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Tasmania worms, flies and lice update - January 2015

Perth: Paul Nilon, Nilon Farm Health (pandonilon@bigpond.com)

The monumental rain event that flooded large parts of central Australia tailed out over Tasmania with most sheep areas receiving between 25 and 50mm. The lower east coast received a deal more, which was a welcome relief from a desperate dry.

Mostly, the prime lambs have been doing well on irrigated crops and brassicas. As always, Merino weaners seem to struggle, and several mobs have returned high counts within 3–4 weeks of a weaning drench. Just like aeroplanes, each case is different so the suggestion is to get some advice on the best approach to reducing pasture contamination. Don’t forget the “smart graze” option: it’s not too late to prepare some autumn/winter paddocks for the weaners.

Some more on Haemonchus: since the December notes another 3 places have had clinical haemonchosus. All 4 places I’ve been involved with to date share these characteristics:

  • Irrigated perennial pastures that were used well into the autumn and early winter.
  • No pre-lamb drench (why would you when the ewes are CS3.5 and the egg counts were less than 150).

I suspect the chain of events is a build-up of contamination in the late summer and autumn when the pastures are grazed by finishing lambs. Each batch of lambs may be multiplying the worms but they are finished before they become clinical cases themselves. Ewes grazing the same paddocks in winter and spring also pick-up and multiply the worms, perhaps aided by emergence of inhibited larvae that have over-wintered in the ewes’ abomasum. This has led to enough contamination and pickup for sheep to be clinically affected by early to mid-summer. Recommendations are:

  • Watch for ill-thrift sheep on irrigated perennial pastures.
  • Egg counts rise rapidly.
  • Affected sheep are pale. Scouring is not a feature of Haemonchus, but it may be present if there is a concomitant scour-worm infection.
  • Monitor constantly (every 3 weeks).
  • If Haemonchus is found or suspected (there are faecal blood tests and larval diff tests as well as PMs), seek advice on what to drench with. However, I suggest that you reinstitute a pre-lamb drench at least for one year if it was not given last year.
  • Seek advice on how to decontaminate paddocks. While overall contamination and larval availability levels are unlikely to get as high as they do in the New England, you must expect larval survivability to be good, so there is a chance larval numbers will build during the autumn and set the stage for repeat problems next summer.