The recent dry spell has not been good for crops across much of WA, but unfortunately it won’t have helped with sheep worm control. Even though pasture growth is reduced, provided there is green pasture and some moisture at ground level (dews, condensation, light rain), worm eggs shed in sheep dung will continue to develop. Recent conditions have therefore been ideal for worm development, and worm larvae will survive for long periods while temperatures remain mild.
Some high worm egg counts in ewes have shown the importance of pre-emptive worm control ahead of the lambing period. Average mob counts over 500 eggs per gram have been seen in some laboratory submissions, often with scouring in the ewes. This has occurred in some cases even where ewes received a pre-lamb drench, because worms had been deposited onto the pasture before then. The recommended mid-autumn drench to ewes usually prevents this—provided that drench resistance has not reduced its effectiveness.
The main implications are for the lambs—if kept on these paddocks, they will be exposed to high levels of worm intake over the next few weeks. A couple of recent cases in prime lambs have shown heavily impaired growth rates due to high worm burdens, and the need for a drench well before one would normally be given at weaning age. In addition to the production cost, the paddocks involved will not be suitable for lamb grazing for many weeks due to high worm larval levels.
Weaning of lambs will be on the agenda for many growers in the next month or so, and this is the ideal time for a drench resistance test. Plan ahead for this—Department of Agriculture and Food WA has a test kit with all the gear needed (phone the Albany office, 9892 8444, or district offices).
A strategic approach to worms in late winter to early spring
This time of year provides an early opportunity to monitor the effectiveness of worm parasite control. Evidence from clients over many years suggests that in this district, a worm egg count on maiden ewes 2–3 months after the start of lambing will provide a good indicator of the success of worm control. Moderate to high worm egg counts in this group not only indicate the need for early treatment, but also provides evidence of a failure of worm control strategies on the farm—arising from inappropriate timing of the last drench, unmanaged larval contamination of pastures in autumn, and/or the emergence of resistance to the chemical(s) being used.
An appropriate response to high counts in early spring might include seeking veterinary advice on strategic significance. Major management changes and/or a resistance test may be required to ensure ongoing sustainable worm control. Treated sheep will continue to pick up worm larvae, so it is not necessary to use a 100% effective drench—I generally advocate chemicals of at least 80% efficacy and not used for strategic control in the previous late spring to autumn period. However, this decision becomes problematic if there is no existing profile of resistance on the farm.
Some consideration needs to be given to the level of contamination of pasture, including whether to move a treated mob to a fresh paddock. It is often advantageous to spell a paddock from which a high egg count mob has been moved, and then re-stock it in 3–6 weeks with another mob that will be drenched in late spring—using the second mob as vacuum cleaners! Well grown hoggets can be used but must be monitored, including if they are in full wool and begin to scour. It is critical that this second mob be treated afterwards with a highly effective drench.
Finally, do not underestimate the impact of worm parasites as a cost to spring shearing. Failure of control may necessitate pre-shearing crutching or be a significant contributor to the occurrence of post-shearing hypocalcaemia.
We have not monitored a lot of mobs this month. On one coastal property where ewes and lambs were drenched 2 months ago with closantal, average counts were 910 epg for lambs (range 250–2300 epg) and ewes 380 epg (100–850 epg). This property has no clean pastures and we do not have information on the drench resistance status of this property. A lectin test for barber’s pole or a larval culture was not performed. It was decided to drench these sheep with Cydectin, which would give them 5 weeks protection for Haemonchus (barber’s pole) as well as killing the majority (hopefully all) of the scour worms.
Another property had drenched ewes late May pre-lambing with Eweguard and were monitoring pre lamb marking. These 2 mobs had average counts of 70 epg and 125 epg. A drench was not required. Monitoring the higher mob in 4 weeks was recommended.