Quicker to slaughter and reduced carbon footprint

By the time a typical Irish pig leaves the farm at 118kg, it has been responsible for about 382kg of greenhouse gas emissions. That is 3.24kg of CO₂-equivalent for every kilogramme of live pig. The figure covers every stage up to the farm gate: growing the feed crops, including seed, fertiliser, sprays and machinery; drying or preserving the grain; producing and shipping imported soya, minerals and amino acids; milling the feed and transporting it; the energy used on the pig farm; and the slurry the pigs produce. A life cycle assessment (LCA) carried out at UCD shows that this figure can be cut by almost 10 per cent, through a change made in the grain store rather than the pig house.

Overlooked source of emissions

Irish wheat and barley are often harvested at about 18 per cent moisture, too damp to store without going mouldy. The standard practice is to run the grain through an energy-intensive dryer until the moisture falls to 14 per cent. This burns a considerable amount of fossil fuel, yet grain drying is rarely included when the carbon footprint of animal feed is calculated. The alternative is to treat the grain at harvest with a preservative based on propionic acid, an organic acid that pigs already produce naturally in their gut. The acid prevents mould from growing, and no drying is required.
Shane Maher, Nick Holden, Torres Sweeney, and John O’Doherty used LCA to compare the two approaches. LCA is an internationally standardised method for calculating the environmental impact of a product at every stage of its production. Their analysis followed Irish-grown wheat and barley from sowing through harvesting, preservation, milling and delivery to a commercial pig farm, where 80 sows and their offspring were followed from the start of pregnancy to slaughter.

Savings in the grain store
Preserving grain with acid rather than drying it cut the fossil fuel used in storage by 74-81 per cent. The carbon footprint of each tonne of grain fell by 15-18 per cent.

Savings in the pig
The larger gains came from the animals themselves. Pigs fed acid-preserved grain throughout their lives ate about the same amount each day as pigs on dried grain but grew noticeably faster. After 24 weeks, they weighed 127.7kg, compared with 117.6kg for pigs on dried grain, and their carcasses were about 8kg heavier. The preserved grain carried fewer moulds after storage, and the pigs that ate it digested more of their feed. At slaughter, about one fifth less of the nitrogen they ate was passing out in their manure. Faster growth meant these pigs reached slaughter weight up to 10 days sooner and needed less feed to get there. Because feed accounts for more than 60 per cent of the environmental impact and cost of pig production, that saving matters. With manure included, the carbon footprint came to 3.24kg of CO₂-equivalent per kilogramme of live pig on dried grain and 2.96kg on acid-preserved grain, a saving of about 33kg for a finished pig. The benefit was greatest when preserved grain was fed to both the sows and their offspring. The true saving is likely to be larger. The calculation assumes that manure emissions are the same in both groups, but pigs losing less nitrogen in their manure should produce slurry that gives off less nitrous oxide and ammonia.

What it means on the farm

For pig producers, the findings go beyond carbon. Pigs that reach slaughter weight up to ten days sooner free up finishing space earlier, and heavier carcasses at the same age mean more saleable meat from each pig. Better use of dietary nitrogen also matters for farms working within nitrates limits. For tillage farmers and grain merchants supplying the pig sector, acid treatment removes the need to dry feed grain, along with the fuel bill and the bottlenecks at the dryer in a wet harvest.

How the figures compare

Carbon footprints for pork are only comparable when calculated the same way: per kilogramme of live pig or of meat, with or without manure, and with or without emissions from clearing South American land for soya.

The first three rows are measured on the same basis: up to the farm gate, per kilogramme of live pig, with manure included. On that footing, both UCD results sit well below the Dutch national average, and pigs fed acid-preserved grain came in lowest of all. The Teagasc figures are expressed per kilogramme of pigmeat, so they are not directly comparable with the UCD results. Converted to a carcass basis, the UCD figure for dried grain would be about 4.3kg, still well below the Teagasc national average of 5.52kg. Much of that difference is likely to reflect herd performance.

The next step: replacing soya

The LCA shows where most of the remaining emissions arise. The finishing stage accounts for most of the footprint because that is when pigs eat the most. Within the feed, imported soya bean meal is responsible for 55per cent of the environmental impact.
The UCD group has already begun to tackle this. In a study published in Animal Feed Science and Technology in 2026, replacing soya bean meal with faba beans in finishing diets reduced global warming potential by 33-38 per cent. That opens a further opportunity for Irish tillage farmers to grow protein for the pig sector. Together, the studies point to a practical route for Irish pig farming: preserve cereals with acid instead of drying them, and replace part of the imported soya with home-grown protein. Better slurry storage and biogas would add further gains.

Ready to use now
Organic acid preservatives are already on the market and can be applied with standard equipment at harvest. The authors describe the approach as an immediately deployable strategy for reducing emissions from pig production.