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Metabolic diseases which affect ewes in late pregnancy and/or early lactation can either be pregnancy toxaemia/ sleepy sickness, hypocalcaemia/ milk fever or hypomagnesaemia/ grass staggers. These diseases generally come about via sudden changes in feeding, inadequate nutrition relative to the current demand, anything causing stress in combination with poor weather, and/or concurrent disease. 

Sleepy Sickness

Sleepy Sickness (Pregnancy toxaemia) strikes ewes carrying twins or triplets, usually in the last few weeks before lambing. It is caused by negative energy balance, as the ewe is unable to supply enough energy to meet her own demands as well as those of the fast-growing foetuses.


The incidence of the disease may typically occur in 10% or more of twin and triplet bearing ewes.

Energy requirements of a ewe in the end stages of pregnancy are double that of a non-pregnant ewe, while twin and triplet bearing ewes need 2.5 to 3 times that energy.


If sufficient energy is not supplied (by pasture or supplements) the first consequence will be reduced birthweight of the lamb, then breakdown of the ewe’s body reserves. If this is accompanied by bad weather or other stressors, the ewe will go into energy deficit and suffer depression, then lie down and die within 2 to 7 days.


Milk Fever

Milk fever is associated with pregnancy in sheep. Despite the name "milk fever" the disease does not result in any raised temperature (fever) or infection.


The disease occurs when insufficient calcium is absorbed by the digestive system or mobilised from the bone tissue, to provide for the growing lamb in the uterus and mammary development. If the blood calcium levels continue to drop significantly, the muscles cease to contract properly and paralysis sets in.


Cereal pastures in winter are often high in phosphate, which makes it difficult for ewes to ingest sufficient calcium and magnesium.

Grass Staggers

Winter pastures are often low in legumes and therefore calcium and magnesium-deficient.


Sheep do not store magnesium in the body, so need to ingest it each day to ensure their daily needs are meet.


Any situation that prevents sheep from eating (mustering, holding in shed before shearing, bad weather) can trigger grass tetany.


  • Nervousness and slight shaking when disturbed

  • Stiff legs, staggering, falling over

  • If the sheep goes down, she will paddle with her legs and hold her head back.