Hi, I have had Shires and Clydesdales for over 20 years now
They are wonderful, but forget the 'gentle giant' myth! They are only 'gentle giants' if correctly handled. If they once have the oportunity to fnd out how big they are then you have lost the game. They weigh in at about a tone and maintaining ground manners is more important than with a light horse. A heavy can quite inadvertantly kill you.
They are totaly the wrong conformation for riding, although people do ride them sucessfuly. they mature late. They are not up to breaking till at least 4 YO. Then you have to go easy till they are 7-8 as before then they are not mature.
It will take about 2 years of ridden schooling, (when they are physicly up to it) to get them balanced and in to any thing aproaching an outline.
They are ruinously expensive to keep. Your farrier may not want to shoe one, so you might have to take them to a specialist forge. Their shoes are on average 120 pounds a set and need new shoes every 5 weeks on average. All that weight makes the shoes wear out faster.
Most heavies need special xx full tack.... this comes at extra expense! You can't just walk in to a saddlery and buy a 7" bit! A plain 7" snaffle costs about 30 pounds, if you want any other sort of bit then it will cost 100 pounds plus as a special order.
In the winter they will eat a bale of hay a day. Some are very poor doers and need buckets of extra feed.
Double the costs of wormers and suplements.
They are notoriously unsound! Lots of problems related to joints (arthritis and djd) EPSM affects half of Shires at some time
http://www.ruralheritage.com/vet_clinic/epsm.htm They also have lots of problems if allowed to grow to fast as youngsters. They need to be grown very slowly to prevent bone and joint deformities. Sadly you see a lot of young heavies forced to look big in the ring. They are usualy in a tin by 10 years old.
Their life expectancy is shorter than an average horse. A heavy is lucky to reach 19 years old.... when you take in to account that they don't realy mature/get going work wise till about 10 years old, it is a very short working life!
This sounds like doom and gloom, but they are beautiful animals and worth it... best way of putting it is that they are specialist horses for enthusiasts!