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Selection to reduce gastrointestinal parasitism in sheep

Results obtained in the context of the Gemanema project have demonstrated that it is possible to select sheep that are resistant to gastrointestinal nematodes without affecting the growth of the animals or triggering an adaptive strategy among the parasites. In parallel, new biomarkers for infestation have been identified.

Updated on 10/23/2018
Published on 09/21/2018

Gastrointestinal nematodes are the principal internal parasites that affect grass-fed small ruminants. They cause major economic losses for livestock farms because of reduced production (milk) and the treatment costs involved. Until now, anthelminthic agents were the principal response to these infestations. But the proven ecotoxicity of certain compounds and the resistance phenomena observed on all continents have led the ovine and caprine sectors to look for new control strategies.  

Towards integrated parasite management

Together with the controlled and selective use of worming agents, the management of grazing or the use of forage containing active substances such as tannins, the selection of animals that are resistant* to parasites may be one of the levers which could ensure an integrated approach to the management of parasitic nematodes. However, this selection of resistant sheep poses numerous questions regarding nematode virulence and animal performance. INRA scientists have performed a detailed study of the effects of selecting resistant animals and alleviated certain doubts relative to this breeding strategy.

Multiple and sustainable resistance that is rapidly transferable to commercial sheep lines

The scientists worked on divergent lines in the Romane breed (one line resistant to infestations, “R”, and the other susceptible, “S”) obtained by phenotypic selection (observation and selection after infestation testing). The team showed that the innate potential for resistance in R sheep was not affected by chronic stress, suggesting that this resistance is robust in the context of changes to environmental conditions. The R animals displayed a real aptitude for resistance under rearing conditions. They excreted up to six times fewer eggs than the S animals, without any deterioration of their growth performance. The resistance obtained was able to control the carriage and dissemination of H. contorchus and, to a lesser extent, of T. colubriformis.
This host resistance also protected against a rapid adaptation of parasite populations. After five successive infestations, the resistance of R sheep was still effective and could not be circumvented by the parasites. These studies were performed in animal lines similar to commercial lines and could therefore be rapidly transferrable to ovine breeding agencies.

 Biomarkers for the diagnosis of infestation

At the same time, the scientists worked on biomarkers to indicate worm infestations in sheep. Analyses of the metabolomes of treatment-naive animals, of animals obtained after an initial infestation and of those which had experienced repeated infestations were performed and compared. Although there was no signature that could differentiate R and S animals, it was possible to identify metabolites that were markers of infestation. These markers could be indicative of metabolic acidosis associated with loss of blood due to the parasites. Further studies are now under way to validate these biomarkers and develop a diagnostic test for severely infested animals.

*resistance is the ability of the host to reduce the number and/or fecundity of colonising parasites.

Scientific contact(s):

  • Guillaume Sallé INRA, Joint Research Unit for Infectiology and Public Health (UMR-ISP), Inra and University de Tours

More information on the GEMANENA project

Gemanena is a project that received financial support from the revitalisation funds of the  France Future Elevage Carnot Institute.

Lasting 36 months (2015 – 2017), the aim of the project was to explore the efficiency of a selection strategy for sheep resistant to gastrointestinal nematodes.

  • By evaluating the impact of this selection on production traits,
  • By evaluating the efficiency of this selection under normal rearing conditions (impact of the environment or stress, etc.) with respect to multiple resistance or crossed resistance to other parasitic worms,
  • By evaluating the possibilities of nematodes developing strategies to circumvent resistance,
  • By evaluating the presence of these markers in several ovine breeds, and
  • By identifying new biomarkers for infestation (in the metabolome or metagenome) that would facilitate diagnosis and measure the efficacy of treatments.  

Several INRA research units based at the centres in Toulouse, Val de Loir and Auvergne Rhone-Alpes worked on the project in collaboration with the Ordiarp Ovine Centre (Pyrénées Atlantiques).

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Carole Moreno-Romieux, et al. Creation of sheep divergent lines for gastro-intestinal parasitism resistance based on a QTL index. Wageningen Academics Publishers, Book of Abstracts of the 67th Annual Meeting of the European Federation of Animal Science, 22 (1ère Ed.), 2016.
67th Annual Meeting of the European Federation of Animal Science (EAAP), Aug 2016, Belfast, United Kingdom.