I have kept eveything from guinea pigs to horses for most of my life, so while I am not an expert in Guinea pigs in particular, I work on the basis of plenty of space, plenty of forage, company of their own kind and not hurting or scaring them as this seem to work for most herbivorous, fluffy creatures! We have a pair of boars who are about 2 years old and they have been brilliant in every way. But I have 3 children, and the youngest was beginning to feel left out of the guinea pig snuggling. So I bought a pair of young boars from the local pets at home (yes, I know I should have known better, and next time I will use a local breeder) but they were not a "pair" in terms of being bonded. we ended up with the alpha and the runt, and the alpha wouldn't let the runt eat. Anyway after much shuffling about, building of extra runs, and giving the smallest one time and space away from the bullying one they are both growing well and getting on together better. Now despite the drama and bullying of the other piggie, the "Alpha" one has always been a delight to handle, and would even escape his run and come and seek out humans to sit on and chat to while his brother was in his other run to eat. He sat on our shoulders, and was generally lovely. very wiggly and chatty, but seemed happy. Then suddenly he has started nipping and jumping about whenever we try to pick him up. He spins on the spot and nips. Once out of his run and with us he doesn't seem scared of us, he will climb into our laps, but if we try to pick him up again he squeaks and spins and nips again. He has never broken the skin, even of my 4 year old, and I have had a good at him and cant see anything that would obviously be hurting him, so I am stumped. I have banned the children from picking him up, and told them to just stroke him in his run. I pick him up when it is quiet in the evenings. Any clues?