Obviously anything to do with the female reproductive organs (pyometra, ovarian cysts, pregnancy-related issues) are going to be female-specific. Other than that, though, I think the bulk of guinea pig ailments (bloat, fungal infections, respiratory illnesses, abscesses, dental issues, etc.) are pretty much equal-opportunity for both genders. I've had sows for the past seven years or so, and although we've run into some health issues, none have been related to their gender (knock on wood!)