Picking rams to sire prolific daughters

Higher input costs mean sheep farmers need now more than ever to maximise output from flocks and that means achieving as many lambs sold a ewe as resources will allow.

For those flocks breeding their own replacements it is worthwhile assessing rams’ maternal estimated breeding values (EBVs) as a recent EBLEX funded study has shown selecting rams with superior EBVs for litter size can significantly increase flock prolificacy.

More than 22,000 Poll Dorset lambing records were analysed to investigate the relationship between a sire’s litter size EBV and the number of live lambs produced by his daughters when they became mothers.

The study showed not only is litter size EBV a good indicator of breeding stock with superior prolificacy genes, but more importantly there is a major opportunity for commercial producers to exploit these genetic differences.

In this study the difference in daughter performance between groups of high and low genetic merit sires generated an extra 25 lambs born for ever 100 ewes lambed – a major difference, which has a real economic value.

In commercial sheep production there is a strong relationship between the number of lambs sold a ewe and flock profitability, this study highlights an important way that selective breeding can enhance flock output.

And Dorset breeders have embraced this discovery and for the first time this year two breeding indexes will be available to ram buyers, a Terminal Sire Index and a Maternal breeding index – enabling ram buyers to select rams most suited to their production system.

The terminal sire index aims to optimise returns from the slaughter generation, while the maternal index highlights sires that will leave more productive female replacements.

The move is part of Signet’s new approach to analysis of Poll Dorset and Dorset Horn data that has resulted in a National Breeding Evaluation combining data from Sire Reference Scheme and within flock recorder into a single nationwide analysis.

The latest evaluation clearly shows the progress recorded flocks have made over time. As well as enhancing the breeding potential of Dorset sheep for growth to eight and 21 weeks old by 3kg and 6kg respectively, significant advances have been made in improving carcass traits, prolificacy and maternal ability. The new indexes will enable even faster progress to be made in future.

Nearly 70 performance recorded rams will have this information on display for the first time at the Dorset breed’s annual sale – the May Fair 6 and 7 May 2008 – with information displayed on Order of Merit Cards produced by EBLEX.


Relationship between a ram’s litter size EBV and the prolificacy of his daughters (22,502 lambing records for 63 sires. Signet, April 2008).

Ranking on Litter size EBV

Average sire litter size EBV

Average live lambs born per daughter*

Impact compared  to average lambing performance

Top 25% (15 sires)



Extra 13 lambs/100 ewes

Group Average




Bottom 25% (15 sires)



12 lambs less/100 ewes

* Data unadjusted for environmental factors farm type, ewe age, year or season.