I'm not sure if Moeee means there is an absolute limit a horse can carry before IT BREAKS IN HALF or.....just that there is a sharp fall off in performance at some point. However I feel it would vary from horse to horse either way,especially when you consider that they put 70 Kg on the Jumpers and then expect them to run MUCH further while leaping over the obstacles as well!!!
As for thw Olympic weightlifters; they are lifting TWICE their bodyweight.In the case of a thoroughbred I can see how being allocated double their bodyweight (ie 1 tonne) might slow 'em up (though, as I've said many times before,I MIGHT bet even them if the odds were long enough!!!).Cheers