Who is breeding for parasite resistance?

There are variations between individual sheep within a flock in the strength of their acquired resistance to parasites. Part of this variation is genetic, and it is therefore possible to selectively breed for sheep that are more resistant to internal parasites.

Signet works closely with a large number of hill and maternal flocks who have a strong focus on parasite resistance as part of their breeding programmes.

As with many projects, collaboration has allowed a significant increase in the number of phenotypes to be collected from projects such as Breed for Ch4nge and the Farming Connect Welsh Sheep Genetics Programme. Within the Signet analysis, over 44,000 Faecal Egg Count (FEC) records have been gathered since 2000. Along with these, more than 20,000 Serum IgA records are now part of UK sheep evaluations, which is a huge leap considering that Serum IgA wasn’t even measured in flocks until 2019.

Recent work from this dataset, has shown a significant increase in heritability for parasite resistance traits. Below is a breakdown of the heritability values:

Trait	Heritability Value
FEC_S	0.30
FEC_N	0.29
Serum IgA	0.38

Breeding for worm resistance provides both a useful way to improve flock performance and a valuable marketing tool for selling stock. If you are looking to locate or source genetics from flocks who measure these traits, a list can be found here.

Posted by Laura Eyles on 03 Mar 2025

Sheep, Articles

About the author

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.