Milk fever — properly, hypocalcaemia — is the classic calving-time emergency. At calving a cow's calcium demand suddenly multiplies as she starts producing colostrum and milk. If her body can't mobilise calcium fast enough, blood calcium crashes, and she goes weak, wobbly, and eventually down. Beyond the dramatic clinical cases, the subclinical form (no obvious signs, just low blood calcium) silently affects a large share of older cows and sets up ketosis, retained placenta, displaced abomasum, and mastitis. Controlling calcium controls a whole cascade.
Who's at risk - Older cows (third lactation and up) — their calcium-mobilising machinery is slower. Heifers rarely get it. - High-yielding cows with big calcium demand at calving. - Cows fed a high-calcium ration in the dry period (counter-intuitively — see below).
The signs (clinical milk fever) Three loose stages: first, unsteadiness, cold ears, muscle tremors, hypersensitivity; then she goes down to her chest (sternal), often with her head turned into her flank; finally, flat out on her side, unresponsive — a true emergency. Sub-normal temperature is a tell; a down fresh cow that's *cold* rather than hot is classic milk fever, not infection.
Treatment — fast, with your vet Clinical cases need calcium, usually intravenously (and slowly — too-fast IV calcium can stop the heart), sometimes with subcutaneous follow-up. Most cows respond dramatically if treated promptly. A down cow is an emergency; don't wait.
Prevention — the real goal The aim is to train the cow's body, in the last weeks of pregnancy, to mobilise its *own* calcium so it's ready the moment she calves. Discuss the right approach for your herd with your vet: - Low-calcium close-up diet — keep dietary calcium low in the last ~3 weeks so the cow "switches on" its calcium-mobilising hormones before calving. - DCAD (dietary cation-anion difference) management — feeding anionic salts in the close-up period to acidify the cow slightly, which primes calcium mobilisation. The most reliable approach in many herds, but it needs proper ration formulation and monitoring (urine pH). - Oral calcium at calving — calcium boluses or gels given to at-risk cows (older, high-yielding) right around calving as insurance. - Don't let dry cows get fat — over-conditioned cows are more prone, and condition control helps the whole transition (see "Body condition scoring" and "Transition cow management").
Why it's worth the effort Every prevented milk-fever case avoids not just the down cow but the string of secondary diseases that follow low calcium. It's one of the highest-leverage parts of a transition program.
Sources Merck Veterinary Manual — Parturient Paresis (Milk Fever). AHDB Dairy — Milk Fever and DCAD. Cornell PRO-DAIRY — Hypocalcaemia Prevention.