Milk fever remains one of the most well-known metabolic diseases in dairy cattle, yet it is far from solved. While clinical cases still occur on most farms, the larger — and often more costly — challenge lies beneath the surface: subclinical hypocalcemia.
That’s why transition cow management continues to be a critical focus for veterinarians and producers alike.
“If you have transition cow issues, you’re going to have metabolic issues. Cows aren’t going to come in and perform the way you think they should. You’re going to have repro issues. You’re going to see a whole host of effects,” Meghan Connelly says, research and technical director at Protekta and guest on the most recent episode of “The Bovine Vet Podcast”.
Against that backdrop, a growing number of nutritionists and veterinarians are turning to zeolite-based pre-fresh diets, a relatively new approach that is reshaping how the industry manages calcium metabolism during the transition period.
The Hidden Burden of Hypocalcemia in Dairy Cows
On most dairies, clinical milk fever rates fall between 1% and 5%, depending on herd management and nutrition strategies. Subclinical hypocalcemia, however, is far more prevalent, affecting an estimated 25% to 45% of cows in many herds.
Unlike clinical cases, subclinical hypocalcemia is difficult to detect — but no less important.
“Subclinical is where we can’t see it, but it’s happening. The cow has low blood calcium, but we can’t tell that she’s low. But that still has consequences for the cow. There’s all these different systems and calcium is such a critical mineral for all those systems. So many different diseases that are influenced by calcium status,” Connelly says.
Instead of obvious signs, these cows often present as subtle inefficiencies that compound over time. Reduced rumination, lower feed intake and increased rates of retained placenta, metritis and mastitis are all commonly linked to inadequate calcium status. These hidden cases can quietly erode both performance and profitability.
DCAD Diets: The Traditional Approach to Milk Fever Prevention
For decades, the primary strategy for preventing milk fever has been the negative DCAD (dietary cation-anion difference) diet, which works by inducing a mild metabolic acidosis that improves the cow’s responsiveness to parathyroid hormone (PTH).
“We feed different feed supplements that contain anions in order to drop urine pH. When urine pH drops, the system is primed for PTH to work and mobilize bone and help support calcium homeostasis when the cow calves,” Connelly says.
This approach is well validated and remains a cornerstone of transition cow nutrition. However, it comes with practical constraints that can limit its use, particularly in larger or more complex feeding systems.
Where DCAD can create friction:
- Requires consistent access to low-potassium forages
- Can reduce dry matter intake due to metabolic acidification
- Depends on monitoring tools such as urine pH
- Often still requires post-calving calcium supplementation
As operations scale and feed variability increases, these limitations have driven interest in alternative strategies that can deliver similar or improved outcomes with fewer constraints.
How Zeolite Works: A New Strategy for Hypocalcemia Management
Zeolite offers a fundamentally different approach to milk fever prevention, one that targets phosphorus rather than acid-base balance.
“When we feed a zeolite diet pre-fresh, we bind dietary phosphorus. The cow goes, ‘Oh, I better go get more phosphorus.’ The main storage for phosphorus is in the bone. When she mobilizes bone, she brings double the amount of calcium with it,” Connelly says, referencing the P:Ca ratio in bone.
By binding dietary phosphorus in the gastrointestinal tract, zeolite creates a mild, controlled drop in blood phosphorus. The cow responds by mobilizing bone reserves to restore balance. Because bone contains both phosphorus and calcium in a fixed ratio, this process results in a simultaneous release of calcium into circulation.
Unlike DCAD diets, which rely on parathyroid hormone sensitivity, zeolite operates through a separate pathway involving fibroblast growth factor-23, a hormone produced in bone cells that acts on the kidneys to regulate phosphate levels, and vitamin D metabolism. The outcome — improved calcium availability at calving — is similar, but the biological mechanism is distinct.
Why Zeolite Adoption Is Increasing on Dairy Farms
Although zeolite has only been available in the U.S. since 2017, adoption has accelerated rapidly, according to Connelly. Much of that momentum is driven by a combination of visible on-farm results and meaningful management advantages.
Producers implementing zeolite programs often report improved calcium status through the first 48 to 72 hours after calving, along with fewer clinical milk fever cases.
“If you go from having 30 down cows a month to four, that’s a pretty big change,” Connelly says, referencing the improvement she has seen on farms changing to zeolite.
Beyond clinical outcomes, zeolite introduces greater flexibility into ration formulation. Because it does not depend on lowering dietary potassium, producers can incorporate a wider range of forages — including haylage, rye and sorghum — that would typically be restricted in DCAD programs. This allows better use of homegrown feeds and can reduce reliance on purchased inputs.
Zeolite programs are also associated with reduced dependence on calcium supplementation after calving. With cows already mobilizing calcium effectively, the need for boluses and intravenous treatments often declines, lowering both labor and treatment costs.
Management simplicity is another advantage. Zeolite eliminates the need for urine pH monitoring and reduces the number of adjustments required in close-up groups. In addition, because it does not induce metabolic acidosis, it avoids the intake suppression sometimes observed with DCAD diets, helping support dry matter intake during a critical window.
Where Zeolite May Not Be the Best Fit
Despite its advantages, zeolite is not universally applicable. Its effectiveness depends heavily on overall diet composition, particularly phosphorus levels.
Situations where DCAD may still be the better fit:
- Diets high in phosphorus (e.g., distillers grains, canola meal)
- Operations with well-optimized DCAD programs already in place
- Systems where tight ration control supports consistent acidification
In high-phosphorus diets, zeolite may become saturated, allowing the absorption of the remaining free phosphorus, reducing its effectiveness and making DCAD the more reliable strategy.
A Technology Still Evolving and the Veterinarian’s Role
Compared to DCAD, which has decades of supporting research, zeolite remains a relatively new tool. Since its introduction in 2017, both research and field experience have rapidly expanded understanding of how best to implement it.
“We didn’t necessarily know everything about it when it came out. I like to say that we continue to learn in real time with this strategy,” Connelly says.
Advances in feeding guidelines, monitoring approaches and troubleshooting frameworks have already improved consistency across farms, and further refinement is expected as adoption continues.
As that evolution continues, veterinarians are playing an increasingly central role. Transition cow programs are becoming more nuanced, and selecting the right strategy requires more than simply choosing between DCAD and zeolite. It involves identifying herd-level challenges, interpreting blood calcium data and aligning protocols with nutrition and management realities on each operation.
Close collaboration between veterinarians, nutritionists and producers remains essential. No single approach fits every farm, and the most successful programs are those tailored to available feed resources, labor capacity and herd goals.
Zeolite is not a replacement for DCAD, it is an expansion of the milk fever management toolbox.
It represents a shift from priming calcium regulation through acidification to directly driving mineral mobilization through phosphorus control. For many dairies, that shift is delivering higher blood calcium, fewer clinical cases and simpler management during one of the most critical periods in the production cycle.
As the industry continues to refine its use, zeolite is quickly moving from a novel concept to a practical, field-proven strategy in transition cow nutrition.
To hear more from Connelly on using zeolite for the management of transition cows to avoid hypocalcemia, listen to the full conversation on the latest episode of “The Bovine Vet Podcast.”
