Positive DCAD is not the target for close-up springer cows. A positive (high) DCAD diet (driven by excess sodium and potassium) pushes cows toward metabolic alkalosis, which reduces tissue responsiveness to parathyroid hormone (PTH) and impairs calcium mobilisation at calving. For pre-calving cows, a negative DCAD strategy is the commonly recommended, evidence-based approach to reduce milk fever risk. Good transition management means fewer down cows and a more successful calving season.
What does positive DCAD mean?
DCAD (dietary cation–anion difference) is a simple balance: (sodium + potassium) − (chloride + sulphate) expressed in mEq/kg. A positive DCAD means more cations (sodium, potassium) than anions (chloride, sulphate). In lactating rations, a positive DCAD supports milk yield. However, in pre- calving diets, positive DCAD works against calcium release.
Why is positive DCAD a problem before calving?
High sodium and potassium levels raise blood bicarbonate and push cows toward metabolic alkalosis. Alkalosis reduces the sensitivity of bone and kidney tissues to PTH, so when the sudden calcium demand arrives at calving, the cow cannot mobilise bone calcium or increase intestinal absorption quickly enough. The result is a higher risk of clinical and subclinical milk fever. If not well transitioned, subclinical milk fever can last up to 36 hours post-calving. This effectively reduces feed intake, lowers immunity, increases ketosis risk, and can also set the cow up for reproductive issues.
How does DCAD affect calcium mobilisation?
Negative DCAD creates mild metabolic acidosis, which increases renal calcium reabsorption and improves tissue responsiveness to parathyroid hormone (PTH). PTH primes the cow’s physiological systems to maintain blood calcium at calving. Conversely, positive DCAD (alkalosis) blunts those responses and delays recovery if hypocalcaemia occurs. This mechanism underpins why negative DCAD feeding before calving reduces milk fever incidence in many studies (see meta-analysis and extension resources below).
Why is negative DCAD used in springer cow diets?
Negative DCAD is used to prepare the cow’s own endocrine system (PTH and vitamin D pathways) to mobilise calcium efficiently at calving. In practice, nutritionists formulate close-up rations to target a slightly negative DCAD and deliver anionic salts or formulated transition products to achieve that balance without depressing intakes. Agvance’s negative DCAD transition products are designed to integrate into these rations and help deliver a consistent acidifying effect while maintaining appetite and nutrient supply.
Is positive DCAD ever useful?
Yes, a more positive DCAD supports high-producing cows after calving. The key is timing. Positive DCAD is appropriate for lactation rations but not for the 2–3 weeks before calving when calcium readiness is most important.
What makes New Zealand pasture a challenge?
Our pastures are often high in potassium, especially in spring, which pushes DCAD positive by default. High-potassium grazing makes it harder to achieve a negative DCAD without targeted supplementation or dietary changes. That’s why feed testing and deliberate ration planning are essential on Kiwi farms.
How can farmers check whether the diet is working?
The following monitoring is suitable for New Zealand farms:
- Feed testing and ration review to calculate DCAD and identify high- potassium sources.
- Milk fever and down-cow records to track outcomes.
- Fresh cow recovery and clinical observations post-calving.
- Vet-led blood calcium testing for objective assessment.
- Springer cow intake checks to ensure additives or anion mixes aren’t depressing appetite.
Note: Routine urine pH testing is common in some countries, but is not widely used in New Zealand; instead, rely on the practical measures above.
What about magnesium, feed choices and low-potassium options?
Magnesium supports PTH activity and should be included in close-up plans. Where possible, reduce high-potassium feeds (excessively clover-rich pasture, supplements) before calving or balance them with low-potassium feeds such as maize silage. Some crops (e.g., fodder beet) are low in phosphorus but may interact with mineral strategies; always test feeds and tailor plans to your system.
Where do Agvance’s negative DCAD products fit in a wider programme?
Agvance’s negative DCAD transition products are designed to reliably deliver the anion load when combined with ration planning, forage management and freshly-calved cow care. They help achieve the pre-calving acidification needed to protect calcium mobilisation without creating intake problems. Use them as part of a comprehensive transition management plan: test feeds, set DCAD targets with your nutrition advisor, monitor outcomes and adjust as needed.
Bottom line
Aim to reduce high potassium feeds, while maintaining good fibre levels in the diet, three weeks precalving. Target a controlled negative DCAD, backed by feed testing, magnesium support and practical monitoring, and use Agvance’s transition products as part of a planned springer cow strategy to reduce milk fever risk.
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