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Should I only breed from rams that are born as a twin?

At a recent meeting, commercial farmers with Dorset sheep were discussing how important it was to select a ram that has been born as a twin.

How to increase prolificacy through ram selection

The number of lambs reared per ewe is a key driver of flock profitability, but simply selecting a ram because it was born as a twin will not guarantee increased prolificacy in his daughters.

Selecting Signet recorded rams with EBVs for terminal sire and maternal traits enables farmers to make more informed decisions based on a ram’s genetic merit, which is a far better predictor of progeny performance.  

The use of EBVs is especially import for maternal traits, such as litter size and maternal ability, where it is impossible to identify the best rams by eye alone. Using EBVs to select rams with positive litter size EBVs will increase the number of lambs produced by their female offspring. For example a ram with an EBV of +0.06 is estimated to produce daughters which produce 3 per cent more lambs than a ram with an EBV of 0.

High EBV Rams Increase Prolificacy by 6%

The value in using EBVs to aid selection compared to selecting on birth type alone is clearly shown in the table below, which shows data for 100 Dorset rams that have been highly recorded for prolificacy, i.e. they are sires with lots of daughters.

The table shows their litter size EBVs broken down by their birth type and by their genetic merit for prolificacy (as determined by the Litter Size EBV).

Within this dataset, selecting a twin born ram over a single born ram resulted in daughters that were about 1% more prolific.

Selecting the 25% of rams with the highest breeding values for litter size compared to those with lower values (over half of which were twins as it happens), resulted in daughters that would be 6.5% more prolific. 


Number of rams

Average Litter Size EBV

All rams



Born a Single



Born a Twin



Born a Triplet




Bottom 25% on Litter Size EBV



Top 25% on Litter Size EBV



Over the past 50 years Dorset breeders have used Signet recording to improve performance across their flocks, with a strong focus on both carcase traits and maternal attributes, including prolificacy.

The proportion of single born lambs has dropped significantly over time.

In 1970, 58 ewes would need to lamb down in the flock to produce 100 lambs, if we fast forward to 2020, only 54 ewes would be required to produce this number.

Buyers are seeing the benefit of looking deeper into an animal’s background before purchase and utilising data to make informed decisions rather than buying on looks alone. An investment in high-performance genetics will increase flock productivity, which, in today’s ever-changing world, has never been more important.

If you are unsure how to interpret breeding values do chat to your ram breeder about your breeding goals. Further information is available in these AHDB publications.

Buying a recorded ram for terminal sire traits.pdf

Buying a recorded ram for maternal traits.pdf

About the author

Laura Eyles

Laura Eyles

Laura has joined the Signet team as a breeding specialist, she comes from an agricultural background having grown up on a sheep farm in Cornwall, where they keep commercial ewes and run a small flock of pedigree Charollais sheep.

Laura has a strong interest in animal breeding and genetics having studied Animal Science (BSc Hons) at Harper Adams University. During her time at Harper, she spent an industrial placement in Cumbria working for a sheep breeding company and some of our clients may recognise her from this role. Since graduating she has worked for a large cattle breeding company before joining us at Signet to lead on a number of Signet’s sheep breeding projects.