Up until she farrows just 2 kilos a day, unless she looks thin then up it a bit, if she looks fat then down a little. When she farrows increase the feed slowly for a few days so that she is on around 3 kilos a day. This should cover the first 4 piglets in the litter, for each additional piglet add a further .25 kilo per day.
Again if she looks thin or the piglets are not thriving increase the feed and vice versa if they all look too fat.
Feeding too much just after farrowing can increase the risk of mastitis.