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Breeding Indexes

Blue Texel Crossbred Lamb - Signet
While EBVs aid the selection of breeding stock for specific traits they can also be combined into breeding indexes.
Each trait is weighted within the index according to its economic importance in meeting a specific breeding objective or set of objectives. The breeding index produced helps breeders to rank sheep.
Signet Breeding Services produces several different breeding indexes


Index Main breeds using the index
Terminal Sire Index Charollais, Hampshire Down, Meatlinc, Poll Dorset, Suffolk, Texel Vendeen
Maternal Index Lleyn, Romney, Exlana and Easycare
Longwool / Crossing Index Blue Faced Leicester
Hill Index Scottish Blackface and North Country Cheviot
Welsh (Hill) Index Welsh hill breeds, such as Beulah, Welsh Mountain and Welsh Hardy Speckles

Terminal Sire Index 

The original terminal sire index, based on work by Simm and Amer was developed to select superior terminal sires with the aim of increasing the yield of lean meat in the carcase, while limiting any associated rise in fatness.

Weight data and ultrasonic measurements of muscle and fat depth were used to predict the total amount of muscle and fat in the carcase. Relative economic weightings of +3 and –1 are then applied to produce an overall index on which rams can be ranked.

In recent years the use of Computed Tomography has enabled breeders to directly measure the quantity of muscle and fat in the carcase. Further refinements saw penalties applied to the indexes of ultra-lean rams (with low fat depth EBVs) and a positive weighting on rams with superior gigot muscularity EBVs. 

In 2019 the National Terminal Sire Evaluation was updated, with all carcase traits re-evaluated and moved on to a weight adjusted basis. The indexes used for Terminal Sire breeds were updated to take these changes into account. Read more.

Maternal Index

Maternal Breeding Indexes were designed to enhance lamb survival and pre-weaning growth rates by improving maternal ability. Maternal indexes are particularly useful within self-replacing flocks, where the number of lambs reared to weaning has a major impact on flock profitability.

Signet's maternal index weightings vary between breeds, but most place a high weighting on litter size, 8-week weight, mature size (shearling weight) and maternal ability. Most now put 

Longwool Index / Bluefaced Leicester (crossing) Index

The original Longwool Index was designed to enhance the carcase quality of the longwool/crossing rams that are used for mating to hill ewes in the production of commercial crossbred ewes, like the mule.

The index aimed to enhance the financial productivity of these crossing sires. Increases in lamb growth rate were deemed important, but these increases were controlled so that ewe mature size did not become excessive. The index aimed to maintain prolificacy at current levels. 

In recent years the index has been adapted to meet BFL ram breeder requirements. The negative weighting on mature size has been removed and an additional penalty introduced to penalise ultra-lean (low fat depth EBV) breeding lines. 

The main EBVs included in the index remain

  • Scan Weight
  • Muscle Depth
  • Fat Depth 
  • Maternal Ability 

The Bluefaced Leicester index aims to highlight rams that will sire commercial ewes of an appropriate mature size that produce lambs with good growth rates and superior carcase conformation. 

Hill Index

The Hill Index has been designed to enhance the overall productivity of the ewe by improving several traits simultaneously, most significantly the number of lambs successfully reared.

Using the index to choose female replacements will result in an increase in ewe mature weight, maternal ability, longevity and the number of lambs reared to weaning. Lamb growth rates will increase resulting in lambs with
heavier carcase weights at a constant age. Most of the EBVs are used to calculate the Hill Index.

Welsh (Hill) Index

The Welsh Index identifies sheep with superior breeding potential for maternal ability, lamb growth and carcase quality. Commercial producers selecting rams with high indexes will breed ewes with superior maternal ability and lambs that grow efficiently and produce an improved proportion of lean meat within their carcases.