Check on-farm semen motility
Here is a useful list of semen-handling principles. In summary, besides temperature monitoring, "check on-farm semen motility or activity ... I have seen many situations where the boar stud discovered a bad batch of semen, called the farm, and the farm had already used all of the semen... If you bred all of your sows before the boar stud conducted their tests, and found that a batch had gone bad, you're going to have to rebreed those females or you're in trouble." Impact of the extender should be taken in account too.