Wintering Under Cover in Canterbury – By Keith Woodford

The Wintering in Canterbury: Infrastructure & Forage Crops conference ran on Wednesday, 1 July 2026, in Ashburton.

Farmers, sharemilkers, and farm managers turned out for a day built around one thing: practical advice on wintering systems that actually hold up. Keith Woodford opened the day with a session on composting barns, and this is his presentation, section by section.

Keith Woodford

Keith Woodford has been promoting the potential of composting barns since 2017. Most of what he has learned has come from watching and working alongside farmers directly, then thinking through what he observed on farm. He is upfront that there is still no formal, structured R&D behind composting barns here in New Zealand, and that everyone working in this space, himself included, is still learning.

Keith Woodford website ➜ 

"There are no experts and we are all learners"
Keith Woodford
Keith Woodford
AgriFood Systems Ltd - kbwoodford@gmail.com

Why might we want our cows under cover in winter:

  • It might be for environmental issues and regulations
  • It might be for animal welfare
  • It might be for farmer wellbeing
  • It might be to increase feed efficiency
  • It might be to reduce labour
  • It might be to increase net income

Or it might be all of the above. We need to know why we are doing it.

There is only one type of barn that can meet all of these requirements:

It is a composting barn

  • All new barns must have soft bedding, either plant based or matting or sand. The days of wintering on wooden slats (e.g. a traditional herdhome) are behind us
  • Free stall barns are another option, but under seasonal calving the economics are highly constraining. Capital cost of free stall is likely to be at least $6000 per cow
  • Free-stall barns have a place for 12-month non-seasonal system-5 milking systems, but this is not the focus here
  • Matting over wooden slats is another option but lots of effluent to deal with

Composting barns have the potential to solve the effluent problem and to be exceptionally cow-friendly. But it has to be done right.

Everything that follows assumes:

  • The barn will be in Canterbury
  • It will involve composting
  • It will be used for wintering, probably 24/7
  • Plus late autumn to get the composting started (and other reasons)
  • It will be used for calving
  • And during big rain events
  • Possibly used as a feed pad throughout the year for say 2 hours per day

If farmers go for hoop structures then they need to be aware of the limitations:

  • Limited life
  • Some have been known to blow away
  • Air movement, evaporation and condensation can all be issues
  • Typically don’t have a venting system (but can have)

You have been warned!

Gable structures:

  • Long life (50 years +)
  • More expensive than hoop designs
  • Pitch of at least 18 degrees
  • Venting system in roof (1-2% of roof area, capped) [chimney effect, venturi effect]
  • Automated opening and shutting of the venting system is possible
  • Lots of other important issues that experienced composting barn builders understand

I will come back to some of those later.

Venturi Principle:

  • Why pitch is so important
  • There must be a narrowing of the area above the bedding
  • This speeds up the removal of the warm high-humidity air
  • The chimney (Venturi) effect
  • Most barns I have seen are deficient in regard to the Venturi effect
  • The Venturi effect does not work in a hoop barn unless there is a vent that also forces air compression

Composting barns are expensive so very careful justification is needed:

  • Capital costs of the system can be between $1500-$3000 per cow, or even more
  • In general, you get what you pay for
  • Flat site, closeness to existing facilities, effluent issues, avoiding unnecessary concrete, all come into it
  • The cost all depends…
  • Cost of the basic gable shed itself is likely to be no less than $200 per square metre of compost
  • Square metre measures need to be clear as to whether overhangs and any central laneway are included
  • There are some economies of scale

Loafing area per cow is critical:

  • But the necessary area per cow depends on all of shed design, hours of use, and compost management
  • Compost management is more complex than pasture management. It is crucial!
  • The cost of getting the required area wrong is very high
  • The necessary area can be anything from 5-10 square metres per cow
  • At 5 and even 6 metres per cow it is important that everything else is optimal
  • I have yet to meet a farmer who regrets having too many square metres per cow
  • Depth of bedding 40-80 mm

Basics of compost management:

  • Temperature and moisture management are the crucial variables
  • Temperature needs to be at least 50 degrees at 15-30 depth. This is not achieved in many NZ barns
  • Moisture must be less than 70%; 65% is a warning
  • Temperature and moisture interact
  • When things are going well its marvellous; but when things go wrong they can go wrong very quickly because of the temperature and moisture interaction
  • Plan on daily tilling. Equipment options
Willesden composting barn

Lignin and Bedding:

  • Lignin is what allows plant stems to stand upright
  • It is also essential to stop bedding turning to mush
  • All wood types should be OK — except perhaps macrocarpa
  • Leafy cuttings are not ideal
  • My preference is sawdust and wood shavings but some will favour fine woodchip
  • Freshly cut green timber will already be 50-55% moisture. To be avoided

Cereal stubbles:

  • These are low in lignin
  • Can be used in modest quantities
  • Also useful in emergencies
  • But cannot be the mainstay of the bedding
  • Maize stubble likely to be better than wheat
  • Can vary between plant varieties

Getting value from bedding:

  • You are buying carbon. You don’t want nitrogen
  • Initial carbon: nitrogen ratio [C:N] if wood-based likely to be of the order of 100:1
  • Aim is to not replace bedding until C:N ratio is about 15:1
  • Most farmers are replacing their bedding when the ratio is between 20:1 and 30:1. This is highly wasteful but is driven by high moisture levels
  • Buy bedding on a tonnage (not volume basis) and with known dry matter
  • Bedding is expensive. Aim should be to keep for multiple years, and dry out over summer
  • Compost is valuable depending primarily on its N and P content

Miscanthus:

  • I am a great fan of Miscanthus for bedding
  • BUT there is a technology to understand
  • It is reproduced by rhizomes. Seed is non-fertile
  • Rhizomes won’t sprout if they are allowed to dry!
  • Harvest green material once a year in early spring when nutrients apart from carbon are in the rhizomes
  • Low bulk density with transport implications [About 100 kg per cubic metre]
  • Miscanthus industry needs to develop
Composting barn in Canterbury

Ambient (air) temperatures in the barn:

  • Cows will be most happy if the temperatures are 10-15 degrees C. But they hate the wind
  • These temperatures also aid composting (relative to colder temperatures)
  • In Canterbury winters, you cannot maintain these temperatures without some form of retractable side walls to manage air movement. Can be shade cloth or similar
  • All American compost barns have side walls and they get much better stocking rates of the compost (cow hours per square and cubic metre) than we do

Feeding Systems:

  • I am a fan for silage
  • Silage at about 35% moisture will probably produce less urine than crops. But we need more data
  • Urine is the enemy of composting systems
  • Physical feed systems can be kept simple
  • Aim for feed utilisation is around 98%
  • Concrete is expensive
  • Feeding can be in-shed or out of shed. Both can work
  • Integrate with forage crops and wearables?

Barn Layout:

  • Central laneway? Maybe
  • Internal poles (apart from laneway)? Need depends on dimensions and materials. Risk when tilling
  • Pens? Try and organise so tilling runs are long
  • Everyone does it differently
  • Flooring can be impermeable clay or cement-stabilised shingle. Requires a consent
  • Try and avoid concrete in the barn — cows should stand on compost when feeding
  • Ensure necessary feed-face as all cows need feed access at the same time

Effluent:

  • The aim is to have no effluent – it should all go up to the sky
  • But things can go wrong
  • If cows are spending any time on concrete then there will be effluent
  • This is a good reason to minimise concrete in the barn itself
  • Impermeable flooring essential
  • Joining in to existing effluent system from the milking shed may be sufficient

Nitrogen leaching:

  • Composting barns are capable of smashing nitrogen leaching, particularly if used in late autumn as well as winter
  • It is all about eliminating the piddle patches

Monitoring:

  • Compost must be monitored and managed
  • Temperatures at say 6 points (high and low pressure points) should be measured weekly with a simple composting thermometer in winter at 15-30cm and recorded
  • Moisture also needs to be recorded weekly in winter. Samples can be dried in a microwave or sent to a lab or measured digitally
  • Monitoring is crucial

The sponge test for moisture (from USA):

  • A simplest hands-on test is to take a handful of compost from between 15-30cm into the bedding, and squeeze it in a gloved hand
  • If the moisture content is between 40%-60% it should react like a wet sponge staying compressed and releasing relatively little water
  • Will Bakx of Sonoma Compost has developed a system that refines the sponge test and classifies the moisture content into seven categories based on the effects of squeezing the compost
  • These ratings were confirmed as accurate by laboratory tests on the samples tested and the ratings may need adjusting when applied to compost from other sources and interpreted by another other individual. The article appeared in BioCycle, a composting journal published monthly by The JG Press, Inc. in Emmaus, PA.

Sponge Test Moisture Estimates (from USA):

  • Less than 40%. Compost too dry and does not form a ball when compressed and the hand is dry after discarding the material [Less than 40% not an issue for dairy]
  • 40-45%. The compost forms a ball when squeezed but does not remain in a ball when the hand is opened
  • 45-50%. A ball forms when the compost is compressed but it falls apart if tapped with the knuckle of the other hand
  • 50-55%. The ball of compost stays intact when tapped but no water is visible on the hands
  • 55-60%. The ball stays intact and sheen can be seen on the skin but no water droplets are produced
  • 60% upper limit. Some drops of water are released when the ball is squeezed and can be seen between the fingers
  • 65%. The compost is too wet with water running between the fingers when the compost is squeezed

We need NZ measures with our bedding materials

Animal Health:

  • There should be no particular health issues
  • A good barn will be warm in winter and acceptably cool in summer
  • Calving should be a dream — calve in barn then out to pasture
  • Transition feeding should be a non-event
  • If lactating cows are lying all day in the compost, particularly straight after calving, then E coli and related mastitis-causing bacteria could become an issue. Has been an issue in the Waikato on some farms
  • Solution is to keep the compost temperature high, and when replacing compost do a complete clean
  • I know of only one South Island farm that had a small outbreak of E coli. Best to avoid (see above) rather than solve!

Labour management:

  • If labour requirements go up then you are doing something wrong
  • It could be shed design or it could be management

Economics:

  • I am confident that well designed and managed barns can be an economic proposition in Canterbury and are a significant part of the way forward
  • Lack of structured R&D is very frustrating. I am trying to do something about that but it needs funds and I need help to find those funds!
Composting barn in Canterbury - Willesden Farms

Final comment: prospective barn farmers need to visit multiple farmers with barns

  • And then visit some more!
  • Farmers learn from farmers
  • Lack of structured R&D in NZ
  • Lots still to learn
  • But we do know enough to proceed with composting barns using existing knowledge

Thanks to Keith Woodford for letting us share this content, and for the years of work and research behind it.

Composting barns are still a young space in New Zealand, without much formal R&D to lean on, and farmers like the ones in that room in Ashburton are better off because Keith has put in the time to learn what works, share it plainly, and keep pushing for more structured research in the years ahead.

Wintering Under Cover in Canterbury

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