A somewhat obscure suggestion
This is probably not near as drastic as stuff you can get on fellow horse kinkster forums, but it's easily obtainable.
Rent the DVD with the EXTENDED version of 'The Lord of the Rings: The Return of the King'. Disks no. 3 and no. 4 have documentary films. Look for the documentary on sound effects. The microphone man does a recording of a stallion getting all excited about a mare close by. I don't remember which of Tolkien's creatures they used the stallion's cry for. If you and your wife observe the scene closely, you will even get a nice view of the stallion's erect penis. (IMHO fine for horses, but too big for humans.)
And to support what Teni says, if I remember correctly, the sound effects guy says it was one of the most dangerous recordings he ever did in his life!!
Almost forgot – the three movies are well worth watching. Amongst other things, beautiful horses.
One last naughty remark about ROTK. Eowyn/Dernhelm sweeps Merry up in front of her. 'Ride with me.' Closeup of Merry getting bumped up and down. Big smile spreads on his face. 'My lady...' What is she doing to him?