Prevalence and distribution of lice on sheep and cattle farms in Great Britain.

Lice are common production-limiting ectoparasites affecting livestock. Up-to-date data on their prevalence and spatial distribution on farms in Great Britain is important given that prevalence is believed to be increasing as a result of insecticide resistance. Here the prevalence of farms reporting lice, and factors associated with louse presence, were assessed using a retrospective questionnaire. For sheep and cattle farms, 16.1 % and 15.8 % reported lice on their livestock, respectively. Beef farms were more likely to report lice than dairy farms, with a prevalence of 18.0 % and 7.8 %, respectively. For sheep farms, prevalence was highest in Wales (27.7 %) and Scotland (22.4 %). For cattle farms, prevalence was highest in Scotland (27.6 %), Wales (18.5 %) and SW England (18.5 %). For sheep farms, statistical hotspot clusters were identified in Wales, NW England and SW Scotland, with prevalence in these areas ranging from 30.7 to 40.0%. For cattle farms clustering of cases was less evident. Multivariable analysis showed that significant factors associated with lice on sheep farms were larger flock sizes and geographic location (Scotland or Wales). For beef cattle farms, significant associated factors were larger herd sizes and upland grazing. More than 90 % of farms that reported lice, also reported treating for lice.