In the new era of accounting for carbon and greenhouse gas emissions, composting cows can help create a closed loop waste system with multiple benefits to the farm business.
Cows can be composted and soil is a disposal mechanism for fatalities — that was the message at recent on-farm workshops where the mechanics of how to compost cows were discussed and demonstrated.
As knackery and rendering facilities have declined in many parts of Australia, the question of what to do with dead livestock has become an issue for the farmer to resolve.
Composting dead animals is an alternative to leaving the cow on the ground in the paddock, where it attracts carrion eaters, or dumping it in waterways, which is illegal in some states.
Ash and Lisa Mezenberg have been composting cows for more than 10 years and hosted one of the workshops on their dairy farm at Denison, in south-eastern Victoria.
“Into the compost piles we add silage waste, calf bedding, green waste and the solids from the dairy effluent pond,” Ash said.
“We don’t waste anything on the farm.”
Ash uses chicken manure for the nitrogen, and sawdust, hay and straw for the carbon component, ensuring the dead cow is tucked up well under the pile.
“The animal has to be cooked up quick,” Ash said.
“Like any composting process, you have to have a carbon and a nitrogen in it, and moisture, to help make the cow decompose.
“We use chicken manure which helps break the cow down in a few weeks. The big bones and heads have become soft by then.”
Ash also designed and built his own turning machine, which he begins using at the week four point.
“Once it’s cooked up, I turn it over every four weeks,” he said.
“That’s when you can add the silage waste, calf bedding, green waste and effluent.
“I normally let a compost pile sit for six months before I spread it. If you can’t pick it up in your hands, it’s not ready.
“After spreading it in the paddock, there’s three weeks to wait before the cows can graze that pasture.”
Since using cow compost on their farm, Ash and Lisa haven’t purchased urea or nitrogen fertilisers.
The workshops were organised by Dairy Australia and the plain message was that a cow is organic matter and when cows and calves die on the farm — so long as death is not the result of a serious disease — the body can be composted and the resultant matter spread on paddocks.
Declan McDonald, a soil scientist with a demonstrated history of working in agriculture and horticulture, led discussions with local farmers from the Gippsland and Bega Valley districts.
“A cow is a big lump of organic matter,” Declan said.
“The organisms in the soil want organic matter to improve soil health and biology, structure and function.”
Declan recommended choosing a site that could be used regularly and won’t leach liquids, then choosing the other ingredients to decompose with the cow.
In particular, run-off from the compost pile during a rain event should be directed to an effluent pond, or a vegetative filtering area, reducing the likely impact on any nearby waterways and into groundwater.
The base of the compost pile should be deep and requires considerable quantities of dry carbon material. Woodchips or sawdust from a sawmill, or out of the calf rearing pens, were options discussed.
“Bulk density is an important component for creating organic matter in soils,” Declan said.
“The healthier the system, the faster that organic matter is turning over. What you’re doing is mixing together nutrient rich green matter, or nitrogen — the cow — with brown matter, a source of carbon — such as woodchips.”
Enough nitrogen by volume will drive organism activity to decompose the cow.
“There are two approaches to making a compost pile,” Declan said.
The layering approach uses cows. The mixing approach is more applicable to small animals — calves, chickens, lambs.
In the first stage, the pile is left undisturbed while the soft tissue decomposes and bones begin to soften. This may take several months.
“So long as the cow is covered well enough, there shouldn’t be a smell and scavengers shouldn’t be attracted to the pile,” Declan said.
The compost can then be turned, using a tractor with bucket, or another bespoke piece of machinery.
Turning the compost leads into the second stage, which is when the larger bones break down further.
The first and second stages are typical for creating high temperatures within the compost pile. High temperatures help eliminate nuisance odours, pathogens (disease-causing organisms) and weed seeds.
“The material below the cow will build moisture as the animal decomposes,” Declan said.
“So you want to use material that will enable air flow — oxygen in, carbon dioxide out.”
In the third stage, the composting process is completed during a curing phase, after the soft tissue and smaller bones are completely decomposed.
The pile can be turned and watered to complete the composting process. Curing is completed as the pile cools down in the sixth or seventh month. After which it is ready for use.
Declan said livestock could be added to the compost pile during the stages. At the end of six or so months, when the compost is ready for spreading on paddocks, any remaining large bone fragments can be retained on the pile, ready for the next composting session.
Obviously, if the animal dies from an unknown cause and/or shows symptoms of an emergency disease, this must be notified to a registered veterinarian, or the appropriate authorities. In those cases, the animal cannot be composted until authorities approve.
Note also that compost material from livestock carcases is classified as restricted animal material (RAM). It is illegal to feed RAM to ruminants or allow them to access a stockpile of material containing RAM.
Where compost containing RAM is spread as fertiliser on a pasture paddock used to graze ruminant animals, the livestock should be kept out of the paddock until there has been sufficient pasture growth to absorb the compost.
In good growing conditions, the grazing withholding period is 21 days.
Dairy Australia has resources available that explain the composting process.