I was looking through old posts but could not find the one that someone had suggested using a back pack to wear their B out. I tried it yesterday since we could not make it to the park. I put a water bottle in each side and walked to pick Greggy up from Kindercare. Dashy hardly pulled at all and he actually started panting-but only for a minute. When we came home he layed down in the sun even as we ate dinner. Which he is usually trying to sneak a bite. So thank you to whomever said that is was very helpful.
You can start them with a empty pack at any age, to get them used to it, ideally near they're adult size so you're not buying two. With adding weight it's just like hard exercise you'd want to wait till 18 months to 2 yrs. You can also add things light weight like empty water bottles or balled up news paper once they are used to the pack. This adds bulk to the pack without weight so they can then learn to wear it with the sides sticking out. Then you can add lighter things around a yr, maybe just house keys, two half empty water bottles, to get them used to gradual weight.
Remember to make the weight even, that is the most important thing. Also when training with added weight don't go until they are tired start with slow times, maybe around the block or so, helps them get used to it and thier body to build up the desired muscle.
Training to pack with any dog should be a gradual event, with a dog I'd say 3 months with a pup again the 18 months and up.
Also a very important thing a dog should not carry more than 15% of thier body weight.