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1. The only thing that matters when getting a new friend is character compatibility. Quite simply a bonding will fail if two piggies don’t have it.
The best and safest way to ensure compatibility is to speak to a rescue centre and get their help in finding a new friend. Not only will they ensure compatibility, you can also rest assured that piggy is properly sexed and healthy.
If a rescue isn’t possible and you have to buy a piggy from a shop (you would have to be certain of the sex the baby and check for yourself - don’t rely on shop staff to be correct) , then a baby boar might be accepted by your older piggy. Babies are looking for companionship and older piggies are often willing to nurture them. Babies can’t challenge the hierarchy so the older one remains in charge. However there are risks with this. Once a baby becomes a teenager (at 4 months old) they can start to challenge so while hopefully they would be bonded enough that a challenge wouldnt work, there is no guarantee of long term success. Equally, not all babies are accepted so a bond can fail within moments of putting the two piggies together.
With all that said, a baby is usually the best option and one most people in this situation go for if they cannot rescue a piggy.
If a bonding fails, then you would need to keep the piggies side by side in separate but adjoining cages so they could still interact between bars - unfortunately that’s very hard to achieve in a hutch).
A bonding is a specific process which must before on neutral territory. You cannot simply add a new piggy into the enclosure belonging to another piggy as it can cause an immediate fight.
Bonding and Interaction: Illustrated Bonding Dynamics and Behaviours
I’m aware that sounds doom and gloom when actually more pairs on this situation make it together than not but it’s important you’re aware.
2. While he is alone, mental stimulation is vital. Things like not using food bowls and instead scattering his one cup of veg per day and one tablespoon of pellets per day in amongst hay and all around his enclosure. This means they can use their natural foraging abilities to keeps his mind occupied
The guides below will also help
Single Guinea Pigs - Challenges and Responsibilities
Enrichment Ideas for Guinea Pigs
I’ve also added this guide below in case he is on grass
Fresh Grass and Lawn Time - Tips for Avoiding Spring Time Deaths
3. In terms of handling, this one is not necessarily easy. It can take a long time to get them used to being handled and a lot of piggies never really like it. It does need to happen for the all important health checks, grooming and importantly the weekly weight checks.
I’ve added other guides below to cover all these aspects
Understanding Prey Animal Instincts, Guinea Pig Whispering and Cuddling Tips
New Guinea Pigs: How to Best Manage Arrival and Settling In
How To Pick Up And Weigh Your Guinea Pigs Safely (videos)
Weight and Weight Loss Explained: BMI, Weighing, Poos and Feeding Support Levels
There is also a guide in looking after a grieving piggy
Looking After a Bereaved Guinea Pig
Do let us know if you have any other questions