I feel your pain.   Been dealing with Strep quite a bit with my groups showing up for 6 months.   Amoxocillin a second time around worked for awhile  but then that stopped working.   We tried a product last time as a preventive after about 2 1/2 weeks.  It showed up as a gallon of white liquid.   Mixed to put in water.   Seemed to work pretty good, I think I only lost 2 from strep this time rather than close to a dozen.   In checking  I think it might have sulfa methazine.   Check with the owner or vet in charge of sow operation.  They should have an idea of what they are dealing with and how to stop it if the pigs are showing up with strep.