You've caught some nice action there partner.
Two things that are quite noticable from the onset. The tilt and the time of day.
The horizon can be easily straightened, but you might be so close to the edge of the frame that you need to be careful not to cut off parts of the main subject. You should be okay with #1 & 2, but #3 may be tricky.
Secondly is the harsh light and the shadows it creates. It looks very close to noon time with the shadows coming straight down. The problem with this is that the faces and expressions of the riders can hardly be seen under the cowboy hats. If you get another chance at this, try to shoot earlier or later in the day. If you have one and you are within the limits, try hitting them with a flash to fill in some of the shadows and underexpose the ambient a little.
Looks like it was a fun day.