Female guinea pigs have a very high incidence of ovarian cysts. Most commonly female guinea pigs are neutered when ovarian cysts are diagnosed but there is a growing opinion that prefers to neuter young before the development of ovarian cysts as some types of cysts can cause serious medical problems.
Male guinea pigs are most commonly neutered for behavioural reasons. Castrated guinea pigs will integrate with others much more successfully than entire males. Medical reasons for the castration of Guinea Pigs are rare so the the main reasons for males are behavioural and the control of reproduction.
Both males and females can be neutered from 4 months of age but they will always be examined before surgery to assess suitability.