Here are two interesting articles on how much weight a horse can carry.
http://www.thehorse.com/articles/31900/how-much-weight-can-horses-comfortably-carry
http://horsetalk.co.nz/2013/04/01/the-great-weight-debate-how-heavy-is-too-heavy/#axzz32qK1tr9F
What do you think is a good way to determine how much weight your center’s horses can carry?
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Note: This is not professional advice, this is a blog. I am not liable for what you do with or how you use this information. The activities explained in this blog may not be fit for every rider, riding instructor, or riding center depending on their current condition and resources. Use your best personal judgment!