Manure and other wastes are flushed regularly into a holding lagoon where they are unavailable for fly breeding. Even were house fly maggots able to survive in the lagoon, there are no adequately dry locations for successful pupation. Admittedly, there is a small amount of fly breeding that occurs on a hog farm, but it is minimal. In general, there is less suitable fly breeding habitat available in a properly managed hog building than there is in a horse barn half its size. The simple answer is no.
Movement is limited.
There have been a number of studies over the years looking at the question of house fly dispersal in urban and agricultural settings. When dispersal does occur, the tendency is toward other potential breeding sites. The consensus among researchers is that house flies will disperse no more than a mile under normal conditions. Now, let's talk about pesticide use. From time to time, insecticides may be needed to reduce fly numbers no matter how well a farm is managed.