Farm Ireland

Wednesday 24 January 2018

Maximise your lamb growth rate

Michael Gottstein

The growth rate achieved by lambs has a big influence on the overall performance of the sheep flock. Achieving target growth rates is key to getting lambs drafted on time and having sufficient grass for the ewes in the run up to and during mating.

If lambs are to meet drafting targets, growth rates should be monitored and action taken if they are consistently falling behind. This is especially important before weaning takes place, as it is during this period that lambs put on most of their liveweight gain.

In general, lambs can be expected to gain in the region of 2kg per week pre-weaning (see Table 1, top right). Post-weaning liveweight gain drops to around half of the pre-weaning level. Therefore, every week of growth that lambs are below target pre-weaning will take them twice as long to put on post-weaning.

If we take the example of two groups of lambs, one group has achieved the target weaning weight of 32kg, while the other group averages 28kg.

With excellent management these lambs can achieve post-weaning growth rate of 1.25kg per week. Therefore, the first group will require on average eight weeks to get to 42kg drafting weight. The second group of lambs will on average take an additional three weeks to finish. Therefore, for the second (lighter group at weaning) there will be a lot of lambs on the farm in October competing with the ewes in the run up to and during mating.

This results not only in the extra cost associated with keeping the lambs for an additional three weeks (ie extra feed, grass, veterinary treatments such as drenches, etc.) but it also carries a cost in terms of loss of grass to the ewes that may well have improved pre-mating body condition and the following year's litter size.

Think back to how your flock performed last year. What was the average weight of your lambs at weaning time? Was it less than 32kg? We have had a couple of bad years in terms of grass growth and weather and this certainly has created a challenge for sheep farmers. This year isn't shaping up to be any better in terms of grass growth but we should still try to keep our eye on the ball and attempt to reach the modest targets set out in Table 1.

Because the biggest factor affecting lamb growth rate is nutrition the aim should be to maximise the quality and quantity of feed available. In the early stages of life the lamb is completely dependent on the ewe for milk. Therefore, the milk yield of the ewe plays a large role in meeting the target. In the current year, when grass quantity and quality is below what is required, extra concentrates will have to be fed to the ewes to make up the shortfall.

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Where ewes are in good body condition they can be allowed to milk off their backs but this will only go some way toward meeting their needs and additional meal feeding will still be required where grass heights are consistently below 4cm.

Once the lambs reach five to six weeks of age they start eating grass and become less dependent on the ewe's milk. Table 2, above, outlines the target grass heights at which animal performance is maximised.

Again, the difficult spring this year has made it impossible to achieve the pre-grazing covers to date. However, once grass growth picks up this is a target that should be set once more.

In the meantime, lambs (especially older lambs) will be underperforming if they are short of grass and meals should be introduced.

In grass shortage situations, feeding up to 0.5kg/hd/day can be justified to lambs pre-weaning. Once grass covers start to increase, the meal can be reduced to half that level or phased out gradually over a period of a few weeks.

Avoid weaning lambs off meal abruptly as this can cause a setback, particularly where the lambs are consuming large quantities of meal.

Once the nutritional requirements of the lambs have been met it is important to also keep on top of any parasitic challenges that they may encounter, but this is a topic that I will cover in another article.


We have had a very difficult spring (growth/weather). The easy option is to feed meals and forget about grass but there is no money in that.

My challenge to every sheep farmer is to start managing grass for the coming year. This can only be achieved by measuring the grass and putting a plan in place to provide good quality grass according to what I have outlined in Table 2.

This is more important this year than ever as it has been a very expensive spring already.

Irish Independent