PRODUCERS must monitor sheep flocks for faecal worm egg counts before the onset of winter, according to Agriculture Department senior sheep vet Brown Besier.
Dr Besier said farmers were moving away from drenching their entire flock in the summer and were leaving some mobs undrenched, as recommended, to help reduce worm drench resistance.
"What producers need to remember is that it is essential to monitor the health of those sheep that haven't received a summer drench," he said.
"Carrying out pre-emptive faecal egg counts now is the best control that producers have to prevent running into trouble in winter with the sheep that haven't been drenched in summer."
Summer drenching has been carried out in many agricultural areas for a long time, allowing good worm control for six to nine months.
However, Agriculture Department research has revealed summer drenching subjects the worms to a very high selection pressure. Worms with a resistance to drenches were favoured, which could worsen drench resistance.
Since spring 2001, a major project involving monthly monitoring of worm levels in weaners, ewes and dry sheep on different WA properties has been in progress.
The objective of the project is to help develop an effective and sustainable sheep worm control program that would not place so much pressure on worms for drench resistance.
Results suggest weaners are highly susceptible to worms because they are still building their immunity and must therefore receive a summer drench.
It is also suggested hogget sheep be monitored with a faecal worm egg count at the normal time of summer drenching.
If an average of more than 200 eggs per gram (epg) is counted, they should also receive a single effective drench after pasture has dried.
If no summer drench is given, it is critical to check hoggets regularly.
Among the older ewes on the demo farms, it was revealed one-third of the mature ewes checked did not need a drench during summer or early autumn.
"As a result of this, we suggest that if ewes appear healthy at the normal time of summer drenching, then farmers should refrain from giving all mobs of mature sheep a summer drench," Dr Besier said.
"Instead, conduct a faecal egg count monitor on a couple of the mobs that are considered a higher risk and then use the results from these as a guide.
"If levels are above 200 epg, then producers should administer a single effective drench."
Dr Besier said none of the sheep on the demo farms needed a second summer drench and if producers considered a second drench necessary, faecal egg counts should be checked first to ensure the drench was worthwhile.
"Extra faecal egg counts are advisable if sheep or seasonal conditions are poor and following atypical events such as summer rain or false breaks," he said.
"In addition, if barber's pole worm is present on the farm, local advice should be sought to include specific treatments in the program."
Dr Besier said the demo farm monitoring had been in progress for two years and shown modifications to summer drenching could successfully reduce drenching.
However, further results were to be collated and it was crucial to remain vigilant and regularly monitor sheep health.