Do cows get frightened by the herd of wild horses and scatter?
Cattle can spook, but it is usually caused by something they are not used to. For example, I check fences on horseback or four wheeler, so our cattle are used to both those things. I also use the four wheeler to take feed out to them, so they associate the sound of the four wheeler with getting fed. They are also used to seeing a large tractor that we use to move round bales to them.
These are things they see daily. Now, if you were to drive a large truck through the area, that might spook them because it is not something they see regularly, the noise it makes is not the same, etc.
Another thing that affects the level of spookiness in a herd of cattle is the way they are handled and worked. If you are calm and gentle on how you handle them, they stay calm. Most people who work with cattle regularly know this.
Could a wild animal spook them? Certainly, particularly if it was an attack of some sort. BUT, there would most likely be evidence of some sort of attack- animals with injuries, dead animals, blood, hair, etc.
We see coyotes here regularly, and yet we have never has any cattle attacked on any of the farms in our immediate area. We do have bears and bobcats here as well, and have had no issues with them and cattle. We have neighbors who claim to have seen evidence of large cats, but no one has ever captured hard evidence of them here.