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Anthelmintic treatments (HA) aimed at controlling the impact of gastrointestinal strangles (GIST, gastrointestinal tract worms) on the growth of young cattle need to be rationalised in order to maintain their effectiveness over the long term. The aim of this study was to validate a selective treatment strategy at the beginning of the stall based on (1) the identification of risk groups by grazing, and (2) in these groups, the identification of heifers to be treated by their lower growth (low GMQ).

At the end of the first grazing season of 24 groups of heifers, the contamination levels of the plots (PCN) with SGI infesting larvae were estimated using an expert system (Parasit'Sim). Based on meteorological and grazing management data (e.g. date of grazing, time spent per plot), this expert system models the number of larval generations (GL) accumulating on the plots throughout the season. The PCN is expressed in two levels (low: < 3 GL/strong: ≥ 3 GL). This approach allowed for a conservative estimate of the actual level of exposure of groups of heifers to IMS, while avoiding the use of costly additional testing.

At the individual level, growth declines were associated with parasitism only in the highly exposed groups (strong ASC). Several treatment thresholds based on individual growth could then be evaluated. A QGD threshold around 683 g/d allowed proper identification of animals suffering most from parasitism exposure.

In conclusion, the implementation of a selective treatment strategy in heifers at the end of the grazing season is possible by combining simple grazing management and individual growth data.

Identification of groups and individuals who might benefit from anthelmintic treatment at the end of the grazing season © Inra-Oniris

Partners: this work was carried out in collaboration with INRA units (UMR 1348 and UE 0326) and the Chambers of Agriculture and with funding from the GISA Strep meta-programme and the AEI Chair.

Associated publication : Merlin A., Chauvin, A., Lehebel, A., Brisseau, N., Froger, S., Bareille, N., Chartier, C., 2017. End-season daily weight gains as rationale for targeted selective treatment against gastrointestinal nematodes in highly exposed first-grazing season cattle. Preventive Veterinary Medicine. 138, 104-112.

Contacts

Scientific contact :

•  Christophe Chartier UMR BIOEPAR

Associated Department: Santé animale

Associated Centres: Pays de la Loire, Bretagne-Normandie