I'm not an expert on horses but to help those who know nothing at all, I'll do my best.
A stallion: is an entire male horse.
A mare: is a female horse.
A gelding: is a neutered male horse. This is the most common of male horses as they are generally of a milder temperament than stallions. This doesn't necessarily make them less spirited, just less aggressive to other horses. That being said, some stallions are just sooks and rather loving horses, gentle beasts.
Height in horses: A hand = 4 inches and a horse is measured from the hoof to the point of the withers (the top of the shoulders). Most race horses are 15 to 16 hands, with the occasional 17 hand thoroughbred.
Warhorses tend to be of the heavier, bulkier breeds, especially if they had to carry knights in full armour. Horses needed to be able to carry the extra weight and finers breeds just weren't capable.
Percherons, a French draft breed, are often considered one of the breeds used for knights in medieval times and average about 18 1/2 hands.
The sizes of horses in medieval times was smaller than those horses around today so the sizes I'm using for the horses in storylines are unlikely to be historically accurate, but at least it gives an idea of the difference between the lighter 'riding' horses and the heavier warhorses.
To get an idea of size, here's a link to Goliath, a percheron that got into the Guiness Book of World Records as the tallest horse in the world in 2003:
Obviously you are more an expert on horses than most of us!
We might conjecture in Oortesia, the elfs, who have had tens of thousands of years to breed, may well have produced horses as large as we have today, so the medieval sizes may not be relevant--much in the same manner we might presume magic and more knowledge of farming and livestock and even basic sanitation would make humans as tall and long-lived as they are now, at least in the more civilized areas with much contact with elfs, rather than the vast numbers of stunted and sickly men which lived in 'real' medieval times. And perhaps the larger and heavier warhorses and draught horses would have originally come from the north, both because of the use of armoured soldiers, and the colder winters, the steep mountains wagons must be pulled up and down. While the southerners, Kin-Darys and The Lowlands, would perhaps have bred lighter and faster horses, they do not have heavy cavalry on the scale seen in the north down there, and the warmer climes would tend to tire a heavier horse more quickly, would it not? Then of course humans, always wanting to improve on what they learned from the elfs, would want to cross-breed these two types, trying for big and fast warhorses, and probably also ending up with some unintended breeds of racehorses and smaller horses which might be useful in other applications. Plus, halflings need little horses they can use without a ladder.
Some thoughts on the amount of care horses need might be great to share with us. A horse is not like a car, one cannot simply put in food and water, then jump on its back and go all the time! On the other hand, horses have intelligence, can often take a tired or wounded man home, might not obey a command to jump off a cliff in the dark even when a drunk man thinks that is the roadway...
I would think there is a great difference in a farmhorse that is left to graze and drink in a corral, and hitched up on market day--up to the other extreme, a warhorse of the Husaria in its prime, its diet regulated, exercised a certain amount every day, trained to kick and trample and obey the commands of the trumpets (as I understand things, most horses will not trample on something living, they have to be trained to do so?), the coat brushed out twice a day, mane and tail trimmed to a precise length, all against the day it is expected to bear a Knight into battle wearing armour and pointing a 17' lance at the forces of evil on the wrong side of the battlefield!
I thought this might be interesting to those venturing into Lys and particularly of interest to anyone running (or running into) Hussars. One point of note is how cavalry could actually defeat determined infantry. I always thought that a horse would not charge a phalanx (i.e. an infantry square or shield wall), perceiving this obstacle to be a solid wall. Apparently a special 18’ lance was used and could break an infantry square before the horses would stop. Some other facts about how one might be able to travel by horse in a day as well including the speed of moving artillery around. Wizards I read are deployed like artillery and I suppose (correct me if I’m wrong) might impose similar logistical challenges given that magic requires some special goodies and wizards being crotchety old men or complaining old biddies probably want to ride in style. Anyway, thought this might be new to someone other than me. Hussars
If infantry with pikes could hold their ranks and keep their pikes leveled, they would nearly always break a cavalry charge. But, that is no easy thing to do!
And we need not even go back to ancient military reports for this information. During the filming of the epic film 'Waterloo' about the events leading up to and then the battle itself (Christopher Plummer plays the Duke of Wellington), Director Sergei Bondarchuk (already famed for having directed and acted in the mammoth 4-part Russian version of 'War and Peace') set up those really fantastic overhead helicopter shots of the French cavalry making a general charge against the British squares. If you watch carefully, you can actually see those squares breaking as the shot ends, which must not have happened historically, and there is a story behind that...
The 'British' troops, the redcoats in the movie scenes, are actually portrayed by Soviet Guards infantrymen. And even against the mock cavalry charges for the movie, they could not hold their ranks, they broke and ran during take after take. Even when tape was stretched across the grass to mark where the 'cavalry' would turn away, the soldiers would not stay and wait for the horses to reach that point. So even though they knew the cavalry charge was fake, even though they knew exactly where the charging ranked horses would turn aside, trained soldiers were unable to face them without running...
Pity, then, the poor peasant levy told to lower the pike and hold the line!
There is something else to consider in this. A horse will generally avoid running over a person and will try to go either side if they can.
Now, I'm using a real-life situation here to explain what can sometimes happen.
I live in a town where they have a strong polocrosse team (it's like lacrosse on horseback and not as 'snobbish' or up-market as polo). Last year one of the goal referees suffered horrible injuries when one of the horses ran straight over the top of him.
Rules say if a horse is running through the goal (they can't just stop dead) the ref is to stand still and let the horse pass either side. The ref did the right thing, he stopped and stood still... the problem was the spectators had crowded so close to the edges of the field that the horse had nowhere else to go but over the top of the ref, trampling the man.
Consider that in the context of the charge where there are horses crowding either side and very little room for manoeuvrability. A charging horse has little choice, regardless of the pikes levelled at them some horses will charge on through, becoming 'sacrificial' in a way to clear the path for any coming up behind them if they have nowhere else to go. Spare a thought for the poor horse
I think I would not be a referee in that game...Particularly if I would not be mounted on a horse of my own!