Development of a dipstick method for on-farm diagnosis of Haemonchus infections in ruminants

Summary

Haemonchus is one of the most significant parasites for sheep. This project aimed to develop a dipstick test to assess risk of death from haemonchus to inform drenching decisions. To achieve this, interfering factors such as green pastures and infection with liver fluke needed to be corrected for.

Field trials were conducted in parallel in Armidale, NSW and Albany, WA. It was found that there was a good relationship between dipstick scores and worm egg counts (WEC), with the test being able to detect haemonchus infection before it became patent. The Armidale research proposed that a test score of 3 should be the decision point for drenching, with a score of 4 indicating imminent risk of death from haemonchus. The Albany trial produced lower dipstick scores, potentially due to dry pasture.

Further studies in a range of geographic and climatic zones are needed to establish the performance of the test in field infections and to determine the final recommended drench decision point.

Objectives

The project addressed the following issues.
1.Examine the capacity of the Haemonchus field test to identify sheep at risk of death from haemonchosis
2.Refine decision points for interpretation of the test results
3.Provide data for input to a drench decision aid
4.Develop methods for removing the non-specific effect of green pastures on test results
5.Assess cross reactivity of experimental Mycoplasma ovis infection with Haemonchus field test in a pen experiment. Assess interference from liver fluke infection in the Haemonchus field test

Key findings

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
indicated imminent risk of death from haemonchosis. A score of 3 indicated the need to drench sheep for Haemonchus infection. The Albany trial found 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 on 2 properties in Queensland gave comparable results to those seen in Armidale.

Benefits to industry

Haemonchus is one of the most significant parasites for sheep causing production losses, costs associated with drenching, and animal welfare concerns.

A reliable test to inform when to drench before the infection becomes patent will help to mitigate these effects.

Future research

Further trials need to be conducted in diverse geographic and climatic zones to confirm scores that indicate the drench decision point. Another study should investigate the effect of storage on results.