Manage ewes during pregnancy to improve lamb survival

Poor survival of newborn lambs is a major source of lost productivity. Most losses are associated with poor ewe nutrition during pregnancy and poor management throughout the lambing period. Foetal losses are relatively small during pregnancy. Toxicities that kill the foetus and induce infectious abortions can occur in some situations (see MMFS Module 11 Healthy and Contented Sheep). 

Single-bearing ewes require a minimum condition score of 3 at lambing (twin-bearing ewes 3.3) to minimise mortality and optimise wool and meat production of progeny.  

Energy requirements for pregnant ewes increase from 100 days after the start of joining. Adequate nutrition during late pregnancy can compensate for poor nutrition during early pregnancy. If ewes lose condition during early pregnancy and gain condition during late pregnancy, the effects are similar to maintaining condition throughout pregnancy. Condition gains during late pregnancy can be difficult to achieve due to the rapidly increasing nutritional demands of the ewe. During late pregnancy feed quality needs to be high to enable sufficient intake of nutrients due to reduced stomach capacity.  

Improving ewe nutrition during late pregnancy normally increases lamb birthweight and survival, as well as increasing wool production and fibre diameter in ewes. The birthweight of a lamb is determined by the following factors: sex, litter size, placental development, whether the ewe is a maiden or mature ewe, ewe condition, genetics, length of gestation and the timing, quality and quantity of pasture during pregnancy. Optimum birthweight for lamb survival is between 4.5 and 5.5 kg. Survival decreases sharply if lambs weigh less than 4 kg or more than 6 kg at birth.