Milk fever, also known as hypocalcaemia, remains one of the most common and costly metabolic disorders affecting dairy cows around calving. While often associated with dramatic clinical cases where cows go down shortly after calving, the greater challenge on most farms is subclinical milk fever, which quietly reduces intake, milk yield, fertility and overall cow health.
Understanding why milk fever occurs, which cows are most at risk, and how nutrition and management can reduce incidence is essential for protecting performance during the transition period.
What Is Milk Fever?
Milk fever is caused by a sudden drop in blood calcium levels around calving. Calcium is essential for muscle function, nerve transmission, immune response and milk production. At calving, demand for calcium increases rapidly as colostrum and milk synthesis begin, often exceeding the cow’s ability to absorb calcium from the diet or mobilise it from bone reserves quickly enough.
When this imbalance occurs, blood calcium levels fall, leading to hypocalcaemia. Despite the name, milk fever is not associated with a fever, the condition is metabolic rather than infectious.
Milk fever can be classified as:
- Clinical milk fever, where cows show obvious signs such as weakness, muscle tremors and inability to stand
- Subclinical milk fever, where blood calcium is low but no visible symptoms are present
Subclinical cases are far more common and often go unnoticed, yet they can have a major impact on performance and disease risk.
Why Milk Fever Occurs Around Calving
The challenge with milk fever lies in the speed of calcium demand at calving. Blood calcium reserves are limited, so cows rely on hormonal systems to:
- Mobilise calcium from bone
- Increase calcium absorption from the intestine
These systems take time to activate. If they do not respond quickly enough, the cow enters a state of hypocalcaemia.
Several factors increase the likelihood of milk fever:
- Older cows, whose calcium mobilisation becomes less efficient with age
- High-yielding cows with greater calcium demand
- Dry cow diets high in potassium, which interfere with calcium regulation
- Excessive calcium intake pre-calving, which reduces the cow’s ability to adapt
- Inadequate magnesium, which is essential for calcium metabolism
Recognising the Signs of Milk Fever
Milk fever usually develops within 72 hours of calving, although subclinical cases may persist longer.
Early signs can include reduced appetite, stiffness and unsteady movement. As calcium levels drop further, cows may struggle to rise, show muscle tremors or adopt a characteristic curved neck posture. In severe cases, cows become recumbent and require urgent treatment.
Even when cows remain standing, low calcium levels reduce rumen motility and feed intake, increasing the risk of other transition disorders such as ketosis, retained placenta, displaced abomasum and mastitis.
Why Prevention Matters
Milk fever is often viewed as a single disease event around calving. In reality, it’s much more than that. Research has shown that when a cow develops milk fever, her risk of suffering from a whole range of other transition‑period disorders increases dramatically.
A landmark study by Curtis et al. back in 1983 quantified just how serious this risk is. Using odds ratios, the researchers demonstrated that cows with milk fever are far more likely to experience several major transition diseases compared with healthy cows.
How Much Does Milk Fever Increase Risk?
In simple terms, milk fever acts like a gateway disorder. Once calcium balance is disrupted, the cow’s muscle function, immune response and energy metabolism are compromised—setting off a chain reaction of health problems.
Here’s what the research found:
- Dystocia (all cases): 2.8× higher risk
- Assisted dystocia: 6.5× higher risk
- Retained fetal placenta: 3.2× higher risk
- Metritis: 1.7× higher risk
- Left displaced abomasum (LDA): 3.4× higher risk
- Foot lameness: 2.8× higher risk
- Ketosis: 8.9× higher risk
- Mastitis: 8.1× higher risk
- Coliform mastitis: 9× higher risk
To put that into perspective, a cow with milk fever is nearly nine times more likely to develop ketosis and over eight times more likely to suffer mastitis than a cow that maintains normal calcium levels at calving.
Why This Matters for Farm Performance
These disorders don’t occur in isolation—and they don’t just affect animal welfare. Each one carries a financial penalty through:
- Reduced milk yield
- Increased veterinary and treatment costs
- Poorer fertility and longer calving intervals
- Higher culling and replacement rates
Nutrition and Mineral Management to Reduce Milk Fever Risk
The Role of DCAD in Dry Cow Diets
Dietary Cation–Anion Difference (DCAD) is central to milk fever prevention. Feeding a slightly negative DCAD diet in the close-up dry period helps acidify the blood, improving the cow’s ability to mobilise calcium at calving.
High-potassium forages, which are common in many grass-based systems, raise DCAD and increase milk fever risk. Where these forages are unavoidable, targeted mineral supplementation becomes essential.
Using Pre-Calver Minerals to Support Calcium Mobilisation
Correctly formulated pre-calver minerals help support calcium metabolism, immune function and energy balance during the dry period and early lactation.
SN Dry Cow Supreme
SN Dry Cow Supreme is designed to meet the high nutritional demands of modern, high-yielding cows during the dry period. Its formulation supports DCAD management to reduce milk fever risk while also addressing broader metabolic challenges.
The inclusion of vitamin E supports immunity, while choline chloride and niacin help support liver function and reduce the risk of sub-clinical ketosis and fat accumulation in early lactation.
OptiMin Precalver
OptiMin Precalver ensures adequate supplementation of essential vitamins and trace minerals during the dry period. Magnesium and vitamin D3 play a key role in calcium mobilisation, while vitamin E helps cows cope with the metabolic stress of calving.
This product suits herds aiming for a balanced, preventative mineral approach in advance of calving.
SN Protected Precalver
SN Protected Precalver is formulated for use around calving and early lactation. High levels of magnesium and vitamin D3 support calcium regulation, while elevated vitamin E and protected selenium enhance immunity in both cow and calf.
The combination of protected and unprotected trace minerals ensures consistent availability, supporting fertility, calf vitality and resistance to metabolic disorders.
SN Dry Cow Special
SN Dry Cow Special is designed for herds facing elevated milk fever risk, particularly where potassium-rich forages are used. With a strongly negative DCAD, it supports calcium mobilisation even under challenging forage conditions.
Its formulation combines high vitamin inclusion, protected trace minerals and rumen-supporting ingredients to limit milk fever and associated metabolic diseases while preparing cows for the next lactation.
Management Practices That Support Prevention
Mineral nutrition works best when combined with strong transition management. Key considerations include:
- Maintaining consistent feeding routines
- Ensuring adequate feed space and fresh feed availability
- Minimising stress and unnecessary movement pre- and post-calving
- Monitoring body condition to avoid over-fat cows at calving
- Using forage analysis to fine-tune mineral balance
Close observation of older cows and high producers around calving allows early intervention before problems escalate.
The Link Between Milk Fever and Other Transition Disorders
Low blood calcium reduces rumen function and immune response, increasing the likelihood of:
- Ketosis
- Retained placenta
- Mastitis
- Displaced abomasum
- Reduced fertility
This highlights the importance of viewing milk fever prevention as part of a wider transition cow strategy rather than a single-issue problem.
Take Action to Minimise Milk Fever on Your Farm
Milk fever is a predictable challenge at calving, but with the right dry cow management and mineral strategy, the risk can be significantly reduced. Focusing on DCAD balance, calcium availability and strong intakes in the weeks before calving helps cows transition more smoothly into lactation and reduces the knock-on effects linked to hypocalcaemia.
Every herd is different, which is why a tailored approach to dry cow nutrition is so important. Getting mineral supplementation right before calving supports better cow health, stronger performance after calving and improved lifetime productivity.
Contact Specialist Nutrition today to discuss your dry cow and transition feeding programme and get practical, farm-specific advice to help minimise the risk of milk fever this spring.
