In working cow horse going down the fence when should I accelerate to get in front of the cow?

Timing your acceleration on the fence run is everything in working cow horse, and it's one of those things that separates riders who have feel from riders who are just reacting. Get in front of the cow too early and you've given her nowhere to go — she'll stop, duck back, and you've lost control of the run. Get there too late and she's already past you, the turn is ugly, and you're playing catch-up for the rest of the run. The window is tight, and learning to read it is a skill that only comes from hours of cow time. The cue to accelerate is the cow's shoulder. When her outside shoulder starts to drop and she begins committing to the fence, that's your signal to move. Not before — not the moment she heads toward the wall, but when her body language tells you she's going there and not changing her mind. That read comes from watching cattle, a lot of them, until the shoulder drop becomes something you see automatically rather than something you have to think about. Your acceleration needs to be aggressive enough to get your horse's head past the cow's head before she reaches the turn point. If your horse's nose and the cow's nose arrive at the turn simultaneously, you're going to get a collision or a duck-back. You need daylight between your horse's head and hers going into the turn so that she has a wall of horse to turn off of rather than a gap to run through. Practice the read on slower cattle first. A big, lazy cow that telegraphs her moves gives you time to learn the timing without the pressure of a fast run. As the timing becomes instinctive, move up to faster cattle. The feel you build on the slow ones transfers directly — the window just gets smaller.