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Signet’s new genetic analysis: The National Terminal Sire Evaluation

In 2019, Signet will relaunch the genetic evaluation service provided for terminal sire breeds. Signet has spent the end of 2018 introducing the new analysis to terminal sire clients with a series of 16 breeder meetings held across the UK and hosted a public ‘Webinar’ shortly before Christmas.

The new service will deliver AHDB-funded research through a multi-breed evaluation, including eight new estimated breeding values (EBVs) and a major change to existing traits, expressing breeding values on a more commercially focused, weight-adjusted basis.

This exciting new approach will result in some of the biggest changes to Signet analyses in the last 20 years, with all breeding values being re-based for the first time since 1990.

Updated EBVs – weight adjusted traits

The biggest change within the new analysis will be to move all carcase traits from being age adjusted (current method) to weight adjusted. This means the updated EBVs will be a better prediction of carcase composition (muscling/fatness) at a fixed weight. As lambs are selected for slaughter based on a combination of weight and finish, rather than age, this will give a more commercial focus to carcase EBVs.

Being weight adjusted will reward those animals who have high levels of muscularity relative to their weight. Currently an animal can receive a high muscle depth in two ways:

  1. By being big – big sheep tend to have bigger muscles
  2. By having a large amount of muscle relative to weight

The scan weight EBV already tells us about big sheep and growth, so the new analysis can tell us about muscling independently of growth.

This will mean a re-ranking of animals for carcase EBVs but makes the figures more commercially relevant.

New CT traits

A new analysis gives the perfect opportunity to introduce new traits. From past and present CT images, we have been able to calculate EBVs for:

  • CT Eye muscle area
  • Vertebrae number (thoracic, lumbar and total)
  • Spine length (thoracic, lumbar and total)
  • Intramuscular fat percentage (IMF%)

Other new traits will include:

  • Birth weight
  • Lambing ease
  • Litter size reared

The new analysis will include ‘publication thresholds’ – these are already used for hard to measure traits in the Lleyn analyses. This means that if an EBV has an accuracy value below a given percentage, the EBV will not be shown – which is useful for traits such as faecal egg count (FEC) where currently flocks/breeds that don’t sample still receive an EBV. The new publication threshold means that these EBVs will still exist, but will not be publicly accessible for flocks that are not recording the trait of interest.


In 2019 all EBVs and Indexes will be re-based. Currently figures are shown relative to the average animal in 1990 e.g. a scan weight EBV of +9kg means that the animal is 9kg heavier at scanning than the average animal in 1990. The re-base will be set to 2010 meaning figures will be reported back to the average animal in 2010 which will have an EBV of 0 or an index of 100.

This means that the scale of figures we are used to seeing will decrease with numbers being smaller e.g. a +9kg scan weight EBV in 2018 might show as +4kg in 2019.

Re-basing is an inevitable part of genetic evaluations and is crucial to keep the figures tangible. It also means that unknown animals/flocks will not start with EBVs as drastically low as they have previously. This will hopefully encourage new flocks to performance record.

New Indexes

The new analysis will lead to the ‘switching off’ of many correlations between traits. This means there is a need for new indexes. Included breeds will now receive two indexes

  • Terminal sire index – optimising growth, muscle depth and CT lean weight while holding the current levels of finish
  • Maternal index – optimising prolificacy, maternal ability and early growth rate without increasing mature size or having a detrimental effect on muscling or lamb finish

Trait emphasis in the indexes will be different to what we are used to seeing due to the changes in weight/age adjustment of carcase traits. For example, the terminal index will have much greater emphasis on scan weight as muscle depth is no longer correlated and is expressed independently of size so we do not have the ‘double-counting’ issue from previous analyses.


Signet will continue to update clients throughout 2019 whilst ensuring the new messages reach the commercial ram buyer.

If you would like to host a meeting to explain the new analyses please contact Emma Steele at [email protected] or call 02476 478721.

About the author

Samuel Boon

Samuel Boon

I am the Manager of Signet Breeding Services, within the AHDB.

Enthusiast on all things genetics to do with sheep and cattle and currently also supporting Bridget Lloyd in running the @RamCompare progeny test with ~18,000 lambs/annum.

I am also involved with the:-

  • Relaunch of Terminal Sire Breeding Programmes (Sheep)
  • AHDB lead for the Welsh Sheep Breeding Project run by HCC - working with Innovis, HCC and Janet Roden
  • Database design and development for this website
  • National Sheep Breeds Survey
  • Development of Carcase Trait EBVs in Beef Cattle
  • Formerly involved with the delivery of the Welsh Sheep Strategy, Northern Upland Sheep Strategy, Suckler Cow Project, Highlands and Islands Sheep Strategy

I can be followed on Twitter @SamBoonBreeding