It can be very distressing if your sow is aggressive towards the piglets. When my sow bit the piglets I blamed myself for not getting the piglets into the box quick enough but if they had been in the wild the piglets would have to fend for themselves so it is difficult.
I think it is important to keep an eye on a farrowing sow, especially if she is a gilt and farrowing for the first time. You can gauge the mood the sow has if you observe discreetly and then you are on hand if you need to intervene.
I would make sure that I have a lamp already set up and plently of straw in a box for the piglets to be placed in under the lamp if you need to remove them from the sow. The box needs to have tall sides as the piglets are very strong and have a strong instinct to suckle and so wriggle about trying to find the sow.
If you don’t have the sow in a farrowing crate then it is better to try to pen off an area where you can still reach the piglets if you need to and you won’t be attacked by the sow. Sows can be aggressive when they are about to farrow or during farrowing and sometimes afterwards.
I have two sows who are very gentle and placid by nature but one of them does get aggressive towards the piglets and they both do not like me to get too close just after the piglets have farrowed and for the next few days. I keep my sows in a large farrowing crate for a few days and this allows me access to the sows and the piglets but gives me protection.
My sows are used to me and my voice but I have only had the sows from when they were about 15 months old. I have wondered how a sow would react if you have raised the sow from a piglet. I hope to find out one day.
If a sow is a aggressive then you have to decide if you want the sow to raise anymore piglets. My sows are very placid all year round and it is only at farrowing time that they show signs of aggression. One of my sows is very gentle and she even farrowed during the night once and all her piglets were ok. Some people say that a human presence can affect the behaviour of a farrowing sow and that it is best to leave nature to it if you can.