Out of the ones on Flickr, you've picked the right ones to show.
One major point is that I'd usually suggest shooting in Av and not TV. Your aperture is all over the place and far too narrow, but you've been saved in this case by two very important factors:
a) You've picked good clean backgrounds
b) Being a lovely day, the tight aperture has really bought out the best in the sky.
If you've got that much light, you really don't need to be up at ISO 400.
That aside, on to the positives...
Those are 3 cracking shots considering the short focal lengths you've used.
1. I'd crop in tighter to lose the random bod in the background. The way that you've shot it, the sky and open field are dead space anyway.
2. Needs a square crop to lose the top third of the photo (which is dead space). That also makes up for the fact that you've lost the ground line.
It might have been slightly improved if you'd managed to get on the inside of the fence, but that's a moot point and the light looks as though it would have been against you.
3. Love it. Definitely the best of the wide shots that you've shown on that fence. The reason is that the horse coming off the fence closes the picture down, whereas on the rise to the obstacle they'd need more space on the left. However it is slightly underexposed, but a 1/3rd of a stop adjustment in PP plus quite a lot of fill light does wonders for it (I've just tried). It also shows that you are looking for something slightly different, rather than obsessing about getting close in to the fence.
Timing is pretty much spot on (possibly fractionally late on 2) and for your first go at equestrian photos these are really very good. NOw go out, take some more and improve!!
