Keeping your animals (or someone else’s) on the correct side of the fence can be quite a challenge. Some kinds of animals are easier to fence in (or out), and some are very difficult. Within a species, some individuals are more determined to escape and some are quite content to stay at home. Keeping them fenced may require some effort and, for difficult critters, some thought.
Take these cows, for example. Right now, they are only about a month old, fairly small and not very strong. They have grass enough, but the grass is always greener on the other side of the fence. Without precaution, they might slip through an opening or loose wire in a fence, or when they are older they may break a fence. Cows don’t mind much about barbed wires, and will push them just them same as smooth wire. Our solution? Tires in combination with barbed wire (we would have used regular smooth wire, but wanted to be using a “legal” fence according to state law, so that we would not be so liable if they get out). Why? They could push over the tires, or they could push through the wire. With both, however, they can’t push hard on the tires because they have some fence in the way. And they can’t push through the fence because there are tires on the other side. Additionally, the tires prevent the cows from trying to reach through the fence to the grass on the other side: they can hardly see the grass, much less reach it.
We have a similar fence for our goats, but instead of barbed wire we use strong mesh fence. The goats are better at climbing the tires, even with wire in the way, and are small enough to climb through and around the wire and tires (as are sheep). A good mesh fence that is tightly strung is hard for them to climb, and tires on the other side prevents them from bending the wire out of shape or pushing their way out from underneath the wire fence. With horses we make a fence similar to the goats, or string lines of wire like with the cows but not barbed: barbed wire should never be used around horses.
In addition to the benefit of helping to keep your animals in their fence, tires are also good for providing a windbreak and shade.