What do your guinea pigs testicals bulge out when around a female?

It sounds like you're asking about a natural response in male guinea pigs called "scrotal sac enlargement." This is a common behavior in male guinea pigs when they are around a female in heat. Here's why:

* Hormones: When a male guinea pig detects a female in heat (estrus), his body releases testosterone. This hormone causes the testicles to swell, becoming more prominent and visible. This is a sign of sexual maturity and readiness to mate.

* Attraction: The increased size of the testicles is a visual cue for the female guinea pig, indicating the male's willingness and ability to mate.

* Competition: In some cases, the size of the scrotal sac can also be a factor in male-male competition for mating opportunities.

Important Note: It's normal and natural for male guinea pigs to display this behavior when they are around females. However, if you observe any unusual swelling, redness, or discomfort in the scrotal area, it's best to consult a veterinarian to rule out any health issues.