Identification of infective Dictyocaulus viviparus larvae isolated from herbage by the bile-agar technique.

A morphological description was given of the infective stage of the cattle lungworm Dictyocaulus viviparus. The larvae were stained with iodine and examined under an ordinary microscope after isolation with the bileagar technique used for processing herbage samples. Under these conditions the internal structures appeared of limited value to the identification. The larvae were characterized by their measurements as well as by their shape and profile. A comparison between larvae isolated from the field and larvae harvested from faecal cultures revealed that field larvae were smaller and more uniform in size. Of the reported characteristics the typical profile, the comparatively small size (range 305–400 µm), and the retaining of iodine stain were found most useful in routine recognition of D. viviparus infective larvae in isolates from herbage samples containing free living nematode species as well as infective stages of parasitic species.