Oversummer and Overwinter Survival of the Cattle Lungworm Dictyocaulus vivipams on Pasture in Louisiana (U.S.A.)1

Two experiments were carried out during summer and winter conditions to determine if Dictyocaulus vivipams infective larvae could survive on pasture during these seasons in Louisiana. Pairs of tracer calves were grazed in August and September on a pasture that was heavily contaminated in May and then left free of cattle during June-July. These tracers were not infected with D. vivipams, indicating that the larvae did not survive summer conditions. However, a pair of tracer calves grazed in February on a pasture heavily contaminated into December and kept free of cattle until mid-February, was infected with lungworms, indicating that larvae could survive during this period on pasture. A second pair of tracers grazed on the overwintered pasture during MarchApril did not become infected with lungworm. Gastrointestinal nematodes, particularly intestinal species, did survive oversummer and overwinter conditions. Ostertagia ostertagi, however, did not survive the oversummer period. Temperature and rainfall patterns during the experiment differed only a little from those for 22-yr average conditions.