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Development of a dipstick method for on-farm diagnosis of Haemonchus infections in ruminants
The project developed a method to remove the effect of pasture on scores in the Haemonchus field test for faecal occult blood by boiling diluted samples for 15 minutes, or placing diluted samples in an esky containing boiled water for 30 minutes. When applied to experimentally infected sheep running at pasture in Armidale a score of 4 was associated with haematocrit < 22 and WEC > 20,000 indicating imminent risk of death from haemonchosis. A score of 3 was associated with a significantly lower haematocrit than occurred in sheep with lower test scores and with WEC > 5000, indicating the need to drench sheep for Haemonchus infection.
The test was applied to experimentally infected sheep running at pasture near Albany WA before the development of the boiling method. Nonetheless, there was little effect of pasture greenness on scores in uninfected sheep. More importantly, WECs and haematocrits indicative of a need to drench sheep for haemonchosis were recorded at lower test scores than seen in Armidale. A trial conducted by QDPI&F on 2 properties in Queensland gave comparable results to those seen in Armidale. A trial of the test on boiled samples showed that infection with Fasciola hepatica resulted in scores less than 3. Experimental infection with Mycoplasma ovis did not cause positive test results.
The project achieved its objectives with the exception of a consistent test score for the decision to drench. These data were obtained from sheep undergoing experimental infections on two research properties. A meeting with Ancare, MLA, AWI and research provider representatives on 15th May 2007 concluded that further results are required from application of the test to samples collected from farms in diverse geographic and environmental regions to confirm the scores from which final drench decision advice can be formulated.
The study is currently being designed, together with a short study on the effect of storage of whole faeces on results obtained with the boiling method. The review expressed a strong view that the test continued to show good evidence of final suitability for use in the field, provided the field trial gave satisfactory results. The final drench decision advice would be determined by performance of the test in the field trial. The ability to remove green pasture effect by boiling samples diluted for assay should greatly simplify the drench decision aid from earlier drafts that included complex corrections for pasture colour.
This page was last updated on 24/07/2017
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