Cattle grid is a type of obstacle to prevent hoofed animals, such as sheep or cows from passing. It consists of a grid of bars ot tubes (usually made of metal) firmly fixed on the ground so that the holes are large enough for animal's legs to fall through, but small enough that a vehicle can pass over it.
These grids are usually installed over countryside roads where they cross a fence. An alternative is to create a gate that would need to be manually or automatically opened when a vehicle comes.
While these barriers are usually effective, they can fall to ingenious animals. Sheep have been known to roll on their backs or sides over grids as wide as 3 meters, traversing them in order to find more and better food.
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