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Green protein is good for pigs

Experiments carried out at Aarhus University in Foulum demonstrate that green protein extracted from clover grass is a very useful diet for pigs. This applies to both pig welfare, growth, feed utilization as well as meat quality and taste.

[Translate to English:] De tre foderblandinger + kontrol (t.v.), som testes i forsøget, hvor kløvergræsprotein udgør en stigende del af foderets råprotein. Jo mørkere farve - jo højere indhold af kløvergræsprotein i foderblandingen. Foto: Linda S. Sørensen
[Translate to English:] De tre foderblandinger + kontrol (t.v.), som testes i forsøget, hvor kløvergræsprotein udgør en stigende del af foderets råprotein. Jo mørkere farve - jo højere indhold af kløvergræsprotein i foderblandingen. Foto: Linda S. Sørensen
[Translate to English:] Grise i forsøget. Foto: Linda S. Sørensen
[Translate to English:] Grise i forsøget. Foto: Linda S. Sørensen


Within the framework of the project (funded by the Green Demonstration and Development Programme) SuperGrassPork, researchers from Department of Animal Science at AU Foulum have carried out a feeding experiment in organic pigs, which were fed compound feed with protein extracted from clover grass.

The project purpose was to examine the effect achieved when part of the traditional protein – typically soya – was replaced by protein extracted from locally produced clover grass. The experiment was accomplished as a dosage-response trial, and the research results demonstrate that the pigs are doing fine with up to 15 percent grass protein in their feed rations.

”Our results are very positive, as the use of protein extracted from clover grass possesses a huge potential in several areas. Firstly, it will secure the supply of locally grown protein for the increasing production of organic pigs in Denmark; and secondly, the cultivation of grass will increase productivity in the fields and – at the same time – contribute to reduce nitrogen leaching and pesticide consumption”, says Lene Stødkilde, Researcher at Department of Animal Science at Aarhus University.  

Extraction of protein from clover grass

The clover grass protein was extracted at a minor biorefining plant at AU Foulum. In 2019, a major demonstration plant was built for the extraction of grass protein, which makes it possible to supply feed for more extensive feeding experiments in the future. Further, the plant will contribute to the continued optimization of technologies and biorefining processes as well as generate more knowledge on costs related to this type of plant.

The feeding experiment

During the feeding project at AU Foulum, 48 pigs (ranging from the age of 6 weeks and until slaughter) were divided into four groups, which were fed the following three types of feed with different amounts of grass protein as well as a control feed with no clover grass protein:

·        Control

·        5% clover grass protein

·        10% clover grass protein

·        15% clover grass protein (Danish raw materials only)

The percentages listed above is the amount of protein included in the feed based on weight. For the feed with 15 % clover grass protein, this means that the clover grass content actually constitutes 41 % of the raw protein content of the feed. The feeds were generally composed based on existing compound feeds used in practice when feeding organic slaughter pigs. The main ingredients comprised barley, wheat, Chinese soya cakes, peas, broad beans and clover grass protein (in the experimental feed).

Excellent growth for all experimental compound feeds

The results from the feeding experiment demonstrate that the pigs were thriving equally on all types of feeds, as there were no difference as to pigs’ weight, growth, feed intake and feed utilization. This means that feed taste did not affect the pigs’ inclination to eat the feed, and the nutrients were utilized equally for all feed types. In addition, no health problems were observed for any of the groups during the experiment.

High grass protein content yielded a higher meat percentage

Regarding the meat percentage after slaughter, the results showed that the group of pigs that were fed 15 % clover grass protein had a significantly higher meat percentage compared to the other groups. The higher meat percentage may be because grass protein has a slightly higher digestibility and a more optimal amino acid composition than the researchers expected.

”The more grass protein we add, the more optimum amino acid composition we will achieve”, says Lene Stødkilde, and she adds: “In other words, we cannot rule out that the pigs in the 15 % feed group were fed more digestible protein and more essential amino acids than we aimed for when we composed the feed mixtures. However, this is good news for our feeds, as a higher digestibility implies that less grass protein is needed in feed in order to achieve an excellent growth and meat percentage”.

More omega-3 fatty acids in the meat

The researchers also examined the fatty acid composition of the meat, and the results demonstrate that the more clover grass protein added to the feed, the higher is the omega 3 fatty acid content of the meat. All four groups displayed the same percentage of unsaturated fat, and thus only the relation between omega-3 and omega 6-fatty acids changes in favour of the content of omega-3 fatty acids.

”From a health perspective, it is good that the meat has a higher content of the useful omega-3 fatty acids. At the same time, we are not interested in too many unsaturated fatty acids as this may increase rancidification. Therefore, additional antioxidants have been added to the feed in the form of vitamin E in order to prevent increased oxidation and thus rancidification”, says Lene Stødkilde.

No difference in texture or taste

There are no differences as to taste whether pigs are fed green protein or not. The experiment was completed in the spring of 2019, and – in cooperation with Danish Crown – a taste event was held including an “informal” blind tasting of the meat from the experiment. None of the participants were able to see or taste any differences, a fact that was subsequently confirmed by a professional tasting panel.

The results thus demonstrated that pigs may easily be fed grass protein. “And it is very positive that we are able to produce ordinary pork based on locally produced grass protein without compromising with quality and taste. The next step will be an optimization of biorefining processes in order to ensure a considerable and stable protein yield of the highest quality, as well as a calculation of costs before we implement this”, says Lene Stødkilde.

More about the SuperGrassPork project

The SuperGrassPork project runs in the period 2017-2020. The project is funded by the Green Development and Demonstration Programme (GUDP) and is coordinated by ICROFS. SEGES is project manager, and in addition to the departments of Animal Science, Agroecology and Engineering at Aarhus University, project participants further include Aarhus University, University of Copenhagen, Friland A/S, Vestjyllands Andel and Institute for Food Studies & Agro Industrial Development (IFAU).

Read more about the project SuperGrassPork.


Further information

Lene Stødkilde, Department of Animal Science, Aarhus University
E-mail: lsj@anis.au.dk