Paddock Selection and Mob Size
There is a large disparity in survival rates between lambs born as singles and those born as multiples. This is often due to the higher energy requirements of multiple bearing ewes and the lower birthweights of their lambs. This means that opportunities exist to increase farm profit by maximising twin survival. Scanning for singles and multiples allows multiple bearing ewes to be managed separately and preferentially, lifting lamb survival.
The amount of feed available (termed Feed on Offer) will influence lamb survival. Good feed availability encourages the ewe to stay at the birth site and mother-up with her lambs. It can take 6 hours for a ewe and lamb to imprint on each other. Any disturbances within this time, especially from other ewes, can mean a higher chance of that lamb being mismothered.
Aiming for at least 1500kg DM/ha of good quality feed for multiple bearing ewes can mean a 15 to 20% increase in twin lamb survival when compared to 500kg DM/ha. Better energy intake also means better milk and colostrum production.
Beyond feed levels, it is also important to consider what else is going on in a paddock. Those with shelter, good access to water and lower worm contamination are often better options for lambing. A paddock aspect that maximises early sunshine (especially for winter lambing mobs) and provides some protection from cold winds can help reduce chill factor and therefore improve survival rates. A pasture height of over 10cm can also contribute to the shelter for a lamb by reducing wind speeds at ground level.
Looking at the previous results for each lambing paddock can help to identify the better performing areas of your farm. The biggest gains can be made by preferentially allocating multiple bearing ewes to these better lambing paddocks.
An AWI and MLA funded trial run over 2016 to 2018 looked into the effects of mob size on lamb survival. Researchers found an increase in twin lamb survival between 1.1 and 3.5% for every 100-ewe reduction in mob size, regardless of breed. The effect was lower for single-bearing ewes. To put this in practical terms, dividing a mob of 400 twin-bearing ewes into two mobs of 200 could mean a 5% increase in survival, or around 40 extra lambs.
Much of this comes down to the number of lambs born per day. In larger mobs of multiples there are a much higher number of lambs being born each day than in a mob of singles, meaning more confusion and higher levels of disturbance and mismothering. For example, in a mob of 500 twin-bearing ewes there are potentially 1000 lambs. For a 5 week joining where two-third of the ewes joined in the first cycle, this can equate to 38 lambs born per day. Compare this to a mob of 200 ewes, where we might expect 16 born per day.
Industry recommendations are to lamb multiple-bearing ewes in mobs as small as possible, with optimum mob sizes for twins at least half that of singles.
Subdividing larger paddocks with temporary fencing can be a useful tool accommodate smaller mob sizes. Running fewer, larger mobs of singles to allow for the extra, smaller mobs of twins may also be an option.
In summary, scanning plays a crucial role in optimising ewe management and lamb survival. Identifying multiple-bearing ewes allows them to be allocated to paddocks with the best quality feed and topography for lambing. Where possible, lamb ewes in paddocks with at least 1500kg DM/ha. Finally, aim to keep mob sizes as small as possible, especially for multiple-bearing ewes.
Emma Shattock, Elders
Published in the Stock Journal, May 2022
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