Quick weight question for an upcoming trip

[Sanhestar]

Is it to prevent chronic injury? Seems odd--when humans are at that stage of development, we can carry a much larger proportion of our body weight.

yes, it is.

I have no data on young humans carrying large amounts of weight and longterm damage. But I know how my discs, knees and hands feel after 30 odd years of lifting, hauling, etc. everything around horse and goat husbandry......

Also, the physics of carrying are different. Humans have a  clavicle that will support the shoulders, goats do not (as any other four-footed animal).

I also second what Nanno already said. Your goats are quite small for that age and I know from experience that a regular saddle will most likely not fit them well. Not only in length but also in width.

It is one more year for you to wait and train your goats without weight. It will be worth it.

BTW - I found two studies a while ago that confirm that castrated goats actually NEVER stop growing. Some growth plates have been found to be still unclosed in ibex at age 12 years (!) - upper arm and lower leg - and in goat wethers at age 9 years - ulna, shin and femur. The one study that compared wethers with intact goats showed that castration can delay closing of the growth plates in all bones for up to four years.

As open growth plates are more prone to injury this should be kept in mind, too.