Guinea Pigs/aggression


QUESTION: We brought home a new male piggy, about one year old today. We currently have two male piggies that are a bonded pair and have always gotten along very well, no problems what so ever. One of our first piggies, Honey, tried mounting our new piggy, Boo, and would not stop chasing after him. I decided to split them up an put the bonded pair in their cage and Boo in his. Well to my surprise Honey started going after his bonded 'brother'. They have always gotten along and now I am terrified Honey is going hurt Skitter. Honey is chasing him around and bitting at Skitter. Right now  have Skitter and the newbie, Boo in the same cage and Honey separated and in Boo's cage. I know this is not an ideal housing situation, but it is late and we are going to bed. The plan was to house the three in the same cage#would be custom built to accommodate the three#, if they all got along. Now we are thinking of getting a fourth piggy to try and pair with Boo in a cage separate from the first two. My biggest worry is Honey's aggression towards his bonded 'brother', not related by blood, just roomamtes. What should I do? I'm terrified Honey will hurt Skitter.

ANSWER: Are you absolutely sure the new pig is a male? It sounds as though it may be a female and Honey is responding accordingly. If that's the case you will continue to have a fight between Honey and Skitter. When a female enters the picture (or in this case the cage) the immediate response is a hormonal one from the males.

If the new pig is a male Honey still view it as a new intruder and you'll have a fight with all three. One or two will be seriously injured. There can only be one alpha in the herd and it sounds like Honey has already taken that position.

A new pig causes the resident boars to go into territorial mode and try to establish dominance by either mounting or by fighting with the new pig. Since they are close to each other and Honey can't reach the new boy, he's taking out his territorial aggression on Boo.

My recommendation is that you keep these boys apart. If they were all babies you might have a chance at getting them to accept one another. But with three boars, especially one of which is a newcomer, they will not sit quietly and the fighting will predictably continue.

---------- FOLLOW-UP ----------

QUESTION: I guess I cant be 100% Boo is male without bringing him to a vet. If I keep the new one separated from the other two, will the  first two get along like they used to? What should I do about Boo? His previous roommate(from another home), was also very aggressive with Boo. That is what lead Boo to being rehomed. Should I try to find Boo a roommate to bond with and just keep the herds separated?

Baby boar
Baby boar  

Baby sow
Baby sow  
If you can take a picture for me I can tell you without taking Boo to a vet. At one year old they are fully developed and should be easy to tell. Look at Honey and Skitter, examine the genitalia. The testes at this age are quite visible.

Check Honey first. With him in a cradled position on his back put your forefinger just at the lower part of his belly, right over the penis. Pull up a bit and press into the belly and the penis will protrude. Do that with Skittle as well. That way you know what to look for.

Do the same with Boo. If the penis is not there you cannot protrude anything. That's a female. I've enclosed a couple of pictures of babies and how to sex them so it might give you some idea. But if you just take a picture of Boo on the belly I will be able to see what you've got. Don't put the camera too close or the picture will come out blurry. I can blow it up on my computer and tell.

As babies the testicles are not developed. The girls have a 'Y' shape to the vent (the opening of the vagina). Boys have a distinct 'i'. That little 'i' is the penis and you can see the separation from the penis to the testicles. In girls you can spread that vent open and see the mucus membranes inside.

If Boo is a female and is near the boys they will be able to smell the scent of her hormones and they will continue to fight. They're fighting for breeding rights, just as herding animals in the wild do. It's a hard wired instinct that we cannot remove.

If that's the case you may want to take Boo out of the room. The other option is to find another home.  

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Pat VanAllen


As is sometimes the case, people in urgent need of information have a higher degree of expectation than those of us as experts are able to give. The experts on this site do their best to give the most accurate and responsible answers possible. We ask that you remember that it is not our intention nor place to criticize the professional advice given by your veterinarian, nor is it appropriate for us to comment on the correctness of a diagnosis made by a licensed physician. Our knowledge is experience based. Although many years of breeding and showing cavies gives me a wealth of experience it cannot change the fact that we as experts are not veterinarians and therefore may occasionally have to reject questions that appear to be asking us to criticize advice given by the licensed professional. Having raised and exhibited cavies for many years I have extensive experience in cavy care and husbandry. I currently have an active breeding program for pedigreed show animals but do not encourage backyard breeding for inexperienced owners. Although I don't encourage breeding for fun I'm always happy to answer any questions from an owner who is in sincere need of help. Pet owners wanting to breed should understand that even experienced breeders have litter losses. The mortality rate is high in cavies. The chance for losing both sow and pups is always present, even with experience. Although this is a site for experts to assist owners, there is no expert in any field who has all the answers. The wisest thing a good expert can know is their limitations. Not having an answer does not diminish one's ability or knowledge. It simply shows that we recognize our limitations and operate within them.


Raised and shown cavies for many years, having aquired my first cavies in the early 1970's as pets. My caviary currently handles 65 + animals in two different breeds and several varieties. Having been in the health care industry as a licensed nurse for 35 years I have hands on experience with care and needs in both humans and cavies. Member of American Rabbit Breeders Association and American Cavy Breeders Association.

Awarded Lifetime Membership in of one of the oldest cavy clubs in the United States, on whose Board I served as Sec/Treas for six years and currently serving as President. Also editor/publisher of the club's quarterly newsletter. We are strong supporters of our youth exhibitors, most of whom are 4H members who are working on cavy projects. Through these projects they become good responsible citizens. We deal with all aspects of showing, breeding, caring for and sharing experiences in the fancy. The cavy fancy is not a new one but in some areas is still relatively unknown. Our goal is to inspire interest in high quality, responsible breeding to improve the species, not just the reproduction of guinea pigs. Our job is to educate owners to help them make the right decisions and choices in the care of their cavies.

Graduate in nursing. Certified in emergency medicine.

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