice. It will typically cost €1 to €1.50/head and will be well worth it if lice is a problem.
Vet's corner: treating itchy cattle