Hi!
An adult piggy can weigh between 700g-1800g and still be perfectly healthy. The range in weights and size is just too big to answer your question in terms of weight. I've had a 700g sow needing an emergency spay, and so did another a sow weighing 1400g 4 years later.
Weight - Monitoring and Management
The other issue is that there are several types of ovarian cysts and that the size and number of cysts can also vary massively so you are working with too many variables there. Add to that the fact that cysts usually cause weight loss and not just weight gain (the latter applies to only to the really huge fluid filled non-hormonal cysts and there is actually balances a weight loss in the rest of the body)...
Sows: Behaviour and female health problems (including ovarian cysts)
If you are worried, please see a vet for a hands-on examination. We cannot tell you whether your sow has one or more cysts sight unseen unfortunately.
