OK folks, I did indeed exaggerate a bit about the weight of armour carried by mediaeval knights. A really full set weighed about forty-five or fifty pounds, well-distributed. (They could become hot and wearisome after a while, but for short periods at least, a fit knight could run, get up from falls or even do acrobatics.)

The horse tabard could be an unwieldy piece of kit. I don't have any weights to hand, but another fifty pounds seems about likely, if only the front of the horse was protected, or a hundred for all-round protection.

However, war-horses did have certain desirable attributes. They were usually stallions, with their own testosterone-fuelled aggressive reaction to noise and stress. They did indeed stand high, allowing the rider an extra inch or two of reach. And they were valuable, and were preserved for the moment of battle.