A new study from Aarhus University shows that fattening pigs do not need additional zinc in their feed when supplemented with the enzyme phytase.

This could have significant implications for both the environment and agriculture.

No need for extra zinc in the feed

Pigs weighing 30-110 kg that received only the amount of zinc naturally found in a feed mixture consisting of barley, wheat, rye, and soybean meal grew just as well as pigs that received extra zinc in their feed.

There were no signs of zinc deficiency in the pigs, which can cause skin problems (parakeratosis), diarrhea, and reduced feed intake.

Pigs that did not receive extra zinc had lower zinc levels in their blood, but this was still within a range with no risk of deficiency symptoms.

Zinc requirements are lower than the current levels used

Based on the study, researchers concluded that fattening pigs do not need as much zinc as is currently practiced. Typically, 70 mg of extra zinc per kg of feed is added, bringing the total content to approximately 100 mg/kg of feed. The permissible content according to EU legislation is 120 mg/kg of feed.

In the experiment, the researchers divided 90 pigs into three groups and fed them with different levels of zinc: One group received only the amount of zinc originating from the raw materials in the feed mixture, 31 mg per kg of feed. Another group received feed with an additional 40 mg of zinc, and a third group received feed with an additional 80 mg of zinc per kg of feed, which approximately corresponds to the level used in practice.

Across all supplementations, there was no significant difference in the productivity of the pigs, meaning that growth rate, feed intake, and feed utilization were similar in the three groups.

Phytase makes minerals available

The researchers emphasize that all feed mixtures were supplemented with the enzyme phytase, which is a common practice in Danish pig production, and this is presumably an important point.

Phytase can release minerals - including zinc - from the plant material present in the feed. This allows the animals to absorb them more easily and meet their needs, resulting in fewer minerals being excreted through manure into the environment.

“We have examined a feed mixture containing the raw materials common in Europe, where it is also standard to add phytase,” says Associate Professor Tina Skau Nielsen, the lead author of the scientific article recently published in the Canadian Journal of Animal Science.

“Thus, it is, of course, in this context that our results should be assessed,” she adds.

Should zinc allocation be reconsidered?

Another significant point is that all pigs in the study had their zinc needs met before the start of the experiment at 30 kg body weight.

This means they were provided more zinc immediately after weaning than the amount permitted for piglets since 2022.

"In a previous study, we showed that piglets' zinc requirements are around 1400 mg per kg of feed during the first 2 weeks post-weaning, which is far above the current allowed amount of 150 mg of zinc per kg of feed," says Tina Skau Nielsen.

"We chose this level, and the study was conducted before the new regulations were enacted."

Tina Skau Nielsen believes there should be a reconsideration of how zinc allocation standards are formulated.

"We have done some calculations; If the goal is to reduce the amount of zinc released into the environment, there is a significantly greater effect from reducing zinc content in feed for fattening pigs than in piglet feed. This is a political decision, and more follow-up studies are needed to change legislation at the EU level," she concludes.