Guinea Pigs Males

Question
I recently brought two guinea pigs males in Dec everything was going fine until recently they have started rattling their teeth, hissing and stiffening their bodies.  Both seemed to have injuries from this so I have separated them in the meantime as I wasn't sure what to do can you advise me.  The pet shop said that two males would live together and they were together when I brought them.

Answer
Vicki,

Keep them separated for a time without being around each other. Boys tend to get a little territorial as they get older and so need to be separated for a time and then reintroduced again slowly to each other. They should live together fine after that with out to much of a problem. Here is a really helpful method for reintroducing them and some normal behaviors and aggressive behaviors to watch out for.

Have patience, take your time, always on neutral territory, and don't give up too soon. Brief words of wisdom for introducing guinea pigs. You've honored the quarantine period, your new piggie is healthy and you are ready to introduce him to your other guinea pig. What you don't want to do is plop the new guinea pig into your existing guinea pig's cage. Never try to introduce guinea pigs in one of their cages. Be prepared. This may happen in one afternoon or it may take months!

Get a large bath towel or two.

Put the towels on the couch (neutral, unfamiliar territory).
Spread them out over the middle of the couch.

Each person holding a pig, sits at opposite ends of the couch.

Make sure the towels are between you and there is a good amount of space (it helps to have a big couch!). Floor works, too. Keep kids quiet and out of reach. No other distractions.

Let the pigs find each other on their own time.
You may need to nudge them in the right direction. Have another towel handy to toss on the pigs if you need to separate them.

Let the games begin!
More often than not, pet owners want to break up guinea pigs exhibiting normal dominant behavior. Everyone looks worried and asks, "Is that normal?" How long and what next?
Usually, the first 15 minutes is just getting acclimated to the new surroundings and the idea that there is another guinea pig there. It's the next 15 to 30 minutes that can get interesting. The nice thing about being on the couch is it makes it easy for them to run to you when they get uncomfortable. But, keep your interactions and interference to an absolute minimum. Some guinea pigs will get along just great. Some will decide on peaceful co-existence right from the beginning. Some will act like long lost buddies! But, most will go through the standard dominance dance getting to know each other and trying to figure out who is going to be the boss of who. They must and will decide this. It may not be now, but it will get decided. When to separate them? Serious blood is drawn or a wound is inflicted. Some nipping or minor biting can be quite normal. Even little tufts of hair in the mouth can be normal.

Safe, non-combative, dominance behavior
 
Rumblestrutting
 
Butt sniffing

Butt nudging
 
Chasing
 
Butt dragging (they are leaving their scent)
 
Mounting (any which way: rear mount, head mount, side mount, flying leap mount!)
 
Nose face-offs (higher in the air wins, one must lower their nose to be subservient to the other)
 
Teeth chattering: a little (signal of dominance)
 
Raised hackles (hair on the back of the neck and along the spine)

Posturing for possible attack, battle for dominance is escalating
 
Teeth chattering: sustained (signal of anger, aggression, warning)
 
Nips, light bites, may result in little tufts of fur in their teeth
 
Wide yawn, but this is no yawn, they are showing their teeth
 
Snorting (like a strong puff or hiss)

These behaviors may sound serious and they should be monitored VERY CLOSELY, BUT do NOT separate the pigs exhibiting this behavior, yet. This is when the average pet owner loses it and pulls the pig out. Most of the time, this behavior will continue for a while until one backs down.

Fighting with intent to harm

Bite attacks are no longer warning nips, they are lunges with intent to harm.

Combination of raised hackles, loud and angry teeth chattering, rumblestrutting in place with the head staying in one position while facing the other guinea pig doing the same thing. Usually a signal of a biting attack. But they may back down before they engage.

Both pigs rear up on their haunches, face to face. This is a clear, brief signal of their intent to launch full attacks at each other. Separate if possible before the attack.

Full battle. The pigs are locked together in a vicious ball of fur. This is very serious. Separate immediately, but be careful. Throw a towel over them and use a dustpan or something other than your hand to separate them. Unintended bites from their very sharp incisors can cause serious damage.

The best indicator to watch for on when to separate guinea pigs is the posturing of the nipping and bite attacks. If that gets more serious, that's the time to separate them. If blood is drawn, it's definitely time to stop that session. Hopefully, you can separate your guinea pigs before any serious harm is done.

I hope this helps and that your males start getting along soon.
    Take care now,
         Jules