A bridge over a ditch consisting of parallel metal bars that allow pedestrians and vehicles to pass, but not cattle WordNet 3.0 & Open English WordNet

A cattle grid – also known as a stock grid in Australia; cattle guard, or cattle grate in American English; vehicle pass, or stock gap in the Southeastern United States; Texas gate in western Canada and the northwestern United States; and a cattle stop in New Zealand English – is a type of obstacle used to prevent livestock, such as sheep, cattle, pigs, horses, or mules from passing along a road or railway which penetrates the fencing surrounding an enclosed piece of land or border. Wikipedia

Bars in the road surface that allow wheeled vehicles but not animals to cross. Sometimes known as a Texas Gate, even outside of Texas. OmegaWiki