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Victoria worms, flies and lice update - December 2016

VIC WormBoss Worm Control Programs

VIC WormBoss Drench Decision Guides





Hamilton: Andrew Whale, Livestock Logic (

There are two things that have become obvious  in regard to sheep parasite levels over the last few weeks in December.

  1. Adult worm burdens have varied widely with a large percentage (%) of sheep not requiring a 1st summer drench to date. NB: always worm egg count (WEC) if not administering a 1st summer drench.
  2. 2015 drop (hoggets) and 2016 drop lambs are suffering the higher worm risk consequences of an extended spring period. We are seeing significant production effects on lambs as soon as 3 weeks post-drenching.

As a general rule, adult sheep in the south west are in good condition, and with some green feed still on offer, they are putting on weight. This improves their immune system enabling them to better cope and eliminate worms from their gastrointestinal tract.

As mentioned, lambs and weaners under 12 months of age are struggling to handle worms. Even lambs on good quality feed are prone to worm crashes if not frequently monitored and drenched.

Factors leading to worm crashes include:

  • Lambs being weaned onto pastures that were previously lambed down on by ewes (highly contaminated).
  • Continued rain and overcast conditions have maintained high worm populations on pasture.
  • Lambs, unlike mature sheep, have no immunity to gastrointestinal parasites.
  • Pastures are now losing quality (particularly annuals), weaner growth rates are slowing, and so susceptibility to worms is increasing. NB: time to start your supplementary feed program.
  • Lack of monitoring post-drenching.

Last season, many lambs were drenched at weaning and not given another until after the autumn break in May/June. We are currently faced with a very different climate to this time last year, and it is imperative that producers take steps to manage their sheep, lambs in particular, to ensure worms do not impact on production.

Steps to take to minimise worm problems include:

  • Worm egg count lambs 4 weeks after a drench, and then every 2 weeks.
  • Utilise clean pastures for weaners where possible.
  • Get lambs onto grain trail now as, most likely, without access to summer crops or lucerne, lambs will need regular grain supplementation to achieve small weight gains.

The following graph from Livestock Logic’s Worm Egg Count Laboratory for December highlights how age plays such a major role in development of immunity: 1-year-old sheep (green) are the most susceptible, 2-year-old sheep (red) still have an increased susceptibility, with many having recently weaned lambs for the first time and are in a lower body condition score, and 3+ year old ewes (blue) have the best immunity.

Figure 1. Worm egg count by age-group. Submissions to the Livestock Logic Laboratory.

Note: we have left this year’s lambs off this chart but they are at extreme worm-risk and most should be monitored every 2­–3 weeks at least, until the relative worm-risk of paddocks they are grazing this summer, is known.

Happy Christmas and a great New Year from the team at Livestock Logic.

For December 2016 state outlooks, please follow the links below:
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