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Sheep and wool prices are up, but has your worm control improved?

by Deb Maxwell, ParaBoss Executive Officer

May 2018


With wool market indicators over 1800c, lamb prices around 600 c/kg carcase weight, and mutton over 400 c/kg, it’s not a bad time to be in sheep.

But has the higher value prompted you to better safeguard your investment and get the best growth from them? Or is the cream being taken off your profit by the invisible cost of worms?

Scour worms in particular cause losses that are not easy to see, but are nevertheless occurring, and of course barber’s pole worms can result in significant and obvious losses.

But the answer is not drenching more often, it’s being smarter about drenching and using other worm control strategies.

The first step is knowing the effectiveness of each drench type, against each worm species on your property because drench resistance can cause significant productivity loss, can degrade the benefits of strategic drenching (summer drenches, pre-lambing drenches), and can shorten the time interval between drenches.

Most properties have some drenches below 80% effectiveness and plenty of properties have one or more drenches below 60% effectiveness.

A WA study where scour worms predominated showed that using a 65% effective drench resulted in nearly half a kilogram less wool and adult body weights 7 kg less compared to a fully effective drench. It also resulted in three times the amount of scouring and a small number of the mob needed a salvage drench to prevent them from dying.

The results of using an 85% effective drench were also compared; the ill-effects of course were less than with the 65%-effective drench, but nevertheless present and with virtually no visible signs.

Single-actives or combinations?

Let’s be clear: WormBoss recommends doing a DrenchTest with single-actives, but not drenching normally with single-actives. Why?

Using combination products compared to singles is one of the most effective means of slowing development of drench resistance.

However, doing a DrenchTest with single-actives provides the best information at the least cost. Because there are so many combinations on the market it is quite expensive to test them all. By testing most of the single actives you can calculate the likely effectiveness of any drench that contains those tested single-actives.

Other key drench strategies that slow the development of drench resistance are using the most effective drench possible, and avoiding the use of mid- or long-acting products. Of course, avoid any unnecessary drenching as well.

Unfortunately, rotation of drench actives has not proven to be particularly useful in slowing drench resistance, except after using a long-acting product or after having used a low worm-risk paddock.

A comprehensive DrenchTest involves drenching 8 groups of 15 sheep each with a different drench (see the recommended list), plus one extra group that is not drenched. Individual worm egg counts are done on at least 10 sheep from each group—collected 14 days post-drenching—and larval cultures are conducted for each group.

If you don’t yet feel confident to do a DrenchTest, it’s easy to do a DrenchCheck.

A DrenchCheck simply involves a before and after worm egg count (WormTest) and culture when you drench a mob—just a test done after drenching is not enough.

When you next think a drench is needed, collect faecal samples from the mob (see instructions) and have a mob worm egg count test done. This should include a larval culture if more than one of the three key worm types are likely to be present: barber’s pole worm, black scour worm and brown stomach worm.

If the test indicates drenching is required, drench normally within a week of when the test samples had been collected. Then collect samples again exactly 14 days after the drench was given and have another worm egg count (and culture) carried out.

Ask your laboratory to calculate the reduction in worm egg count achieved for each species as an indication of the effectiveness of that drench.

While knowing drench effectiveness should be one of your first steps towards better worm control, WormBoss provides regional annual programs that include methods to lower exposure to worms and increase the resistance and resilience to worms.

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