NSW WormBoss Worm Control Programs
NSW WormBoss Drench Decision Guides
I was just eyeballing some sheep WormTest results for June. Roughly 10% of the WormTests for Armidale had mean egg counts >1000 eggs per gram (epg). As a rule of thumb, the highest egg counts in a WormTest are often 3–4 times the mean. Most of these were mainly Haemonchus. The highest mean was approximately 3000 epg, with the highest individual count being about 10000 epg. And this is winter!
Over in Dubbo, there was a mob (ewes/lambs) with a mean of about 2200 epg, and the highest count was 9400 epg (mostly Haemonchus). In the northern New England, there was a mob with a mean epg of about 2200 epg, highest about 9000 epg.
And how about Yass? A mob of weaners there had a mean epg of about 2400 epg, highest 12000 epg (all Haemonchus).
So, why some high-ish Haemonchus counts even now, in winter? A common response is that Haemonchus has changed i.e. it has become more cold-adapted. Sure, this can and does occur, but most of the explanation is to be found elsewhere. (If you hear galloping (in AU), think 'horses' rather than 'zebras').
(Editor's note: in other words look for the most common explanation first.)
Once temperatures are consistently below 10°C overnight, and below 18°C during the day, it is too cold for Haemonchus eggs to develop and hatch and, as they only live for ~5 days anyway, they reach a dead-end. Maybe the eggs of cold-adapted strains can 'do their thing' at slightly lower temperatures? Certainly when you get into regular frosts, or close to temperatures that produce frosts, there won't be any new Haemonchus larvae appearing on pasture.
But the 3rd stage larvae (infective larvae) produced in autumn, when conditions were kinder, are a different kettle of fish. They will survive over winter and into spring, albeit in declining numbers.
So, regarding these sheep (as discussed above) that are from areas with cold winters, and which have decent Haemonchus egg counts: where did their worms come from? They either picked up ‘autumn-born' larvae off pasture, and/or they are carrying existing burdens from summer/autumn.
There are no magic bullets, but the practical solutions—tried and tested—are known: it's all in WormBoss. Start by checking out Your Program.
We have had limited rainfall in the last month, with just a few light showers. In the results from the WormTests submitted from sheep flocks I have seen a range in worm counts of 140 eggs per gram (epg) to 1324 epg.
Haemonchus (barber’s pole worm) has been the dominant worm present on the larval differentiation. Teladorsagia formerly Ostertagia (brown stomach worm) has also been popping up in cultures (one result of 16% and another of 33%). The brown stomach worm will become more of a problem if there is more rain in the next month or so. This little worm can cause a large loss in production prior to obvious signs of scouring occurring, highlighting the importance of early detection and requesting a differential with the WormTest when submitting a sample.
The ongoing dry conditions have seen worm burdens remain low in most sheep flocks. Many producers are now drought feeding stock. With the forecast for dry weather to continue, it is envisaged that worm burdens will remain low until we (hopefully) get spring or summer rain.
The season continues to deteriorate in the Forbes area of the Central West LLS and most egg counts remain low. I have had one case of scour worms causing weight loss in hogget rams drenched and put back out onto what must have been a very contaminated pasture. Producers are reminded to prepare low risk paddocks for those sheep that are most susceptible to worm infestations— weaners, hoggets and lambing ewes.
Winter rainfall has been lower than expected and lower than what the district has become accustomed to. As such, feed issues are rising on certain properties and now supplementary feeding has begun. While we have had the odd frost, and even though temperatures had plummeted to all time monthly lows about 2 weeks ago, day time temperatures have remained above average and would, under these conditions still lead to worm eggs hatching into larvae. A great feature article by Deb Maxwell goes through and dispels myths about what frosts do to the free-living states of internal parasites on pastures, and I encourage all of you to read it.
The few worm egg counts that have come through have been low, except for a mob of hogget ewes that registered the highest counts of the past month, averaging 1500 eggs per gram (epg). This producer was not noticing any of the typical signs associated with internal parasitism, such as weight loss, scouring, a tail to the mob, or even deaths. While we waited for typing of these egg counts, we considered—based on our district history—that Trichostrongylus spp (black scour worm) would make up the vast proportion of worm types in the larval differentiation, but on the other hand, a high count, with no signs yet evident, could suggest barber’s pole worm, especially if summer/autumn was wetter than usual. So there are good reasons for either result and only a culture can show the actual proportion of worm types. In this case it was 91% Trichostrongylus, 9% Teladorsagia and no barber’s pole worm.
While cold weather does reduce the activity level of worm larvae, it does not affect their numbers or their ability to infect sheep. It just means they can actually live for more months during cold weather as lower activity uses less of their finite store of energy. With the moisture levels and sufficiently warm day time temperatures currently being experienced, the life cycle of scour worms will to continue.
Many mobs of sheep throughout the district are being grazed on cereal crops, and a few producers are noticing scouring from these ewes. While this may likely be attributed to the green feed on hand in these paddocks, it is important to keep worms at the back of your mind and look for any clinical signs of disease.
A few production alerts for producers: bloat and grass tetany. Lactating cattle and sheep are at risk of developing grass tetany at this time of year. As such, Causmag (magnesium oxide) should be made available to both species post lambing and calving to ensure that no development of clinical disease occurs. Even though rain has been lower than what we would normally expect at this time of year, producers have already begun enquiring about grazing cattle on fresh legume pastures. Legume pastures pose a risk of bloat in cattle, especially where legumes dominate a paddock (greater than 50%). Appropriate bloat prevention methods should be utilised when putting cattle onto such pastures.
Feed is currently a bit shorter than what is expected at this time of year in the Riverina. I have been finding that producers have been pressured into grazing pastures more heavily and wean lambs earlier than they otherwise would. Heavy grazing has resulted in some unexpected internal parasitism in dry stock this year. Cold weather will stop most eggs from hatching but will not reduce the numbers of existing worm larvae on pasture, only slow their movements and extend their life. Current moisture levels have been further favouring their viability. This, in combination with the fact that most worm larvae will sit within 5 cm of the soil line, will provide enough factors to cause a production risk.
Early weaned lambs have been facing all the same factors as dry adult sheep, however, they lack the developed immune system of older sheep to resist heavy worm infestations. In this situation, I find the majority of producers rely on a weaning drench—which will, most times be of a significant benefit to their production. However, potential resistance development needs to be considered and if the lambs do present with scouring soon after weaning other factors may be at play such as inappropriate age of weaning and nutritional scours (from lush green cereal crops), uncommon bacterial infections or even coccidiosis.
Scouring sheep or lambs need a Worm Egg Count (WEC) test performed as a first step in their disease investigation.
There are no worm-related investigations or test results to report for this month.
It has been one of the driest starts to winter for decades, to the extent that shortages of surface water are looming. Pasture quality has declined dramatically following a series of heavy frosts, and many fodder crops have been over-grazed. But there is some good news—for most producers, worm levels in sheep are generally low.
There are still some residual barber's pole worms showing up in worm tests, resulting from autumn-hatched larvae that happily survive the cold. There are enough of these to give counts into the thousands where contamination levels had been pretty high, but more commonly worm counts are less than a couple of hundred eggs per gram.
A few mobs already have significant levels of mainly brown stomach worms, a reminder that these scour worm eggs hatch at winter daytime temperatures. With declining feed levels for lambing ewes, these worms could be a threat. Ironically, it has been too dry lately for worm eggs to hatch (both temperature and moisture need to be right). But it will pay to check worm levels in lambed ewes before lamb marking is due.
Two goat herds affected by worms this month had vastly different signs. Both problems occurred in young animals. In one herd, there was bottle jaw (fluid swelling under the chin), anaemia and weakness, typical of barber's pole worms; the other had a few young does scouring and losing weight due to black scour worms. Enquiries about worms from goat producers are always difficult to answer. One concerned owner recently explained that while she was careful to not drench too often, she was having to use the same drench on every occasion in order to empty the drum, and was worried this may encourage drench resistance. Veterinarians in many rural areas recognise the problem, and often dispense drench in smaller quantities. You also need written instructions from a veterinarian before being able to use a sheep drench on goats, if that drench is not also registered for goats or is being used at a different dose rate (and very few of them are).
(Ed:tor's note: WormBoss includes information specific to goat worm control. See the top of this page for links to both the sheep and the goat programs and DDGs.
Except in quite specific situations, rotating drenches is NOT particularly useful at preventing drench resistance (contrary to popular opinion). But continuing to use an already poorly effective drench repeatedly will fast-track further development of resistance. See more here about rotation versus combinations.)
For this month I’ve decided to include a case study to highlight the value of WormTests.
In June, three WormTest results were received from a producer running Merino sheep. All mobs were in good condition and no deaths had been observed. The results are below:
1. 1120 mixed age Merino ewes due to lamb in September.
2. 1000 Merino hoggets due to lamb in September.
3. 660 Merino weaners.
(Editor’s note: Startect® is a short acting drench with an action of less than 1-2 days.)
Consider the results from the first two mobs, and why it was recommended that these mobs should NOT be drenched now.
Assuming the larval burden in the paddocks now grazed by the ewes and hoggets is low, most new infection would come from eggs shed by existing worms in the sheep, which developed into infective larvae.
However, the weather has been dry and cool. It is too cold for barber’s pole worm to develop into larvae (daily maximums above 18°C), but generally warm enough for Trichostrongylus eggs, which only require maximum temperatures of 10°C. Nevertheless, they still require moisture, and with this lacking eggs won’t develop into larvae. In fact, most will die within 1-2 weeks.
So the worms in both ewe mobs would generally have been acquired in previous paddocks, and further pick up would be limited if the paddocks now being grazed had low levels of contamination.
The producer was therefore advised to repeat the worm egg count in 6 weeks; 4 weeks if he’s feeling nervous leading up to the lambing or if we get some warm wet weather, and to hold off on drenching for now. My hunch is that if seasonal conditions remain dry and cool the producer won’t need to drench either of these mobs until he gives a pre-lambing drench.
The mob of weaners was drenched with a short-acting triple combination drench known to be effective against barber’s pole worm and scour worms as per the WormBoss Drench Decision Guide.
Let’s do a bit of arithmetic. The cost of the WECs for all three mobs was $181.50. Assuming the producer would otherwise have drenched all three mobs with a combination drench containing three different actives he would have unnecessarily drenched the mob of ewes and the mob of hoggets at a cost of $1,272 (2120 ewes at 60 kg at approximately $0.60 per dose for the average triple combination drench. If the producer had rotated to a product containing a newer active he would have been looking at somewhere around $2000).
I’m no investment banker but those WormTests sure look like money well spent. And of course it’s impossible to put a price on the avoidance of the future cost of drench resistance caused by unnecessary drenching.