Worm Resistant Sheep?
How do you breed worm resistant sheep?
Internal parasites are the largest economic health problem in worldwide sheep farming systems and are the cause for more lamb deaths than any other individual factor
The industry combats worms by treating with anthelmintic drugs but resistance to these drugs is becoming more common, they are no longer working with full efficacy
All sheep have the natural ability to combat these internal worms and like all traits some sheep exhibit higher resistance to worms than others
We measure resistance to worms by doing individual Faecal Egg Counts & IgA serum level tests in our sheep . We record this data over many generations and select animals that are genetically resistant to worms just as we select animals that are better mothers or have better carcass attributes
See https://signetdata.com/technical/genetic-notes/breeding-for-worm-resistance-a-technical-update/ for details
The result is that we have bred ewes that ingest and kill more worm eggs , this leaves fewer eggs on the pasture for young susceptible lambs to ingest and leaves all stock healthier
Trials
We conducted trials along with Bristol University in 2014 to measure the difference in worm resistance between our best and worst ewes
The ewes that we predicted would have the better worm resistance were shedding up to 50% fewer worm eggs than the control group
See the attached report for details
Research at Glasgow University has shown the antibody responses against the larval stage of Teladorsagia circumcincta, (an important member of the Strongyles family) can be used as a biological marker for host response to infection.
This potential phenotype provides a new way to identify genetic differences between sheep in their resistance to worm challenge. High levels of IgA have been shown to regulate both worm growth and fecundity – leading to a decrease in egg output.
These differences will be even more useful in a breeding programme, where they can be converted into breeding values.