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Ewe Mature Weight

Recording Ewe Weight to Breed More Efficient Ewes

Using genetic selection to breed more efficient ewes provides a great way to improve both the profitability and the environmental credentials of your farm.

What makes an efficient ewe?

An efficient flock produces a high level of output relative to the inputs required to run it over the year. To achieve this we need to be breeding ewes that are:

  • Prolific, rearing lots of lambs and with good lamb survival
  • Milky and attentive mothers
  • Produce fast growing lambs, with a high meat yield in their carcase
  • Have a long and productive life, with few health concerns
  • Are not expensive to feed throughout the year and will readily retain the right Body Condition Score (BCS).
Why is ewe mature weight important?

Ewe mature weight is important because although heavier ewes can produce faster growing lambs and are ultimately worth more as culls, they tend to be more expensive to feed and have to be run at a lower stocking density.

Work for AHDB by AbacusBio highlights that there is an optimum ewe size for maternal breeds that balances these gains in outputs with increases in production costs. The review proposed that the optimum ewe mature weight on many farms is around 55-65kg, though it acknowledges this will vary with farming system. You can read the full report here or watch this webinar to learn more.

Selecting purely for faster lamb growth rates (Eight Week Weight EBV and Scan Weight EBV), will lead to an increase in ewe mature weight. However, there are sheep that are ‘curve benders’, which have fast early growth and a more moderate mature weight.

Breeders can enhance this attribute by recording ewe weights with Signet and using EBVs produced for this trait to enhance their selection decisions and avoid larger increases in ewe mature size.

When to measure ewe mature weight

EBVs will be calculated for ewe mature weight and ewe body condition score records that are taken at any of three key times during the year. Initially only the pre-mating EBV will be published and this should be our main focus.

Focus on mating weight

Please try and weigh your shearling and older ewes at mating time. Record differences in their management groups and where practical collect a record of body condition score, though we recognise this won’t be possible in all flocks.   

Table 1. The three periods when breeders can supply ewe mature weight data


When to measure

Mature Weight at Mating

Within the 3 weeks prior to tupping

Mature Weight at Eight Week Weighing

When recording lamb eight week weights

Mature Weight at Weaning

At weaning (any time between 12 and 19 weeks post lambing)

It is recognised that in some fast finishing flocks, weaning may take place before 12 weeks and thus the earlier weighing event will be the “weaning” weight. This is absolutely fine.

You can submit the ewe weights online or send Signet a spreadsheet in the format you can find here.

Signet’s new maternal evaluation

We are in the process of updating our genetic evaluations for lowland maternal breeds with funding from CIEL and AHDB as part of the EweBenefit project.

The new evaluation will:

  • update all of the current EBVs
  • express muscle and fat depth on a weight adjusted basis
  • produce ewe mature weight and BCS EBVs
  • provide monthly evaluations for all maternal breeds
  • produce breeding values for carcase traits where abattoir data is available
  • report a new EBV for IgA serum (worm resistance)
  • generate a new maternal Index to optimise ewe efficiency

The new evaluation will be launched in early 2022.

To get the most from this exciting new evaluation it is important to provide the best data that you can – and this year it would be great if this could include mating weights.


Frequently asked questions about collecting ewe mature weights

What are Estimated Breeding Values (EBVs)

EBVs are an estimate of a sheep’s genetic potential for key economic traits, calculated using a sheep’s pedigree and measurements (and those of its flock mates). EBVs allow the direct comparison of sheep to be made based purely on their genetic potential and independently from their management.

Why ewe mature weights important?

Selecting sheep to improve lamb growth rates will lead to an increase in the mature weight of ewes. A recent review proposed that the optimum weight for lowland ewes in the UK is in the range 55-65kg and suggested that further increases to the mature weight of ewes would lead to reductions in flock efficiency.

The Ewe Mature Weight EBV can be used to select ewes with a moderate mature weight, while progressing performance in other traits.

The Ewe Mature Weight EBV will be correlated to the Scan Weight EBV, so sheep with a high Scan Weight EBV will be predicted to have a high Ewe Mature Weight EBV. Only by measuring ewe mature weight will the analysis have the information required to identify those sheep that are curve benders, with fast early growth and yet more moderate mature size.

Will controlling increases in ewe mature size affect the growth rate of my lambs?

This will depend how great a penalty is placed on ewe mature size within the breeding indexes that are being used. The new maternal index being developed will allow some increase in mature size, so the breeders will still be able to increase the growth rate of their lambs through selective breeding.

When is a good time to take these measures?

There are three times in the year when breeders can collect these measurements.

  • Pre-mating – In the three weeks leading up to tupping and are being sorted into mating groups
  • When lambs are weighed at 8 weeks
  • At or shortly after weaning, between 12 and 19 weeks post lambing

How should the data be submitted?

  • You can enter your ewe weights online via
  • You can submit spreadsheets for ewe mature weights and body condition scores. You can find file templates here

How do you get accurate data? 

Check your scales with a known weight (a bag of feed or a weight)

  • Check your scales accurately repeat the measurement, remove the weight and re-weigh 3 or 4 times.
  • Record management group for the ewes. Ewes that have been managed differently should be recorded in different management groups.
    • For example a thin group of ewes separated from the main flock after weaning should be recorded in a different management group.
  • Where possible keep management groups as large as possible
  • Record a weight for a ewe every year that she is in the flock

What can you do with additional ewe weights if you weigh more frequently?

  • If you weigh your ewes more frequently you can still submit this data using the same forms. We will store them on the database to be used in the future.
  • The weight taken closest to the optimum date will be used in the evaluation.

Where can you get advice on recording body condition score (BCS)?

  • Breeders can collect BCS at the same time that you weigh your ewes so that a BCS EBV can be calculated. For guidance on collecting BCS you can check the manual ‘Managing Ewes for Better Returns’

What happens if I can’t weigh my ewes?

  • If you can’t weigh all your ewes try and weigh a representative proportion from a number of different sires.
  • If you are unable to weigh any of your ewes, other weight measurements will be used to derive this EBV. This means sheep that do not have measurements for mature weight will still receive an EBV, but it will be driven by assessments of lamb growth rate

Should I still weigh shearling ewes?

Yes, weigh your shearling ewes pre-mating as before. This data will be used to calculate the Shearling Ewe Weight EBV, which in turn will be correlated to the Mature Weight EBVs.

What happens if half my shearling ewes lambed as ewe lambs?

If you lambed your ewes as ewe lambs still collect a pre-mating shearling weight to produce a Shearling Ewe Weight EBV, but it is important to record the two groups of shearlings in different management groups, those that lambed and those that didn’t, so they are no directly and unfairly compared

Do I need to weigh mature males (i.e my stock rams)?

No, an EBV is calculated for rams from their female relatives. There tend to be fewer rams on individual farms and this makes useful comparisons more difficult, especially when they have been reared on different farms in different years.

In most flocks there are large enough numbers of ewes that are run together in large contemporary groups over several seasons to give us the information needed.

Is the Ewe Mature Size EBV included in the new Maternal Index for lowland breeds?

Yes, a small negative weighting has been placed on indexes of sheep whose Ewe Mature Size EBV exceeds a certain threshold value, above this the index weighting will increase to more severally penalise the largest ewes.

These ewes may still get high indexes, if their EBVs for other traits are high – but the index is lower than they would have had without the penalty. This step will help to moderate larger increases in ewe mature size, without favouring very small ewes.

What does the Maternal Index reward?

The new Maternal Index being launched for lowland maternal breeds in 2022 is designed to select the most efficient sheep. The index rewards high performing sheep in for lamb growth rates, maternal ability, muscling and body condition score while seeking to optimise prolificacy and ewe mature weight.

Which breeds are getting Ewe Mature Size EBVs?

All lowland maternal and hill breeds will be getting access to a Ewe Mature Weight EBV over the next 18 months, so they are strongly encouraged to submit weights and BCS if they can. Terminal breeders can also record these weights with a view that we may create an EBV for these traits in the future.