Effect of level of infection by gastrointestinal nematodes and anthelmintic treatment on milk yield in dairy sheep.

The effects of gastrointestinal nematode infections and anthelmintic treatment on milk yields was compared between flocks with a low level (LL) of eggs per gram (epg) before partum and with a high level (HL). Faecal egg count reduction tests (FECRTs) were carried out before partum comparing a treated group with netobimin with an untreated group. Ewes belonging to LL flocks produced 55.4% more milk than ewes from HL flocks. A negative correlation was found between the mean epg before treatment and the mean milk yield per flock (r = -0.860; p < 0.01). However, treated ewes produced 10.1% more milk than untreated ewes in LL flocks, although in HL flocks, treated ewes produced less milk (-2.7%). The treatment of flocks even with low levels of infection can improve the milk yields. In this study, the epg before partum had a greater influence on total milk yield than the anthelmintic treatment.