You have cold blooded horses? Are they reptilian?
In my experience, I would install a gate. A single cable might subject you to legal action. I was told by LEO and an attorney that I could be sued by anybody who got hurt riding into a single cable gate while on an ATV, motorcycle etc,etc. The single cable can be classified as an attractive nuisance and that's one of the reasons I abandoned my cable and installed a gate. Besides a horse or cow will soon figure it out...........
If you have ever had to put down your horse with a broken leg after a dog ran it through a cattle guard, you would never use a cattle guard for horses again.
Cold bloods are draft horses. Hot bloods are the ones like Arabians. Warm bloods were bred to carry knights. They have the strength and temperament of the cold bloods and the agility and speed of the hot bloods. Ours are Holsteiners and Hanoverians, named after the region in Germany where they originated.