Ambitious exercise! Looks like you used this classic ref, but mixed it with some frames from this one too?
The 1st one has 16 frames, so picking every other one was a good idea for your 8, but somehow you got it wrong in the end. The last 2 of your frames don't fit the right ones in the ref, or are a mixup of refs, or a mixup of legs from one ref. Also you may have swapped the first and last, not sure. All of this makes the anim jumpy at one point.
Also, look in both refs at the changes and moves of the body and head (different in both). You should aim at reproducing this too, not just the leg moves.
There are many stray pixels.
Finally, do not use 0 frame delay if you can avoid it. Most browsers will display it as 0.1" which fits this anim, but you can never be sure.
neck feels a little short, head and tail might be a little small
I haven't used any of these :)
Well, I just took this www.loshadenky2004.narod.ru/galop.jpg and turned it into GIF - just wanted to see what it's gonna look like, 'cause the moves on the ref seemed... questionnable to me. As to those odd bright pixels, they looked good on white BG, but I forgot that the standart PJ background is grey, so I'm going to remove them.