Franklin Vets Blog

There’s a silent war on our paddocks, and the parasites are winning…

March 26, 2020

For the most part, intestinal worms are harmless critters living in low numbers putting very little strain on a healthy grazing animal’s system. However, when these accumulate in large numbers, we can start to see the following issues:

  • General dullness and poor appearancehorse grazing
  • Difficulty maintaining body conditions
  • Digestive disorders
    • Loose faeces
    • Colic.

For the sick, very young and old horses these signs are more severe and more likely.

Over the past couple of years, there has been a worrying trend towards high worm burdens, even in horses on properties which previously had good control. A big part of this issue is drench resistance.


Unfortunately, traditional overuse of drenches has placed horses at risk and, despite many owners using egg counts and targeted drenching, we are now seeing problems.

Most at risk are heavily grazed properties where horses are more likely to pick up large amounts of worms whilst grazing. However, horses from these properties can quickly spread very high burdens of resistant worms to any new property, including shared grazing at event grounds.

We can still use drenches to help us, but we need to be more mindful in when and what we give to preserve the limited action left.

Key points in tackling the problem:

  • Awareness & Monitoring
    • Regular faecal egg counting under the guidance of your vet
  • Paddock hygiene
    • Avoid overgrazing paddocks and feeding out close to dung piles
    • Poo picking as frequently as possible, if this can’t be done at least every other day it may have limited use
    • Avoiding harrowing unless done on long sunny days when the paddock can be left clear or cross grazed by other stock for preferably a few weeks
    • Paddock rotation with other grazing species
    • Resting paddocks is not that useful in NZ conditions unless the paddock is horse free for at least 9mths.
  • Isolation
    • Any horse that arrives from grazing elsewhere should be isolated and have a faecal egg count performed. Previous drench history is important in the interpretation of these results.

Dr Katie Kindleysides BVSc CertAVP Equine Dentistry