Two experiments to determine the seasonal incidence of nematode parasites
of sheep are described. These were based on differential egg counts and a comparison
between critical slaughter trials and egg counts.
Trichostrongylus, the dominant parasite, reached peak worm egg counts in
May, Oesophagostomum in September, Ostertagia in March, Nematodirus in April
and Trichuris in June.
Haemonchus contortus reached peak egg counts in December, January or
February and, in the critical slaughter trials, in May. Since there was close correlation
between egg counts and worm burdens, the summer peak would probably
have been noted if sheep had been killed during these months.
Except for H. contortus, egg count data could not be correlated with worm burdens
in the slaughtered sheep.
Strategic dosing is recommended in December, March and June.
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