The effect of a preparturient fenbendazole treatment on lactation yield in dairy cows.

Studies carried out on nine farms in north-west England indicated that fenbendazole treatment of adult winter calving dairy cows in the dry period caused an overall increase of 173 kg in their subsequent lactation yield. There was some evidence to suggest that a correlation existed between pasture Ostertagia ostertagi larval burdens and subsequent serum pepsinogen and milk yield responses post treatment. Marked interherd and regional differences existed in the milk yield response to anthelmintic treatment and possible reasons for such results are discussed.