Feed requirements cannot be met from meadow hay. Because of its poor quality, ewes cannot eat enough to meet their demand. In flocks that lamb on a good supply of green feed, there will be no need for supplementation in late pregnancy. Under-nutrition in late pregnancy and early lactation can harm the ewes. Pregnancy toxaemia is also known as 'twin lamb disease' since it is more unlikely to affect ewes having twins than ewes bearing a single fetus.
Milk fever is another fatal disease arising from deprivation of feed at lambing time.
It is caused by low levels of calcium in the blood. If lactating ewes are yarded or otherwise suddenly deprived of feed shortly after lambing, they can become weak and collapse. Recovery is rapid if affected ewes are injected with calcium borogluconate. However, by the time symptoms are seen it is usually too late to treat them. The appetite of ewes increases enormously immediately after they give birth.