Last month we talked about the history of deworming in horses, how rotation as a resistance management strategy has not proved effective and how we must now ‘deworm smarter, not harder’.

Essentially, we need to identify which horses have the most worms, and target our worming to those individuals, not the whole herd. The aim is to try and keep worms to a manageable level, but not try and eradicate them. Eradication attempts are doomed to fail and will drive further resistance. I should say now that this advice is aimed at horses over 12 months old and at strongyle control, because the major health risk for this age group are the small strongyles (cyathostomins). Foals are most affected by roundworms (ascarids) and we don’t have a good resistance-management plan for them yet. If you have ascarids you should treat them, but equally if you don’t have ascarids then don’t treat for them! We might need a separate article on roundworms and pinworms in the future. Back to small strongyles; we also want to look at non-chemical control methods, which can reduce our reliance on drugs.

In general, 2 treatments per year will be sufficient for most adult horses. We identify ‘most adult horses’ by doing faecal egg counts (FECs) once or twice a year, and that tells us if a horse is a ‘high shedder’ of strongyle eggs, which might need more than 2 treatments per year, or a ‘low shedder’, for which 2 treatments is usually enough. The great news is that most horses are low shedders! Of course, if your vet says an individual horse is suffering illness from worms at any time then the rules go out the window and you treat the horse.

The following is an example of how this might look:

Step one – get a manure sample from every horse on your farm and take it to your vet for egg counting.  Alternatively, you could get in touch with your local LLS or DPI person and they might be able to arrange counts for you. Egg counts will routinely detect strongyle eggs and ascarid eggs

A good time to do this is when you are itching to worm the horses; collect the poo instead! This helps you understand what exactly is on your property and which horses are the high and low shedders.

When the results come back TALK TO YOUR VET! Together you can decide what your adult horses need for strongyle control (in a stud situation this would normally be the mares) and what your youngsters need, especially if ascarids were also found.

For your mares, we usually recommend that the twice-yearly treatments occur in spring and autumn, and you could space them to fit in a pre-foaling treatment if you prefer. For the high shedders you can give extra doses in between. You will find that horses tend to stay within the same category, with only a few swapping between the high and low groups each time you test.

Moxidectin (brand name Equest® Plus Tape) is a good choice for the twice-yearly treatments because it will kill those pesky encysted small strongyles that we mentioned in the last article and will suppress worm egg excretion in the poo for longer than other wormers. I am less fussy what you use in between for the high shedders.

Let’s look at cost.  Shall we say a wormer is about $20?

Many of you are worming every 6 – 8 weeks, which is about 7 times a year.  That would cost you $140 per horse.

On the new regime most horses will cost you $40 to worm for a year.  The high shedders (about 20% of your adults) will cost you $80.

You do have to factor in a worm count each year, so let’s add $20 per horse.

This means that you could more than halve your worming bill each year.

Pasture management (non-chemical worm control) is also critical – something as simple as having staff pick up manure regularly can drastically reduce the worm burden. Twice a week would be ideal. Take the manure off-site or put it in a compost pile as future fertiliser, but make sure it composts properly to kill eggs before spreading it on pasture, otherwise all the good work will be undone.

Another way to reduce the parasite burden in your paddocks is to graze cattle or sheep for a few months instead of horses. As the parasites are different for ruminants, they can ingest the horse parasites without getting sick and reduce the pasture burden for horses.

Resting pastures for a few months can also help and is best during hot and dry periods to burn off parasite eggs and larvae.

There has been a lot of info presented in the last two columns, so let me sum it up quickly.

  1. Be strategic! Test to know what worms you need to treat for. Faecal egg counts are a MUST!
  2. Worm less – you will save money, and help prolong the efficacy of drugs for the years to come
  3. Cyathostomins (small strongyles) are the parasite of concern in adult horses – Equest Plus Tape is a good choice as it is effective against encysted small strongyles with a single dose.
  4. Twice a year treatment is enough for the vast majority of adult horses
  5. Implement some non-chemical control methods to take the pressure off the wormers.