Too Many Lambs For The Ewe.
How Can She Cope? 

Barry Potter, Livestock Specialist

Producers strive to have as many lambs as possible per ewe, especially in intensively managed sheep flocks.  But sometimes death loss and newborn mortality rates in flocks with highly fertile sheep can be extremely high.  Research by P.R. Amer out of New Zealand found that when the number of lambs born per ewe exceeded 2.3, farm profitability was reduced.  In these flocks, as average litter size rises above 1.7 lambs, the number of triplets increases, and lamb mortality is highest in triplets or more.

 While we place emphasis on genetic selection to improve ewe lamb-rearing ability and lamb survival, recent research indicates that the environment that the litter is raised in is much more important than the directly transmitted lamb survival genetics. 

What can we do to improve the environment for these highly productive ewes and their litters? 

A ewe needs more energy in late lactation.  Usually this is met by increased feed intake, except in late pregnancy when intake actually declines.  A ewe can also mobilise maternal tissues, improve the effectiveness of digestion, or increase the efficiency of utilisation of nutrients by body tissues.  Fetal growth is determined by the ewe’s plane of nutrition and by placental growth.  In ewes lambing 150 % or more, placental development becomes increasingly important in ensuring lamb survival.

 By feeding a higher energy ration to ewes we can increase lamb survival significantly.   Another study from New Zealand showed that for every 10 kg. increase in ewe liveweight during the last six weeks of pregnancy, singles increased in weight by 0.46 kgs, and twins by 0.52 kgs.  By pregnancy scanning and separating ewes with multiples, you can preferentially feed your high-producing ewes to increase litter weight.  This increases survival dramatically.

 It is fairly easy to monitor nutrient intake for highly productive ewes in a barn or confined setting, but what about grazing?  A recent study by J.M. Everett Hincks of New Zealand looked at the impact of increasing pasture allowance from just two cm to four cm to six cm of plant height.  By increasing pasture height from two to four cm ewes with triplets increased litter weight at birth by two kg, increased weight of lamb weaned by eight kg, and improved litter survival within 48 hours by 4 %.   When comparing the lowest pasture allowance to the highest, triplet survival increased by 15 %.  Triplet survival was similar to twins at the highest pasture allowance (95 % Vs 92 %)

 The biggest effect of pasture allowance was on lamb behaviour.  Ewes with more pasture tended to stay with their litter.  Ewes on the least amount of pasture were less likely to make contact with their lambs.  Lambs born on lower amounts of pasture were less likely to stand, to locate their dam’s udder, and to follow their moving momma.  They also were less likely to bleat when separated from their mother, lowering the dam’s ability to relocate her lambs. 

In assessing lamb survival, you should look at the percent survival from birth to 48 hours old, and from then until weaning.  The first two days are very critical for lamb survival.  In using genetics to select ewe replacements for reproductive and survival traits, emphasis should be placed on the survival rate to 48 hours.

 For larger litters from highly productive ewes, rearing success is often determined by the environment provided to the ewe and her newborn lambs.