Know more

Grazing cows are infested with digestive tract worms (gastrointestinal strongles), including Ostertagia ostertagi found in the abomasum of cattle. These parasites can, under certain conditions, lead to decreased milk production. However, "blind" deworming all cows in order to secure production is not appropriate: systematic treatments may lead to the emergence of parasite populations resistant to anti-parasitic molecules. It is therefore necessary to know the profile of the herds at risk and the animals to be treated.

The variation in milk production after treatment against these worms was analysed in 22 dairy cattle herds. Several criteria were evaluated to characterize (i) cows with an increase in post-treatment production (cows to be treated) and (ii) herds with a high proportion of these cows (>50% among young cows), i.e. herds at risk. To properly identify such herds and cows, it has been shown that it is ideal to combine several criteria rather than considering them one by one: the profile is more specific and the risk of mis-treating is minimized. For example, the multi-criteria treatment profile of "young dairy cows from herds with insufficient immunity to gastrointestinal strangles but high exposure to these parasites" appeared relevant to reduce the treatment rate while optimising milk production. In this profile, immunity was indirectly assessed by the Effective Contact Time (ECT) of heifers with these parasites before first calving. Indeed, it is known that the immunity to digestive tract infections depends largely on the length of contact time with these parasites: by estimating the ECT, via data on grazing management and treatments before first calving, it is possible to assess whether or not heifers' rearing conditions are conducive to high immunity or not before entering the adult herd.

This multi-criteria profile, made up of operational and low-cost indicators, would make it possible to create a treatment decision tree that must now be validated in a larger number of herds. Such a reasoned deworming strategy should make it possible to reduce the risk of resistance emergence, control the environmental impact of these antiparasitic molecules, and meet societal expectations of reducing chemical inputs on farms.

Partners: This study was conducted in the BioEpAR joint research unit in partnership with the Institut de l'Elevage (CIFRE thesis), GDS Bretagne, URGTV Bretagne and Pays de la Loire, and the Regional Chamber of Agriculture of Brittany as part of the CASDAR project n°1127.

Associated publication : Nadine Ravinet, Anne Lehebel, Nathalie Bareille, Carlos Lopez, Christophe Chartier, Alain Chauvin, Aurélien Madouasse, 2017. Design and evaluation of multi-indicator profiles for targeted-selective treatment against gastrointestinal nematodes at housing in dairy cows. Veterinary Parasitology 237, 17-29.

Contacts

Scientific contact:

•  Nadine Ravinet UMR BIOEPAR

Associated Department: Santé animale

Associated Centre: Pays de la Loire