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ELECTRIC FENCE DESIGN
By David W. Pratt
Oct 28, 2002, 11:10pm
David W. Pratt, U.C.C.E. Farm Advisor
LIVESTOCK & RANGE REPORT NO. 922 SPRING 1992
Napa & Solano Counties U.C.C.E., Livestock/Range Management Program
The effectiveness of any electric fence depends on the ability of the fence to deliver a painful shock to animals that touch it. The ability of the fence to deliver that shock depends on:
- The energizer
- The grounding system
- The fence design
Energizer and grounding considerations are discussed in detail in Livestock & Range Report 913 & 914. There are several important aspects of fence design including bracing structures, materials and wire number and spacing. This article describes wire number and spacing for electric fences for cattle, sheep, horses and wildlife for various sites. Bracing and evaluation of material will be addressed in future publications.
The ideal fence is inexpensive to build and effectively control animals. There is no single design that meets these criteria for every application. The effectiveness of any design depends on the type of animal that must be controlled, the materials used in construction and site characteristics (e.g. soil moisture, terrain, etc.)
"FENCE THE DESIRE"
Al Coyle of High Tensile Fencing in Sacramento, California once told me, "You must fence the desire." The more the animals want out or in, the more elaborate the design you'll need. Before we design a fence we must answer three questions:
1. How much do the animals want to get out?
If feed and water are plentiful, animals have little desire to challenge the fence and minimal designs of one to three wires can be effective.
2. How much do animals want to get in?
In our hot dry California summers, orchards and vineyards may be the only green, growing plants for miles. Deer have a great desire to get in. As a result, deer fence designs in California usually need to be more elaborate than designs used in the eastern U.S. where green feed is available year- round.
Like deer, the pressure predators put on fences depends on available food. For example, a sheep rancher might find that three hot wires retrofitted on an existing fence stops predation if none of their neighbors have electric fences on their ranches. If all of the ranchers in the area have electric fences, more elaborate designs will probably be needed.
Whether it's a cow's desire to get out or a mountain lion that wants in, training animals about the fence is important to reduce the desire to challenge the fence. Training is discussed in a separate Livestock & Range Management Report.
3. How much do you want to keep animals in or out?
Convicts occasionally escape from even the highest security prisons. Likewise no fence provides 100% animal control. The importance of control depends on your desire to keep your stock in or wildlife and your neighbors' stock out. For example, it would be more important to keep stock from getting out along a busy road than between paddocks. Therefore the design of perimeter or boundary fences are usually more elaborate than internal or subdivision fences.
For every application there are many potentially effective designs, each with dozens of variations. The following are six basic designs I have found effective for the applications described.
CATTLE ON IRRIGATED PASTURE
Whether you are grazing stocker cattle or cows with calves, one electrified wire can be an effective internal paddock subdivision fence where soil moisture is sufficient to provide a good ground system.
The wire should be installed 30-32 inches off the ground. Posts can be over 100 feet apart. No stays are required. Calves may leak through this type of fence. This won't upset the cows so long as calves are within sight. It may actually prove to be a benefit since calves can creep themselves on the fresh feed in front of the cows. If you want to keep the calves in (e.g. fencing along a county road), install a second hot wire 18 to 20 inches high.
CATTLE ON RANGELAND
Three wire fences with two hot wires installed at heights of 10-12 and 30-32 inches and one ground wire installed at a height of 18-20 inches has worked effectively on dryland range. Posts can be placed up to 100 feet apart. No stays are required.
SHEEP ON IRRIGATED PASTURE
Sheep are more difficult to control with electric fencing than any other livestock species. Training is critical if sheep are to be controlled. In addition, fence design must be more elaborate.
Sheep can be controlled on irrigated pasture using three hot wires installed at heights of 8-10, 18-20 and 28-30 inches. Many ranchers prefer using four wires at heights of 8-10, 15-17, 24-26 and 34-36 inches. Posts are generally spaced 40 to 50 feet apart.
SHEEP ON RANGELAND
Five wires are generally required to effectively control sheep on rangeland. Wires are installed at heights of 6, 13, 21, 30 and 40 inches with the second, third and top wires hot. The fourth wire is a ground wire. The first wire (bottom wire) is switchable. When soil moisture is adequate this wire is hot. When soil moisture is lacking this is switched to a ground wire. Posts are typically 40 to 50 feet apart.
Several fence designs have effectively protected sheep from predation. Producers report that even temporary electric fences have discouraged predation.
A simple design which proved effective on one Solano County ranch consisted of three hot wires mounted on plastic off-set brackets attached to the posts of the existing woven wire/barbed wire fence. The hot wires were installed at heights of 4, 22, and 42 inches.
More elaborate designs are often needed for predator control. A high-tensile fence design that has effectively prevented dog and coyote predation consists of nine wires mounted at heights of 5, 11, 17, 23, 30, 37, 44, 52 and 60 inches. Every other wire is hot (including both top and bottom wires). Wood posts are spaced 75 to 100 feet apart with fiberglass stays installed at 20 foot intervals.
Don't waste your time with the five wire deer fences promoted back East. Most electric fences providing effective deer control in California are at least six feet tall (taller is better) and include a minimum of nine wires. A high tensile electric fence with wires at 8, 16, 24, 32, 40, 50, 60, 72 and 84 inches would be effective for deer and elk. Every other wire is hot (including both top and bottom wires). Wood posts are spaced 75 to 100 feet apart with fiberglass stays installed at 20 foot intervals.
OVERBUILD AND UNDERPOWER
Many feel uneasy using only one or two wire fences to control stock. We tend to add more wires to increase our level of security. Unfortunately while we go overboard on the wire, we skimp on the energizer and the grounding. The New Zealanders are right when they say that Americans "overbuild and underpower" our fences. Your fence will become far more secure by investing in a good energizer, developing an adequate grounding system and training stock to respect electric fences.
With a good energizer, proper grounding and livestock training, the designs described in this paper can be effective in most situations.
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