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Sheep breeders at forefront of roundworm study

June 4, 2015 by  
Filed under Profiles

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A new way of measuring roundworm resistance pioneered by Lleyn sheep breeders could have widespread benefits for commercial lamb producers.

Commercial flock masters could benefit from harnessing the genetics of the Lleyn sheep – with bloodlines selected because they offer built-in resistance to roundworm, according to early results from a ground-breaking scientific study.

Initial results from the study appear to confirm the long held belief among some breeders that certain lambs within a group are more genetically resistant to roundworm – a parasite which can determine whether a flock makes a healthy profit or a substantial loss.

Although still early days, the experiment looks extremely promising, says Herefordshire producer Edward Collins, who is also secretary of the Performance Recorded Lleyn Breeders Group (PRLB). “We are definitely seeing lambs that are showing more resistance than others.”

Based at Bearwood Farm, Leominster, Mr Collins established the Bearwood Lleyn Flock in 1998. It now totals 400 ewes. He mainly uses Lleyn rams and the majority of lambs going for meat meet the R3L classification or better with an average carcase weight of 20 kg.

The impact of roundworms on sheep production in the UK is an industry-wide concern, with the traditional use of drenches to combat the issue under threat from the increasing prevalence of anthelmintic resistance. But assessing resistance hasn’t always been easy.

Roundworm-infected lambs are subject to reduced feed intakes and poorer conversion of feed, resulting in reductions of live weight gain of up to 60-100%. Infectious roundworm larvae are found on blades of grass in pasture, where they are ingested by sheep and lambs.

In some sheep, roundworm populations in the gut will grow and reproduce relatively unopposed. In other individuals which are resistant to roundworm, the growth and reproduction of worms in the gut is less successful, and hence fewer eggs are shed.

PRLB members have long recognised the quality of their sheep – including the belief that some individual animals were resistant to roundworm. But to promote the Lleyn more widely, scientific evidence was needed to select sheep which possessed this trait for breeding.

The current approach to measuring worm resistance in sheep is the measurement of Faecal Egg Counts (FEC). The technique involves exposing lambs to worms on ‘dirty’ pasture before and then extracting a faecal sample before sending it away for analysis.

However, uptake of the technology has been relatively low. Lack of awareness among commercial producers, concerns over the level of worm challenge required and complications of sample collection are all see as barriers to uptake among breeders.

In conjunction with Glasgow Veterinary School and KN Consulting, the Performance Recorded Lleyn Breeders Group drew up a proposal for a research project funded by the EBLEX Farm Innovation Grant (FIG).

The proposal was to develop a method of improving detection and uptake of genetic resistance to roundworms in the UK national sheep flock. It revolved around testing sheep saliva for parasite specific antibody (IgA) levels as a novel indicator of worm resistance.

Saliva IgA levels are seen as a better reflection of roundworm resistance because they reflect the worm challenge over a period of months whereas a faecal egg count only measures the current level of adult worm infection in an animal.

This means that the actual level of worm infection at the point of saliva sample collection is less important than when relying on a faecal sample and does not need an adult worm infection to the be present. Saliva sample collection is also easier to integrate into flock management practices.

Another attraction is that equipment for sample collection is readily available. It consists of a dental swab to absorb the saliva and a pair of forceps which are used to manoeuvre and hold the swab. Finally, a plastic container is needed to hold the swab after saliva collection.

Some 3000 saliva and FEC samples were collected across 12 PRLB members’ flocks from June to December 2014. Preliminary analysis of IgA levels yielded interesting results – confirming an expected relationship between FEC and IgA levels.

Animals with higher IgA levels tended to have lower FEC values – and were therefore perceived as being more resistant to roundworm infection. IgA measurements have since been used to produce preliminary Estimated Breeding Values (EBVs).

There were no unfavourable correlations found between IgA and production traits. This indicates that selection for resistance using IgA levels would not lead to any reduction in animal performance.

The EBLEX funded study indicates that IgA could offer itself as a feasible alternative, or improvement to the current FEC system. Additional research is required to predict the response to selection using salivary IgA and to incorporate salivary IgA into selection indices.

Further work is already planned, and the Performance Recorded Lleyn  Breeders Group intend to collect a similar number of samples again in 2015 – making this one of the biggest datasets of this kind anywhere in the world.

From a handful of farmers just two years ago, the Performance Recorded Lleyn Breeders Group now has 22 members across the length and breadth of the country – from Perth to Devon and Norfolk to Ceredigion – including flock masters who have anything from 50 to 3000 ewes.

As well as roundworm resistance, the Lleyn ewe has other qualities too, says Mr Collins. “She is prolific, a good mother and rears two lambs easily,” he says. “And with the correct breeding, Lleyn lambs will finish off grass without the use of expensive concentrate.”

Contact

Edward Collins

Email: edward@bearwoodfarm.com

Mobile: 07970 015186

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