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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, Domestic pig, , or from passing along a road or railway which penetrates the fencing surrounding an enclosed piece of land or border. It consists of a depression in the road covered by a transverse grid of bars or tubes, normally made of metal and firmly fixed to the ground on either side of the depression, so that the gaps between them are wide enough for an animal's feet to enter, but sufficiently narrow not to impede a wheeled vehicle or human foot. This provides an effective barrier to animals without impeding wheeled vehicles, as the animals are reluctant to walk on the grates.
A study of the bars of traditional cattle grids in the Flint Hills of Kansas found that 80 percent were made of pipe, while smaller percentages were made of , , planks, and other materials. The size of the bars varied from ; the spaces between bars varied from ; the number of bars per grid varied from 4 to 22. Grids differed in length from and in width from , while the pits beneath grids were deep.
Cattle grids, as they are called in Great Britain, Ireland, and South Africa, are known by a wide variety of other names in other parts of the world. In the United States, they are cattle guards. Mata burro ('donkey killer') is the preferred name in Brazil and Venezuela, while guarda ganado ('cattle keeper') is what they are called in Argentina. Alternatives in the United States include car crossing, auto gate, corduroy gate, stock gap, cattle pass, run-over, and many others. Canadians use pit gate, vehicle pass, and Texas gate, as well as cattle guard, which in Canada refers mainly to guards at railway lines.Hoy, pp. 117–18
Why they work is unclear, but it is most likely related to the bovine visual system. Experts say that "a cow's depth perception is such that it makes little or no distinction between painted stripes on a dark background and bars over a pit."Hoy, p. 154 Cattle may acquire the behavior of avoiding grids over pits either from individual experience or through imitation of other cattle. However, painted grids have been reported to work with semi-wild cattle with no prior exposure to virtual grids.
Cattle can sometimes defeat virtual guards. A station owner in Queensland, Australia, told a reporter that after some of his old bulls leaped a painted grid, the younger ones lost their fear of walking across. This is common; if one member of a herd discovers it can step safely on the lines, others will follow. Other incentives that lead cattle to test a virtual guard include placing food on the opposite side, or using strong driving pressure to run panicked cattle over a virtual grid.
James Hoy in The Cattle Guard discusses four kinds of electric guards. One that was patented in Illinois in 1955 and another invented in New Zealand in 1979 are similar; each resemble "something like the framework of an old-fashioned metal bed" connected to a battery or high-powered fence charger. They are easy to drive across, but may pose a danger to children or animals that get stuck in the guard.Hoy, p. 152 Another type was patented in two versions by an Oregon inventor in 1956–57; it consisted of 20 current-carrying synthetic rubber strips mounted on a wooden frame. The invention proved highly effective in deterring all animals, including dogs, and it was maintenance free, easy to drive over, and safe. However, the company that acquired the manufacturing rights stopped production in 1960. A fourth type, homemade, consists of two sections of woven wire or steel plate laid on a concrete slab and set apart from one another on either side of a fenceline. The wire sections are then connected to an electric fence or to a separate charger, either conventional or solar-powered.
Wider grids are used where wildlife is to be contained. Some animals can jump across them, and a barrier that stops deer needs to be at least wide. Bison, and bulls in particular can easily jump across an barrier, and have been known to jump widths of up to .
In areas with heavy snowfall and long periods without a thaw, snow can accumulate beneath a grid and allow animals to walk across.
Horses are particularly vulnerable to cattle grid injuries, as their single-toed Hoof can slip between the bars and trap their legs in an easily broken position. The same risk exists for in Australia's outback, with additional risk of entrapment.
Cattle grids are generally useless for containing . However, a Texas Highway Department official reported that adding three painted stripes—arranged yellow, white, yellow—on the road in front of a cattle grid deterred goats from approaching or crossing the guard.Hoy, p. 155
Cattle grids produce noise when vehicles pass over them and people living in a 100 m radius from the grid can be affected.
There is a British Standard for cattle grids: BS4008:2006. The US standards are put forth by The American Association of State Highway and Transportation Officials (AASHTO). AASHTO provides load rating guidelines for cattle grids that are used on public roads in the US. All cattle grids used on US public roads must be certified by a qualified engineer that the grid meets AASHTO guidelines.
Patents and standards
The United States Patent and Trademark Office (US PTO) issued patent on January 15, 1915, to William J. Hickey, Reno, Nevada, for a cattle grid.
See also
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