Doc #43 — Fencing: Livestock Management Infrastructure Under Isolation

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RECOMMENDED ACTIONS

First weeks (Phase 1)

1. Inventory fencing material stocks at farm suppliers (Farmlands, PGG Wrightson, local rural merchants), hardware stores, and on-farm. Feed results into Doc #8 census.
2. Classify Gallagher and Tru-Test as critical manufacturing facilities. Secure staff, inventory, and production equipment.
3. Register fencing contractors and equipment in the skills and asset census (Doc #8).

First months (Phase 1)

4. Establish a fencing materials allocation system prioritising: repairs to failing productive fences; fencing for emergency cropping (Doc #76); critical boundary fencing (roads, waterways); then new subdivision for rotational grazing.
5. Coordinate with Pacific Steel (Doc #89) to prioritise fencing wire in the product mix.
6. Assess treated post stocks nationally and allocate to highest-priority needs.
7. Begin trials of alternative post treatments – charring, pine tar (Doc #102), hot linseed oil.

First year (Phase 1–2)

8. Establish a post supply programme using naturally durable timber species (Section 4).
9. Begin concrete post production (Doc #35) for permanent high-priority fencing.
10. Gallagher and Tru-Test to shift to simplified energiser designs using NZ-available components and lead-acid batteries (Doc #35).
11. Establish regional fencing training (Doc #157).
12. Begin live hedging plantings as a long-term supplement.

Ongoing (Phase 2+)

13. Monitor fence condition nationally and adjust wire production priorities.
14. Expand electric fencing coverage wherever grid power or batteries support it.
15. If trade develops, prioritise zinc, treatment chemicals, and battery components.

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ECONOMIC JUSTIFICATION

Fencing is the mechanism by which NZ manages pastoral livestock, which produces the majority of NZ’s food (Doc #74).

Without functional fencing: rotational grazing fails, reducing per-hectare production by an estimated 15–30%⁵; breeding control collapses; stock losses to roads, waterways, and overgrazing increase; and disease management breaks down because quarantine and treatment depend on the ability to hold and separate animals.

Electric fencing economics: Electric fencing uses approximately 70–90% less wire per kilometre than conventional fencing – 1–3 wires instead of 7–8.⁶ A kilometre of single-wire electric fence uses approximately 40–80 kg of wire versus 500–800 kg for 8-wire conventional.⁷ Where electric fencing can substitute for conventional, the same wire tonnage covers 5–10 times more fence line. This is the single most effective wire conservation measure available, and the case for expanding electric fencing coverage under isolation is strong wherever power sources exist.

Labour: NZ’s pre-event fencing workforce included an estimated 3,000–5,000 professional contractors plus farm staff.⁸ Basic farm fencing can be taught in days to weeks – this is one of the more accessible trade-training priorities (Doc #157). Construction requires approximately 15–40 person-hours per kilometre depending on terrain.⁹

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1. NZ’S FENCING SYSTEMS

1.1 Post-and-wire fencing

The standard NZ pastoral fence: timber posts at 4–10 metre intervals with horizontal high-tensile galvanised steel wires (typically 2.5 mm diameter) strained between them.¹⁰

• 7–8 wire sheep/cattle fence: The general-purpose fence. Wires spaced 100–250 mm, total height ~1,000 mm.
• 6–7 wire cattle fence: Wider spacing, sometimes supplemented with electrified wires.
• 10–12 wire deer fence: Taller (1,500–1,900 mm), closer-spaced, more material-intensive.¹¹

Intermediate supports are provided by battens (light timber or steel droppers at 3–5 m intervals). Strainer assemblies at ends and corners use heavy posts (150–200 mm diameter) with angled stays.

1.2 Electric fencing

Electric fencing delivers a short high-voltage, low-current pulse (4,000–10,000 V, 0.1–15 joules) through the wire once per second.¹² Animals learn avoidance from the shock, so the fence’s effectiveness depends on psychology, not physical strength. Key components: energiser, steel fence wire, insulators, and earth (ground) system.

Electric fencing is extensively adopted across NZ – the majority of dairy farms use it for paddock subdivision, and adoption is growing on sheep and beef properties.¹³ NZ’s moist climate provides good soil conductivity, favouring electric fence performance.

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2. WIRE SUPPLY AND ALLOCATION

Wire production is covered in the companion wire-drawing document (Doc #97). From a field fencing perspective, the key points:

Domestic production: NZ can produce fencing wire: Waikato ironsand to NZ Steel Glenbrook (Doc #89) to Pacific Steel Otahuhu (Doc #89). This is NZ’s most important agricultural manufacturing chain.

Galvanising constraint: Zinc is entirely imported. After zinc stocks are exhausted, ungalvanised wire corrodes in 5–15 years versus 20–40 years galvanised.¹⁴ This roughly doubles long-term replacement demand. Mitigation options (oil/tar coatings) are covered in Doc #97.

Allocation priorities when wire is rationed: (1) repairs to failing productive fences; (2) boundary fences on roads and waterways; (3) subdivision for rotational grazing; (4) new fencing on marginal land.

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3. FENCE MAINTENANCE AND LIFE EXTENSION

Every year of additional life from an existing fence is a year of wire production freed for other needs.

Wire: Regular re-tensioning prevents stock push-through and wire fatigue. Broken wires can be spliced with figure-eight knots or compression sleeves. Monitor galvanised fences approaching zinc exhaustion for priority replacement before unexpected failure.

Posts: Replace individual failed posts without rebuilding entire fences. Protect post bases: drainage gravel, tar or bitumen on the below-ground section, or concrete collars all extend life at low cost. Steel posts (star pickets, Y-posts) cannot be produced from NZ’s current steel-making infrastructure, which is configured for long products (rod, bar, reinforcing) rather than the rolled and formed sections used in steel fence posts.¹⁵ Maintain and reuse existing stocks.

Battens and stays: Easily replaced individually. Timber battens can be sawn from small-diameter NZ timber (Doc #97).

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4. FENCE POSTS: THE TIMBER TREATMENT CONSTRAINT

4.1 The problem

Standard NZ fence posts are CCA-treated radiata pine rounds, treated to H4 or H5 hazard class.¹⁶ CCA extends service life from 3–8 years (untreated) to 25–50+ years. All treatment chemicals (CCA salts, copper azole, boron) are imported. NZ uses an estimated 5–20 million posts per year.¹⁷ When treatment stocks are exhausted, untreated pine posts become a short-lived, high-turnover consumable.

4.2 Rationing treatment chemicals

Prioritise: (1) ground-contact structural posts for permanent boundaries, yards, bridges; (2) paddock posts in wet, high-decay regions (Waikato, Taranaki, Southland, West Coast); (3) lower priority for dry regions where durable species may serve; (4) do not treat battens or above-ground components.

4.3 Naturally durable timber species

Totara (Podocarpus totara): NZ’s traditional fence post timber. Heartwood lasts 30–60+ years untreated in ground contact – some posts survive a century.¹⁸ Supply is limited by slow growth, but existing farm totara (shelterbelts, bush remnants) should be identified for post production. Totara on private land can be harvested under the Forests Act 1949.¹⁹

Macrocarpa (Cupressus macrocarpa): Widely planted as shelterbelts across NZ. Heartwood lasts 15–30 years untreated.²⁰ Available in significant quantity on farmland. Sapwood is non-durable – only heartwood from larger-diameter trees should be used.

Other species: Black and red beech heartwood (10–20 years); eucalyptus species (E. globoidea, E. muelleriana) with durability comparable to macrocarpa; redwood (Sequoia sempervirens) in parts of the North Island.²¹

4.4 Alternative post treatments

Charring: Burning the post surface to 3–8 mm depth creates a decay-resistant charcoal layer. Free, requires no chemicals. Estimated 5–15 additional years in moderate conditions, though NZ-specific data is limited.²² This extends untreated pine life to roughly 8–23 years – an improvement, but well short of CCA-treated service life (25–50+ years). Charring is best understood as a low-cost partial mitigation, not a CCA replacement.

Pine tar: A byproduct of charcoal production (Doc #102), used as timber preservative in Scandinavia for centuries. Hot application penetrates the wood surface. Estimated 50–100% life extension over untreated pine, yielding roughly 5–16 years in ground contact.²³ Better than untreated pine, but still 40–70% shorter service life than CCA-treated posts. Requires periodic reapplication, adding ongoing labour cost.

Hot linseed oil: Water-resistant treatment. Linseed can be grown in Canterbury (Doc #102). Estimated 30–60% life extension over untreated pine (roughly 4–13 years in ground contact), well below CCA performance.²⁴ Requires heating oil to 80–120°C for penetration and periodic reapplication. The performance gap to CCA is larger than for charring or pine tar, making hot linseed oil best suited as a supplementary treatment in combination with charring rather than a standalone solution.

4.5 Non-timber alternatives

Concrete posts (Doc #89): Essentially permanent. Heavy (20–40 kg), labour-intensive to install. Suitable for permanent dairy lanes, yards, and road boundaries. Impractical for hill-country subdivision fencing.

Stone posts/walls: Permanent, requiring no manufactured materials. Practical only where surface stone is abundant (Central Otago schist country, volcanic regions). Heritage skills preservation (Doc #160) should document surviving stone-walling knowledge.²⁵

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5. ELECTRIC FENCING UNDER ISOLATION

5.1 Power sources

Mains (230V AC): Most reliable power source. Energiser consumption is low (10–50 watts).²⁶ Under the baseline grid assumption (Doc #67, Doc #75), mains power is the preferred option wherever available. Most NZ dairy farms have grid power at or near the homestead.

Battery (12V DC): For remote locations. A typical unit draws 100–500 mA, running a standard 80–100 Ah lead-acid battery for 1–4 weeks between charges.²⁷ Under recovery, battery supply transitions to NZ-produced lead-acid (Doc #35) – roughly 3–5 times heavier per unit of stored energy than lithium, with shorter cycle life (300–500 cycles versus 1,000+ for lithium), but adequate for fence energiser duty where weight is not a primary constraint.

Solar: Self-contained with integrated panel, controller, and battery. Panel degradation (~0.5–1% per year) means existing units remain functional for 15–25+ years.²⁸ The vulnerability is the charge controller – electronic components NZ cannot manufacture.

5.2 Energiser production under isolation

Gallagher and Tru-Test have the engineering knowledge to design energiser circuits but rely on imported electronic components.²⁹ Their simplification pathway:

Ignition coil energiser: An automotive ignition coil driven by a relay or simple switch – Gallagher’s original 1930s design. NZ has millions of ignition coils in vehicles. Performance is significantly degraded compared to modern energisers: uncontrolled pulse shape reduces fence-line reach (effective range roughly 3–10 km versus 20–50+ km for modern units), and battery drain is 2–5 times higher, requiring more frequent recharging.³⁰ Adequate for small paddock systems, not for long fence runs.

Capacitor-discharge energiser: A capacitor charged and discharged through a step-up transformer. Key components – high-voltage capacitors (1–10 microfarad, 400V+), thyristors or mechanical switches, and step-up transformers – can be salvaged from NZ’s stock of consumer electronics, appliances, and industrial equipment. Gallagher and Tru-Test could design simplified versions using NZ-wound transformers (requiring copper wire and ferrite or laminated iron cores) and recycled capacitors. The binding constraint is capacitor supply: electrolytic capacitors degrade in storage and salvaged units have uncertain remaining life.

Production would decline from thousands of units per year to hundreds, then dozens, as electronic component stocks deplete. The earlier simplified designs are adopted, the longer production continues.

5.3 Insulators

Porcelain: Extremely durable (indefinite life). NZ has raw materials (china clay, feldspar, silica sand) and ceramics capability.³¹ Porcelain fence insulators require mixing and forming clay, bisque firing at 900–1,000°C, glazing, and a final firing at 1,200–1,300°C – standard pottery practice, but dependent on kiln fuel (wood, coal, or gas) and a skilled ceramicist. Any established pottery or ceramics workshop with a high-temperature kiln could produce them.

Plastic: Current standard but degrades from UV in 5–15 years. Cannot be locally produced. Treat existing stocks as finite.

Improvised: Rubber hose sections, glass fragments, PVC pipe lengths. Significantly inferior to purpose-built insulators – higher leakage current reduces fence voltage, and UV and weather degrade improvised materials in 1–3 years versus 5–15 years for manufactured plastic or indefinitely for porcelain.³² Temporary expedients to keep systems operational while porcelain production is established.

5.4 Stock-type considerations

Cattle respect electric fencing well – a single live wire is often adequate for trained cattle, making them the easiest stock to fence under wire-constrained conditions.

Sheep require 4–5 electrified wires including coverage at lamb height (bottom 300 mm), making electric-only sheep fencing more complex but still feasible.

Deer require 5–6 electrified wires to 1.5+ metres. If wire supply is severely constrained, the fencing cost per kilogram of food produced from deer is significantly higher than for sheep or cattle – a trade-off the national agricultural framework (Doc #74) should address.

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6. ALTERNATIVE FENCING METHODS

6.1 Natural barriers

Waterways, steep terrain, and bluffs can be incorporated into paddock boundary design to reduce artificial fencing needs. Many NZ farms already use natural features as stock barriers.

6.2 Live hedging

Hedge-fencing was the primary stock containment method in Europe before wire. Several species suit NZ conditions:

Gorse (Ulex europaeus): Already ubiquitous in NZ. Established gorse hedges are impenetrable to cattle and sheep – thorny, fast-growing, nitrogen-fixing. The objection is its invasive vigour, but in a recovery context, managed gorse hedges are pragmatic. Can be shaped by cutting or traditional hedge-laying.³³

Hawthorn (Crataegus monogyna): The traditional British hedging plant. Dense, thorny, stock-proof when laid. Slower to establish (3–5 years) but more manageable than gorse.

Some native NZ species also form effective stock barriers: kānuka and mānuka establish as dense hedgerows in many NZ environments, and kiekie (Freycinetia banksii) forms impenetrable tangles in wetter conditions — these offer the additional advantage of serving as wildlife corridors and soil stabilisers.

Limitations: Hedges take 3–7 years to become stock-proof, occupy 1–3 metres of land width,³⁴ require periodic management (annual trimming or laying every 10–15 years), and do not contain deer. Live hedging is a long-term supplement, not a near-term replacement.

6.3 Post-and-rail and stone walls

Timber post-and-rail fencing uses 10–20 times more timber per kilometre than post-and-wire – suitable for yards, races, and horse paddocks but not practical at pastoral scale.³⁵ Stone walls are permanent and require no manufactured materials but are highly labour-intensive – a regional option where surface stone is abundant (Central Otago, volcanic regions).

7. CRITICAL UNCERTAINTIES / KEY RISKS

Uncertainty	Why It Matters	Resolution Method
Total NZ fence line length and condition	Determines wire replacement demand	National fencing assessment via Doc #8
Ungalvanised wire corrosion rates by region	Determines post-zinc replacement frequency	Field trials in representative NZ conditions
Timber treatment chemical stocks	Determines treated post production window	Inventory of treatment plants. Doc #8
Naturally durable timber availability	Post supply after treatment chemicals exhaust	Farm and forest timber inventory (totara, macrocarpa)
Energiser component stocks and life	Determines electric fencing system longevity	Gallagher/Tru-Test component inventory
Lead-acid battery production timeline	Battery-powered electric fencing viability	Doc #35 development programme
Wire rod supply from Glenbrook	Underpins all wire production	Doc #89 adaptation programme
Alternative post treatment effectiveness	Post life without CCA	Field trials under NZ soil conditions

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CROSS-REFERENCES

• Doc #8 — National Asset and Skills Census (fencing material inventory, contractor census)
• Doc #35 — Battery Management and Lead-Acid Production (electric fencing batteries)
• Doc #74 — Pastoral Farming Under Nuclear Winter (why fencing matters for food)
• Doc #76 — Emergency Crop Expansion (fencing for new cropping)
• Doc #89 — NZ Steel Glenbrook (wire rod supply)
• Doc #89 — Cement and Concrete (concrete fence posts)
• Doc #99 — Timber Processing (post and batten supply)
• Doc #102 — Charcoal Production (pine tar byproduct for post treatment)
• Doc #97 — Wire Drawing, Fencing Wire, and Nails (companion document: wire production)
• Doc #150 — Treaty of Waitangi and Māori Governance (Māori land tenure and fencing; requisition protocols for Māori freehold land; engagement framework)
• Doc #157 — Trade Training (fencing contractor training)
• Doc #160 — Heritage Skills Preservation (hedging, stone-walling; traditional boundary and timber knowledge)

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1. NZ livestock numbers from Statistics NZ Agricultural Production Statistics. Approximately 26 million sheep, 10 million cattle, 800,000 deer on ~9.2 million hectares. https://www.stats.govt.nz/topics/agriculture↩︎

2. No published figure for total NZ fence line exists. Estimate derived from ~55,000 farms averaging 40–90 km of fence, at 0.5–0.8 tonnes wire per km of conventional fence (mixed with electric fencing reducing the average). These are rough order-of-magnitude estimates.↩︎

3. Untreated radiata pine rated Class 4 (non-durable) under NZS 3602:2003. Service life in ground contact typically 3–8 years. See: NZS 3602:2003; Scion timber durability publications.↩︎

4. Gallagher Group Limited, Hamilton. Founded 1938 by Bill Gallagher Sr., originally using a car ignition coil to deter a horse. Now one of the world’s largest electric fencing manufacturers. Tru-Test Group, Auckland, also a major NZ-based manufacturer. See: https://www.gallagher.com/↩︎

5. Rotational vs. set-stocked grazing productivity: varies by species, climate, and management. The 15–30% estimate is based on NZ pastoral research. See: Hodgson, J. (1990), “Grazing Management: Science into Practice”; DairyNZ research.↩︎

6. Electric fences typically use 1–3 wires vs. 7–8 for conventional. See: Gallagher fencing guides; DairyNZ recommendations.↩︎

7. Wire mass per km: 2.5 mm diameter wire weighs ~38 kg/km. Eight wires plus stays, tie wire, and staples totals ~500–800 kg/km. Single electric wire: ~40–80 kg/km including earth return wire and lead-outs.↩︎

8. No precise published figure for NZ fencing contractors. Estimate based on ~55,000 farms and industry directory listings. The NZ Fencing Contractors Association may hold more accurate data.↩︎

9. Fencing labour: 15–40 person-hours/km on accessible terrain with mechanical post driving. Hill country: 50–100+ person-hours/km.↩︎

10. NZ fencing specifications from agricultural extension publications. See: Beef + Lamb NZ fencing guides; DairyNZ infrastructure publications.↩︎

11. Deer fencing: 10–12 wires or woven netting, 1.5–1.9 m height. See: Deer Industry NZ guidelines. https://www.deernz.org/↩︎

12. Electric fencing specifications from manufacturer guides. Typical output 4,000–10,000 V at 0.1–15 J. Battery units draw 100–500 mA continuous. See: Gallagher “Electric Fencing Manual.”↩︎

13. Electric fencing adoption data not precisely published but industry sources indicate majority dairy adoption and growing sheep/beef adoption. See: DairyNZ farm surveys.↩︎

14. Galvanised wire 20–40 years; ungalvanised 5–15 years in NZ pastoral conditions. See Doc #74 footnote 6; BRANZ corrosion data. https://www.branz.co.nz/↩︎

15. NZ Steel Glenbrook and Pacific Steel Otahuhu produce steel slab, rod, bar, and reinforcing products. Steel fence post profiles (star pickets, Y-posts) require rolling mills configured for light formed sections, which NZ does not currently operate. See: Doc #89; NZ Steel product range.↩︎

16. NZS 3640:2003 specifies timber treatment requirements. H4 = ground contact; H5 = ground contact, critical. CCA has been the dominant treatment for decades.↩︎

17. Fence post consumption estimate from total network size, post spacing (4–10 m), and 2–5% annual replacement rate. Wide uncertainty.↩︎

18. Totara (Podocarpus totara) heartwood rated Class 1 (highly durable) under NZS 3602. Posts commonly last 30–60+ years; some documented over a century.↩︎

19. Totara on private land (outside DOC conservation areas) can be harvested under the Forests Act 1949, subject to conditions. See: MPI indigenous forestry provisions.↩︎

20. Macrocarpa (Cupressus macrocarpa) heartwood rated Class 2 (durable) under NZS 3602. Posts last ~15–30 years untreated. Sapwood non-durable. See: Scion, “Properties of New Zealand Timbers.”↩︎

21. NZ beech heartwood Class 3 (moderately durable), NZS 3602. Eucalyptus species (E. globoidea, E. muelleriana) rated Class 1–2 in Australian standards. See: Bootle, K.R., “Wood in Australia.”↩︎

22. Charring (shou sugi ban): Japanese technique, centuries of use. NZ-specific ground-contact data limited. The 5–15 year estimate is extrapolated from Japanese and European experience.↩︎

23. Pine tar (Stockholm tar): Scandinavian tradition. Preservative action from moisture exclusion and phenolic compounds. See: Reunanen, M. et al., “Composition of tar and pitch from wood,” Holzforschung.↩︎

24. Hot linseed oil as a timber preservative: water-resistance mechanism based on polymerisation of unsaturated fatty acids in the wood surface. Performance data limited for ground-contact applications in NZ soils. The 30–60% life extension estimate is extrapolated from European exterior timber treatment experience. See: Treu, A. et al., “Wood protection with linseed oil – review,” Wood Material Science & Engineering, 2020.↩︎

25. Stone walls present in Central Otago (local schist), built by early settlers. See: Central Otago heritage publications.↩︎

26. Mains energiser power consumption from manufacturer specifications. Gallagher mains units range from approximately 10 W (small garden units) to 50 W (large farm units powering 100+ km of fence). See: Gallagher product specifications.↩︎

27. Electric fencing specifications from manufacturer guides. Typical output 4,000–10,000 V at 0.1–15 J. Battery units draw 100–500 mA continuous. See: Gallagher “Electric Fencing Manual.”↩︎

28. Solar panel degradation ~0.5–1% per year. See: Jordan, D.C. and Kurtz, S.R., “Photovoltaic Degradation Rates,” Progress in Photovoltaics, 2013.↩︎

29. Gallagher Group Limited, Hamilton. Founded 1938 by Bill Gallagher Sr., originally using a car ignition coil to deter a horse. Now one of the world’s largest electric fencing manufacturers. Tru-Test Group, Auckland, also a major NZ-based manufacturer. See: https://www.gallagher.com/↩︎

30. Ignition coil energiser performance: original Gallagher designs powered single-paddock systems of a few kilometres. Modern capacitor-discharge energisers achieve 20–50+ km effective range through controlled pulse timing and impedance matching. Battery drain comparison based on continuous relay switching (ignition coil) versus timed thyristor discharge (modern). See: Gallagher company history; Gallagher “Electric Fencing Manual.”↩︎

31. NZ kaolin deposits located in Northland and the West Coast (South Island). NZ has established ceramics capability including high-temperature kilns. Historical NZ porcelain power-line insulator production documented. See: GNS Science mineral resource publications; NZ ceramics industry records.↩︎

32. Improvised insulator performance: rubber and PVC degrade from UV exposure and ozone, losing insulating properties. Leakage current across degraded insulators can reduce fence voltage by 30–60% over the affected section. Purpose-built plastic insulators use UV-stabilised polymers. See: Gallagher “Electric Fencing Manual”; general electrical insulation references.↩︎

33. Gorse hedging documented in NZ colonial agricultural history. Hedge-laying: see Brooks, A. and Adcock, S., “Hedging: A Practical Handbook,” BTCV.↩︎

34. Hedge width and establishment time from British hedgerow management literature. A stock-proof managed hedge typically occupies 1–3 m at the base including maintenance access. See: Brooks, A. and Adcock, S., “Hedging: A Practical Handbook,” BTCV; Defra hedge management guides.↩︎

35. Post-and-rail uses ~0.15–0.25 m3 timber/metre vs. ~0.01–0.02 m3/metre for post-and-wire (excluding wire). Ratio roughly 10–20:1.↩︎