Environmental Impact Assessment in Pig Production

by 5m Editor
23 May 2008, at 11:26am

DENMARK - A more efficient use of nitrogen on pig farms and pig feed with digestion-promoting qualities can help reduce the effect on the environment when farmers produce pigs, according to a PhD thesis from the Faculty of Agricultural Sciences.

Life cycle assessment (LCA) is a tool used to evaluate environmental effects.

In a PhD thesis from the Faculty of Agricultural Sciences, University of Aarhus, this tool is used to show that pig farms are the link in the pork production chain with the greatest environmental impact with regard to global warming, eutrophication (nutrient pollution) and acidification.

The thesis also proves that the production of fertilizer and feed contributes significantly to global warming, whereas the slaughterhouse and meat transport by ship do not affect the environment very much.

Laughing Gas the Villain

The largest contribution to global warming comes from laughing gas, which is primarily emitted from manure and denitrification of nitrate. The largest contribution to eutrophication and acidification comes from nitrate and ammonia, respectively.

"All these compounds contain nitrogen. An obvious way to improve pork’s environmental profile would therefore be to improve efficiency of nitrogen use on the pig farms and in the production of pig feed," says Randi Lundshøj Dalgaard, who is the author of the thesis.

Global Warming Can be Mitigated

She points out that it is possible to reduce potential global warming per kg pork by approximately five per cent.

This can be done by adding the digestive enzyme xylanase to the pig feed.

However, the enzyme has only a limited effect on the eutrophication potential.

The reduction of greenhouse gas emissions is primarily due to reduced feed uptake because with the addition of xylanase to the feed the pigs can digest their feed better and thus eat less at a given growth rate.

Biogas Reduces Greenhouse Gas Emissions

Separation of pig slurry into a liquid fraction and a fibre fraction or degassing slurry in a biogas plant after which the biogas is used for the production of heat and electricity was also studied in order to see if these processes reduced environmental impact.

"Even though slurry separation resulted in less slurry transport and less use of phosphorus fertilizer on the farm on the receiving end, the reduction in greenhouse gas emission was very limited compared to the amount of greenhouse gasses emitted from the other links in the pork production chain," Randi Lundshøj Dalgaard explains.

Producing biogas from slurry and using the energy to produce electricity and heat can, however, reduce greenhouse gas emission per kg pig significantly.

"On the other hand, production of biogas does not have the same potential for reducing the amount of phosphorus ending up in the fields on the pig farm as slurry separation has," she says.

Randi Lundshøj Dalgaard points out that there is a need for further development of methods to quantify emission of laughing gas and phosphorus as well as CO2 emission caused by changed land use in order to improve the quality of future life cycle assessments of agricultural products.

5m Editor