Western Australia worms, flies and lice update - March 2017

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

Last call for pre-emptive action against sheep (and goat) worms!  Worm counts need to be low across the whole flock or herd, as seasonal conditions will only become more favourable for worm development.

Already, the worm potential is higher than in a normal year, as it also was at this time last year when we had green feed across much of the state. In a drive recently from Albany to Badgingarra, I was struck by the extent of new pasture growth south of Perth, although it was patchier to the north. However, as we move into autumn, cooler conditions will mean better survival of worm larvae than when temperatures were over 30°C.

Green means worms

Where much of the farm is now green, or there are large areas of new pasture in low-lying parts of the paddocks, the worm cycle has started. However, even if still dry, it will not be far away.

Whether or not there are big worm problems in the months ahead depends on how many worm eggs are being put out by the sheep (or goats) at present. This usually goes back to the effectiveness of summer drenches (recommended for young stock) or autumn treatments. Drenching in early autumn is recommended for adult stock, but after the February rains, the earlier the better. 

Action in weaners/hoggets

Check worm egg counts now, unless this was done within the last month. If counts are over 100 eggs per gram on average, a re-drench is recommended. Although this is a very low trigger figure, we know that if much higher, it can lead to worm problems in winter. 

Action in adult sheep (or red tags or older)

The recommendation for pre-emptive drenches to sheep of this age (2½ to 3 years and over) is to either drench in autumn or, if drenching in summer, to leave 10–20% undrenched.  

If no drench has yet been given, drench now. Alternatively, sample a couple of mobs, and drench if over 100 eggs per gram. After the February rains, it is likely most ewe mobs will be above this figure.

If the sheep received a summer drench (whether or not some were left undrenched), check worm egg counts, and as for the lambs, use a count of 100 eggs per gram as the maximum before drenching.  

Note that in low-rainfall districts, worm burdens in mature sheep are likely to be low through summer. A worm egg count, rather than a routine drench, will be worthwhile, especially after the February rains.

Drench resistance

We know that summer drenching is linked to the development of resistance by worms to drenches, hence the different recommendations for mature animals. They can handle the small worm burdens necessary to ensure the survival of some worms not recently exposed to a drench—we want these to dilute any resistant worms that survive in sheep that are given summer drenches.   

However, with conditions for worms now generally good across the agricultural regions, the concern is more for worm control, as in most situations there will already be more than enough low-resistance worms in the system.

The main action to reduce the development of resistance from now on will be to minimise the number of treatments needed, through the monitoring of worm egg counts. 

Barber’s pole worm

The barber’s pole worm risk will be higher across the state than in most years, as the early rainfall of 2016 has predictably increased its population base. I’ve seen recent cases of barber’s pole disease in areas on the fringes of its main zones, and worm egg counts come into their own in such situations. The sheep may look well at present but have surprisingly high counts. 

As always, the barber’s pole worm risk will be greater where the pasture has stayed green through summer, or was boosted by rain over the last few weeks. 

In most cases, however, sheep (and goats) will have both barber’s pole and other worm types, so a broad-spectrum drench will normally be needed at this time of year. (You can get the species types checked by a laboratory test, if you want to establish the annual pattern over the years.) 

Cattle worms

The long-established recommendation for control of worms in cattle is to drench yearlings (i.e., at present, if born in 2016) in summer. This will often be at weaning, but needs to be before green pasture has developed.  

However, even if not done so far, as for sheep, it is not too late to get some benefit from this preventative treatment. Bulls should also receive a summer (or dry-pasture) drench. 

There is rarely much point in drenching mature cows. These have a much stronger immunity to worms than do ewes or does, and many studies have shown that no production benefit results from drenching entire breeder herds. A small number will experience worm problems, seen mostly as scouring in winter, and here individual treatment is warranted. This has a strong genetic basis, and it can be worth culling cows that show these signs when the others are clean.