Tuesday 9 February 2021Liquid Feed - The Key to a Greener Future for Pig Farming?

Published in the Pig World Magazine 

Martin Barker, National Pig Specialist at Duynie Feeds, explains why he believes liquid feed isn’t just better for the environment, but is the route to net-zero carbon use in pig systems.

Whatever kind of pig feed you choose, only about 60% of its energy goes into the production of meat. The remaining 40% is wasted through excretion, heat loss and gas production. But by choosing feed carefully and applying innovative thinking, there are ways to harness and exploit this lost 40%.

Heat capture

Wasteful heat production accounts for around 20% of feed energy. Most traditional pig housing lacks adequate insulation to prevent thermal gain in summer and thermal loss in winter. That means over-heated pigs with suppressed appetites in summer and the need for increased winter rations to keep stock warm. Both scenarios are inefficient.

Warming or cooling rations to balance seasonal thermal variations improves efficiency and can be environmentally friendly if done using heat energy generated by the pigs. Heat is relatively simple to capture. Normally it’s expelled along with stale air through ventilation systems, which cost money to operate. If warm air is instead run through a simple heat exchanger, it can be used to cool or warm water. You don’t need anything too sophisticated – a plastic feed trough with a pond pump and net curtain will work as components. Piped water from the system can then be used to warm and cool feed. Choosing liquid feed makes sense, as it’s far easier to change the temperature of liquids rather than dry concentrates.

Exploiting slurry

Pigs that eat liquid feed inevitably produce more slurry than their dry-fed counterparts. This can have environmental benefits if the slurry is processed. While slurry is most often exploited as fertiliser, it can also yield water and ammonia.

Water sustainability is vital when you’re striving for net zero. There are several off-the-shelf systems available to harvest and process water from slurry. It’s even possible to use heat from pigs to evaporate the water before condensing it back to drinking water.

Ammonia – and hydrogen – can also be harvested from pig waste without complex or costly systems. “The Green Pig Project 2018 at Coventry University, funded by Innovate UK, calculated the hydrogen in ammonia at around £20 per finished pig. That’s £600 per sow per year. It was the first hydrogen to be fossil fuel free. And if used to power machinery for crop cultivation, it really starts to deliver environmental benefits”, said Duynie’s Martin Barker.

Big players such as New Holland and Toyota have developed technology that uses ammonia as a hydrogen source to power fuel cells. As yet, most ammonia comes from fossil fuels and the potential of more environmentally friendly ammonia harvested from pig slurry hasn’t been realised. For cars, tractors and aircraft, ammonia is less volatile than gasoline, so is safer to use.

Reducing carbon

By feeding a 50/50 mix of dry feeds and liquid co-products, it’s possible to reduce carbon use by 33%. It cuts land-use by half, freeing up area for tree planting and kick-starting a virtuous circle.  

Low-carbon pig production is likely to attract a premium on both meat and fuel in the near future, increasing the income streams from pigs fed on low-carbon liquid feeds. Growth relies on liquid feeds like potato peelings, citrus pulp and whey being made more available. If government, retailers and processors see the opportunity, they can use it as an opportunity to meet the carbon-reduction targets they’re signing up for.

As Mr Barker observes, “By nourishing humans and powering machinery, pig farming could rank among the greenest systems on the planet.”


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