The study I linked to showing the effectiveness of Ivermectin was only done subcutaneously. I did not find a study on the effectiveness of non-subcutaneous Ivermectin treatments on screw worms.
Given one of the areas they focused on the study is the scrotal area post castration, I don't expect that a pour on would cover that area well enough to be an effective treatment. Happy to read other studies if you have them showing otherwise.
There are injectable and transdermal (pour-on and ear tag) forms for cattle and pigs. I'm not aware of an oral formulation for food animals, even though that's pretty common for horses.
is quite funny, where they found that the lambs were licking the topically applied ivermectin, but also that they didnt notice any decrease in parisites for any of the ingestion/injection/topical
they also say theres nothing showing any applicability to cattle
