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Queensland worms, flies and lice update - October 2016

Brisbane: Maxine Murphy, Veterinary Parasitologist (maxine@paraboss.com.au)

The November/ December drench is the most important drench of the year. After good rains in winter and spring, and with day temperatures above 20°C, worm eggs on pasture will now be hatching much faster than during September. Any eggs and larvae that were exposed to the strong dry winds of recent weeks would have died, only to be replaced by increasingly more eggs dropped by increasingly wormier sheep. New waves of infective larvae could be on pasture in 4–10 days.

Working through the questions on the Drench Decision Guide (DDG) for Qld/ NSW summer rainfall / slopes and plains: last question on the first screen:

Yes, these sheep have been crowded for 4 weeks or more (due to tall thick grass or heavy rain/flooding)

Recommended action: WormTest with a larval culture now. When sheep are confined to small areas by tall grasses or flooded areas of country, grass becomes heavily contaminated with worm eggs and infective larvae, quickly leading to significant worm infections. Monitoring for signs of barber’s pole infections and dosing with long-acting drenches are indicated.

As weaners can become rapidly re-infected, it is advised that they are weaned onto low worm-risk pastures that also have the best quality feed. Preparation by spelling, and grazing by worm-free sheep for 20 days only, after a short-acting drench will take about 10 weeks, less if hot dry conditions prevail.

Back to basics, when setting-up for drenching, read the drench label and follow its recommendations. Weigh a few of the heaviest looking sheep in the mob and calculate the dose based on the weight of the heaviest. If there is a range of weights in the mob, regroup sheep into weight categories and adjust the dose accordingly. Calibrate drench equipment to ensure the right dose is delivered with the right procedures into the gullet not the lungs. Work methodically. Do not mix drenches unless the label states they are compatible. Instead, either purchase a multi-active drench or drench with one drench up the race and then up the race again with the next drench. Check withholding periods and export slaughter intervals, this is important for meat sheep, and if you are still shearing.

As weaners are very valuable and this is a high worm-risk time of the year, it would be wise to test some drenches (DrenchTest) for efficacy and to ensure they actually kill worms. A good drench is considered to be a short-acting combination of 2 or more drench ingredients, and the combination needs to reduce the worm egg count by at least 98%. If you are inclined to guess instead of testing, do a DrenchCheck after drenching—it’s an egg count 14 days after drenching and an egg count of not more than 100 epg is acceptable. Individual egg counts rather than bulk counts will give information about your drenching technique. For example, if you test 10 samples individually, nine may have a zero egg count and the 10th a much higher count indicating that at least one sheep was misdrenched.