While minimum cage size requirements for two guinea pigs is 7.5 square feet (or a 2x3 grid cage), we recommend a 10.5 square-foot cage (or a 2x4 grid cage). Even one guinea pig needs 7.5 square feet. Adding a few more square feet for two should be possible in most cases. Two boars should not be housed in less than 10.5 square feet.

If you need to separate your guinea pigs because they stop getting along, provide them both adequate cage space with a common grid wall so that they can be next to each other for company and safe interaction. Ideally, that means a 2x6 grid cage (requiring a 7.5-8-foot long table) with a common grid wall divider to provide the minimum cage space of 2x3 grids (or 7.5 square feet) per guinea pig. A 15 square foot cage is large, so many people will compromise on cage space in these instances, or try to compensate with additional floor time. A split 2x4 grid cage will provide each guinea pig with 5.25 square feet of space. That does not meet the suggested minimum, but is still almost 2 square feet larger than the typical "large" cage.

When you bring home a new friend for an existing guinea pig, or get guinea pigs from two different sources, keep them in separate rooms with separate cages for 2-3 weeks before trying to put them together. This will ensure that the new guinea pig does not have any medical problems which could be transmitted to the other. If the new guinea pig is sick or has any parasites or fungal infections, you will want to treat it first, rather than risk spreading the condition to the other guinea pig.

You should handle the new guinea pig last and wash your hands after handling. It's a good idea to keep a smock in the room with that guinea pig. That way you have less risk of transmitting parasites or other things on your clothing.

Examine your new guinea pig very closely and carefully while in quarantine. Look for signs of mites (scratching and hair loss). Mange mites are not visible to the naked eye. Look for lice, fleas, fungus (ringworm), eye or nasal discharge, excessive sneezing, wheezing, loud breathing, and more. If you suspect your new guinea pig is not well, take it to your vet as soon as possible. Do not delay. Guinea pigs can go downhill fast.

You've honored the quarantine period, your new pig is healthy and you are ready to introduce him or her to your other guinea pig. Have patience, take your time, always do this on neutral territory, and don't give up too soon. Bonding may happen in one afternoon or it may take months.

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. Follow these steps instead.

The dating game

This initial introduction system, developed by Cavy Spirit, is done to determine how fast or prolonged the process will be.

1. Get a large bath towel or two.
2. Put the towels on the couch (neutral, unfamiliar territory). Spread them out over the middle of the couch.
3. 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). The floor works, too. Keep kids quiet and out of reach with no other distractions.
4. 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.
5. Let the games begin!
6. 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 great. Some will decide on peaceful co-existence right from the beginning. Some will act like long lost buddies or lovers. Most, however, will go through the standard dominance dance, getting to know each other and trying to figure out who is going to be the boss. They must and will decide this.

Standard safe, non-combative, dominance Dating Game behavior:

These behaviors may sound serious and they should be monitored very closely, but do not separate the pigs exhibiting these behaviors. Most of the time the behaviors will continue for a while until one backs down.

• Butt sniffing
• Butt nudging
• Chasing
• Butt dragging (they are leaving their scent)
• Mounting
• 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

• Teeth chattering: sustained (signal of anger, aggression, warning)
• Nips, light bites (may result in little tufts of fur in their teeth)
• Wide yawn (they are showing their teeth)
• Snorting (like a strong puff or hiss)

Fighting with intent to harm:

If the posturing of the nipping and bite attacks gets more serious, it's time to separate the guinea pigs. If blood is drawn, it's definitely time to stop the session. Look for these behaviors as an indicator of when to separate them.

• 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 "Piggies who Bathe Together, Stay Together" game

Here is another technique used for harder-to-introduce couples or trios, especially when adding a new male to a bonded male pair. You will only want to try this method if you are already competent at handling guinea pigs and giving baths.

1. When you are ready to "introduce" the three, take everybody out and put them on the floor. Lay a blanket down and enclose it so they can't escape. Make it big enough so they have room to roam around. They will all notice each other.
2. Watch their behavior closely. You will notice some things right away. If they dislike each other, it will be apparent pretty quickly. There will be teeth chattering along with more serious fighting. They may leap at each other and start fighting, in which case you should have an oven mitt, dust pan or towel you can wrap around your hand to separate them. Do not use bare hands. Fighting pigs will bite anything, and may draw blood. Even if they are not actively fighting but are in "fight mode," they may bite. Make sure no small children are around. See the Dating Game behavior above to help you determine if they should be immediately separated.
   
   If nobody fights right away, you can relax a bit. They may rumble around and mount each other. This is all normal. You will notice a lot of bum-sniffing and chasing, also fine. If the guinea pigs start fighting, refer to the above.
   
   The ideal outcome is instant acceptance. They will run up to each other, sniff, maybe mount a few times, and then settle down to groom the other pig. This is fantastic, but unfortunately doesn't happen all that often right from the start.

1. If the pigs fight, or fight after a little while, give them all a bath. You can put all three pigs in the bathtub (keep the oven mitt handy) and run about 1 inch of warm water. Soap them all up at the same time with something that smells good. Use a small-animal shampoo that is kitten or bunny-safe (not a baby or human shampoo). The pigs will be distracted by the bath and forget that they are mad at each other. Don't get any water in the eyes, nose, or ears. Rinse them off carefully and well making sure that you get all the soap out. 
2. Put them on some towels on the bathroom floor and dry them off as much as possible with a towel. Finish drying them with a hairdryer. Make sure it's on the WARM setting, and never get it too close to their skin. Make sure your hand is always on their fur so you can feel the level of heat you are giving them. They may try to run away, but continue drying them until all three pigs are completely dry. When you're done, they will all smell exactly the same.
3. Try the introductions again, this time on a new blanket that's just out of the dryer or is completely clean. They shouldn't fight. The bathroom scare will hopefully cause them to bond together, and they will group together out of necessity.
4. If the introductions go well, clean the two boars' cage very thoroughly. Use a vinegar and water solution to clean the Coroplast and throw all other items (pigloo, food dish, etc.) in the dishwasher. Clean any other hidey boxes or toys. You want to remove ALL scents from the cage. When you replace all the items, move them around so that nothing is in the same place as it used to be.
5. Then put all three boars in the new cage. They will feel that it's an entirely new home and won't be so territorial about defending it against the new boar.