Trichostrongylid infections in sheep after rainfall during summer in southern Australia

• Published in: Australian veterinary journal Vol. 80; no. 9; pp. 567 - 570
• Main Authors: NIVEN, P, ANDERSON, N, VIZARD, AL
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-09-2002
• Subjects: Animal Husbandry; Animals; Feces - parasitology; Rain; Seasons; Sheep; Sheep Diseases - parasitology; Sheep Diseases - prevention & control; South Australia; Trichostrongyloidea - isolation & purification; Trichostrongyloidea - pathogenicity; Trichostrongyloidiasis - parasitology; Trichostrongyloidiasis - veterinary; South Australia
• ISSN: 0005-0423; 1751-0813
• DOI: 10.1111/j.1751-0813.2002.tb11041.x

Objective To relate trichostrongylid infections acquired by sheep during summer to prevailing weather conditions.
Procedure Groups of worm‐free ‘tracer’ sheep were put onto pastures, previously contaminated with trichostrongylid eggs, for successive periods of 2 weeks from December to March. After grazing the sheep were housed for 6 weeks. Weekly worm egg counts and worm counts were used to estimate the numbers of worms acquired and related to weather conditions during the grazing period.
Results No worm eggs were detected in the faeces of sheep that grazed at the end of January when only 7 mm of rainfall was recorded. At other times rainfall between 12 and 24 mm occurred and strongyle egg counts were generally either < 50 or > 150 eggs per g (epg). Mean counts of 1100 Ostertagia and Trichostrongylus adults gave rise to mean counts of about 350 epg whereas about 6000 Nematodirus spp were associated with mean egg counts of about 200 Nematodirus spp epg.
Conclusions Rainfall events during summer determine the numbers of trichostrongylid larvae acquired by sheep in summer but further studies are necessary before the implications for strategic control programs in southern Australia can be fully assessed.