Periparturient hypocalcemia (also known as milk fever or parturient paresis) is a metabolic disorder of adult dairy cattle characterized by acute hypocalcemia occurring at or soon after parturition.
Overview and Clinical Importance
Periparturient hypocalcemia (also known as milk fever or parturient paresis) is a metabolic disorder of adult dairy cattle characterized by acute hypocalcemia occurring at or soon after parturition. This condition represents one of the most economically significant metabolic diseases in dairy cattle, with clinical incidence ranging from 5-10% of cows calving, though subclinical hypocalcemia affects approximately 50% of multiparous cows. Understanding the pathophysiology, clinical presentation, treatment, and prevention of this condition is essential for NAVLE success and clinical practice.
The term "milk fever" is a misnomer as the disease does not cause elevated body temperature. In fact, affected cows are typically hypothermic in advanced stages. The condition occurs because calcium demand for colostrum and milk production dramatically exceeds the cow's ability to mobilize calcium from bone stores and absorb it from the diet.
| Mechanism |
Explanation |
| Metabolic Alkalosis |
High dietary potassium and positive DCAD diets induce metabolic alkalosis, which reduces tissue responsiveness to PTH and impairs bone calcium mobilization |
| Vitamin D Receptor Decline |
Intestinal vitamin D receptor numbers decrease with age and decrease precipitously at parturition, reducing calcium absorption efficiency |
| Inactive Bone Remodeling |
High calcium diets prepartum suppress PTH and osteoclast activity, leaving bone unprepared to rapidly mobilize calcium at calving |
| Age-Related Changes |
Older cows have reduced osteoclast populations, decreased vitamin D receptor density, and slower intestinal calcium absorption adaptation |
| Hypomagnesemia |
Low magnesium impairs PTH secretion and reduces tissue responsiveness to PTH, compounding hypocalcemia |
Calcium Homeostasis in Dairy Cattle
Normal Calcium Regulation
Calcium homeostasis is maintained through the coordinated actions of three primary hormones acting on three target organs. The normal plasma calcium concentration in cattle is 8.5-10.5 mg/dL (2.1-2.6 mmol/L). Approximately 50% of serum calcium is ionized (biologically active), with the remainder bound to proteins (primarily albumin) or complexed with anions.
Key Hormones
Parathyroid Hormone (PTH): Released by parathyroid glands in response to decreased serum calcium. PTH increases calcium by: stimulating bone resorption (osteoclast activation), increasing renal calcium reabsorption in the distal tubule, and stimulating renal 1-alpha-hydroxylase to convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D3.
1,25-Dihydroxyvitamin D3 (Calcitriol): The active form of vitamin D increases intestinal calcium absorption through upregulation of calcium-binding proteins and transporters, enhances bone resorption synergistically with PTH, and increases renal calcium reabsorption.
Calcitonin: Released by thyroid C-cells in response to hypercalcemia. Calcitonin inhibits osteoclast activity and decreases bone resorption, though its physiological role in cattle is less significant than PTH and vitamin D.
High-YieldRemember the "3 B's" of PTH action: Bone (resorption), Bowel (indirectly via vitamin D activation), and (renal tu)Bule (calcium reabsorption). PTH raises calcium; calcitonin lowers it ("Calci-TONE-it-DOWN").
| Classification |
Serum Calcium |
Clinical Significance |
| Normocalcemia |
Greater than 8.5 mg/dL (greater than 2.14 mmol/L) |
Normal calcium status; no clinical signs |
| Subclinical Hypocalcemia |
5.5-8.5 mg/dL (1.38-2.14 mmol/L) |
No obvious clinical signs but increases risk of other periparturient diseases; affects up to 50% of multiparous cows |
| Clinical Hypocalcemia (Milk Fever) |
Less than 5.5 mg/dL (less than 1.38 mmol/L) |
Clinical signs present; progresses through 3 stages; affects approximately 5% of dairy cows |
Pathophysiology of Periparturient Hypocalcemia
Calcium Demands at Parturition
During the dry period, a cow requires approximately 30 g of calcium per day for fetal growth and maintenance. At the onset of lactation, this requirement increases dramatically to 50-80 g per day for colostrum and milk production. A single 10-liter production of colostrum contains approximately 23 g of calcium, which represents nearly the entire circulating calcium pool of the cow (the plasma pool contains only 3-4 g of calcium).
Why Homeostatic Mechanisms Fail
Most cows experience some degree of hypocalcemia around calving, but those that develop clinical milk fever have a more profound and prolonged decrease in blood calcium. Research has demonstrated that milk fever is NOT primarily due to inadequate PTH or vitamin D production in most cases. Instead, it results from tissue resistance to these hormones (a state of "pseudohypoparathyroidism").
Key Pathophysiological Mechanisms
NAVLE TipWhen a question asks WHY high-calcium prepartum diets increase milk fever risk, remember: High Ca suppresses PTH, which keeps osteoclasts "dormant." At calving, these cows cannot rapidly mobilize bone calcium because their osteoclasts are inactive. Think: "If you don't use it, you lose it!"
| Stage |
Clinical Signs |
Pathophysiology |
| Stage 1 (Excitation) |
Cow is ambulatory but shows hypersensitivity and excitability
Fine muscle tremors over flanks and triceps
Ear twitching, head bobbing
Mild ataxia, stiff gait
Anorexia, restlessness |
Initial hypocalcemia causes neuronal hyperexcitability due to decreased threshold potential for sodium channel opening; this stage is often missed |
| Stage 2 (Recumbency) |
Sternal recumbency (unable to rise)
Characteristic S-shaped neck (head turned toward flank)
Depression, obtunded mentation
Cold extremities, dry muzzle
Subnormal temperature (36.5-38 degrees C)
Tachycardia (80 bpm) with weak pulse
Decreased heart sounds
Rumen atony, bloat
Decreased defecation and urination |
Progressive hypocalcemia blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis; smooth muscle paralysis affects GI and cardiovascular function |
| Stage 3 (Coma) |
Lateral recumbency (cannot maintain sternal)
Complete flaccid paralysis
Severe depression to coma
Marked hypothermia
Irregular, weak pulse; severe tachycardia
Dilated, unresponsive pupils
Severe bloat
Death within hours if untreated |
Severe hypocalcemia causes circulatory collapse and CNS depression; without treatment, 60-80% mortality rate |
Clinical vs. Subclinical Hypocalcemia
| Risk Factor |
Clinical Significance |
| Increasing Age/Parity |
Risk increases approximately 9% per lactation; first-calf heifers rarely affected; most common in 3rd lactation and beyond |
| Breed |
Jersey and Guernsey (Channel Island breeds) at highest risk due to fewer vitamin D receptors; Holsteins commonly affected due to high milk production |
| High Milk Production |
Greater calcium demand in high producers; colostrum yield is a key driver of hypocalcemia |
| High Prepartum Calcium Diet |
Suppresses PTH and calcium homeostatic mechanisms; bones are unprepared for rapid calcium mobilization |
| High DCAD (Positive) |
High potassium forages induce metabolic alkalosis, reducing tissue responsiveness to PTH |
| Over-conditioned (BCS greater than 4.0) |
4.3 times higher risk of becoming recumbent; fat cows have reduced dry matter intake and exacerbated metabolic stress |
| Previous Milk Fever |
History of clinical hypocalcemia significantly increases risk at subsequent calvings |
| Hypomagnesemia |
Low magnesium impairs PTH secretion and tissue responsiveness; always consider concurrent magnesium status |
Clinical Stages of Milk Fever
Clinical milk fever typically occurs within 72 hours of calving, with most cases occurring within 24 hours before to 48 hours after parturition. The disease progresses through three distinct stages if untreated:
High-YieldRemember the stages with "EST": Stage 1 = Excited/Standing, Stage 2 = Sternal (down but chest up), Stage 3 = Terminal/Total down (lateral). The S-shaped neck in Stage 2 is pathognomonic - if you see a recently calved cow with her head turned toward her flank, think milk fever first!
| Associated Condition |
Odds Ratio (Increased Risk) |
| Ketosis |
5.5x more likely |
| Metritis |
4.3x more likely |
| Displaced Abomasum |
3.7x more likely |
| Retained Placenta |
3.4x more likely |
| Mastitis |
8.1x more likely (clinical hypocalcemia) |
| Dystocia |
6.5x more likely (clinical hypocalcemia) |
Risk Factors and Breed Predispositions
Major Risk Factors
| Stage |
Recommended Treatment |
Rationale |
| Stage 1 (Standing) |
Oral calcium supplementation only
Calcium chloride or calcium sulfate boluses (40-55 g elemental Ca)
Acidogenic sources preferred |
Oral Ca rapidly absorbed without risk of hypercalcemia; stimulates natural homeostatic mechanisms; IV calcium not recommended for standing cows |
| Stage 2-3 (Recumbent) |
IV calcium borogluconate (STANDARD)
500 mL of 23% solution provides 10.7 g Ca
Dose: 2 g Ca per 100 kg BW
Rate: 1 g/minute with cardiac monitoring
Follow with oral Ca to prevent relapse |
IV provides rapid correction; cardiac monitoring essential as hypercalcemia can cause fatal arrhythmias; warm solution before administration; SC calcium can supplement but slower onset |
Consequences of Subclinical Hypocalcemia
Subclinical hypocalcemia (SCH) is often called the "gateway disease" because it predisposes cows to multiple other periparturient disorders. Research demonstrates that cows with SCH have significantly increased odds of developing secondary diseases:
NAVLE TipThe mechanism behind these associations: Calcium is essential for smooth muscle contraction (uterus, abomasum, teat sphincter), immune cell function (neutrophil chemotaxis and phagocytosis), and appetite regulation. Remember: "Calcium keeps things moving and fighting!" Low calcium = uterine atony (retained placenta, metritis), GI atony (displaced abomasum, decreased DMI leading to ketosis), and impaired immunity (mastitis).
| Parameter |
Target Value |
| Target DCAD |
-100 to -200 mEq/kg DM (optimal around -100) |
| Urine pH (Holsteins) |
6.0-6.8 (target 6.2-6.5) |
| Urine pH (Jerseys) |
5.5-6.0 (more acidification needed) |
| Duration of feeding |
Minimum 10 days, preferably 21 days prepartum |
| Expected milk fever reduction |
From 16% to 3% (5-fold reduction) |
Diagnosis
Clinical Diagnosis
Diagnosis is typically based on clinical signs combined with history of recent calving. The combination of a recently calved cow (especially multiparous, high-producing) presenting with sternal recumbency, characteristic S-shaped neck posture, hypothermia, and depression is highly suggestive of milk fever.
Laboratory Confirmation
- Serum total calcium: Less than 5.5 mg/dL (less than 1.38 mmol/L) in clinical cases
- Ionized calcium: More accurate but requires specialized equipment
- Concurrent findings: Hypophosphatemia and hypomagnesemia common
- Hematology: Neutrophilia, lymphopenia, eosinopenia (stress leukogram)
- Sulkowitch test: Field test using urine - absence of white precipitate indicates hypocalcemia (calcium normally excreted in urine)
Differential Diagnosis
For recumbent periparturient cows, consider: Downer cow syndrome (post-milk fever muscle/nerve damage), obturator/sciatic nerve paralysis (dystocia), hip dislocation or femoral fracture, toxic mastitis (coliform), acute toxic metritis, severe ketosis, hypomagnesemia (grass tetany - more excitable presentation), and acute carbohydrate engorgement.
| Strategy |
Application and Notes |
| Low Calcium Prepartum Diet |
Less than 20 g available Ca/day; difficult to achieve in practice; "primes" PTH and bone remodeling; less commonly used than DCAD |
| Low Potassium Forages |
Use corn silage over legume hay; reduce K fertilizer on pastures; K is the main driver of positive DCAD in typical dairy diets |
| Oral Calcium at Calving |
Prophylactic calcium boluses (40-50 g Ca) at calving and 12-24 hours later for high-risk cows; acidogenic sources (CaCl2, CaSO4) preferred |
| Adequate Magnesium |
0.4% dietary Mg in close-up period; Mg essential for PTH secretion and action |
| Avoid IV Ca Prophylaxis |
NOT recommended - causes hypercalcemia followed by rebound hypocalcemia; prophylactic IV Ca at calving increases risk |
Treatment
Treatment by Clinical Stage
Critical Treatment Considerations
- Calcium borogluconate is preferred over calcium gluconate due to improved solubility and over calcium chloride due to severe tissue necrosis if given perivascularly
- Cardiac auscultation during IV administration: Slow or stop if arrhythmias develop (transient bradycardia, irregular rhythm)
- Relapse rate is 25-30%: Hypercalcemia from IV calcium triggers calcitonin release, causing rebound hypocalcemia within 4-12 hours
- Subcutaneous calcium: Maximum 125 mL per site; multiple sites on lateral thorax; warm solution; NOT calcium chloride
- Nursing care essential: Keep in sternal recumbency, turn every 2 hours, soft bedding, shelter from elements
High-YieldResponse to calcium indicates diagnosis! Classic response to IV calcium: muscle tremors during infusion, defecation/urination, eructation. Most cows rise within minutes to hours. If no response after 2-3 treatments within 24 hours, consider downer cow syndrome or other differentials.
| Scenario |
Expected Outcome |
| Prompt treatment (Stage 1-2) |
Greater than 95% recovery rate; most rise within minutes to hours |
| Relapse (25-30% of cases) |
Usually responds to repeat treatment; oral calcium reduces relapse risk |
| Untreated milk fever |
60-80% mortality rate |
| Recumbent greater than 24 hours |
High risk of downer cow syndrome; recovery rate drops to 8-32% |
| Alert downer cow (post-milk fever) |
20-67% case fatality; often due to ischemic muscle/nerve damage; hypophosphatemia may contribute |
Prevention Strategies
Dietary Cation-Anion Difference (DCAD)
DCAD manipulation is the gold standard for milk fever prevention. The principle involves feeding a diet rich in anions (chloride, sulfate) relative to cations (sodium, potassium) during the close-up dry period (final 21 days before calving) to induce a mild compensated metabolic acidosis.
DCAD Formula
DCAD (mEq/kg DM) = (Na + K) - (Cl + 0.6S)
Common Anionic Salts
Ammonium chloride, ammonium sulfate, calcium chloride, calcium sulfate, and magnesium sulfate are commonly used. Commercial anionic products may be more palatable than individual salts. The key is achieving adequate anion intake without excessively depressing dry matter intake.
Other Prevention Strategies
NAVLE TipDCAD works by inducing mild metabolic acidosis, which: (1) Improves PTH receptor sensitivity in bone and kidney, (2) Increases bone calcium mobilization, (3) Enhances intestinal calcium absorption, and (4) Increases urinary calcium excretion, which paradoxically "trains" the cow to absorb more calcium. Remember: "Acid helps calcium!"
Prognosis and Complications
Prognosis for uncomplicated milk fever is excellent when treatment is prompt. Most cows respond to a single IV calcium treatment within minutes to hours. However, delayed treatment or relapse can lead to serious complications.
High-YieldDowner cow syndrome is the dreaded complication of delayed milk fever treatment. Prolonged recumbency (greater than 4 hours) causes ischemic necrosis of pelvic limb muscles (especially semitendinosus) and pressure damage to nerves. Prevention is key: treat milk fever EARLY and aggressively, and ensure good nursing care (soft bedding, frequent turning) for any recumbent cow.
Memory Aids for NAVLE
"MILK FEVER = MILK For Eventual Victory through Early Response"
M - Multiparous cows (3rd+ lactation) at highest risk
I - IV calcium borogluconate for recumbent cows
L - Low temperature (hypothermia, not fever!)
K - K (potassium) in diet drives metabolic alkalosis - reduce it!
F - First 72 hours post-calving is danger zone
E - Excitation (Stage 1) then Exhaustion (Stages 2-3)
V - Vitamin D receptor numbers decrease with age
E - Early treatment = excellent prognosis
R - Relapse common (25-30%); give oral calcium to prevent
"DCAD = Don't Create Alkalosis in Dairy cows"
Negative DCAD (more anions) = mild acidosis = better PTH response = more available calcium at calving