How to troubleshoot poor lamb growth rates

Assessing lamb performance early on is essential to ensure steps can be put in place to maintain growth rates post-weaning.

The AHDB Sheep Key Performance Indicators project found light lambs at eight weeks old were light lambs at weaning.

Acting early and moving lighter lambs on to creep or high-quality forage can help get them back on track.

Below, independent sheep and beef consultant, Liz Genever, advises on what targets lambs should be achieving and what may be causing a check in growth.

See also: 7 ways to help hit lamb growth targets

Growth rate targets

As a first port of call farmers should assess lamb growth at the eight-week mark. On lowland systems, they should be hitting about 20kg liveweight at this time.

Recording and tracking the proportion of lambs that are about 5kg off this eight-week target is a useful benchmark. The aim should be less than 10% of your total lambs fall into this category.

If these targets aren’t being achieved, questions need to be asked as to why (see “Troubleshooting growth”, below).

“An average [weight] is lovely, but you need to know the range. Those light lambs tell you about mastitis or other common factors that cause lamb growth rates to drop,” adds Dr Genever.

Most farmers will have a grasp of how many lambs are in this category based on visual assessment. However, it’s important to record this number and question if the group is bigger than last year.

Steps can then be taken in the future to reduce this number; perhaps by focusing on younger ewes, lowering mastitis rates through body condition score management or addressing trace element deficiencies.

Do you need to wean early?

Some ewes that came out of a wet winter in low body condition, and were then faced with a far from ideal start to spring, could benefit from an early weaning.

The decision as to whether to wean early can be taken in advance by assessing ewe condition when lambs are eight weeks old.

Lamb growth and availability of quality forage for lambs to be weaned on to will also influence this decision.

Dr Genever urges against taking any drastic steps but suggests bringing weaning forward by about two to three weeks compared to a farm’s “normal”.

This could mean taking lambs off ewe lambs at 10-11 weeks old and weaning lambs off older ewes at 12-13 weeks. Thinner ewes can then be managed accordingly to put condition back on in time for breeding.

Weaning targets and post weaning management

The aim is for lowland lambs to be hitting a weaning weight of about 30kg at roughly 12 weeks of age.

At weaning, lambs should be batched into weight groups (see table below) so feed can be targeted to meet required growth rates. This will be influenced by when you want to market them.

Lamb weaning weights and target growth rates

Lamb weaning weight (kg)

Below 30kg


Over 35kg

Length of keep 

Long keep

(more than 12 weeks)

Medium keep

(six to 12 weeks)

Short keep

(less than six weeks)

Total gain required 




Daily gain needed 




*Source: AHDB Beef & Lamb’s Growing and Finishing Lambs for Better Returns Manual

Short keep lambs As they’re close to finishing, avoid making any drastic changes to the diet that might detrimentally impact growth rates. Keep them on a diet similar to what they’re used to.

Medium keep lambs Prioritise quality grassland or any red clover or herbal leys as they have time to adjust to the new diet and grow.

Long keep lambs Put on forage crops or grass leys so they continue to “tick over” – depending on when you are going to market them.

Troubleshooting growth

If lambs are not hitting the growth rates you need post-weaning, Dr Genever suggests thinking about the following.

These areas are also worth considering if weights are not on track pre-weaning, together with other factors such as milk yield.

1. Are you providing lambs with high-quality grazed forage?

Weaned lambs should be going on to 4-8cm high grass and clover leys with lots of quality leaf. Rotational grazing will improve forage energy levels and overall quality.

Consider adopting a leader-follower system so lambs have a first bite of quality pasture, followed by ewes or cattle.

2. Do you need to supplement with creep?

Depressed lamb prices mean it’s crucial to do the maths before turning to the bag; understand your margins.

See also: Guide to creep feeding lambs when grazing limited

It may be a strategic decision, for example, targeting creep towards larger lambs to get them off forage quicker. Early season creep feeding will always be better as lamb feed conversion efficiency is at its highest.

3. Are you meeting lamb requirements for trace elements?

Start by testing forages for trace elements and minerals. If there’s an issue, speak to your vet and blood test eight to 10 lambs per group. Cobalt, selenium and copper are particularly important for lambs.

If you’ve changed breeding or feeding since you last checked for trace element levels, it’s well worth doing it again as flock status may have changed.

Required trace elements can be provided via creep, boluses, drenches, buckets or blocks. Make sure any amendments to trace elements are having the desired effect by monitoring growth rates

It’s also worth checking with your vet if there’s any health issues that could be compromising growth. 

4. Are lambs being challenged by worms?

If you are unable to graze lambs on clean pasture, are they being exposed to worm challenge? Carry out faecal egg counts (FECs) to assess contamination levels, visually assess sheep and monitor weight changes.

Worming decisions can then be made accordingly.

5. Breeding

In the long-term it may be worth considering if genetics are affecting lamb growth rates. Can you choose rams with estimated breeding values (EBVs) for better early-season growth?

However, ultimately genetics need good management to realise their full benefit. 

In numbers

  • 20kg – target lamb weights by eight weeks old (lowland systems)
  • 30kg – target lamb weights by weaning at 12 weeks (lowland systems)
  • <10% – the proportion of lambs you want 5kg under a 20kg target at eight weeks old (lowland systems)
  • 2-3 weeks – look to bring weaning forward by 2-3 weeks from normal if ewe body condition is low when lambs are about eight weeks old