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Western Australia worms, flies and lice update - February 2017

Albany: Brown Besier, Brown Besier Parasitology (brown@bbpara.com.au)

Across the state:

The deluge through the agricultural areas of the state in mid-February will have numerous side-effects, good and bad. Where some rain continues it could become a very early season’s break, but where hot and dry conditions resume and the germination dies off, there may be little increase to the worm risk.

Green pasture and mild temperatures favour sheep parasites, so it is important to consider whether there is now an increased parasite risk. In some parts of the state we’ll see more severe worm problems than usual later in the year, and probably barber’s pole worm in the shorter term, in at-risk areas.

Sheep worms

Whether pasture germination has a significant effect on worms on any particular property depends on how long it lasts and whether the sheep have significant worm burdens at present. The longer that green pasture remains, the greater the risk that worm eggs will develop and sheep pick up larval worms. However, if they don’t have many worms to begin with, there will be few worm eggs shed onto the pasture, and no out-of-season worm cycle will result.

A short period of improved conditions for sheep worms in summer does not usually cause immediate problems. Burdens of “scour worms” (i.e., other than barber’s pole worm) generally reach only moderate levels, but are still much higher than wanted at this time of year, as it means the worm population starts from a higher base when the normal worm cycle resumes after the true break. A mob average dung count at this time of year of 50 eggs per gram will probably not lead to a significant winter worm problem – but if it is 200 eggs per gram, severe worm disease is likely.

Recommended action: Firstly, assess whether there has been any change to the worm risk. If you’ve missed out on significant rainfall and the pasture is still generally dry, or the pasture has since dried off, there is no change to the usual advice. Ewes should be drenched late-March or early April, and younger sheep that were given drenches in summer should have worm egg counts checked at that time.

However, where a general germination occurs and it looks like staying green for a while, even in only part of the paddock:

Sheep given a summer drench (or onto a crop stubble): Take dung samples for worm egg counts on some representative mobs. If the average count is more than about 100 eggs per gram, a drench within a week or two is recommended. If it’s lower, but still over about 50 eggs per gram, re-check in 4–6 weeks, and again, drench if over 100 eggs per gram.

Ewes not drenched in summer: If not yet drenched, bring this drench forward, by the end of March. (You can take worm egg counts to check the need, but in the great majority of ewe mobs that have not been drenched since winter or spring, a drench will be warranted.) If ewe mobs were drenched in summer, but a percentage were left undrenched (a strategy to reduce drench resistance), check worm egg counts and drench where counts are more than 100 eggs per gram.

Barber’s pole worm risk areas

Green pasture in summer boosts the risk of barber’s pole worm burdens, and we’ll certainly see more of this than in most years. Significant burdens will take 5–6 weeks after the rains to develop (if low before the summer rain started), and it’s difficult to predict whether they will be significant in any particular mob. Unlike the “scour worms”, barber’s pole worm outbreaks can occur in summer where green pasture persists.

The best guide is whether or not green pasture has persisted, which is especially likely on perennial pastures. Worm egg counts on a couple of representative mobs will indicate whether a drench is needed, and whether a product with a long-acting effect against barber’s pole is justified.

A blowfly strike risk?

It is unusual to see significant flystrike at this time of year as the factors that attract flies to sheep are not usually present. However, there could be cases if rain continues and temperatures are lower than usual, possibly along the South Coast. It would be worth keeping an eye out for fly activity in these situations, although the hot and dry weather since the rains will have reduced the risk.

 

Esperance: Nicole Swan, Swan’s Veterinary Services (nicole@swansvet.com)

The last week has been horrendously wet and wintery. Bridges have been washed away west of Esperance and some properties have been cut off in all directions.  Farmers with perennial pastures are welcoming the rain, which, with this week’s sunny weather, should get the pastures cranking. However, some of our sheep farmers were not so lucky. With sheep recently shorn they had large numbers suffering from hypothermia and suffered some losses.

As far as worms go, the rain and now the sun will get larvae hatching and potentially we will see some properties where worms could become a problem. This is likely to become apparent in the next 3–4 weeks. Monitoring of susceptible mobs in 4 weeks time is recommended. Weaners, hoggets, as well as mobs of older sheep that did not receive a summer drench, will be most at risk. The risk will be minimal for mobs grazing stubble.

Worm Egg Counts (WEC) conducted in January averaged between 130 and 295 eggs per gram (epg). None of these mobs had received a summer drench onto stubbles.