17/02/2025
We hate bot flies!! We always wait till at least the first frost before deworming! 🪱🪰🪱
We’re halfway through February, which means it is nearly March, which means it is almost “autumn”, which means it's time for this annual post, to catch you all before you drench your horses on the 1st of March.
Mid - late autumn is the No. 1 time of year to worm your horses, because it ties in best with breaking the bot-fly life cycle. A bot fly’s lifecycle is 12 months, so treating just once a year will break that lifecycle (and overtime decrease bot fly populations). By mid-autumn/early winter, the entire population of bot flies will be inside your horse, which means you can target all the bots on your property with a single dosage of a boticide dewormer (ivermectin, abamectin, moxidectin).
If you deworm your horses too early in autumn, you will not be targeting all the bot flies as they are often present well into autumn, laying eggs on your horses coat. If you deworm on the 1st of March, there will be bot flies, and subsequently bot eggs and larvae that come after the treatment and will remain within your horse for the year.
Therefore, hold off on the autumn deworming a little longer, if your horses are in good condition. Wait until the nights cool down and the bot flies disappear before deworming – and make sure that the dewormer you purchase is active against bots, otherwise it will all be in vain. If your horses need to be treated now, do so, but make sure you target bot flies again in early winter. The “first frost” method simply means it is cold enough that the bots will be finished. Australia frosts are not cold enough to actually kill any worms in the ground – these need consistent days of below zero temperatures (think Northern European/American winters)
So that’s my bot-fly spiel. Normally I write about strongyles (my favourite), and so I shall of course make a mention of them here too.
I always recommend a mid-late autumn deworming for ALL HORSES because it a) cleans out any bots and b) all horses really should have a strongyle clean out once a year as well. I may be against deworming for the sake of deworming, however that is only if you are doing it 3 or 4 or more times a year.
Strongyles can have a lifecycle of as little as 6 weeks. In addition, at any one point, about 90% of the strongyle population is living on the pasture, not in the horse. Therefore, the concept of using chemical dewormers inside the horse to break the lifecycle of strongyles would not work. At all. So, we chose our annual deworming-clean-out to line up with as many other parasites as possible.
All boticide dewormers are also effective against strongyles so deworming in autumn is a 2 for 1 type deal. You should also consider using a dewormer that also contains praziquantel to treat for tapeworms to get a complete clean out, just in case tapeworms are present. WormCheck does offer a tapeworm specific FEC now, if you wanted to check beforehand to avoid the overuse of praziquantel. (There have been some scary reports of praziquantel resistance in Europe.)
Lastly… wait, second lastly.. this is a topic too complex to get into here, but: this time of year is key for larval cyathostomins, where encysted larvae have mass emergences from the intestine wall, in response to changes in weather (e.g. in VIC as it cools and becomes wetter again). Deworming and removing adult populations of worms can act as a trigger for larval re-emergence, which is also why I often baulk at deworming horses now. The larvae may slowly re-emerge coming into the cooler weather and treating in mid-late autumn may be a safer bet to remove adults and emerged larvae. The research on this is sketchy as best, however these are patterns shown in cattle and hypothetically should translate over into horses.
And lastly (pat on the back for reading this far): just because I’m recommending deworming all horses does not mean I am not recommending FECs in autumn. A FEC will tell you important things about your horses health, and pick up anything odd that may be happening (e.g. a spike in EPG in a horse that is usually a low shedder; this is a sign of an impaired immune system, e.g. EMS, cushings). Doing an autumn FEC will also allow you to test drug efficacy. Autumn should be a key time for everyone to do a FECRT (faecal egg count reduction test), where you get FECs done before and after deworming to make sure that it worked. If you only deworm once a year, then you’ve only got one chance for a FECRT, and you cannot, I repeat, you CANNOT do a FECRT without a FEC before to compare to.
If you’d like to organise FECs and FECRTs for your horses this autumn, check out the website (link on the FB page) for postal submission and drop off points/events.
