Milk Fever

What is Milk Fever?

Milk fever (hypocalcemia) is a metabolic disorder that occurs when blood calcium levels drop below normal at or shortly after calving. Calcium is needed for muscle function, nerve signaling, and milk production. The sudden demand for calcium in colostrum and milk production can overwhelm the cow's ability to mobilize calcium from bone and absorb it from the diet.

Milk fever typically affects mature cows (3+ lactations) in the first 24–48 hours after calving. Clinical signs progress through three stages: Stage 1 — restlessness, weight shifting, ear twitching; Stage 2 — staggering, inability to stand, S-shaped neck posture; Stage 3 — recumbent (down cow), cold extremities, decreased heart rate, potentially fatal.

Subclinical hypocalcemia (blood Ca <8.0 mg/dL without visible signs) is far more common — affecting 25–50% of fresh cows. It reduces immune function, increases risk of ketosis, DA, and retained placenta, and reduces milk production by 5–10 lbs/day in early lactation.

Prevention is far more effective than treatment. Strategies include: feeding a low-calcium pre-fresh diet (reduces calcium mobilization signals), anionic salts to create mild metabolic acidosis (enhances calcium absorption), adequate vitamin D, and calcium supplementation at calving (oral or IV for high-risk cows).

Subclinical Hypocalcemia

Subclinical hypocalcemia is defined as blood calcium below 8.0 mg/dL without visible clinical signs. It affects 25–50% of fresh cows — far more common than clinical milk fever (5–8% prevalence). Subclinical cases are invisible without testing but cause significant economic damage: reduced immune function increases mastitis risk by 2–3x, delayed uterine involution increases retained placenta risk, reduced rumen motility predisposes to displaced abomasum, and milk production drops 5–10 lbs/day in early lactation. The combined cost per subclinical case is $100–$200. Test fresh cows at 24–48 hours post-calving using blood calcium analysis (target >8.5 mg/dL). For herds with >30% subclinical prevalence, implement a DCAD feeding program and evaluate pre-fresh calcium levels. Prevention of subclinical hypocalcemia through nutrition typically costs $5–$10 per cow but saves $100–$200 per case in avoided disease.

DCAD Diet Management

Negative DCAD (dietary cation-anion difference) creates mild metabolic acidosis that enhances calcium absorption from the intestine and bone mobilization. Target DCAD of -10 to -15 mEq/100g of dry matter for 3 weeks before calving. Anionic salts used to achieve negative DCAD include: magnesium chloride (MgCl₂), calcium chloride (CaCl₂), and ammonium sulfate ((NH₄)₂SO₄). These salts taste bitter, so they must be mixed thoroughly into the ration and fed with palatable forages. Monitor urine pH — target 6.0–6.5 (below 6.0 indicates excessive acidosis, above 7.0 indicates insufficient anionic salts). A DCAD pre-fresh ration typically contains 0.5–1.5% anionic salts by weight. Cost is $1.50–$3.00/cow/day for the pre-fresh period (21 days = $32–$63/cow), but the return is substantial — clinical milk fever incidence drops from 8–12% to 1–3%, and subclinical hypocalcemia drops from 40–50% to 10–20%.

Calcium Supplementation at Calving

For high-risk cows (mature, high-producing, history of milk fever), provide an oral calcium bolus (23–50g calcium) immediately after calving. Boluses containing both calcium carbonate (fast-acting) and calcium chloride (sustained release) provide immediate and extended calcium support. Repeat the bolus 12–24 hours later for high-risk cows. For clinical milk fever (recumbent cow), administer IV calcium: 400–500 mL of 40% calcium gluconate solution slowly over 10–15 minutes (too fast causes cardiac arrhythmia). Monitor heart rate during IV administration — if heart rate exceeds 80 bpm, slow the infusion. Keep calcium gluconate on the farm ($20–$40/bottle) and a calcium bolus kit in the fresh pen. Response to IV calcium is usually dramatic — cows stand within 15–30 minutes. However, relapse can occur 12–24 hours later, so follow up with oral supplementation. For herds with chronic milk fever problems, consider a prophylactic IV calcium treatment for all fresh cows at high risk (mature, high producers).