Grazing outside on impoverished soil? Measure the B12 chain first and steer smartly with clover pastures instead of supplementing blindly
When reducing nitrogen and extensifying dairy farming, a forgotten risk looms: too little cobalt in grass can interfere with B12 production in cows, resulting in less vitamin B12 in milk and meat. Ellen van Gijsel therefore advocates structural monitoring of cobalt in soil and functional B12 markers in cattle, including MMA measurements and regional milk B12 samples. Only then will nitrogen reduction, animal welfare and public health remain in balance.
You can reduce nitrogen, but safeguard public health at the same time: monitor cobalt in grass and B12 intake in cows
NETHERLANDS, Sept. 23, 2025
While The Hague steers for land-based dairy farming and lower stocking densities (such as 1.5 LU/ha in social farming areas), Ellen van Gijsel warns of a forgotten link: on cobalt-poor pastures, the cow's internal B12 factory can falter. Without targeted measurement and management, an unintended effect on B12 levels in milk and meat - the very foods from which Dutch people get their vitamin B12 - is imminent.
"Grazing outside is wonderful, but 'outside' does not guarantee cobalt in the grass. And simply supplementing to feed without checking whether B12 is actually being absorbed is gambling with public health," said Ellen van Gijsel.
Why this matters to public health
Vitamin B12 is essential for blood cell production and a properly functioning nervous system. Deficiency can lead to megaloblastic anemia, tingling, balance and memory disorders; permanent damage is possible with late treatment.
- B12 occurs naturally almost exclusively in animal foods (dairy, meat, fish, eggs).
- Enriched plant products and supplements also exist.
- According to recent food consumption surveys, the average intake in the Netherlands is adequate, but averages hide differences between groups.
So chain quality remains relevant - from soil to plate.
The chain in the cow: cobalt → rumen microbes → B12 → milk and meat
Only microorganisms make vitamin B12. It happens in the rumen, provided there is enough cobalt in the ration. With cobalt deficiency, rumen B12 production drops within days. Therefore, policy focuses on ensuring sufficient cobalt in the feed.
Adding B12 directly to feed usually works moderately well in ruminants because much of it is lost in the rumen. Supplementing cobalt is more effective: the rumen microbes can then produce B12 on their own.
Why 'just supplementing' is not enough
Serum B12 in cattle can appear misleadingly high due to inactive B12 analogues that some tests weigh in. Those who want to know if B12 is actually functioning are better off measuring methylmalonic acid (MMA) as a functional marker - possibly supplemented by milk B12 or liver status. In short: measure first, then guide.
Outdoor grazing on impoverished soil - and the role of clover pastures
Cobalt supply from grass fluctuates with soil type and pH. Liming (higher pH) decreases cobalt availability; light sandy soils and leaching increase the risk of low Co levels in the crop.
Clover and herb-rich pastures can improve micronutrient profiles and soil life, contributing to more robust sod. Still, a clover pasture is no guarantee: cobalt levels can be low there too. Therefore, monitor herbage-Co and make targeted adjustments via pH management, overseeding or Co-fertilization where necessary.
What we know about B12 in Dutch milk
Research shows that B12 concentrations in raw milk vary widely between farms and animals. That means management, feed and genetics make a difference. Nationwide monitoring of milk B12 therefore makes sense, especially as grazing and extensification increase.
Nitrogen policy and B12 monitoring: it can work together
Steering for fewer animals per acre and more grazing can reduce ammonia emissions. On cobalt-poor soils, however, extensification explicitly requires mineral and B12 monitoring so that emission reductions do not unintentionally affect nutritional value.
Three concrete calls (nationwide)
- Measure in the field as well as in the animal: determine herbage-Co per field and monitor in the barn MMA ± B12 in a representative group of animals as soon as feed or grazing intensity is altered.
- Steer for clover pastures, but evidence-based: overseed to clover/herbs and check if plasma or milk B12 improves; make targeted adjustments to pH and cobalt availability.
- Make chain monitoring public: conduct sampling of milk B12 by region, season and system, and publish trends so citizens can see that nitrogen reduction and nutritional quality can go hand in hand.
"A clover pasture is an opportunity to connect nature and nutrition. But even there, measurement is knowledge. Fewer cows per acre helps for nitrogen, provided we secure the cobalt and B12 chain at the same time."
