Production impact of a targeted selective treatment system based on liveweight gain in a commercial flock.

The sustainability of sheep production is hindered by anthelmintic resistance. Options to slow down or prevent resistance have been widely studied but their application in the field is still limited. In this study, the practical application and effect of a targeted selective treatment (TST) approach for the treatment of parasitic gastroenteritis was investigated in lambs (n = 385) over a 2 year period. At 14-day intervals during the grazing season, liveweight, breech soiling and anthelmintic treatments were individually recorded. Selection of lambs for anthelmintic treatment in the TST group was based on pre-calculated individual growth rates, with a matched cohort routinely treated (RT) with anthelmintic drug every 6 weeks. The adoption of a TST approach had no negative effect on the liveweight gains of the lambs, time to finishing or breech soiling measures compared to RT lambs; however a 50% decrease in anthelmintic treatment was observed in the TST group. The time to implement this system averaged 2 min per lamb. It is concluded that the TST could be suitable for commercial sheep farms, in association with automated weighing systems, potentially reducing selection for anthelmintic resistance, while having no negative effect on production.

Hepatogenous photosensitisation in Scottish sheep casued by Dicrocoelium dendriticum.

Dicrocoeliosis was identified as the probable predisposing cause of weight loss and hepatogenous photosensitisation affecting half of a group of 14 month-old ewe lambs on a farm on the Inner Hebridean island of Coll. Oral dosing of the ewe lambs with 15 mg/kg albendazole only achieved a 79.2% reduction in Dicrocoelium dendriticum egg count, 21 day post treatment. Thus, this report of dicrocoeliosis differs from the disease that occurs elsewhere, both in the severity and nature of its clinical signs, and in the response of the parasite to anthelmintic drug treatment. These differences could indicate the existence of a genetically divergent D. dendriticum population, which may have evolved within the unique and isolated biotope afforded by the machair on the island of Coll. Better understanding of these factors is a prerequisite for effective and sustainable disease control.