As we begin a new year, Irish dairy farmers are planning for spring calving. One area that deserves attention is the transition period the critical weeks before and after calving. This stage sets the tone for the entire lactation and poor management can lead to costly health issues and reduced milk yield.
Among the most significant challenges during this period is hypocalcaemia, commonly known as milk fever. While clinical cases are visible, subclinical hypocalcaemia often goes unnoticed (“ the iceberg effect”) yet it can trigger a cascade of metabolic disorders, including ketosis, displaced abomasum and retained placenta.
Eight major periparturient disorders have been strongly associated with milk fever, and researchers have quantified the risk using odds ratios (Curtis et al., 1983). In simple terms, a cow that develops milk fever is significantly more likely to suffer from other health issues. For example, she is 8.1 times more likely to develop mastitis and 8.9 times more likely to experience ketosis. The table below illustrates the increased risk for each condition:
| Disease | Odds Ratio |
| Dystocia All | 2.8 |
| Dystocia Assisted | 6.5 |
| Retained Fetal Placenta | 3.2 |
| Metritis | 1.7 |
| LDA | 3.4 |
| Foot Lameness | 2.8 |
| Ketosis | 8.9 |
| Mastitis | 8.1 |
| Coliform Mastitis | 9 |
These conditions not only compromise animal welfare but also have a direct impact on farm profitability through reduced milk yield, increased treatment costs, and higher culling rates.
To put this into perspective, achievable targets and alarm levels for these disorders have been established based on U.S. herd data (Caixeta & Omontese, 2021):
| Disease | Achievable Rate |
| Clinical hypocalcaemia | <2% |
| Displaced abomasum | <3% |
| Clinical ketosis | <2% |
| Subclinical ketosis | <15% |
| Retained placenta | <5% |
| Metritis | <10% |
| Mastitis | <1% |
Why Consider DCAD?
Dietary Cation-Anion Difference (DCAD) is a proven nutritional strategy to reduce milk fever risk. By adjusting the balance of positively charged cations (sodium, potassium) and negatively charged anions (chloride, sulphur) in the pre-calving diet, we can induce a mild metabolic acidosis. This primes the cow’s calcium mobilization system, improving blood calcium levels at calving and reducing disease risk.
Full DCAD programs aim for urine pH below 6.5, requiring precise formulation and regular monitoring. While effective, this approach can be complex and costly especially for block-calving herds during the busy winter housing period.
Partial DCAD – A Practical Alternative
Partial DCAD offers a middle ground. Instead of aggressively lowering urine pH, the goal is a moderate reduction from around 8.2 to 7–7.5. This still stimulates calcium mobilization without compromising dry matter intake (DMI) or adding excessive complexity.
Research shows that partial DCAD diets improve pre-calving DMI and maintain body condition score (BCS), while reducing the risk of clinical milk fever compared to standard diets. In one study, cows on partial DCAD consumed more feed pre-calving and maintained better BCS in early lactation than those on full DCAD or control diets. Milk yield and solids also improved slightly, supporting the case for this strategy on Irish farms.
How Does It Work?
Partial DCAD diets typically involve:
- Reducing dietary cations by limiting high-potassium forages (common in Irish silage).
- Adding anionic salts (chloride and sulphur sources) to lower DCAD moderately.
- Balancing minerals—adequate magnesium and phosphorus are essential for calcium homeostasis.
- Monitoring urine pH—target 7.0–7.5 for partial DCAD.
Unlike full DCAD, partial DCAD requires less frequent urine testing and lower inclusion rates of costly anionic salts, making it more farmer friendly.
Benefits Beyond Milk Fever
Hypocalcaemia is a gateway disease. Reducing its incidence lowers the risk of retained placenta, metritis, and mastitis. These production diseases impact fertility and milk yield. Improved calcium status also supports immune function, helping cows cope better during the stressful transition period.
Practical Steps for Implementation
- Forage Analysis – Test forage for mineral status. High-K silage increases milk fever risk.
- Mineral Supplementation – Ensure dry cow minerals include magnesium, phosphorus and Vitamin D.
- Diet Formulation – Work with your nutritionist to calculate DCAD and adjust the diet accordingly.
- Urine pH Monitoring – Sample 8–10 cows, 6–9 hours after feeding, at least 72 hours after diet changes.
- Target High-Risk Cows – Multiparous cows and late calvers are most susceptible.
Why Now?
Christmas is the perfect time to plan. With housing in full swing and calving just weeks away, reviewing your dry cow strategy now can prevent costly problems later. A proactive approach beats reactive treatments every time especially when labour is tight and margins are under pressure.
Bottom Line
Partial DCAD is not a silver bullet, but it’s a practical, cost-effective tool for Irish farms aiming to reduce milk fever and improve transition cow health. By making small adjustments now, you can protect herd performance and profitability in the year ahead.
Talk to your nutrition advisor today about implementing a partial DCAD strategy. A few simple changes this winter can make a big difference to calving success, milk yield, and herd health in 2026.
