The relative susceptibility of Soay and Blackface sheep to natural infection with Dictyocaulus filaria.

Simultaneous studies by faecal larval counts on a mixed flock of Blackface and Soay ewes, yearlings and lambs suggested that the Soay animals were less able to develop resistance to Dictyocaulus filaria. This susceptibility resulted in a greater proportion of the Soay ewes developing heavy burdens of these lung worms, and in a greater proportion of the yearlings and ewes excreting D filaria larvae in their faeces.