Many farms are transitioning to outdoor lambing to reduce feed, infrastructure, and labour costs and, with skilled labour often in short supply, are developing a system where one labour unit can lamb 600 to 1200-plus ewes is key to success.

Appropriate easy lambing maternal genetics, and often a later lambing date that best matches ewe feed demands with spring pasture growth, as well as resting lambing pastures over winter, are essential to promote performance and lamb survival.

The Scottish Farmer: A motherly ewe and sheltered fields are essential when lambing outsideA motherly ewe and sheltered fields are essential when lambing outside

Field allocation – which ewes are put in which fields – also has a major impact on lamb survival:


Lambing field allocation by:

Which: Ewes grouped on the number of lambs carried

What: Set stocked over lambing across a range of fields

When: Seven days pre-lambing to let ewes select a birth site

Where: Fields of varying merit e.g. pasture covers, shelter, field size

Why: Maximise lamb survival – optimise nutrition, reduce miss-mothering and exposure

How: Match ewe groups to specific fields and adjusting stocking rate and mob size

Field assessment

The first step is to map the fields available for lambing and assess each field’s merits in promoting lamb survival.

These include:

Field factor: Aim for improved lamb survival

Pasture covers: Aim 6-4cm min to maximise ewe pasture feed intakes

Pasture quality: Fresh leafy pasture. Maximise feed quality and nutrition

Field size: In line with mob size targets reduce mob size

Water supply: Adequate and accessible, reduce travel time

Shelter: Shelter from several directions, reduce exposure

Natural isolation sites: Adequate desirable birthing sites, reduce competition and exposure

Aspect and steepness southerly, avoiding steep slopes warmer, reduce risk factors and bunching

Impact of mob size on lamb survival

The National Lamb Density Project in Australia found a 2% decrease in twin lamb survival for every +100 ewes in the mob. Another study, The Triplets Project, found the impact of mob size to be seven times greater in triplets than in twins.

Stocking density (ewes/ha) and mob size influence lamb survival because ewes are attracted to birth fluid and newborn lambs. This can lead to miss-mothering, cross-fostering and ewe-lamb separation leading to lamb deaths from starvation and exposure. Both can further impact lamb survival where shelter and lambing areas are limited meaning ewes have less time to bond.

Greater mob size, independent of stocking rate, means more ewes lambing each day with greater presence of fluid and newborn lambs (especially in twin mobs) which increases the risk of miss-mothering and lamb mortality.

Field allocation

Given the above, we want to allocate the best fields in terms of pasture covers, shelter etc to priority groups – triplets over twins, twins over singles – to optimise nutrition, reduce exposure and limit miss-mothering to promote lamb survival. But we also want to prioritise smaller fields for priority groups to reduce mob size – this can also pay dividends. What’s more, the simple act of sub-dividing larger fields to produce smaller mobs can further improve lamb survival.

Use field areas to budget mob size potential at different stocking rates. Overall land area may put a cap on minimum stocking rate but there will be flexibility within groups and different field sizes.

Ultimately, aim to have a lower stocking rate and mob size for multiple bearing ewes, prioritising triplets over twins. Singles can be stocked tighter and in larger mobs. Consider separating out thin twin-bearing ewes BCS <2.5 for priority field allocation.

Suggested targets

Lambs carried Mob size (ewes) Stocking rate (ewes/ha)

Singles <100 10-11(+)

Twins <50 8-9

Triplets <30 6-7

Record and reflect

Record field allocation each year, the number of ewes and lambs carried, and record information on lamb losses and any issues that arise specific to that field. This helps generate a picture of how different fields perform and identify those fields that consistently perform better, and helps flag up poor-performing fields where investment (e.g. subdivision, shelter, water etc) may be beneficial.

Use this information in subsequent years to influence group field allocation, adjust future stocking rates and mob size, and prioritise infrastructure investment on problem fields. A lot of insight can be gained through recording and reflection.