In several studies on both sides of the Atlantic, pigs of all classes and stages of production have been found to be highly adaptive to noise. In particular, one experiment demonstrated that sows kept in portable huts located at the take-off end of a large-jet runway continued reproducing normally. If the noise is extremely loud, the first time they hear it they may be startled, but on successive hearings they become less and less so, until eventually they do not react at all. This is called habituation to the stimulus, a mechanism that is part of an animal's nature so it can not waste time and energy and stress hormones reacting to a stimulus that has proved to be inconsequential.

There is one exception to this general rule of which I am aware. Ekesbo's group in Sweden investigated a farrowing house where suckling behavior was abnormal, and found that interference between abnormal high-frequency noise from the fans was interfering with vocal communication between sows and piglets. But this, of course, is a masking/interference phenomenon, and not a startle situation.