A study was initiated to 1) determine which species of
gastrointestinal nematodes are present in cattle in selected areas of
Oregon, 2) examine the seasonal abundance of these nematodes as an
indicator of periods of transmission and 3) determine at what season
developmental inhibition occurs in the major genera of nematodes
encountered. Four study sites representative of the major geographic
regions within the state of Oregon were chosen: Corvallis, Langlois,
near Fort Rock and southeast of Klamath Falls on the Oregon-California
border. Eight sets of 3-4 tracer calves each were introduced onto
pasture at each site over a 2 year period. Time of turnout onto pasture
was dictated by the grazing season and corresponded to late spring, mid
summer, late fall and late winter.
At Corvallis, a distinct seasonality in parasite transmission (as
indicated by nematode abundance) was evident with peaks occurring during
the fall and winter. At Langlois, transmission was fairly constant
throughout the year. However, no discernible patterns were evident at
either Klamath Falls or Fort Rock.
A total of eight genera of nematodes were encountered during the
study. Four (Ostertagia. Cooperia. Nematodirus and Trichostrongylus)
were present at all study sites and were the most common genera at each.
Trichuris was found at all sites except Klamath Falls. Oesophagostomum
was present in tracers only from Langlois and Corvallis while Haemonchus
was found only at Klamath Falls and Fort Rock. Capillaria was only
present at Klamath Falls. Where possible, specific transmission patterns for Nematodirus.
Cooperia. and Ostertagia were determined for each site. Nematodirus was
transmitted fairly steadily at both Langlois and Corvallis but was quite
variable at Fort Rock. Developmental arrest was detected in this genus
at all study sites during the fall and/or winter. Cooperia exhibited
the most seasonally defined pattern of transmission with peak abundances
during the fall and winter at Langlois, Corvallis and Klamath Falls.
Hypobiotic larvae of Cooperia were present during the fall and/or winter
only at Langlois and Corvallis. Peak transmission of Ostertagia at
Langlois and Corvallis occurred during the fall and winter. At Fort
Rock, transmission was lowest in the fall and increased in the winter.
Hypobiotic larvae were evident in the fall and winter at Corvallis, Fort
Rock and Klamath Falls. These data suggest Type II ostertagiasis may
occur in late winter through spring in these areas. Hypobiotic larvae
of Ostertagia were not detected at Langlois. The lack of appropriate
environmental stimuli is one possible explanation for the apparent lack
of hypobiosis at that site
