In production experiments, an increasing amount of clover grass protein was added to the feed for broilers and slaughter pigs as an alternative to soy protein, according to researchers from Aarhus University in Denmark.

Since 2016, a series of production experiments in broilers and slaughter pigs has been carried out in which an increasing amount of clover-grass protein products was added to feed rations, Aarhus said.

The experiments were conducted with a view to circular bioeconomy and the development of biorefined fresh clover grass intended as a replacement for other protein products such as soy, which often needs to be imported into Denmark and other European countries.

Researchers from Aarhus University’s departments of food, agroecology and animal science have examined how the change in feed composition may affect meat quality, and the results are available in a new report from DCA — Danish Center for Food & Agriculture.

Quality is crucial

In the broiler experiments, grass-clover protein products constituted 0%, 8%, 16% or 24% of the feed rations, respectively, while grass-clover protein products used in feed rations for slaughter pigs constituted 0%, 5%, 10% and 15%, respectively, Aarhus said.

However, the researchers noted a difference in the quality of the clover-grass protein product used in the feed for broilers and slaughter pigs. The protein product used for broilers contained 36% raw protein, whereas the product fed to slaughter pigs was 47% protein.

"The broiler experiment demonstrated that an allocation of more than 8% clover-grass protein resulted in poorer growth and reduced feed utilization. On the other hand, there was no difference in production results for slaughter pigs at an allocation of up to 15% clover-grass protein," said Margrethe Therkildsen, associate professor with the Aarhus department of food science. "This is probably due to the higher clover-grass protein concentration — and, thus, higher quality — in the slaughter pig feed."

Changed fat, vitamin contents

The experiments further demonstrated a change in the composition of the meat as a result of increasing the clover-grass protein in the feed rations, the university noted.

"We witnessed a change in the fatty acid composition for both broilers and slaughter pigs. The change was towards more n3 polyunsaturated fatty acids, which is positive from a nutritional perspective. The concentration of vitamins acting as antioxidants was reduced. Thus, we observed a lower concentration of, e.g., vitamin E in the meat at increased amounts of clover-grass protein. We expect this to be due to an increased consumption of antioxidants in the meat in order to inhibit oxidation of unsaturated fat," Therkildsen said.

No sensory changes

The report further includes results from an organic project with free-range broilers and slaughter pigs as well as results from peer-reviewed literature.

"No additional meat and eating quality analyses have been carried out in relation to broilers fed clover-grass protein, but experiments with free-range broilers given access to grass and herbs demonstrate the same change in fatty acid composition," Therkildsen explained. "However, there are no changes in oxidation or sensory perception of meat taste and aroma.

"Meat and eating quality of meat from slaughter pigs remain unaffected by increased amounts of clover-grass protein products. The results from free-range slaughter pigs support these findings, and we did not identify any effect of increased grass and herb intake on the taste and aroma of two examined muscles, cooked as pork chops and roast, respectively," she added.

Aarhus said the experimental results indicate that an allocation of refined clover-grass protein in feed for broilers and slaughter pigs constitutes a promising alternative to soy protein.

"We are able to identify a level at which major parts of, e.g., soy protein may be replaced by clover-grass protein products without affecting meat and eating quality. However, further studies should be accomplished in order to examine how much high-quality clover-grass protein should be added to broiler feed. At the same time, we need to study the level of vitamin E, or other antioxidants, to be added to both broiler and slaughter pig feed in order to avoid undesirable oxidation of the meat," Therkildsen concluded.