Skip to content
Home / Blog / Composting Barns By The Numbers: My Takeaways From Ashburton

Composting Barns By The Numbers: My Takeaways From Ashburton

Wintering in Canterbury conference in Ashburton

I spent Wednesday at the Wintering in Canterbury conference in Ashburton, and if you’re weighing up a composting barn for your own place, there’s a fair bit here worth your time.

Keith Woodford opened by putting it plainly: under our seasonal system, only one barn type ticks the box on welfare, environment, labour and income at the same time, and that’s the composting barn.

Wooden slats and bare concrete herd homes are on the way out. New consents are heading in one direction, so it’s worth planning with that in mind rather than fighting it later.

Gable vs hoop: know what you’re actually buying

This is where I’d start if I were you. Hoop and tunnel barns are cheaper upfront, but you’re looking at a 10 to 12 year life, weaker air movement, and condensation problems that a lot of manufacturers still won’t fix with proper venting.

Gable roof barns cost more to build, but they’re built for 50 plus years. You need an 18 degree plus pitch and roof venting covering 1 to 2 percent of the roof area to get the chimney effect that actually pulls moisture out of the barn. Skip that and you’re just building a bigger version of the same problem.

I wasn’t the only builder in the room. Matt Hoyle from Aztech was there too, and between us there was a lot of practical, hard-won experience on the table for farmers to draw on.

Keith Woodford at Composting Barn event in Ashburton

The three numbers Keith says matter most:

If you take nothing else away from the whole day, Keith said make it these three:

  • 50°C plus. The compost temperature you want at 15 to 30cm depth
  • Under 70 percent. Your moisture ceiling, with 65 percent as the warning sign
  • 8m² per cow. The recommended area, with a working range of 5 to 10m²

Bedding carbon to nitrogen ratio should start around 100:1 and get replaced closer to 15:1. A lot of farmers are pulling bedding out far too early, around 20 to 30:1, and wasting money doing it.

If your compost smells sweet, you’re in good shape. Any hint of ammonia and your C:N ratio has blown out. As Keith put it, compost management is more complex than pasture management, and most farmers are giving it a fraction of the attention.

Composting barn

Bedding: what to use and what to steer clear of

Sawdust, wood shavings, and fine wood chip are your best options, and buy them on tonnage, not volume. Avoid macrocarpa, which is toxic, and fresh green timber, which starts out at 50 to 55 percent moisture before you’ve even begun. Miscanthus is a solid option too, but the rhizomes can’t dry out before planting and it needs harvesting in early spring rather than winter, or you’ll be re-fertilising every year.

The one health issue worth watching

E. coli mastitis has turned up in the Waikato where compost hasn’t been fully cleaned out between seasons, and it’s a nastier version than standard mastitis. Keep your compost temperature up and do a full clean-out between seasons. The South Island has only had one minor case so far, so we’re in a good position, but it pays to stay on top of it.

What farmers are actually seeing

This is the part that stuck with me most. One farmer is running 800 cows on just 200ha with a composting barn in place. Others reported roughly a 10x EBIT uplift compared with the previous land use, and a typical payback period of 5 to 6 years.

Feed use dropped by around 50 percent on lower-energy, higher-straw diets, simply because the cows aren’t burning energy staying warm or walking around outside. No pugging means more pasture gets harvested elsewhere on the farm too, which is a saving on top of the feed saving.

One farmer swapped steel for laminated wood beams in the barn structure and saved on cost, with the bonus that birds can’t perch on wood the way they do on steel. Less mess, less hassle.

Worth knowing before you go into a revaluation: valuers still don’t put much capital value on a barn itself. The return comes from what the barn lets you do differently on farm, not from the structure’s resale value.

And the one comment every farmer in that room agreed on: the cows love it. More than one mentioned trouble getting them to go back outside.

Hybrid Composting Barn - Creaming It

The bottom line

There’s no formal R&D programme behind composting barns yet, and there’s no single design or feed regime that suits everyone. But the farmers doing it well are seeing genuine gains in EBIT, feed efficiency, welfare, and environmental performance.

The advice from the room was consistent: visit a few farms, talk to more than one builder, and plan on 2 to 3 years to see the full economic benefit come through.
Under our seasonal system, only one barn type ticks the box on welfare, environment, labour and income at the same time, and that's the composting barn.
Keith Woodford
Keith Woodford
Leading authority on dairy infrastructure

Thanks to ALIL, MHV Water, SIDDC, Acton Farmers Irrigation Cooperative, BCI, and Rangitata South Irrigation for putting the day together. Events like this are how good information gets in front of the farmers who need it, and that matters when it comes to future-proofing farms across the region.

Jacob Judd

Let’s Price It Right

Get real numbers, not guesses.

We’ll show you the smartest way to build your composting barn: cost-efficient, practical, and built around your farm.

Related articles