Overflow source of oxygen depletion: Silage juice from cattle farms suffocates life in small streams
Økologisk NuWhen silage juice and residual water run from the silage storage into drains and streams, it can lead to oxygen depletion and kill all life in the small watercourses. The problem is much more widespread than many believe, assesses environmental technician Sten Bøgild Frandsen from Kolding Municipality. This is reported by DM Bio. The juice from silage — which is preserved, juicy forage — contains so much easily degradable organic material that it has a biochemical oxygen demand of up to 50,000 mg/l. In other words, bacteria use 50,000 milligrams of oxygen per liter to break down the organic matter. For comparison, values in untreated wastewater are 200-300 mg/l. Thus, only small amounts of silage juice are needed for bacteria to deplete all the oxygen in the water, causing fish and small animals to flee or die. Kolding Municipality investigated in 2024 and 2025 the streams near 18 larger cattle farms at risk of silage juice runoff. In March 2024, pollution was detected from 11 of the farms. By January 2025, the number was 10. One farm was reported to the police because it had sprayed silage juice onto a water-saturated field with runoff into a stream. “The course of events suggests to me that even with close monitoring, it remains a problem — especially at cattle farms. In my opinion, it is a severely overlooked environmental issue across Jutland, where we have large cattle operations,” says Sten Bøgild Frandsen to DM Bio, explaining that undiluted silage juice can be more than 200 times more oxygen-consuming than untreated wastewater. The pollution mainly occurs during wet winters, when older or expanded silage storage facilities have outlets that cannot keep up. As a result, the juice runs into drains and further into streams. The rules are clear: silage juice and residual water must be collected. Few cases result in penalties Kolding is not alone. In an article in the trade magazine Vand & Jord, Ievgeniia Biletska, a master's student at Aalborg University, reports that she found pollution problems at 18 of 22 examined cattle farms in Hjørring Municipality. She concludes that these pollution issues are a recurring pattern and not isolated incidents. The Danish Sportsfishing Association has requested access to documents from 23 municipalities, mainly in Jutland. There are 308 recorded cases of pollution of streams with silage juice or manure from 2022 to 2025, including cases where the source was not identified. Less than ten percent of these cases resulted in police reports and/or fines. The association’s nature and environmental consultant, Torben Hansen, believes that most cases end with a warning, even when clear legal violations occur. He calls for more police reports and stricter penalties. Advisor: Exceptions, not the rule At Spiras, which advises farmers in Southern and Southern Jutland, CEO Nikolaj Schulz admits that silage juice can be a serious burden on watercourses. However, he does not believe the problem characterizes the industry: “When pollution occurs, it is serious and unacceptable. But it is important to distinguish between specific cases where practices, maintenance, or technical solutions have been inadequate, and a general characterization of the entire industry. In our view, these are exceptions — not a picture of the typical cattle farm,” he writes in an email to DM Bio. According to Nikolaj Schulz, access to documents in selected municipalities cannot prove the extent of the problem nationwide. And that few cases end with penalties is not necessarily a sign of lax enforcement, he believes. At Seges Innovation, they are aware of the problem but not its scope, says chief consultant Kristina Rasmussen to DM Bio. She points out that during very wet or frost-cold winters, it is almost impossible to spray the juice out. Therefore, good collection capacity is crucial. Both Seges, Ievgeniia Biletska, and Kolding Municipality emphasize closer cooperation between municipalities, advisors, and farmers as the way forward. Kolding Municipality is already in dialogue with environmental officials at Spiras.
When silage juice and residual water run from the silage storage into drains and streams, it can lead to oxygen depletion and kill all life in the small watercourses.
The problem is much more widespread than many believe, assesses environmental technician Sten Bøgild Frandsen from Kolding Municipality. This is reported by DM Bio.
The juice from silage — which is preserved, juicy roughage — contains so much easily degradable organic material that it has a biochemical oxygen demand of up to 50,000 mg/l. That is, bacteria use 50,000 milligrams of oxygen per liter to decompose the organic matter. For comparison, values in untreated wastewater are 200-300 mg/l.
Thus, only small amounts of silage juice are needed before bacteria have exhausted all the oxygen in the water, causing fish and small animals to flee or die.
Kolding Municipality investigated in 2024 and 2025 the streams near 18 larger cattle farms at risk of silage juice runoff. In March 2024, pollution was detected from 11 of the farms. In January 2025, the number was 10.
One farm was reported to the police because it had sprayed silage juice onto a water-saturated field with runoff into a stream.
"The course of events tells me that even if you keep a close eye, it is still a problem — especially at cattle farms. In my opinion, it is a severely overlooked environmental issue throughout Jutland, where we have large cattle operations," says Sten Bøgild Frandsen to DM Bio and explains that undiluted silage juice can be more than 200 times more oxygen-consuming than untreated wastewater.
The pollution mainly occurs during wet winters, where older or expanded silage storage facilities have outlets that cannot keep up. As a result, the juice runs into drains and further into watercourses. The rules are clear: silage juice and residual water must be collected.
Few cases end with penalties
Kolding is not alone. In an article in the trade magazine Vand & Jord, Ievgeniia Biletska, a master's student at Aalborg University, describes how she found pollution problems at 18 out of 22 investigated cattle farms in Hjørring Municipality. She concludes that the pollution is a recurring pattern and not isolated incidents.
Denmark's Sportsfisheries Association has requested access to case files from 23 municipalities, mainly in Jutland. Here, 308 cases of pollution of watercourses with silage juice or manure have been registered from 2022-2025, including cases where the source was not identified. Less than ten percent of the cases resulted in police reports and/or fines.
The association's nature and environmental consultant, Torben Hansen, believes that most cases end with a warning, even when there are clear legal violations. He calls for more police reports and harsher penalties.
Adviser: Exceptions, not the rule
At Spiras, which advises agriculture in Southern and Southern Jutland, political director Nikolaj Schulz admits that silage juice can be a serious burden on watercourses. However, he does not believe that the problem characterizes the industry:
"When pollution occurs, it is serious and unacceptable. But it is important to distinguish between specific cases where practices, maintenance, or technical solutions have been insufficient, and a general characterization of an entire industry. In our assessment, these are exceptions — not a picture of the typical cattle farm," he writes in an email to DM Bio.
According to Nikolaj Schulz, access to case files in selected municipalities cannot document the extent of the problem nationwide. And that few cases end with penalties is not necessarily a sign of lack of enforcement, he believes.
At Seges Innovation, they are aware of the problem but not its scope, says chief consultant Kristina Rasmussen to DM Bio. She points out that in very wet or frost-cold winters, it is almost impossible to spray the juice out. Therefore, good collection capacity is crucial.
Both Seges, Ievgeniia Biletska, and Kolding Municipality emphasize closer cooperation between municipalities, advisors, and farmers as the way forward. Kolding Municipality is already in dialogue with environmental officials at Spiras.