Milk Fever (Parturient Hypocalcemia)

Milk fever (parturient paresis, periparturient hypocalcemia) is a metabolic disease of high-producing dairy cows characterized by acute hypocalcemia around the time of calving. It is one of the most economically important metabolic diseases in dairy cattle.

Signalment:

• High-producing dairy cows (3rd parity and older most susceptible)
• Peak incidence: within 48 hours of calving (most within 24h)
• Jersey breed >> Holstein (higher susceptibility)
• Rare in beef cattle and heifers

Pathophysiology:

• Sudden onset of lactation → massive calcium drain into colostrum (up to 10g Ca in first colostrum)
• Homeostatic mechanisms (intestinal absorption, bone resorption) cannot compensate fast enough
• Older cows have reduced bone mobilization capacity (PTH receptor downregulation)
• High-producing cows have greater colostral calcium loss

Clinical stages:

• Stage I (mild): Excitability, restlessness, anorexia, ataxia, tremors, cold ears
• Stage II (classic): Sternal recumbency, flaccid paralysis, S-shaped neck curvature, bloat, constipation, subnormal temperature
• Stage III (severe): Lateral recumbency, coma, progressive bloat, aspiration risk, circulatory collapse, death if untreated

Clinical diagnosis: Classic presentation in a high-producing dairy cow within 48h of calving is diagnostic.

Laboratory confirmation:

• Total serum calcium: < 1.5–2.0 mmol/L (normal ~2.2–2.6 mmol/L)
• Ionized calcium: More accurate; < 0.8 mmol/L
• Magnesium: Often low concurrently (hypomagnesemia impairs PTH secretion and action)
• Phosphorus: May be low or normal

Differential diagnosis:

• Hypomagnesemic tetany (excitable, tetany rather than flaccid paralysis; often grazing cattle)
• Ketosis (acetone breath, positive urine ketones, standing but anorexic)
• Mastitis/metritis (toxic, fever, localizing signs)
• Trauma/nerve damage (history of dystocia or handling)
• Downer cow syndrome (prolonged recumbency, muscle damage)

IV calcium therapy (treatment of choice):

• Calcium borogluconate: 500–1000 mL of 23% solution IV slowly over 10–20 minutes
• Cardiac monitoring essential: Auscultate heart during administration; stop if arrhythmias develop
• Warming: Warm solution to body temperature before administration
• Never give calcium SC: Causes severe tissue necrosis and sloughing
• Oral calcium: Bolus or drench (calcium propionate, chloride, carbonate) after IV therapy to maintain levels; repeat 12–24h later

Supportive care:

• Positioning: Sternally recumbent if possible; roll frequently if lateral to prevent bloat and muscle damage
• Bloat relief: Trocharize if necessary
• Protect eyes: Lubricate if recumbent
• Fluids: Correct dehydration
• Blankets: Maintain body temperature

Prevention:

• DCAD diet (dietary cation-anion difference): Feed negative DCAD diet (more anions: chloride, sulfate) prepartum for 2–3 weeks. Acidifies blood, increases bone calcium mobilization and intestinal calcium absorption.
• Low calcium prepartum diet: < 50g Ca/day during dry period (stimulates calcium homeostatic mechanisms)
• Vitamin D3: Injections prepartum may help (controversial, timing-dependent)
• Oral calcium at calving: Prophylactic calcium bolus at calving and 12h later for high-risk cows