Evaluation of a Targeted Selective Treatment Protocol based on Parity and Body Condition in Dairy Sheep in Field Conditions in France: Impact of Fecal Egg Counts and Treatment on Production

When using a dewormer in a sheep flock, the concept of refugia needs to be kept in mind to postpone the appearance of anthelmintic resistance in a flock (Kenyon et al., 2009). Refugia refers in this case to gastro-intestinal nematodes (GIN) not exposed to the drug used, i.e., present in the environment or in untreated sheep. Targeted selective treatment (TST) strategies are an application of this concept. Determining which animals to treat is however a challenge, and strategies probably need to be adapted to local constraints (Hodgkinson et al., 2019). For dairy-producing small ruminants that have access to pasture, maintenance of eprinomectin (EPN) efficacy is essential for an effective management of production-limiting life-threatening GIN such as Haemonchus contortus. During the ANTHERIN project, a TST protocol using injectable eprinomectin (Eprecis®, Ceva Santé Animale, Libourne, France) was evaluated in 5 dairy sheep flocks in central and south-western France.

• EPN efficacy was maintained in farms where it was initially very high (3 farms /5).
• The combination of criteria allowed for a significant reduction in GIN egg output: treated ewes had significantly higher FEC than the untreated ewes.
• Body condition was the main treatment criteria, and was correctly identified by farmers (figure 2).
• Other treatment criteria depended on the farm. On the only farm for which DAG score was a treatment criteria, nemabiome analysis showed Teladorsagia circumcincta and Trichostrongylus colubriformis were the main GIN present. Nemabiome analysis showed most farms (4/5) were however mainly facing Haemonchus contortus.
• 21% to 74% of lactating ewes were left untreated, depending on the farm and the year.
• Higher milk-producing ewes had significantly higher FEC pre-treatment in the RR. Milk response post-treatment was however not correlated to FEC in both study areas.
• Use of a targeted selective treatment: At time of mating had no impact upon ewe fertility in the PA Led to an increase in milk production of 8 to 9% in treated ewes (figure 3).

References:

BEAUMELLE, Camille, TOÏGO, Carole, PAPET, Rodolphe, et al. Cross-transmission of resistant gastrointestinal nematodes between wildlife and transhumant sheep. Peer Community Journal, 2024, vol. 4. HODGKINSON, Jane E., KAPLAN, Ray M., KENYON, Fiona, et al. Refugia and anthelmintic resistance: concepts and challenges. International Journal for Parasitology: Drugs and Drug Resistance, 2019, vol. 10, p. 51-57. KENYON, F., GREER, A. W., COLES, G. C., et al. The role of targeted selective treatments in the development of refugia-based approaches to the control of gastrointestinal nematodes of small ruminants. Veterinary parasitology, 2009, vol. 164, no 1, p. 3-1