A study of three composting barns on the West Coast looked at the effect of composting barns on cows, the environment and farm labour.
The study, Composting Mootels in a West Coast Context, was done with support from Our Land Our Water, Peak Agricultural Consultants, Rural Consulting and Agrifood Systems.
Speaking at a DairyNZ discussion about composting “mootels” in Invercargill, Peak Agricultural Consultants farm adviser Robb Macbeth said one of the key motivators for the farmers who took part in the study to start using composting barns was to secure and maintain environmental social licence.
Another driver was moving away from intensive winter grazing and minimising winter and spring pasture damage, Macbeth said.
None of the farmers were primarily driven by finances, Macbeth said.
The three farms that participated in the study were Prospect Farm, run by Murray and Gaye Coates; Mangawaro, run by Matt and Carmel O’Regan; and Turkey Creek, run by Tegel and Wendy Oats.
The study said it was expected that feed use would increase due to the ability to feed into dedicated feed lanes or troughs in all weather.
A DairyBase analysis showed a 12% increase of feed use at Prospect over three seasons from 2020 to 2023.
Mangawaro had a 26% increase and Turkey Creek a 7% increase in feed use over the same period.
Farmers expected an increase in pasture production “of between 1-2tDM/ha through reduced pugging pasture damage and improved utilisation”.
The study showed no clear increase in pasture harvested, but it was noted that the data was inconclusive and “further study is warranted”.
A financial analysis of the three farms showed total capital investment of between $3200/cow to $4000/cow, but this could be as high as $6000 per cow, depending on area per cow.
There was an estimated net increase in farm working expenses of between 12-22c/kgMS, predominantly from bedding costs.
Macbeth said a discounted flow analysis of the systems showed on average a farm had to lift production by 11% to cover the cost of a composting barn.
There were however significant savings made, with saving in winter crop costs and from pasture and supplementary feed use, he said.
The study showed “there will be significant savings from a feed utilisation perspective if moving from a winter crop system to a cut-and-carry system on the same land”.
Depreciation or operating capital will be the biggest cost increase, ranging from 14c/kg to 27c, depending on the farm.
Key benefits to the cows (from one season’s data) showed less heat stress, 2% to 3% lower death rates, a likely decrease in days in milk of up to 10 days and a likely increase in per-cow production of 10% to 5% and the ability to manage body condition score gain better.
There was no evidence of improvement in mastitis.
Macbeth said due to cows possibly lying in their own muck, there could be increased incidence of E coli mastitis, although none was reported.
There was also no evidence to date of an increased six-week in-calf-rate or evidence to date of effect on lameness.
Farmers who attended the DairyNZ discussion in Invercargill said they found feed utilisation surprisingly efficient, to such an extent that some cows grew fat very fast and they had to learn how much feed cows needed in a composting barn environment and that feed should therefore not just be ad lib available.
Foggy sites reported more moisture in the bedding, but there was no apparent odour or drainage observed from any of the three mootels. The study showed.
woodchip used for bedding cost around $22.50 to $30/m³.
Tilling woodchips is required as it aerates the woodchip and facilitates the aerobic composting process and moisture evaporation.
Farmers in the study used a range of tilling equipment and frequencies, with some tilling twice a day and some only once every two days.
At the DairyNZ event farmers said they experienced challenges when temperatures dropped and composting material stopped composting.
In such a case composting material often did not reach optimal temperature again to restart the composting process, they said.
Tilling wood chips was also not always effective, with some farmers at the discussion not able to lift bedding from the bottom half of the layer.
The study suggested a composting material temperature of 50degC to 60degC at 15cm to 30cm depth, with a dry matter content of x 50%.
The farmers in the study said none of the samples reached optimal temperatures.
This was echoed by farmers attending the Invercargill discussion.
Moisture in feed areas was a problem due to higher urine and dung content.
“Lower DM feeds such as pasture silage introduced a lot of moisture into the mootel during winter. Moving to a higher DM feed such as PKE or concentrates may lead to system creep and increased costs, particularly if it is replacing home-grown feed,” the study showed.
Macbeth said despite challenges, farmers who took part in the study “were pretty much sold” on composting barns and that “improvement in cow comfort” played a large role in this.
Farm workers are just as busy, but say they often more productive and enjoy work more, the study showed.
