Every weekend we have the boys' school's guinea pig at our house (DS#2 is responsible for it at school - and must bring it home for weekends and holidays).
Anyway....so the schools piggy is a male (still young). We have an adult male in one cage and three females in another cage (bought one of them...the other two were 'bonuses' born a few weeks later - and our male is not the father). Our visiting pig stays in the carrier while here - he is still small and has plenty of room in there for the 1.5 days he is here for the weèkend).
DS had the school's pig out last night to play with/cuddle (the piggy is REALLY sweet). We didn't realize it right away, but when he went to put the school's piggy back, without thinking, he put it in the cage with our three females. I don't think the male was in there long...5 minutes, maybe. He is only about 5 weeks old - but piggies are sexually mature at only 3 weeks. The females are 4 months and 6.5 months old.
So - should we start taking bets on how many pregnant piggies we have? :-/