Ketosis is the classic disease of the fresh cow — the high-producing animal in the first weeks after calving whose energy demand outruns what she can eat. Her body burns fat for the shortfall, and the by-products (ketones) build up and poison her appetite, creating a vicious cycle: less eating → more fat burning → more ketones → even less eating.
When it strikes Mostly days 3–30 after calving, peaking in the second and third weeks. High-yielders and over-fat cows (body condition over 3.5 at calving) are most at risk.
Signs to watch - Sudden drop in milk off the expected fresh-cow rise. - Reduced or selective appetite — she leaves concentrate, picks at forage. - Rapid weight/condition loss in early lactation. - A sweet, acetone-like smell on the breath or in the milk (some people can't smell it — that's normal). - Dullness, a "tucked-up" look, sometimes mild nervous signs (licking, staggering) in the rarer nervous form.
Test, don't guess Cow-side ketone tests make this easy: blood BHB meters (the gold standard — over 1.2 mmol/L = subclinical ketosis, over 3.0 = clinical) or milk/urine ketone strips. Testing fresh cows routinely catches the subclinical cases — the ones losing milk before you'd ever notice — which are far more common than the obvious clinical ones.
Treatment (with your vet) Oral propylene glycol (a glucose precursor) is the mainstay; severe cases may need an IV dextrose drip and sometimes steroids. The earlier you catch it, the simpler the fix.
Prevention is the real win - Don't let cows get fat in late lactation or the dry period — a body condition of ~3.0–3.25 at calving, not 3.75. Over-fat cows eat less after calving and crash hardest. - Maximise fresh-cow intake: palatable feed, plenty of bunk space, comfortable cows that want to eat. - Smooth the transition — the 3 weeks either side of calving decide whether she sails through or stumbles (see "Transition cow management"). - Test routinely in the first two weeks so subclinical cases get caught.
Ketosis rarely travels alone — a ketotic cow is far more likely to also get a displaced abomasum, metritis, or mastitis. Controlling it lifts your whole fresh-cow program.
Sources Merck Veterinary Manual — Ketosis in Cattle. Cornell University — Transition Cow Ketosis Monitoring. AHDB Dairy — Metabolic Disease in Fresh Cows.