Riding and Horses
"A steed isn't praised for it's might, but for it's thorough-bred quality"
CricketHomeRiding 2
Equus - Steed - Horse - Polo Ponies - and a Trusty Steed.

And John Steed is a horseman indeed because he is an excellent rider. Obviously, this is one of his favorite hobbies and a sport he knows well.
He's playing polo (Death of a Batman), he had some polo ponies (The Medicine Men) and a few other horses (TNA House of Cards, TNA Target, TNA To Catch a Rat, and TNA Medium Rare). His mansion Steed Stud Farm has its own stables, which can be seen in To Catch a Rat.
Obviously, Steed owned some price winning jumping or racing horses, as there is a collection of rosette ribbons visible which are fixed at the photos of his horses in TNA House of Cards. The horses were awarded a first price (blue ribbon) and with two prices for the second place (red rosettes).

Steed is on horseback in Silent Dust, Two's Crowd, TNA House of Cards and TNA Target.
There are further episodes with horses, such as Trojan Horse in which Steed gets a horse as a gift.
Horses are also part of a few tag scenes such as in A Touch of Brimstone when Steed and Mrs. Peel depart in a vintage coach or a horse-drawn carriage in Too Many Christmas Trees. Steed rides a rocking horse in Requiem, and there is another one in his flat in Escape in Time.

Trophies as seen in
The Midas Touch
Steed is combing down his horse
in Medium Rare.
Steed at the stables in
To Catch a Rat.
Silent Dust is the episode showing John Steed's (Patrick Macnee's) skills as a rider. Steed is a man who has mastered riding and knows how to deal with the horse. He's Mrs Peel's knight in shining armor on horseback.
...always a gentleman.
Link to an article about Patrick Macnee doing showjumping.in a French magazine on the website on

http://www.chapeaumelonetbottesdecuir.com/
TV Times article 1964