Hi!
If your sow is straining to pee, then the stone is large enough to get stuck and block the urethra completely; that is always a risk with waiting. In this case, you are dealing with a life or death emergency operation as soon as you notice her suddenly looking very off, being lethargic and stopping to eat/accepting any food.
Most stones in sows are eventually fetching up just before the exit. My Teggy had an usually large stone wedge itself in there in October. While it is often fairly easy with a smaller stone to manipulate it out or to get it out with smaller incision, hers turned out to be a rather tricky operation and it was touch and go for a few days whether she would be incontinent or not able to pee at all; she also needed extra feeding support. There were also worries about about bladder/urethral trauma from the damage the stone had done on its way down in view that this is about as large a stone that can possible pass down a female urethra. I have had larger stones removed from the bladder in years past, which was in some ways an easier operation. Teggy's stone was the first in 7 years and after adopting about 40 piggies since the last one.
These are the pictures from Teggy's operation. She has since then thankfully made a good recovery.
View attachment 166358 View attachment 166356
In your case, it is very much a balance act between hoping that the stone will eventually fetch up in an easier to operate place near the end of the urethra and the risks the wait will bring with it. the stones that struggle to come down the urethra are not the ones that will come out on their own in my experience. Sadly, stones that pass naturally are usually too small to cause any problems. In the majority, this is a vain hope, as we have seen repeatedly on this forum over the years.
Emergency, Crisis and Bridging Care until a Vet Appointment
Tips For Post-operative Care