Parasite Resistance - IgA

Breeding for Parasite Resistance – Measuring IgA levels in blood serum

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.

In 2020, as a one off activity AHDB funded a large project to collect Serum IgA and FEC measurements. From this data SRUC have estimated encouraging heritabilities for Serum IgA (~35%) and in one breed, they also found an encouraging genetic relationship with FEC traits. This work was followed up with additional samples submitted in 2021.

While acknowledging the practical application of this new measurement into breeding evaluations is at an early stage, these results are encouraging. AHDB are currently funding work at SRUC to incorporate this data into future breeding programmes and deliver this service to Signet clients in 2022, having provided participating breeders with some preliminary EBVs in 2021.

With support from Moredun and Biobest the project team have been looking at refinements to the approach that we use to assess IgA levels in blood serum. One consideration has been the use of an antigen developed to respond to a slightly different stage in the worm’s lifecycle. It is thought this new approach may provide a more accurate picture of the parasite burden faced by the sheep. Work is currently on-going to see if this (L4) test is more useful in our breeding programmes than the current (L3) test. The validation work associated with assessing this new measure may result in a small delay in getting results back to breeders in the early part of the 2022 sampling season. 

Funding for breeders in autumn 2022

In 2022 AHDB can offer the following funding to English flocks. 

• £5.00/sample for Serum IgA. This will cover a large proportion of the lab costs at Biobest, see below for the full costs. Please note that breeders will have some additional costs associated with materials, labour, postage and veterinary assistance where required.
• AHDB will support the IgA testing for a maximum of 500 lambs/flock

Please note:

• There is no funding for FEC samples this year, though we would be delighted to receive and include the data in our analyses
• There is no funding for vet blood sampling costs this year or training by vets to show farmers how to take their own samples.
• AHDB no longer fund Saliva IgA samples

This offer is only for:

• Clients in England, as this work is supported and funded by AHDB.  
• Lambs known on the Signet database with accurate date of birth, weights recorded and both parents known and listed on the Signet database
• The Lleyn and Exlana breeds as maternal breeds already engaged in this work
• Samples taken between end September and the end of October - last year samples were received as late as mid-November, this creates problems for the lab. This year we aim for a tighter testing window, if you wish to be involved but will struggle to provide samples by the end of October, please contact me to discuss.

How to claim funding from AHDB

• Please email [email protected] directly to confirmation participation
• Confirm the number of lambs involved and intended date for sampling lambs
• Bridget will ensure you have an AHDB supplier number and raise a purchase order (PO), this will be sent to you when available
• Once results are received from the lab, Bridget will prompt you to submit your invoice for AHDB to reimburse £5.00/sample - you will need to quote your PO on the invoice

Who provides IgA testing services and what does it cost?

In 2022 IgA testing will be provided by Biobest Labs. The test is priced by Biobest at £7.05/sample from which farmers can be reimbursed £5.00/sample from AHDB (for individual samples which link to lambs registered on the Signet database).

Please contact Biobest before samples are dispatched as the test is offered on the basis of prior agreement only.

Samples need to be accompanied by a submission form, which can be obtained from the link or directly from Biobest - please ensure different management groups are clearly identified on submission forms.

Please contact Rebecca Mearns [email protected] if you have any questions about serum or saliva IgA submissions

Send your samples to:

Biobest Laboratories Ltd
6 Charles Darwin House
The Edinburgh Technopole
Milton Bridge
Nr Penicuik
EH26 0PY

Sampling advice

In order that lambs have a high enough egg count for variation between individual animals to be expressed it is vital that lambs are exposed to a parasite infection.

The lambs being tested need to be under a worm challenge (ideally worm count >300) and a mob FEC sample should be taken to determine this.

Please ensure as far as is practical that all animals included have the same or similar grazing history and management treatments (this will mean that results are more comparable as the animals will have been exposed to the same types and levels of parasitic infection). If lambs are kept in different groups/mobs – please submit samples in separate groups and identify the groups clearly on your submission forms so that this information is clear for the lab on receipt and can be included in the result report.

Submitting data to Biobest

IgA measurements are completed relative to a set of controls, which may vary slightly between tests. So all the samples from a flock that are to be compared together must be run on the same test. This would normally be the case where results come as a single submission, but if the submission is split and posted separately and this is not the case it is important to let Biobest know so they can hold off testing until they have all the samples and can test all the flock samples together. 

IgA Submission form can be found here, please do not worry about stating the senders unique reference, you may not have one. You could state “AHDB project” in this place with your contact details. Complete the first form to the best of your knowledge with flock history.

On the lamb submission form if all lambs have the same prefix/UK flock number just state this once at the top of the form and then indicate each individual lamb ID (last 4 or 5 digits), age, sex and management group (if different).

Samples need to be submitted in the red topped vacutainer tubes, where possible as these contain no anticoagulant. Please request these from your vet as soon as possible to ensure supply.

Further information on breeding for parasite resistance, breeding for worm resistance -FEC and breeding for worm resistance - technical update