Five types of fences are used in sheep production. In this edition each of these types of fences will be discussed and examples of typical constructions and construction materials will be given. This is however not the alpha and omega as other requirements than those discussed here are also possible.
We thank the ARC Agricultural Engineering in South Africa for making their manual on sheep production and facilities available to the readers of ProAgri Zambia.
In sheep production systems, mainly five types of fences are used, namely:
- Fences for handling facilities
- Fences for feedlots and alleys
- Inner fences for grazing camps
- Boundary fences for grazing camps and feedlots
- Fences for intensive holding facilities
Fences for handling facilities
In the handling complex where groups of sheep are flocked together and are handled, the sheep are exposed to abnormal stress conditions and may try to break out. Sturdy fence constructions must therefore be provided.
The fences for crushes and pre-collection camps must preferably be of the steel construction type. Although it is a more expensive type of fence than the normal wire construction, the lifespan is much longer. Often, when sheep become distressed or panicky, they tend to run into fences or to jump over them. A wire fence will soon be sagging, lose its effectiveness and will have to be replaced eventually.
There are many possibilities for steel construction fencing. The fences can be permanent with straight poles fixed with concrete. It can also be of the portable type steel gates. The type and size of the production unit, as well as the farmer’s choice, will determine the type of fence construction.
Figure 1 shows an example of a camp fence. Fences for holding pens can be the same as those for feedlots and alleys.
Fences for feedlots and alleys
In feedlots and alleys, sheep are still in a relatively enclosed area. Sturdy fences that can withstand the pressure are therefore necessary, although they need not have to be steel constructions as in handling facilities.
The following types of wire fencing can be used:
- Barbless wire fence
This type of construction is the cheapest and consists of barbless wires that are spaced at intervals and supported by standards and droppers. Depending on the type of sheep breed and occupational density of the sheep, the wires can sag with time as the sheep push against them and try to crawl through. To prevent this, wire-strainers must be affixed at each new line wire at the anchor pole with the single wires, to strain the wires when they become slack.
- Woven or welded fences
This type of fence consists of welded mesh wire, woven diamond wire, mesh, or “Bonnox” or “Veldspan”. These fences must be at least 600 mm high and they prevent the sheep from crawling through. The fence can be increased in height by placing barbless wires above the complete fence, and is cheaper than making the entire fence out of woven or welded mesh wire.
Internal fences for grazing camps
The construction of these fences is much the same as feedlot fences. The minimum height is 900 mm.
Alternatively, temporary or permanent internal fences can be erected by putting up two to three electric wires. Round steel (10 mm diameter) can be used as standards at a spacing of four to five metres. Most types of plastic isolators fit the 10 mm diameter round steel.
The wires can be ordinary galvanised wire or the so-called “polywire” nylon wire.
The latter is more practical in portable fences, since it can be easily rolled up. Wires must preferably be between 250 mm to 300 mm apart depending on the breed, camp layout and specific conditions. The round steel standards must be driven into the ground to a depth of at least 300 mm.
The energiser that provides the wire with electricity can be driven by one of the following power sources:
- A normal 12 V battery
- 12 V battery or 220 V electricity
- 12 V battery charged by a solar panel
If 220 V electrical power is not available near the grazing camps, a 12 V battery will have to be used. A battery charger is then also required to charge the battery in the evenings when the sheep are not in the camps and the battery can be taken to the nearest electricity supply point. If theft is a problem, the battery and the energiser must be locked up in a steel box.
Sheep must be trained to “respect” an electrical fence, since their wool is too thick to get a shock effect. The nose and ears must therefore touch the wire. This can be done by hanging empty cans or other metal objects on the wire. The sheep will inspect the objects out of curiosity and thus receive a shock.
Regular maintenance must be done on the fence:
- Ensure that the system is properly earthed at all times.
- The standards must always be erect, and the wires connected to the isolators on the standards.
- Ensure that the wires are always tight. This is done by connecting a wire strainer at the beginning of each main line. As soon as the wires begin to sag, the wire strainer is turned to tighten the wires.
- Remove or spray all grass and weeds directly beneath the wires with herbicide to ensure that no plants touch the wires and form an earth connection that will decrease the effectiveness of the fence.
The benefits of an electric fence are briefly as follows:
- Low material costs
- Simple and easy erection
- Permanent or portable fences are possible
- Can be used to strengthen or lengthen old permanent fences.
There are however a few disadvantages to electric fences, namely:
- Sheep must be taught to “respect” the fence.
- The electric wire’s effectiveness can decrease if the lines are not kept clean and the wire comes into contact with the grass and weeds.
- A home-made or nonapproved energy source and controller can be very dangerous.
Boundary fences for grazing camps and feedlots
Boundary fences are designed to keep sheep in and predators out. Barbless wire fences are therefore not recommended, since jackal and other animals can crawl through them. Woven or welded fences must preferably be erected.
The heights and construction of the fences can be as follows:
- Woven or welded wire fencing
1 200 mm high
- Woven or welded wire fencing
900 mm high with three or four barbed wires above them to a total height of 1 200 mm.
Fences for intensive holding facilities
Fences that are mainly used for ram pens and lambing pens must be sturdy enough to contain the animals in limited spaces. Steel construction fences or steel gates similar to those of handling facilities can be used. Alternatively, fences or gates consisting of steel frames and covered with a woven or welded wire covering can be erected.
Next month we shall look at slated floors, gates and wool handling equipment.
Published with acknowledgement to the ARC Agricultural Engineering for the use of their Sheep Facilities Manual. Visit www.arc.agric.za for more information.