</font><font color="blue" class="small">( if a horse bolts through the fence they will just pop out of the posts rather than staying rigid and injuring the animal. )</font>
Here's my .02$ , and keep in mind I own horses, both studs and geldings, and cattle as well.
As long as a fence is high enough, a horse won't try to go over it... Stud horses and jumpers usually get a 5' fence.. while most others get a 48"-50" fence.
Horses ~generally~ won't rush a visible barrier.. though I have seen a couple horses bully another horse into a corner.
As far as boards go... don't think for one minute that a 'rigid' coral board on a 3 board fence will in the least stop a horse... IF the wanted out... A horse kan kick a fence board off all day long. Wire on the other hand is nice and strong...and generally will hold back a horse that is bad about leaning.
The last thing you want is a 'break-away' panel on a horse fence.. like a board that pops off 'easilly' to prevent hurting the animal. For one.. you now have that animal wandering the streets.. and hitting a horse with a car generally totals the care, and either kills the horse.. or injuries it to the point it has to be put down.. not to mention possible injuries to the driver.
Down here in fl, game code enforcement will cite you for 'insuficient fencing' if you have horses, if the fence is not 'sturdy'.
A month ago, a horse farm had a fence go down.. something like 7 horses got out.. 4 died and caused a multi car accident and closed the road for hours. A nearby vet ran across the street and was helping passing motorist corall the animals, and then they started euthanizing suffering animals right on the pavement. Not a good site.... I would never reccomend 'pop-away' panels on a horse fence.. my horses are like my children.
Cattle are another thing entirely. They will run down a barrier, especially if being chased. Again.. a board fence isn't sufficient to keep a charging bull in.. if he really wants out.
I have a longhorm that once was ran into my front pasture gate at full charge by a couple of our horses.. it was a tube gate and not a pannel gate. I had the gate wires with 2x4 woven 'redtop' wire, and that is the only thing that held the gat together and kept the animals in... the chain went around the corner brace post and around the pipe gate and the fencing on it. The gate bowed out about 3' and the wire is the only thing that held it...
Commonly you see horse and cattle in the same pasture, and some farms even swap cows into horse pasture during different seasons. Except for a few limited incedental's.. horses and cows don't share the same parasite problems.. so cross grazing like this doesn't spread parasite infections around.
Just my opinion...
Soundguy