Milk fever, ketosis and other production diseases
Why dairy cows fall sick around calving: milk fever, ketosis, fatty liver, displaced abomasum, acidosis and grass tetany, prevention, and a DCAD sum.
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A dairy cow's body undergoes enormous change around calving. Within days she goes from a dry, pregnant animal to one producing 30 litres or more of milk a day, which drains calcium, glucose and energy faster than her appetite can supply them. Most of the diseases of high-yielding dairy cows, called metabolic or production diseases, strike in this transition period, from about three weeks before to three weeks after calving. They cost farmers through treatment, lost milk, poor fertility and culling, and one problem often leads to another: a cow with milk fever is more likely to develop a displaced abomasum, retained placenta, ketosis and mastitis in the following weeks.
Production diseases of dairy cattle are a core topic in veterinary medicine and dairy husbandry exams.
The transition period
- Feed intake falls in the last weeks of pregnancy and rises only slowly after calving.
- Milk yield rises steeply, so energy, glucose and calcium demands jump.
- The cow mobilises body fat and calcium from bone to fill the gap: a state of negative energy balance.
- Immunity is also depressed, raising the risk of mastitis and uterine infections.
The main production diseases
Milk fever (parturient paresis, hypocalcaemia)
At the start of lactation, calcium leaves the blood in colostrum faster than the cow can mobilise it from bone and absorb it from the gut. Blood calcium falls; muscles weaken; the cow goes down, often lying with her head turned to her flank, with cold ears and a weak pulse, usually within 72 hours of calving. Older, high-yielding cows and Jerseys are at higher risk. Subclinical hypocalcaemia, without obvious signs, affects many more cows and predisposes to other diseases.
Treatment: slow intravenous calcium borogluconate. Prevention: low-potassium, negative DCAD (anionic) diets before calving; low-calcium diets or calcium binders in the dry period; oral calcium boluses at calving.
Ketosis (acetonaemia)
Severe negative energy balance leads to excessive fat mobilisation; the liver cannot fully oxidise the fatty acids and produces ketone bodies (β-hydroxybutyrate, acetoacetate, acetone). Cows lose appetite, especially for concentrates, drop in milk and lose weight; breath may smell sweet. Blood β-hydroxybutyrate (BHB) of about 1.2 mmol/L or more indicates subclinical ketosis.
Treatment: oral propylene glycol, intravenous glucose, sometimes glucocorticoids. Prevention: avoid over-fat cows at calving (body condition score about 3 to 3.5 on a 5-point scale), maximise intake after calving, transition diets.
Fatty liver
Massive fat mobilisation fills the liver with triglycerides, impairing its function; closely linked to ketosis and over-conditioned cows.
Displaced abomasum
The abomasum fills with gas and moves, usually to the left side, causing reduced appetite and milk, with a characteristic "ping" heard on percussion. Risk is raised by low intake, hypocalcaemia, ketosis and diets low in fibre. Correction is often surgical.
Retained placenta and metritis
Failure to expel the foetal membranes within about 24 hours, linked to hypocalcaemia, poor immunity, twins and difficult calving; it often leads to uterine infection and poor fertility.
Rumen acidosis
Rapid feeding of grain or low-fibre rations causes acid build-up in the rumen. Subacute ruminal acidosis (SARA) reduces intake, milk fat and digestion and causes laminitis (lameness).
Grass tetany (hypomagnesaemia)
Low blood magnesium in cows grazing lush, fast-growing spring pasture, especially high in potassium and nitrogen; causes nervousness, staggering, convulsions and sudden death. Prevented by magnesium supplements.
Calculating dietary cation–anion difference (DCAD)
DCAD measures the balance of the main cations and anions in the diet, in milliequivalents per 100 g of dry matter:
DCAD = (Na ÷ 0.023 + K ÷ 0.039) − (Cl ÷ 0.0355 + S ÷ 0.016), with minerals as per cent of DM.
A close-up dry cow ration contains 0.15% Na, 1.5% K, 0.6% Cl and 0.25% S:
- Cations: 0.15 ÷ 0.023 = 6.5; 1.5 ÷ 0.039 = 38.5; total 45.0.
- Anions: 0.6 ÷ 0.0355 = 16.9; 0.25 ÷ 0.016 = 15.6; total 32.5.
- DCAD = 45.0 − 32.5 = +12.5 mEq per 100 g DM.
Programmes to prevent milk fever often aim for about −10 mEq per 100 g in the last three weeks before calving. Reducing potassium by choosing low-potassium forages and adding anionic salts (chlorides and sulphates) lowers DCAD, causing a mild metabolic acidosis that improves calcium mobilisation at calving. A urine pH of about 6.0 to 7.0 shows the diet is working.
Herd-level prevention
- Body condition management: avoid over-fat and over-thin cows at calving.
- Dry and close-up cow diets balanced for energy, protein, minerals and DCAD.
- Maximising intake after calving: fresh feed, enough bunk space, comfort, low stress.
- Monitoring: blood or milk BHB, calcium checks, rumination and activity sensors, milk fat-to-protein ratio.
- Good calving hygiene, clean, roomy calving pens and early treatment of sick cows.
Key points
- Most production diseases occur in the transition period, driven by negative energy balance and calcium drain.
- Milk fever: hypocalcaemia near calving; treat with IV calcium; prevent with negative DCAD and low-calcium dry diets.
- Ketosis: excess ketone bodies from fat mobilisation; BHB ≥ 1.2 mmol/L is subclinical; propylene glycol treats it.
- Others: fatty liver, displaced abomasum, retained placenta and metritis, acidosis and laminitis, grass tetany.
- DCAD = (Na/0.023 + K/0.039) − (Cl/0.0355 + S/0.016) mEq per 100 g DM.
What the exams ask
- School-leaving and entrance papers: causes and signs of milk fever and ketosis.
- Degree and research-fellowship entrances: pathophysiology of transition diseases, diagnosis, treatment and prevention, DCAD and body condition scoring.
- Veterinary and professional examinations: herd monitoring, nutritional management of dry and fresh cows, and economic impact.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why do older cows get milk fever more often?
They produce more milk and colostrum, and their ability to absorb calcium from the gut and mobilise it from bone declines with age.
Can a cow have ketosis without looking sick?
Yes. Subclinical ketosis is common and only detected by testing blood, milk or urine, but it still lowers milk yield and fertility and raises the risk of other diseases.
Why are fat cows at calving a problem?
They eat less after calving and mobilise more body fat, leading to fatty liver and ketosis.
Sources
- Goff, J. P. "Calcium and magnesium disorders." Veterinary Clinics of North America: Food Animal Practice 30, 359–381 (2014).
- Drackley, J. K. "Biology of dairy cows during the transition period: the final frontier?" Journal of Dairy Science 82, 2259–2273 (1999).
- Constable, P. D., Hinchcliff, K. W., Done, S. H. and Grünberg, W. Veterinary Medicine, 11th edition. Elsevier, 2017.
- Duffield, T. "Subclinical ketosis in lactating dairy cattle." Veterinary Clinics of North America: Food Animal Practice 16, 231–253 (2000).
- National Academies of Sciences, Engineering, and Medicine. Nutrient Requirements of Dairy Cattle, 8th revised edition. National Academies Press, 2021.
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