The phrase "environmental pig" will soon have a new, positive ring to it following a study from the Faculty of Agricultural Sciences, Aarhus University, in which the pigs ranged in paddocks with energy crops. [Photo: Janne Hansen]

It is almost like camping in Denmark’s great outdoors. At night they sleep in outdoor huts and during the day they explore the surrounding forest. Outdoor pigs that range in areas planted with energy willow and Miscanthus may give a new, positive meaning to the phrase "environmental pig".

For several weeks during the spring, pigs at the Faculty of Agricultural Sciences, Aarhus University, have ranged freely in a mini forest of energy crops so the scientists could observe how the pigs react when they have free access to the plants and if they damage the plants in any way.

"It was a positive experience, says scientist Anne Grete Kongsted from the Department of Agroecology and Environment at the faculty.

"The concept benefits both the pigs, the environment and the farmer," she says.

Active outdoor life

Wandering about in a forest of energy willow or Miscanthus provided the pigs with lots of stimulation. They spent a great deal of their time exploring, rooting, digging and poking their snouts into the soil. The results have been more or less weed-free plots with crops that have managed to make it through without any serious damage.

The pigs’ active efforts may actually also be seen to be beneficial to the plants. The study shows that the pigs use the planted area to defecate. In this way the plants receive “free” nutrients and this benefits their growth. At the same time, the plants ensure that the nutrients, which could otherwise have gone to waste, and, in the worst case, have damaged the environment, are absorbed.

The plants also contribute to the mutual setup by providing shade and shelter for the pigs. The plants also improve the working conditions for the farmer because they absorb rainwater.

"Wet and muddy fields can be a problem in outdoor pig farming, especially during the winter and especially on clay soils. The energy plants have a very high water uptake so they contribute to keeping the fields nice and dry," says Anne Grete Kongsted.

The plants pulled through

The scientists have also kept an eye on how the plants have fared.

It went best with energy willow. The pigs munched the roots, shoots, and leaves a bit and there was also a bit of damage to the bark but not enough to damage the plants seriously. The pigs were, however, rather rough on the Miscanthus and ate the new shoots. There should probably not be pigs ranging in the grass right after it has been harvested, when there are new, delicate shoots.

On the whole, pigs should not be let out in the willow before it is a year old and well-established.

There is a difference in the impact of the pigs on the plants, depending in part on how many pigs are in the plots. Finding the optimal stocking density is one of the goals of the study because at the end of the day the results will be used on organic pig farms. The study will be repeated at the end of the summer and again next on commercial organic pig farms on a larger scale and with lactating sows.

"The study has gone surprisingly well. We feared the worst – that they would knock over the plants and dig up all the roots – but that has not happened," says senior scientist Uffe Jørgensen from the Department of Agroecology and Environment.

Miscanthus and willow are grown as climate-friendly crops that benefit the environment. The study indicates that the combination of outdoor pigs and energy crops can be a win-win situation in which the environmental impact of outdoor pig farming is reduced and the pigs are offered an interesting and stimulating environment.