The hormonal teenage months It is a myth that boars cannot live together; the vast majority can be bonded and rebonded at any age. The key to any successful boar bond is character compatibility and mutual liking. An age difference (preferably as large as possible), especially when one of the pair is a teenager or baby, can additionally help to stabilise the bond, as only one boar hits the hormone spikes at any time. Sadly, the vast majority of boars are sold as unmatched babies in often far too small cages or hutches, which is what has given boars their undeserved bad reputation. It is not their fault; they are failed by sellers who don't have the time, knowledge and largely no interest whatsoever in carefully bonding boars for character compatibility and buyers specifically requesting cute little baby boars, preferably litter brothers - yet another persistent myth! The safest place to get a stable boar pair is a good standard rescue (links see further down in this thread). If you would love boars (which are often more personable than sows), consider getting an already stably bonded pair if possible; if one or both boars are adult, it will contribute to the stability. The Myth About Boys What are the most difficult times? Guinea pig boars go through a hormonal phase roughly between 4-14 months old. These months are characterised by bouts of testosterone which manifest in lots of dominance behaviours. Things can be kick-started a bit earlier, often during an introduction shortly before the teenage months would start. While boars are able to make babies from 3-5 weeks old, it is usually the descent of the testicles that triggers the teenage months. Typically, boars experience a strong spike of testosterone when the testicles start descending at around 4 months old, then again at around 6 months of age when testosterone output is at an all time high. These are generally the times when the worst personality clashes and fights/fall-outs happen between boars that are not character matched and too dominant to get on with each other; this age is also the most tricky age for bonding/rebonding boars. Another very difficult period is usually the period between 8-10 months old, but it results much less often in full-out fights although boars can often be right up at the bearable limit of scrapping and winding each other up for several weeks. Boars that have had a very smooth ride so far can suddenly wake up and get into trouble right at the end at a year old or slightly over when the other pairs are already over the worst. Boars generally reach a hormonally more settled adulthood by around 15 months of age. Occasionally adult boars can experience a sudden short-term hormonal spike or get into fights when they experience major changes to their cage or environment, which triggers a renewal of dominance as they re-establish their hierarchy in new surroundings. Many adult pairs can be rebonded again after cooling down overnight with some time out from each other unless the fight has resulted in serious feep bites or unless the bond has already been dysfunctional before the move. You can minimise the risk of dominance fights in new territory by rubbing the new or extended cage with some soiled bedding and by using their current bedding in the new cage to make it smell 'right' and 'theirs'. What are your boars’ chances of making it together? - Pairs: the good news is that more baby boar pairs than not make it together. It doesn’t matter whether they are siblings or not; the key to success is whether their individual personalities balance well enough. Two dominant brothers will inevitably clash the same as any other all-dominant pairings. - Trios: 90% of baby boar trios will not make it to adulthood together. They usually end up with either one dominant boar making war on the other two or two ganging up on a third (bullying). If you are unlucky, you will end up with three boys that won’t get on with any of the others. - Quartets or quintets: virtually no chance whatsoever. At the best, you end up with two working pairs, but it is more likely that you end up with one pair and two singles. We even have had a sad case where all four boars fell out with each other. Please don't be tempted to add another boar to a working couple or to merge two happily bonded boar pairs - it is usually a recipe for mayhem and disaster! Boars are best kept either in pairs or otherwise in bachelor herds of over 10 boars with ideally at least 1 square metre per boar and separate accommodation available in case of bullying/fights or illness.