Fence Systems for Dairy Grazing Cattle.
Published on Wed, 09/18/2019 - 11:45am
Fence Systems for Dairy Grazing Cattle.
By Ben Bartlett
Permanent Fencing Location
Where to put the fence is the first and most important decision. Other important questions about locating fencing include:
• What are the fence laws in your state?
• Where are your property lines?
• Where will your cow and equipment lanes be located?
• How will this fence fit into your grazing plan?
A good fencing plan should start with the clear identification of the expected production needs, goals, and resources. These considerations will give you the initial idea on where, when, and how permanent and/or temporary fences should be used. Consider from the very beginning the strategic location of the milking barn and laneways. It is very useful to have an aerial map of your farm with your fencing plan drawn in since people rarely build their entire fencing system at one time.
Consider what is going to be your expected stocking rate (i.e., animals/area) and what grazing system (i.e., strip versus rotational) you will be adopting to manage your stocking density (i.e., animals/area/time) on a daily basis. Whenever applicable, also include in the plan future ideas for herd size expansion and/or irrigation. Keep in mind that the location of the milking barn and laneways are the heart of the dairy because together they will “permanently” define the overall walking distance to pastures and the flexibility that you will have in grazing management (e.g., paddock and/or strip sizes and shapes).
Your initial fencing plan should allow for efficient water system development and should also include gates, location of fence strainers, and corner and end fence brace assemblies. This planning detail will help you keep the fence as simple to build as possible and also provide you with a materials list.
Fences can be either “physical barriers” like a wooden board fence or a “psychological barrier” like an electric fence. A physical fence is usually more costly, but animals need no training for the fence to be effective. An electric fence is effective because the animals have been trained that the fence will “hurt” them with an electric shock, and the shock is sufficient to deter them from enduring the “pain for the gain” of fresh pasture. For an electric fence to be effective, the animals need to learn both that touching the wire will hurt and the “hurt” is sufficient to make it a memorable experience.
Although dairy animals are usually very easy to train to respect an electric fence and people often use only one wire, it is recommended that all farm perimeter fences be at least three-wire or your state legal requirement, whichever is greater. The easiest and lowest cost time to add a wire to the fence design is when it is being built. If there is any doubt about the number of wires needed, add one more. The three-wire fence should be 42” to 46″ high with 10” to 12” wire spacings starting from the top down. For one-wire paddock division fences, the wire should be as high as the point of the shoulder or about 30” to 34” for most Holstein cows.
Electric fencing can be very effective but may not be appropriate if animals will be crowded by other animals and not able to move away from the fence, or if the cost of escape is very high. If your pasture is next to a busy highway or a neighbor’s high-value crop, use a physical barrier fence.
It is recommended to have at least 2,000 volts on the fence and have a fence tester that can provide an accurate analysis of the fence performance.
• Do not use barbed wired for electric fencing.
• Be cautious about exposing small children to electric fencing.
• Make sure all family and employees know where and how to turn off the electric fence energizer.
Electric Fence Energizers
When selecting an energizer to put a “charge” on your fence wire, your main options will be battery or mains power and size of the energizer. The more fence you have and the more resistance (weeds /grass on the fence, poor connections, small wire) you have, the more powerful an energizer you will need to maintain at least 2,000 volts on the fence wire.
The best estimate of energizer size is the “joule” rating. For most dairy operations that have a limited number of wires that are often above wet vegetation, a small to medium energizer, 1 to 10 joules, will be adequate. Most battery or solar energizers are only 1 to 2 joules. A mains-powered, 110-volt unit is the preferred option.
If you use a lot of poly wire or poly tape, a larger energizer may be required because the small wires have a lot of resistance. The best advice is to work with a knowledgeable fence supplier who can provide reliable equipment, good advice, and support when things don’t work, such as when your energizer gets hit by lightning on a holiday weekend. There are no guaranteed ways to prevent lightning damage to your energizer, but always use a surge suppressor on the power input side of your energizer and a wire “choke” or “induction coil” on the energizer to the fence leadout wire.
When you are troubleshooting poor fence performance, 80% of the time inadequate grounding is at least part of the problem. As a general rule, a minimum of 3 feet of ground rod is required for each 1 joule of energizer output. The way to test the ground system is to ground out the fence by leaning steel rods against your electrified wire and then testing the voltage on your grounding system. If you have over 400 volts on the ground rod, you need to improve your grounding system which usually requires adding more ground rods.
Temporary or Portable Fencing
Portable fencing, most often poly wire or poly tape, is a great tool to help you manage your grazing system. The wire or tape is best utilized with windup reels, and the line posts, often “step in” plastic posts, allow paddocks to be divided very quickly. The small wire in temporary fence has a lot of electrical resistance, and temporary fences should usually be limited to less than ¼ mile or 1,320 feet per connection to a source of electric charge. Since temporary fence can be set up and taken down many times each grazing season, the better-quality poly wire and the well-made geared reels may have a larger purchase cost but in the long run may be the most time-efficient and lowest-cost systems.
Fence Building Materials and Tools
The two key items in a fence are the corner/end posts and the fence wire. The perimeter wire should be 12.5 gauge, triple galvanized, and high tensile. The breaking strength can vary between 1,000 and 1,800 pounds with the wire getting “stiffer” and more difficult to bend by hand as the breaking strength increases. The larger 12.5-gauge wire has about one-third of the electrical resistance and over five times the breaking strength of the smaller 16-gauge wire. The fence wire is only fastened at each end, and the natural elasticity allows the wire to stretch if needed (for example, if a tree falls on the fence) and not be permanently overstretched. This allows the wire to snap back into place and minimizes the repair needed. Since the wire is only fastened tightly at the corner/end posts, these posts are critical and should never be compromised. If an end post goes down, you lose tension on the fence, and all wires will go slack. As the expected life of the wire is 30 to 40 years minimum, the corner posts should also last this long. Large, 6” to 8” top diameter treated wooden posts, properly installed are most often the best option.
Line posts are often the largest cost in the fence project but are also the easiest to replace if they fail and, if a line post does fail, the fence is still most often fully effective. There are many options for line posts: wood, treated wood, fiberglass, plastic, and steel. All options have their pros and cons; no one post is best. The general rule is that the materials are 50% of the total fence cost, and the installation labor is 50%. If you use “cheaper” materials and have to prematurely replace them, the cheap option can end up as the most expensive.
If you are going to build or repair your own fence, a couple of specialized tools are critical. Most high-tensile smooth wire comes in 4,000-foot rolls, and a “play out” reel is necessary to keep the wire from becoming impossibly tangled. The other recommendation is to use “figure 8” shaped compression sleeves to fasten wire together. The compression sleeves will not weaken wire, are quick to put on, and provide a good electrical connection. Use two or three sleeves when connecting two wires together and one or two when wire is wrapped and fastened to itself.
Building anything that is expected to last 40+ years should not begin with a shovel or posthole digger. The first steps should include:
• Having a paper plan of the fence with gates, stretches of wire, and location of fence wire strainers.
• Checking state and local fence regulations, and being sure you are building the fence on your own property.
• Doing any needed site preparation. Be sure to level the land under the fence to minimize the number of posts you need and also allow for a roadway by the fence so that you can check and maintain it in the future with the vehicle of your choice.
The actual fence building starts with the end posts that are literally the foundation of your fence project. The corner post should be as deep in the ground as the post is tall above the ground: a fence 48” high means the post should be 48” in the ground. From one to three wires can be secured by a single large post, but more than three wires require a figure “4” or H brace as assembly. If the design in the figure below is used, it is recommended that the joint of the diagonal post and the corner post be at two-thirds of the fence height. This will keep corner posts in the correct position. For a five-wire fence, this height is equivalent to a height between the second and third wire (starting from the top).
If you have a five-wire fence with over 1,500 pounds of breaking strength per wire, a falling tree could apply over three tons of “pull” to the corner post before the wires break. Proper size and construction of end posts are critical. Since failure of most corner posts is either leaning toward the fence or uplifting, it is critical to properly install the end/corner posts. It takes time to build end/corners correctly, usually about 50% of the total time to build the fence. After the corners are in, lay out a guide wire for proper placement of the line posts. The job of line posts is to keep the wires the proper distance apart and the correct distance from the ground. Distance between line posts can be from 20 to over 50 feet apart, depending on the number of wires and whether the terrain is level.
The next step is to lay out the remaining wires, fastening them at each end but not applying any tension. The in-line strainer is used to properly tension the wire to about 200 to 250 pounds. This will remove most of the “sag,” but the wire will not be “piano string” tight as a perfectly straight wire is overtightened with no “stretch” left.
The remaining construction steps are minor but critical:
• Insulators need to installed.
• The leadout wire from energizer to fence needs to be done.
• A good grounding system needs to be created.
• Any needed undergate insulated connecting wires still need to be done (do not rely on tape or even wire gates to conduct current across gateways).
• Finally, turn on your energizer and “test” your fence with a voltmeter to make sure you have the desired level of voltage.
Here is a sample materials budget for one mile of four-wire fence around 40 acres of level terrain and two pipe farm gates:
• Wire – 6 rolls @ $100 = $600.
• Six corner/end post assemblies – $200.
• Line posts every 30 feet (180 + insulators) – $1,400.
• Strainers, gates, misc. – $500.
• 5-joule energizer and connections – $400.
• For a total cost of $3,100, or about $0.60 per foot for materials.
• PLUS labor.
If you double the cost to $6,000 and divide by 40 acres for 20 years, you get a per acre cost for the fence of $7.50 per acre per year.
Grazing pasture can be a very low-cost way to harvest high-quality forages while allowing the animals to spread their own manure. Most producers tend to underinvest in good fence and fence equipment and undervalue pasture as a high-quality forage alternative. Good fence is a “tool” that can provide a high rate of return.