My guinea pig is just about to have a litter - how soon can

Please think very carefully before breeding your pigs at all - any breeding carries risks for the mother and the resulting babies - and breeding straight away would put a terrible strain on the mother - as she recovers from the stress of giving birth to the first litter ! Perhaps you can offer a home to a needy/homeless pig from a rescue organisation instead ? If you really are intent on breeding your pig again please be as responsible as you possibly can. Do not let the boar have access to your sow after the first birth as she will be able to get pregnant again if he mates with her and this would really be too much of a strain on her and could have tragic consequences- on this note, also ensure you remove any male babies from her at approx 3 weeks old. Leave at least 3-4 months before even considering breeding from her again to ensure she is strong and healthy. But I would encourage you to be very careful and responsible.