Wormy Woes - Parasites & Colic

WRITTEN BY DR TIAS MUURLINK & LYNETTE JACKSON

Let's talk about parasites—those wiggly worms we all despise—and their potential risk of causing colic in horses.

Last year, Tias observed an increase in colic cases as the season transitioned from winter to spring. Many of these cases involved horses with a heavy worm burden, often ranging from 3,000 to 10,000 eggs per gram. Ideally, faecal egg counts in horses should be less than 500 eggs per gram.

Parasites in manure

The parasites in this manure were observed after deworming. There are a number of different species in this sample, ascarids (large white worms) and strongyles (small red worms) in particular.

Dry weather during winter can reduce the availability of grass, forcing horses to graze closer to manure piles. A few falls of rain can exacerbate parasite burdens by allowing worm eggs and larvae to survive better in the manure, especially in heavily grazed paddocks where fresh grass is often found near manure piles.

In some cases involving weanlings, Tias encountered ascarid (roundworm) impactions, which can cause complete obstruction of the intestine due to the amount and size of the worms. Other internal parasites, such as strongyles, can cause damage to the intestinal wall. Both of these will result in colic (abdominal pain) signs, such as frequently getting up and down, rolling and pawing.

Ascarid Impaction

The intestine of this weanling had to be opened (enterotomy) to remove the ascarids that had caused an obstruction resulting in colic.

Given the risks of colic it is important that steps are taken to minimise parasites in horses.

However, effective parasite control involves more than just relying on anthelminthics (deworming pastes), as resistance to these products has been increasing.

So, what can you do to prevent internal parasite burdens?

Good paddock hygiene is crucial. This includes regularly collecting manure, rotating pastures, and possibly grazing other species like cattle or sheep alongside horses, as their parasites do not cross over.

Judicious use of anthelminthics is also important—use the right drug at the right time and only if necessary. Regular faecal egg counts (FEC) are essential to determine if there is a significant worm burden present, and only deworm if needed.

Faecal Egg Count

FECs are a non-invasive test that only requires a small sample of manure from your horse.

This approach can save the cost of deworming products and help reduce the risk of resistance, ensuring the health of your horses.