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Guinea Pigs/Happy brothers not so happy now.


QUESTION: Our "boys" are brother's that have never been separated. They are approximately 6 months old and up until recently they have been happy together.  They have started to show aggression toward each other and have engaged in at least 2 all out fights that I have seen.  Now it seems like they are showing aggression toward each other for a good part of the day - butt wagging, teeth chattering, chests puffed up and raised fur.  I am afraid to leave them alone because there has been blood spilled - scratched up noses & lips.  When they are out of their cage playing, they seem mostly fine with each other but in the cage they spat over food & water. They have separate dishes & hiding places but one seems to want all the "real estate". They also seem more aggressive when the we are active in the house and are more calm when it is quiet and/or dark.  I have tried to find information online that is credible and I've not found any information that addresses my issue.  Do you know of a reliable website I can go to?  Is there anything I can do to get these guys to love each other again?  I don't want to separate them because I have read they will never go back together if I do separate them.  Please help.......

ANSWER: You've come to the right website.

What you are seeing is normal animal behavior. Unfortunately there is no way you can alter or change behavior that is hard wired in males that are raging with testosterone.

These are herding animals. In any herd there is always an alpha male and an alpha female. Young male babies are allowed to stay in a herd as long as they follow the rules. The rules are: The alpha male makes the rules. The alpha female enforces them. Period. When a youngster begins to reach sexual maturity their natural hormonal balance tells them it's time to mate. That's when the trouble begins.

Your two boars are not capable of thinking and rationalizing that: 1.they are brothers and should get along  2.there are no females to fight over.  

Their issues are not just behavioral. They are hormonal. Their testosterone is running high and their instincts tell them to fight for supremacy. They're not being hateful, they're being animals who are governed by their instincts. It's nature's way.

If you think of two stallion horses their behavior is the same. They will get along while they are young, but once the hormones begin to rage the battles begin. The only cure for that is gelding them. That stops the hormones.

In wild horse herds the young males are allowed to stay in the herd until they begin to act out their normal urges and start moving in on the alpha stallion. He is the only one allowed to breed the mares. That's nature's way of preventing inbreeding. A pack of wolves have the same dynamic. Since horses and wolves cannot be castrated in the wild the young males are banished from the herd. But there is always another male who will come along and try to dethrone the alpha.

Domestic dogs have the same behavior. Two intact males will fight to establish dominance. Hence the need for castration if you are to have a happy home. If you are able to have your boars castrated they will be able to live together again in peace. BUT even after castration there is a time frame for the hormones to burn themselves out before you can keep them in the same cage.

You're going to have to separate these boys at this point and leave them that way. To leave them together now is dangerous for both of them. And it's also dangerous to you because you will reach into the cage and be severely bitten sooner or later. In the meantime the bite wounds will cause one or both of them to get an infection and there is the danger of someone being killed or severely maimed.

I'm sure this isn't want you wanted to hear, but you're up against nature and you are not going to be able to find a happy resolution with the two of them living in the same space as they are. The only time I can get males to get along is when I put a youngster in with an elderly boar who is past his prime. Even then, when the young boar begins to reach sexual maturity he will attempt to push the elder out. Most of the time the old boar just gives in because he really doesn't care.

The best thing to do is to keep them separated. They will get along fine if there is a barrier between them, but in the same cage there is and will be an ever present danger. When they begin to rumble (sway) and growl with their hair standing up, that is a severe warning that blood is about to be shed.

If you do need to break up a fight by all means do not reach you hand in the cage in the hopes of picking one of them up by the back of their neck. To break up a fight just use a garden glove, holding it in your hand by the cuff, not wearing it.  Use it to give a couple of fairly hard smacks to the two of them to get their attention. You won't hurt them, you just want them to knock it off.  Unfortunately as soon as you retreat they will return to the fight. To remove one of them while their emotions are high, throw a towel over him and keep him covered as you lift him out of the cage.

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

QUESTION: Thank you so much for all your help! Your information was very informative & much appreciated.  I have already separated the boys and they are not happy about it at all.  They are squeaking and their noses are in the air looking for the other one.  They can smell each other as I have the more docile male in a laundry basket next to the cage until I can get a cage divider in there.

    I do have a few more questions to ask if I may.  By putting a wire separator in the cage, their personal space is drastically reduced.  I won't be able to put a potty on each side because it takes up too much room.  Will the smaller living area be ok until we have them castrated, if we make sure they get playtime outside of the cage?  Will they ever use a potty again after having to go without?  Will they want to be together again after castration and how long will it take for their hormones to "burn out" after castration?  I really want for them to be able to live together in harmony with each other.  Is there any other information we should know?

Forgive me for saying so, but I'm amused at the fact that they actually use a potty. Rabbits can be trained to a litter box, but guinea pigs are not so neat as a rule. I've had a few that would go in one corner of their cage only, but for the most part they are a bit like goats. They drop their business wherever they happen to be standing. And that often includes their bowl of pellets.

They will be fine with lesser space. I don't know where you live, but if you are in an area where you have mild winters and are able to utilize your yard you can always take them outside now and then to graze in the grass. Do not leave them unattended, but if you have a way of fencing off an area of grass they will probably get along there, especially if they have sufficient space to get away from one another.

It will most likely take at least a month, perhaps more for their hormones to give up. They are in production all the time, so once they are castrated the residual hormones will take awhile to begin to change their behavior.

They won't attempt to fight or show aggression if there is a wire barrier between them. They will each have their own space and the barrier eliminates the attempt to dominate the space they are in.

I honestly can't answer the question about the potty. I wish you well with that and I would love to know how that works out. Fortunately guinea pig urine and stool is not particularly odorous, and is fairly easy to keep fresh.

Please keep in touch and let me know how everything goes for you.  My best to you and your boys.  

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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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