Environmental benefits gained from feeding pigs peas and grains

Take-home message: Home-grown soya bean alternatives could reduce global warming potential of grower and finisher pigs by 20%. 

Using peas and beans as alternatives for soyabean meal in pig rations can reduce the global warming potential of grower and finisher pigs by about 20% if land-use change is incorporated into pigs' life-cycle analysis.

Scientists in Edinburgh and Newcastle compared the environmental impact arising from using typical soybean meal (SB)-based pig diets with diets where the major protein source is either faba beans or peas.

The UK’s most important source of protein in pig diets is SBM, which is primarily imported from Brazil and Argentina.

“There are increasing concerns about the environmental impact associated with soya production and its long term sustainability, particularly in relation to deforestation and conversion of rangelands to croplands,” said the Scottish Agricultural College’s Kairtsy Topp.

“In order to promote sustainable pig farming and reduce the environmental impact of the UK pig industry, there is a need to find viable home-grown protein sources as an alternative to SBM in pig diets,” she said, explaining the rationale behind her team’s work.

Life cycle analysis (LCA) methodology was used to estimate the global warming potential (GWP), acidification and eutrophication (a process where water bodies receive excess nutrients that stimulates an increase in biomass) per kilogramme of live weight gain (LWG). It was assumed that maximum inclusion rates for peas and faba beans were 30% and 20% replacing 55% and 100% of SBM in grower and finisher diets, respectively.

A pig growth model was used to determine the amount of starter, grower and finisher diet required to grow pigs from 20 to 120 kg. With the exception of SBM and pure amino acids, a rotation was designed that incorporated all crops required to produce the diets. It was been assumed that the slurry produced by the pig was returned to the crops.

“In the absence of land use change, global warming potential was the lowest for the pea diet,” said Dr Topp. “However, there was only 5% difference between the pea and the SBM diet. The soyabean meal diet has an appreciably higher global warming potential per kilogramme of live weight gain with land use change inclusion.”

With respect to the eutrophication potential, pea and SBM diets proved similar, with the faba bean diet being 7.7% higher than the pea diet. The acidification potential of the pea diet was the lowest, with the faba bean and SBM based diets being respectively 25% and 50% higher.

“The largest contributors to global warming potential per kilogramme of pig produced arise from crop growth (23%) and slurry management (24%),” said Dr Topp.

“Variation in LUC arises from country of soya origin and relative proportions of the crop planted on land that has recently been converted to croplands from either forests or rangelands. Consequently, the higher the proportion of SBM originating from sustainable sources, the lower the environmental benefits of using peas or faba beans.

“In addition, results will also be sensitive to the relative prices of SBM and soya oil as they were used to determine the economic allocation, global feedstuff prices, and the drive for alternative sources of energy,” she added.

Full details: Topp CFE, Houdijk JGM, Tarsitano D, Tolkamp BJ and Kyriazaki I: “Quantifying the environmental benefits of using home grown protein sources as alternatives to soyabeal meal in pig production through life cycle assessment.”

For further information contact: BSAS on 01314 454508